Internet DRAFT - draft-ietf-megaco-3015corr

draft-ietf-megaco-3015corr





   Media Gateway Control (Megaco)                   C. Groves, M. Pantaleo 
   Internet Draft                                              LM Ericsson 
   Document: draft-ietf-megaco-3015corr-03.txt                 T. Anderson 
   Expires: June 2003                                  Lucent Technologies 
                                                                 T. Taylor 
                                                           Nortel Networks 
                                                                 (Editors) 
                                                             December 2002 
       
       
                       Gateway Control Protocol Version 1 
       
       
   Status of this Memo 
       
      This document is an Internet-Draft and is in full conformance with 
      all provisions of Section 10 of RFC2026.  Internet-Drafts are working 
      documents of the Internet Engineering Task Force (IETF), its areas, 
      and its working groups.  Note that other groups may also distribute 
      working documents as Internet-Drafts. 
       
      Internet-Drafts are draft documents valid for a maximum of six months 
      and may be updated, replaced, or obsoleted by other documents at any 
      time.  It is inappropriate to use Internet-Drafts as reference 
      material or to cite them other than as "work in progress." 
       
      The list of current Internet-Drafts can be accessed at 
           http://www.ietf.org/ietf/1id-abstracts.txt 
      The list of Internet-Draft Shadow Directories can be accessed at 
           http://www.ietf.org/shadow.html. 
       
   Abstract 
       
      This document defines the protocol used between elements of a 
      physically decomposed multimedia gateway, i.e. a Media Gateway and a 
      Media Gateway Controller.  The protocol presented in this document 
      meets the requirements for a media gateway control protocol as 
      presented in RFC 2805. 
       
      This document is intended to replace RFC 3015.  It is the result of 
      continued cooperation between the IETF Megaco Working Group and ITU-T 
      Study Group 16.  It incorporates the original text of RFC 3015, 
      modified by corrections and clarifications discussed on the Megaco E-
      mail list and incorporated into the Study Group 16 Implementor's 
      Guide for Recommendation H.248.  The present version of this document 
      has undergone ITU-T Last Call as Recommendation H.248 Amendment 1.  
      Because of ITU-T renumbering, it will be published by the ITU-T as 
      Recommendation H.248.1 (03/02), Gateway Control Protocol Version 1.   
       
       
    
    
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   Conventions used in this document 
       
      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
      "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this 
      document are to be interpreted as described in RFC-2119. 
       
   Table of Contents 
       
      Conventions used in this document.................................2 
      Table of Contents.................................................2 
       
      1 Scope...........................................................7 
      1.1 Changes From RFC 3015.........................................7 
      1.2 Differences From ITU-T Recommendation H.248.1 (03/2000).......7 
       
      2 References......................................................8 
      2.1 Normative references..........................................8 
      2.2 Informative references.......................................10 
       
      3 Definitions....................................................11 
       
      4 Abbreviations..................................................13 
       
      5 Conventions....................................................14 
       
      6 Connection model...............................................14 
      6.2 Terminations.................................................18 
      6.2.1 Termination dynamics.......................................22 
      6.2.2 TerminationIDs.............................................22 
      6.2.3 Packages...................................................23 
      6.2.4 Termination properties and descriptors.....................24 
      6.2.5 Root Termination...........................................26 
       
      7 Commands.......................................................27 
      7.1 Descriptors..................................................28 
      7.1.1 Specifying parameters......................................28 
      7.1.2 Modem descriptor...........................................29 
      7.1.3 Multiplex descriptor.......................................29 
      7.1.4 Media descriptor...........................................29 
      7.1.5 TerminationState descriptor................................30 
      7.1.6 Stream descriptor..........................................31 
      7.1.7 LocalControl descriptor....................................31 
      7.1.8 Local and Remote descriptors...............................32 
      7.1.9 Events descriptor..........................................36 
      7.1.10 EventBuffer descriptor....................................39 
      7.1.11 Signals descriptor........................................39 
      7.1.12 Audit descriptor..........................................41 
      7.1.13 ServiceChange descriptor..................................41 
      7.1.14 DigitMap descriptor.......................................42 
    
    
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      7.1.15 Statistics descriptor.....................................47 
      7.1.16 Packages descriptor.......................................47 
      7.1.17 ObservedEvents descriptor.................................47 
      7.1.18 Topology descriptor.......................................48 
      7.1.19 Error Descriptor..........................................51 
      7.2 Command Application Programming Interface....................51 
      7.2.1 Add........................................................51 
      7.2.2 Modify.....................................................53 
      7.2.3 Subtract...................................................54 
      7.2.4 Move.......................................................55 
      7.2.5 AuditValue.................................................56 
      7.2.6 AuditCapabilities..........................................59 
      7.2.7 Notify.....................................................61 
      7.2.8 ServiceChange..............................................61 
      7.2.9 Manipulating and Auditing Context Attributes...............66 
      7.2.10 Generic Command Syntax....................................66 
      7.3 Command Error Codes..........................................66 
       
      8 Transactions...................................................67 
      8.1 Common parameters............................................68 
      8.1.1 Transaction Identifiers....................................68 
      8.1.2 Context Identifiers........................................69 
      8.2 Transaction Application Programming Interface................69 
      8.2.1 TransactionRequest.........................................69 
      8.2.2 TransactionReply...........................................70 
      8.2.3 TransactionPending.........................................71 
      8.3 Messages.....................................................72 
       
      9 Transport......................................................72 
      9.1 Ordering of Commands.........................................73 
      9.2 Protection against Restart Avalanche.........................74 
       
      10 Security considerations.......................................75 
      10.1 Protection of Protocol Connections..........................75 
      10.2 Interim AH scheme...........................................76 
      10.3 Protection of Media Connections.............................77 
       
      11 MG-MGC Control Interface......................................78 
      11.1 Multiple Virtual MGs........................................78 
      11.2 Cold start..................................................79 
      11.3 Negotiation of protocol version.............................79 
      11.4 Failure of a MG.............................................80 
      11.5 Failure of an MGC...........................................81 
       
      12 Package definition............................................82 
      12.1 Guidelines for defining packages............................82 
      12.1.1 Package...................................................82 
      12.1.2 Properties................................................83 
      12.1.3 Events....................................................84 
    
    
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      12.1.4 Signals...................................................85 
      12.1.5 Statistics................................................86 
      12.1.6 Procedures................................................86 
      12.2 Guidelines to defining Parameters to Events and Signals.....86 
      12.3 Lists.......................................................87 
      12.4 Identifiers.................................................87 
      12.5 Package registration........................................87 
       
      13 IANA considerations...........................................87 
      13.1 Packages....................................................87 
      13.2 Error codes.................................................88 
      13.3 ServiceChange reasons.......................................89 
       
      ANNEX A  Binary encoding of the protocol.........................90 
      A.1 Coding of wildcards..........................................90 
      A.2 ASN.1 syntax specification...................................91 
      A.3 Digit maps and path names...................................110 
       
      ANNEX B Text encoding of the protocol...........................112 
      B.1 Coding of wildcards.........................................112 
      B.2 ABNF specification..........................................112 
      B.3 Hexadecimal octet coding....................................126 
      B.4 Hexadecimal octet sequence..................................126 
       
      ANNEX C Tags for media stream properties........................127 
      C.1 General media attributes....................................127 
      C.2 Mux properties..............................................129 
      C.3 General bearer properties...................................129 
      C.4 General ATM properties......................................129 
      C.5 Frame Relay.................................................132 
      C.6 IP..........................................................132 
      C.7 ATM AAL2....................................................133 
      C.8 ATM AAL1....................................................134 
      C.9 Bearer capabilities.........................................136 
      C.10 AAL5 properties............................................147 
      C.11 SDP equivalents............................................147 
      C.12 H.245......................................................149 
       
      ANNEX D Transport over IP.......................................150 
      D.1 Transport over IP/UDP using Application Level Framing (ALF).150 
      D.1.1 Providing At-Most-Once functionality......................150 
      D.1.2 Transaction identifiers and three-way handshake...........151 
      D.1.3 Computing retransmission timers...........................152 
      D.1.4 Provisional responses.....................................153 
      D.1.5 Repeating Requests, Responses and Acknowledgements........153 
      D.2 Using TCP...................................................155 
      D.2.1 Providing the At-Most-Once functionality..................155 
      D.2.2 Transaction identifiers and three-way handshake...........155 
      D.2.3 Computing retransmission timers...........................155 
    
    
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      D.2.4 Provisional responses.....................................156 
      D.2.5 Ordering of commands......................................156 
       
      ANNEX E  Basic packages.........................................157 
      E.1 Generic.....................................................157 
      E.2 Base Root Package...........................................159 
      E.3 Tone Generator Package......................................161 
      E.4 Tone Detection Package......................................163 
      E.5 Basic DTMF Generator Package................................166 
      E.6 DTMF detection Package......................................167 
      E.7 Call Progress Tones Generator Package.......................169 
      E.8 Call Progress Tones Detection Package.......................171 
      E.9 Analog Line Supervision Package.............................172 
      E.10 Basic Continuity Package...................................175 
      E.11 Network Package............................................178 
      E.12 RTP Package................................................180 
      E.13 TDM Circuit Package........................................182 
       
      APPENDIX I EXAMPLE CALL FLOWS (INFORMATIVE).....................184 
      A.1 Residential Gateway to Residential Gateway Call.............184 
      A.1.1 Programming Residential GW Analog Line Terminations for Idle 
      Behavior........................................................184 
      A.1.2 Collecting Originator Digits and Initiating Termination...186 
       
      APPENDIX II  Changes From RFC 3015..............................197 
       
      INTELLECTUAL PROPERTY RIGHTS....................................213 
       
      Acknowledgments.................................................213 
       
      Authors' Addresses..............................................214 
       
       
















    
    
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   1  Scope 
       
      The present document, which is identical to the prepublished version 
      of ITU-T Recommendation H.248.1 (03/2002) except as noted below,  
      defines the protocols used between elements of a physically 
      decomposed multimedia gateway. There are no functional differences 
      from a system view between a decomposed gateway, with distributed 
      sub-components potentially on more than one physical device, and a 
      monolithic gateway such as described in ITU-T Recommendation H.246. 
      This document does not define how gateways, multipoint control units 
      or interactive voice response units (IVRs) work. Instead it creates a 
      general framework that is suitable for these applications. 

      Packet network interfaces may include IP, ATM or possibly others. The 
      interfaces will support a variety of Switched Circuit Network (SCN)
      signalling systems, including tone signalling, ISDN, ISUP, QSIG and 
      GSM. National variants of these signalling systems will be supported 
      where applicable. 

   1.1 Changes From RFC 3015 
       
      The differences between this document and RFC 3015 are documented in 
      Appendix II. 
       
   1.2 Differences From ITU-T Recommendation H.248.1 (03/2000) 
       
      This document differs from the corresponding ITU-T publication in the 
      following respects: 

      -  Added IETF front matter in place of the corresponding ITU-T 
         material. 

      -  The ITU-T summary is too H.323-specific and has been omitted. 

      -  The IETF conventions have been stated as governing this document.  
         As discussed in section 5 below, this gives slightly greater 
         strength to "should" requirements. 

      -  The Scope section (just above) has been edited slightly to suit 
         its IETF context. 

      -  Added normative references to RFCs 2026 and 2119. 

      -  Figures 4, 5, and 6 show the centre of the context for greater 
         clarity.  Also added Figure 6a showing an important additional 
         example. 



    
    
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      -  Added a paragraph in section 7.1.18 which was approved in the 
         Implementor's Guide but lost inadvertently in the ITU-T approved 
         version. 

      -  This document incorporates corrections to the informative examples 
         in Appendix I which also appear in H.248.1 version 2, but which 
         were not picked up in H.248.1 (03/2002). 

      -  This document includes a new Appendix II listing all the changes 
         from RFC 3015. 

      -  This document includes an Acknowledgements section listing the 
         authors of RFC 3015 but also many other people who contributed to 
         the development of the Megaco/H.248.x protocol. 

      -  Moved the Intellectual Property declaration to its usual place in 
         an IETF document and added a reference to declarations on the IETF 
         web site. 

       
   2  References 
       
      The following ITU-T Recommendations and other references contain 
      provisions which, through reference in this text, constitute 
      provisions of this Recommendation. At the time of publication, the 
      editions indicated were valid. All Recommendations and other 
      references are subject to revision; all users of this Recommendation 
      are therefore encouraged to investigate the possibility of applying 
      the most recent edition of the Recommendations and other references 
      listed below. A list of the currently valid ITU-T Recommendations is 
      regularly published. 

   2.1   Normative references 
       
      -  ITU-T Recommendation H.225.0 (1999), Call signalling protocols and 
         media stream packetization for packet-based multimedia 
         communication systems. 

      -  ITU-T Recommendation H.235 (1998), Security and encryption for H-
         Series (H.323 and other H.245-based) multimedia terminals. 

      -  ITU-T Recommendation H.245 (1998), Control protocol for multimedia 
         communication. 

      -  ITU-T Recommendation H.246 (1998), Interworking of H-series 
         multimedia terminals with H-series multimedia terminals and 
         voice/voiceband terminals on GSTN and ISDN. 


    
    
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      -  ITU-T Recommendation H.248.8 (2002), H.248 Error Codes and Service 
         Change Reasons. 

      -  ITU-T Recommendation H.323 (1999), Packet-based multimedia 
         communication systems. 

      -  ITU-T Recommendation I.363.1 (1996), B-ISDN ATM adaptation layer 
         (AAL) specification: Type 1 AAL. 

      -  ITU-T Recommendation I.363.2 (1997), B-ISDN ATM adaptation layer 
         (AAL) specification: Type 2 AAL. 

      -  ITU-T Recommendation I.363.5 (1996), B-ISDN ATM adaptation layer 
         (AAL) specification: Type 5 AAL. 

      -  ITU-T Recommendation I.366.1 (1998), Segmentation and Reassembly 
         Service Specific Convergence Sublayer for the AAL type 2. 

      -  ITU-T Recommendation I.366.2 (1999), AAL type 2 service specific 
         convergence sublayer for trunking. 

      -  ITU-T Recommendation I.371 (2000), Traffic control and congestion 
         control in B-ISDN. 

      -  ITU-T Recommendation Q.763 (1999), Signalling System No. 7 - ISDN 
         user part formats and codes. 

      -  ITU-T Recommendation Q.765.5 (2001), Application transport 
         mechanism - Bearer independent call control (BICC). 

      -  ITU-T Recommendation Q.931 (1998), ISDN user-network interface 
         layer 3 specification for basic call control. 

      -  ITU-T Recommendation Q.2630.1 (1999), AAL type 2 signalling 
         protocol (Capability Set 1). 

      -  ITU-T Recommendation Q.2931 (1995), Digital Subscriber Signalling 
         System No. 2 (DSS2) - User-Network Interface (UNI) - Layer 3 
         specification for basic call/connection control. 

      -  ITU-T Recommendation Q.2941.1 (1997), Digital Subscriber 
         Signalling System No. 2 - Generic identifier transport. 

      -  ITU-T Recommendation Q.2961.1 (1995), Additional signalling 
         capabilities to support traffic parameters for the tagging option 
         and the sustainable call note parameter set. 



    
    
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      -  ITU-T Recommendation Q.2961.2 (1997), Additional traffic 
         parameters: Support of ATM transfer capability in the broadband 
         bearer capability information element. 

      -  ITU-T Recommendation Q.2965.1 (1999), Digital subscriber 
         signalling system No. 2 - Support of Quality of Service classes. 

      -  ITU-T Recommendation Q.2965.2 (1999), Digital subscriber 
         signalling system No. 2 - Signalling of individual Quality of 
         Service parameters. 

      -  ITU-T Recommendation V.76 (1996), Generic multiplexer using V.42 
         LAPM-based procedures. 

      -  ITU-T Recommendation X.213 (1995), Information technology - Open 
         Systems Interconnection - Network service definition plus 
         Amendment 1 (1997), Addition of the Internet protocol address 
         format identifier. 

      -  ITU-T Recommendation X.680 (1997), Information technology - 
         Abstract Syntax Notation One (ASN.1): Specification of basic 
         notation. 

      -  ITU-T Recommendation X.690 (1997), Information Technology - ASN.1 
         Encoding Rules: Specification of Basic Encoding Rules (BER), 
         Canonical Encoding Rules (CER) and Distinguished Encoding Rules 
         (DER). 

      -  ATM Forum (1996), ATM User-Network Interface (UNI) Signalling 
         Specification - Version 4.0. 

      -  RFC 1006, ISO Transport Service on top of the TCP, Version 3. 

      -  RFC 2026, The Internet Standards Process -- Revision 3. 

      -  RFC 2119, Key words for use in RFCs to Indicate Requirement 
         Levels. 

      -  RFC 2234, Augmented BNF for Syntax Specifications: ABNF. 

      -  RFC 2327, SDP: Session Description Protocol. 

      -  RFC 2402, IP Authentication Header. 

      -  RFC 2406, IP Encapsulating Security Payload (ESP). 




    
    
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   2.2   Informative references 
       
      -  ITU-T Recommendation E.180/Q.35 (1998), Technical characteristics 
         of tones for the telephone service. 

      -  CCITT Recommendation G.711 (1988), Pulse Code Modulation (PCM) of 
         voice frequencies. 

      -  ITU-T Recommendation H.221 (1999), Frame structure for a 64 to 
         1920 kbit/s channel in audiovisual teleservices. 

      -  ITU  T Recommendation H.223 (1996), Multiplexing protocol for low 
         bit rate multimedia communication. 

      -  ITU-T Recommendation H.226 (1998), Channel aggregation protocol 
         for multilink operation on circuit-switched networks 

      -  ITU-T Recommendation Q.724 (1998), Signalling procedures. 

      -  ITU-T Recommendation Q.764 (1999), Signalling system No. 7 - ISDN 
         user part signalling procedures. 

      -  ITU-T Recommendation Q.1902.4 (2001), Bearer independent call 
         control protocol - Basic call procedures. 

      -  RFC 768, User Datagram Protocol. 

      -  RFC 791, Internet protocol. 

      -  RFC 793, Transmission control protocol. 

      -  RFC 1661, The Point-to-Point Protocol (PPP). 

      -  RFC 1889, RTP: A Transport Protocol for Real-Time Applications. 

      -  RFC 1890, RTP Profile for Audio and Video Conferences with Minimal 
         Control. 

      -  RFC 2401, Security Architecture for the Internet Protocol. 

      -  RFC 2543, SIP: Session Initiation Protocol. 

      -  RFC 2460, Internet Protocol, Version 6 (IPv6) Specification. 

      -  RFC 2805, Media Gateway Control Protocol Architecture and 
         Requirements. 

       

    
    
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   3  Definitions 
       
      This document defines the following terms: 

      Access gateway:  
      A type of gateway that provides a User-Network Interface (UNI) such 
      as ISDN. 

      Descriptor:  
      A syntactic element of the protocol that groups related properties. 
      For instance, the properties of a media flow on the MG can be set by 
      the MGC by including the appropriate descriptor in a command. 

      Media Gateway (MG):  
      The media gateway converts media provided in one type of network to 
      the format required in another type of network. For example, a MG 
      could terminate bearer channels from a switched circuit network (e.g. 
      DS0s) and media streams from a packet network (e.g. RTP streams in an 
      IP network). This gateway may be capable of processing audio, video 
      and T.120 alone or in any combination, and will be capable of full 
      duplex media translations. The MG may also play audio/video messages 
      and perform other IVR functions, or may perform media conferencing. 

      Media Gateway Controller (MGC): 
       Controls the parts of the call state that pertain to connection 
      control for media channels in a MG. 

      Multipoint Control Unit (MCU): 
      An entity that controls the setup and coordination of a multi-user 
      conference that typically includes processing of audio, video and 
      data. 

      Residential gateway: 
      A gateway that interworks an analogue line to a packet network. A 
      residential gateway typically contains one or two analogue lines and 
      is located at the customer premises. 

      SCN FAS signalling gateway:  
      This function contains the SCN Signalling Interface that terminates 
      SS7, ISDN or other signalling links where the call control channel 
      and bearer channels are collocated in the same physical span. 

      SCN NFAS signalling gateway:  
      This function contains the SCN Signalling Interface that terminates 
      SS7 or other signalling links where the call control channels are 
      separated from bearer channels. 

      Stream:  

    
    
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      Bidirectional media or control flow received/sent by a media gateway 
      as part of a call or conference. 

      Trunk:  
      A communication channel between two switching systems such as a DS0 
      on a T1 or E1 line. 

      Trunking gateway:  
      A gateway between SCN network and packet network that typically 
      terminates a large number of digital circuits. 

       
   4  Abbreviations 
       
      This Recommendation document uses the following abbreviations: 

      ALF   Application Layer Framing 

      ATM   Asynchronous Transfer Mode 

      CAS   Channel Associated Signalling 

      DTMF  Dual Tone Multi-Frequency 

      FAS   Facility Associated Signalling 

      GSM   Global System for Mobile communications 

      GW    GateWay 

      IANA  Internet Assigned Numbers Authority (superseded by Internet 
            Corporation for Assigned Names and Numbers - ICANN) 

      IP    Internet Protocol 

      ISUP  ISDN User Part 

      IVR   Interactive Voice Response 

      MG    Media Gateway 

      MGC   Media Gateway Controller 

      NFAS  Non-Facility Associated Signalling 

      PRI   Primary Rate Interface 

      PSTN  Public Switched Telephone Network  

    
    
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      QoS   Quality of Service 

      RTP   Real-time Transport Protocol 

      SCN   Switched Circuit Network 

      SG    Signalling Gateway 

      SS7   Signalling System No. 7 

       
   5  Conventions 
       
      In the H.248.1 Recommendation, "SHALL" refers to a mandatory 
      requirement, while "SHOULD" refers to a suggested but optional 
      feature or procedure. The term "MAY" refers to an optional course of 
      action without expressing a preference.  Note that these definition 
      are overridden in the present document by the RFC 2119 conventions 
      stated at the beginning of this document.  RFC 2119 has a more 
      precise definition of "should" than is provided by the ITU-T. 

       
   6  Connection model 
       
      The connection model for the protocol describes the logical entities, 
      or objects, within the Media Gateway that can be controlled by the 
      Media Gateway Controller. The main abstractions used in the 
      connection model are Terminations and Contexts. 

      A Termination sources and/or sinks one or more streams. In a 
      multimedia conference, a Termination can be multimedia and sources or 
      sinks multiple media streams. The media stream parameters, as well as 
      modem, and bearer parameters are encapsulated within the Termination.  

      A Context is an association between a collection of Terminations. 
      There is a special type of Context, the null Context, which contains 
      all Terminations that are not associated to any other Termination. 
      For instance, in a decomposed access gateway, all idle lines are 
      represented by Terminations in the null Context. 

      Following is a graphical depiction of these concepts. The diagram of 
      Figure 1 gives several examples and is not meant to be an all-
      inclusive illustration. The asterisk box in each of the Contexts 
      represents the logical association of Terminations implied by the 
      Context. 




    
    
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            +------------------------------------------------------+ 
            |Media Gateway                                         | 
            | +-------------------------------------------------+  | 
            | |Context                          +-------------+ |  | 
            | |                                 | Termination | |  | 
            | |                                 |-------------| |  | 
            | |  +-------------+             +->| SCN Bearer  |<---+-> 
            | |  | Termination |   +-----+   |  |   Channel   | |  | 
            | |  |-------------|   |     |---+  +-------------+ |  | 
          <-+--->| RTP Stream  |---|  *  |                      |  | 
            | |  |             |   |     |---+  +-------------+ |  | 
            | |  +-------------+   +-----+   |  | Termination | |  | 
            | |                              |  |-------------| |  | 
            | |                              +->| SCN Bearer  |<---+-> 
            | |                                 |   Channel   | |  | 
            | |                                 +-------------+ |  | 
            | +-------------------------------------------------+  | 
            |                                                      | 
            |                                                      | 
            |                    +------------------------------+  | 
            |   (NULL Context)   |Context                       |  | 
            |  +-------------+   |              +-------------+ |  | 
            |  | Termination |   | +-----+      | Termination | |  | 
            |  |-------------|   | |     |      |-------------| |  | 
            |  | SCN Bearer  |   | |  *  |------| SCN Bearer  |<---+-> 
            |  |   Channel   |   | |     |      |   Channel   | |  | 
            |  +-------------+   | +-----+      +-------------+ |  | 
            |                    +------------------------------+  | 
            |                                                      | 
            |                                                      | 
            | +-------------------------------------------------+  | 
            | |Context                                          |  | 
            | |  +-------------+                +-------------+ |  | 
            | |  | Termination |   +-----+      | Termination | |  | 
            | |  |-------------|   |     |      |-------------| |  | 
          <-+--->| SCN Bearer  |---|  *  |------| SCN Bearer  |<---+-> 
            | |  |   Channel   |   |     |      |   Channel   | |  | 
            | |  +-------------+   +-----+      +-------------+ |  | 
            | +-------------------------------------------------+  | 
            | ___________________________________________________  | 
            +------------------------------------------------------+ 
       
               Figure 1: Examples of Megaco/H.248 Connection Model 
       

      The example in Figure 2 shows an example of one way to accomplish a 
      call-waiting scenario in a decomposed access gateway, illustrating 
      the relocation of a Termination between Contexts. Terminations T1 and 
      T2 belong to Context C1 in a two-way audio call. A second audio call 
    
    
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      is waiting for T1 from Termination T3. T3 is alone in Context C2. T1 
      accepts the call from T3, placing T2 on hold. This action results in 
      T1 moving into Context C2, as shown in Figure 3. 

       
            +------------------------------------------------------+ 
            |Media Gateway                                         | 
            | +-------------------------------------------------+  | 
            | |Context C1                                       |  | 
            | |  +-------------+                +-------------+ |  | 
            | |  | Term. T2    |   +-----+      | Term. T1    | |  | 
            | |  |-------------|   |     |      |-------------| |  | 
          <-+--->| RTP Stream  |---|  *  |------| SCN Bearer  |<---+-> 
            | |  |             |   |     |      |   Channel   | |  | 
            | |  +-------------+   +-----+      +-------------+ |  | 
            | +-------------------------------------------------+  | 
            |                                                      | 
            | +-------------------------------------------------+  | 
            | |Context C2                                       |  | 
            | |                                 +-------------+ |  | 
            | |                    +-----+      | Term. T3    | |  | 
            | |                    |     |      |-------------| |  | 
            | |                    |  *  |------| SCN Bearer  |<---+-> 
            | |                    |     |      |   Channel   | |  | 
            | |                    +-----+      +-------------+ |  | 
            | +-------------------------------------------------+  | 
            +------------------------------------------------------+  
        
        Figure 2: Example Call Waiting Scenario / Alerting Applied to T1 
       
            +------------------------------------------------------+ 
            |Media Gateway                                         | 
            | +-------------------------------------------------+  | 
            | |Context C1                                       |  | 
            | |  +-------------+                                |  | 
            | |  | Term. T2    |   +-----+                      |  | 
            | |  |-------------|   |     |                      |  | 
          <-+--->| RTP Stream  |---|  *  |                      |  | 
            | |  |             |   |     |                      |  | 
            | |  +-------------+   +-----+                      |  | 
            | +-------------------------------------------------+  | 








    
    
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            |                                                      | 
            | +-------------------------------------------------+  | 
            | |Context C2                                       |  | 
            | |  +-------------+                +-------------+ |  | 
            | |  | Term. T1    |   +-----+      | Term. T3    | |  | 
            | |  |-------------|   |     |      |-------------| |  | 
          <-+--->| SCN Bearer  |---|  *  |------| SCN Bearer  |<---+-> 
            | |  |   Channel   |   |     |      |   Channel   | |  | 
            | |  +-------------+   +-----+      +-------------+ |  | 
            | +-------------------------------------------------+  | 
            +------------------------------------------------------+ 
           
             Figure 3. Example Call Waiting Scenario / Answer by T1 
       

      6.1   Contexts 

      A Context is an association between a number of Terminations. The 
      Context describes the topology (who hears/sees whom) and the media 
      mixing and/or switching parameters if more than two Terminations are 
      involved in the association. 

      There is a special Context called the null Context. It contains 
      Terminations that are not associated to any other Termination. 
      Terminations in the null Context can have their parameters examined 
      or modified, and may have events detected on them. 

      In general, an Add command is used to add Terminations to Contexts. 
      If the MGC does not specify an existing Context to which the 
      Termination is to be added, the MG creates a new Context. A 
      Termination may be removed from a Context with a Subtract command, 
      and a Termination may be moved from one Context to another with a 
      Move command. A Termination SHALL exist in only one Context at a 
      time. 

      The maximum number of Terminations in a Context is a MG property. 
      Media gateways that offer only point-to-point connectivity might 
      allow at most two Terminations per Context. Media gateways that 
      support multipoint conferences might allow three or more Terminations 
      per Context. 

      6.1.1 Context attributes and descriptors 

      The attributes of Contexts are: 

      -  ContextID. 

      -  The topology (who hears/sees whom). 

    
    
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         The topology of a Context describes the flow of media between the 
         Terminations within a Context. In contrast, the mode of a 
         Termination (send/receive/...) describes the flow of the media at 
         the ingress/egress of the media gateway. 

      -  The priority is used for a Context in order to provide the MG with 
         information about a certain precedence handling for a Context. The 
         MGC can also use the priority to control autonomously the traffic 
         precedence in the MG in a smooth way in certain situations (e.g. 
         restart), when a lot of Contexts must be handled simultaneously. 
         Priority 0 is the lowest priority and a priority of 15 is the 
         highest priority. 

      -  An indicator for an emergency call is also provided to allow a 
         preference handling in the MG. 

      6.1.2 Creating, deleting and modifying Contexts 

      The protocol can be used to (implicitly) create Contexts and modify 
      the parameter values of existing Contexts. The protocol has commands 
      to add Terminations to Contexts, subtract them from Contexts, and to 
      move Terminations between Contexts. Contexts are deleted implicitly 
      when the last remaining Termination is subtracted or moved out. 

   6.2   Terminations 
       
      A Termination is a logical entity on a MG that sources and/or sinks 
      media and/or control streams. A Termination is described by a number 
      of characterizing Properties, which are grouped in a set of 
      Descriptors that are included in commands. Terminations have unique 
      identities (TerminationIDs), assigned by the MG at the time of their 
      creation. 

      Terminations representing physical entities have a semi-permanent 
      existence. For example, a Termination representing a TDM channel 
      might exist for as long as it is provisioned in the gateway. 
      Terminations representing ephemeral information flows, such as RTP 
      flows, would usually exist only for the duration of their use. 

      Ephemeral Terminations are created by means of an Add command. They 
      are destroyed by means of a Subtract command. In contrast, when a 
      physical Termination is Added to or Subtracted from a Context, it is 
      taken from or to the null Context, respectively. 

      Terminations may have signals applied to them (see 7.1.11). 
      Terminations may be programmed to detect Events, the occurrence of 
      which can trigger notification messages to the MGC, or action by the 
      MG. Statistics may be accumulated on a Termination. Statistics are 
      reported to the MGC upon request (by means of the AuditValue command, 
    
    
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      see 7.2.5) and when the Termination is taken out of the call it is 
      in. 

      Multimedia gateways may process multiplexed media streams. For 
      example, Recommendation H.221 describes a frame structure for 
      multiple media streams multiplexed on a number of digital 64 kbit/s 
      channels. Such a case is handled in the connection model in the 
      following way. For every bearer channel that carries part of the 
      multiplexed streams, there is a physical or ephemeral "bearer 
      Termination". The bearer Terminations that source/sink the digital 
      channels are connected to a separate Termination called the 
      "multiplexing Termination". The multiplexing termination is an 
      ephemeral termination representing a frame-oriented session. The 
      MultiplexDescriptor for this Termination describes the multiplex used 
      (e.g. H.221 for an H.320 session) and indicates the order in which 
      the contained digital channels are assembled into a frame.  

      Multiplexing terminations may be cascades (e.g., H.226 multiplex of 
      digital channels feeding into a H.223 multiplex supporting an H.324 
      session). 

      The individual media streams carried in the session are described by 
      StreamDescriptors on the multiplexing Termination. These media 
      streams can be associated with streams sourced/sunk by Terminations 
      in the Context other than the bearer Terminations supporting the 
      multiplexing Termination.  Each bearer Termination supports only a 
      single data stream.  These data streams do not appear explicitly as 
      streams on the multiplexing Termination and they are hidden from the 
      rest of the context. 

      Figures 4, 5, 6, and 6a illustrate typical applications of the 
      multiplexing termination and Multiplex Descriptor. 

       
       














    
    
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                     +-----------------------------------+ 
                     | Context     +-------+             | 
                    +----+         |       |             | 
      Circuit 1 -|--| TC1|---------+ Tmux  |             | 
                 |  +----+ (Str 1) |       |  Audio    +-----+ 
                 |   |             |       +-----*-----+     |----- 
                 |  +----+         | H.22x | Stream 1  |     | 
      Circuit 2 -|--| TC2|---------+ multi-|           | TR1 | 
                 |  +----+ (Str 1) | plex  |           |(RTP)| 
                 |   |             |       |  Video    |     | 
                 |  +----+         |       +-----*-----+     |----- 
      Circuit 3 -|--| TC3|---------+       | Stream 2  |     | 
                 /  +----+ (Str 1) |       |           +-----+ 
                /    |             +-------+             | 
               /     +-----------------\-----------------+ 
      Audio, video, and control         \ 
      signals are carried in frames    Tmux is an ephemeral with two 
      spanning the circuits.           explicit Stream Descriptors 
                                       and a Multiplex Descriptor. 
       
         Figure 4: Multiplexed Termination Scenario - Circuit to Packet 
                 (Asterisks * denote the centre of the context) 
       
       
                       Context 
                     +--------------------------------------+ 
                     |       +-------+        +-------+     | 
                    +----+   |       |        |       |   +----+ 
      Circuit 1 ----| TC1|---+ Tmux1 |  Audio | Tmux2 +---| TC4|--- 
                    +----+   |       +---*----+       |   +----+ 
                     |       |       |  Str 1 |       |     | 
                    +----+   | H.22x |        | H.22x |   +----+ 
      Circuit 2 ----| TC2|---+ multi-|        | multi-+---| TC5|--- 
                    +----+   | plex  |        | plex  |   +----+ 
                     |       |       |  Video |       |     | 
                    +----+   |       +---*----+       |   +----+ 
      Circuit 3 ----| TC3|---+       |  Str 2 |       +---| TC6|--- 
                    +----+   |       |        |       |   +----+ 
                     |       +-------+        +-------+     | 
                     +-----------------\-----/--------------+ 
                                        \   / 
                Tmux1 and Tmux2 are ephemerals each with two 
      .         explicit Stream Descriptors and a Multiplex Descriptor. 
       
         Figure 5: Multiplexed Termination Scenario - Circuit to Circuit 
                 (Asterisks * denote the centre of the context) 
       
       
       
    
    
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                     +-----------------------------------+ 
                     | Context     +-------+             | 
                    +----+         |       |             | 
      Circuit 1 -|--| TC1|---------+ Tmux  |             | 
                 |  +----+ (Str 1) |       |  Audio    +-----+ 
                 |   |             |       +-----*-----+ TR1 |----- 
                 |  +----+         | H.22x | Stream 1  |(RTP)| 
      Circuit 2 -|--| TC2|---------+ multi-|           +-----+ 
                 |  +----+ (Str 1) | plex  |             | 
                 |   |             |       |  Video    +-----+ 
                 |  +----+         |       +-----*-----+ TR2 |----- 
      Circuit 3 -|--| TC3|---------+       | Stream 2  |(RTP)| 
                 /  +----+ (Str 1) |       |           +-----+ 
                /    |             +-------+             | 
               /     +-----------------\-----------------+ 
      Audio, video, and control         \ 
      signals are carried in frames    Tmux is an ephemeral with two 
      spanning the circuits.           explicit Stream Descriptors 
                                       and a Multiplex Descriptor. 
       
         Figure 6: Multiplexed Termination Scenario - Single to Multiple 
                                  Terminations 
                 (Asterisks * denote the centre of the context) 
       
       
       
               Context 
             +---------------------------------------------+ 
             |       +-------+       +-------+             | 
      Cct 1 +----+   |       |       |       | Audio     +-----+ 
        ----| TC1|---+ Tmux1 |       | Tmux2 +-----*-----| TR1 |----- 
            +----+   |       |       |       | Stream 1  |(RTP)| 
             |       |       | Data  |       |           +-----+ 
      Cct 2 +----+   | H.226 +-------+ H.223 |             | 
        ----| TC2|---+ multi-|(Str 1)| multi-| Control   +-----+ 
            +----+   | plex  |       | plex  +-----*-----+ Tctl|----- 
             |       |       |       |       | Stream 3  +-----+ 
      Cct 3 +----+   |       |       |       |             | 
        ----| TC3|---+       |       |       |           +-----+ 
            +----+   |       |       |       +-----*-----+ TR2 |----- 
             |       +-------+       |       |  Video    |(RTP)| 
             |                       +-------+ Stream 2  +-----+ 
             |                                             | 
             +---------------------------------------------+ 
           Tmux1 has a Multiplex Descriptor and a single data stream. 
           Tmux2 has a Multiplex Descriptor with a single bearer and 
           three explicit Stream Descriptors. 
       
       Figure 6a: Multiplexed Termination Scenario - Cascaded Multiplexes 
    
    
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                 (Asterisks * denote the centre of the context) 
                                         
        Note: this figure does not appear in Rec. H.248.1 Amendment 1. 
       
      Terminations may be created which represent multiplexed bearers, such 
      as an ATM AAL Type 2 bearer. When a new multiplexed bearer is to be 
      created, an ephemeral Termination is created in a Context established 
      for this purpose. When the Termination is subtracted, the multiplexed 
      bearer is destroyed. 

   6.2.1 Termination dynamics 
       
      The protocol can be used to create new Terminations and to modify 
      property values of existing Terminations. These modifications include 
      the possibility of adding or removing events and/or signals. The 
      Termination properties, and events and signals are described in the 
      ensuing subclauses. An MGC can only release/modify Terminations and 
      the resources that the Termination represents which it has previously 
      seized via, e.g. the Add command. 

   6.2.2 TerminationIDs 
       
      Terminations are referenced by a TerminationID, which is an arbitrary 
      schema chosen by the MG. 

      TerminationIDs of physical Terminations are provisioned in the Media 
      Gateway. The TerminationIDs may be chosen to have structure. For 
      instance, a TerminationID may consist of trunk group and a trunk 
      within the group. 

      A wildcarding mechanism using two types of wildcards can be used with 
      TerminationIDs. The two wildcards are ALL and CHOOSE. The former is 
      used to address multiple Terminations at once, while the latter is 
      used to indicate to a media gateway that it must select a Termination 
      satisfying the partially specified TerminationID. This allows, for 
      instance, that a MGC instructs a MG to choose a circuit within a 
      trunk group. 

      When ALL is used in the TerminationID of a command, the effect is 
      identical to repeating the command with each of the matching 
      TerminationIDs. The use of ALL does not address the ROOT termination. 
      Since each of these commands may generate a response, the size of the 
      entire response may be large. If individual responses are not 
      required, a wildcard response may be requested. In such a case, a 
      single response is generated, which contains the UNION of all of the 
      individual responses which otherwise would have been generated, with 
      duplicate values suppressed. For instance, given a Termination Ta 
      with properties p1=a, p2=b and Termination Tb with properties p2=c, 
      p3=d, a UNION response would consist of a wildcarded TerminationId 
    
    
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      and the sequence of properties p1=a, p2=b,c and p3=d. Wildcard 
      response may be particularly useful in the Audit commands. 

      The encoding of the wildcarding mechanism is detailed in Annexes A 
      and B. 

   6.2.3 Packages 
       
      Different types of gateways may implement Terminations that have 
      widely differing characteristics. Variations in Terminations are 
      accommodated in the protocol by allowing Terminations to have 
      optional Properties, Events, Signals and Statistics implemented by 
      MGs. 

      In order to achieve MG/MGC interoperability, such options are grouped 
      into Packages, and typically a Termination realizes a set of such 
      Packages. More information on definition of packages can be found in 
      clause 12. An MGC can audit a Termination to determine which Packages 
      it realizes. 

      Properties, Events, Signals and Statistics defined in Packages, as 
      well as parameters to them, are referenced by identifiers (Ids). 
      Identifiers are scoped. For each package, PropertyIds, EventIds, 
      SignalIds, StatisticsIds and ParameterIds have unique name spaces and 
      the same identifier may be used in each of them. Two PropertyIds in 
      different packages may also have the same identifier, etc. 

      To support a particular package the MG must support all properties, 
      signals, events and statistics defined in a package. It must also 
      support all Signal and Event parameters. The MG may support a subset 
      of the values listed in a package for a particular Property or 
      Parameter. 

      When packages are extended, the properties, events, signals and 
      statistics defined in the base package can be referred to using 
      either the extended package name or the base package name.  For 
      example, if Package A defines event e1, and Package B extends Package 
      A, then B/e1 is an event for a termination implementing Package B. By 
      definition, the MG MUST also implement the base Package, but it is 
      optional to publish the base package as an allowed interface.  If it 
      does publish  A, then A would be reported on the Package Descriptor 
      in AuditValue as well as B, and event A/e1 would be available on a 
      termination.  If the MG does not publish A, then only B/e1 would be 
      available.  If published through AuditValue, A/e1 and B/e1 are the 
      same event.  

      For improved interoperability and backward compatibility, an MG MAY 
      publish all Packages supported by its Terminations, including base 
      Packages from which extended Packages are derived.  An exception to 
    
    
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      this is in cases where the base packages are expressly "Designed to 
      be extended only". 

   6.2.4 Termination properties and descriptors 
       
      Terminations have properties. The properties have unique PropertyIDs. 
      Most properties have default values, which are explicitly defined in 
      this protocol specification or in a package (see clause 12) or set by 
      provisioning. If not provisioned otherwise, the properties in all 
      descriptors except TerminationState and LocalControl default to 
      empty/"no value" when a Termination is first created or returned to 
      the null Context. The default contents of the two exceptions are 
      described in 7.1.5 and 7.1.7. 

      The provisioning of a property value in the MG will override any 
      default value, be it supplied in this protocol specification or in a 
      package.  Therefore if it is essential for the MGC to have full 
      control over the property values of a Termination, it should supply 
      explicit values when ADDing the Termination to a Context.  
      Alternatively, for a physical Termination the MGC can determine any 
      provisioned property values by auditing the Termination while it is 
      in the NULL Context. 

      There are a number of common properties for Terminations and 
      properties specific to media streams. The common properties are also 
      called the Termination state properties. For each media stream, there 
      are local properties and properties of the received and transmitted 
      flows. 

      Properties not included in the base protocol are defined in Packages. 
      These properties are referred to by a name consisting of the 
      PackageName and a PropertyId. Most properties have default values 
      described in the Package description. Properties may be read-only or 
      read/write. The possible values of a property may be audited, as can 
      their current values. For properties that are read/write, the MGC can 
      set their values. A property may be declared as "Global" which has a 
      single value shared by all Terminations realizing the package. 
      Related properties are grouped into descriptors for convenience. 

      When a Termination is added to a Context, the value of its read/write 
      properties can be set by including the appropriate descriptors as 
      parameters to the Add command. Similarly, a property of a Termination 
      in a Context may have its value changed by the Modify command. 
      Properties may also have their values changed when a Termination is 
      moved from one Context to another as a result of a Move command. In 
      some cases, descriptors are returned as output from a command. 

      In general, if a Descriptor is completely omitted from one of the 
      aforementioned Commands, the properties in that Descriptor retain 
    
    
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      their prior values for the Termination(s) upon which the Command 
      acts. On the other hand, if some read/write properties are omitted 
      from a Descriptor in a Command (i.e., the Descriptor is only 
      partially specified), those properties will be reset to their default 
      values for the Termination(s) upon which the Command acts, unless the 
      package specifies other behavior. For more details, see clause 7.1 
      dealing with the individual Descriptors. 

      The following table lists all of the possible descriptors and their 
      use. Not all descriptors are legal as input or output parameters to 
      every command. 

      Descriptor name  Description 

      Modem            Identifies modem type and properties when 
                       applicable 

      Mux              Describes multiplex type for multimedia 
                       Terminations (e.g. H.221, H.223, H.225.0) and 
                       Terminations forming the input mux 

      Media            A list of media stream specifications (see 7.1.4) 

      TerminationState Properties of a Termination (which can be defined 
                       in Packages) that are not stream specific 

      Stream           A list of remote/local/localControl descriptors for 
                       a single stream 

      Local            Contains properties that specify the media flows 
                       that the MG receives from the remote entity. 

      Remote           Contains properties that specify the media flows 
                       that the MG sends to the remote entity. 

      LocalControl     Contains properties (which can be defined in 
                       packages) that are of interest between the MG and 
                       the MGC 

      Events           Describes events to be detected by the MG and what 
                       to do when an event is detected 

      EventBuffer      Describes events to be detected by the MG when 
                       Event Buffering is active 

      Signals          Describes signals (see 7.1.11) applied  to  
                       Terminations 

    
    
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      Audit            In Audit commands, identifies which information is 
                       desired 

      Packages         In AuditValue, returns a list of Packages realized 
                       by Termination 

      DigitMap         Defines patterns against which sequences of a 
                       specified set of events  are to be matched so they 
                       can be reported as a group rather than singly 

      ServiceChange    In ServiceChange, what, why service change 
                       occurred, etc.  

      ObservedEvents   In Notify or AuditValue, report of events observed 

      Statistics       In Subtract and Audit, report of Statistics kept on 
                       a Termination 

      Topology         Specifies flow directions between Terminations in a 
                       Context 

      Error            Contains an error code and optionally error text; 
                       it may occur in command replies and in Notify 
                       requests 

       

   6.2.5 Root Termination 
       
      Occasionally, a command must refer to the entire gateway, rather than 
      a Termination within it. A special TerminationID, "Root" is reserved 
      for this purpose. Packages may be defined on Root. Root thus may have 
      properties, events and statistics (signals are not appropriate for 
      root). Accordingly, the root TerminationID may appear in: 

      -  a Modify command - to change a property or set an event 

      -  a Notify command - to report an event 

      -  an AuditValue return - to examine the values of properties and 
         statistics implemented on root 

      -  an AuditCapability - to determine what properties of root are 
         implemented 

      -  a ServiceChange - to declare the gateway in or out of service. 


    
    
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      Any other use of the root TerminationID is an error. Error code 410 - 
      Incorrect identifier shall be returned in these cases. 

       
   7  Commands 
       
      The protocol provides commands for manipulating the logical entities 
      of the protocol connection model, Contexts and Terminations. Commands 
      provide control at the finest level of granularity supported by the 
      protocol. For example, Commands exist to add Terminations to a 
      Context, modify Terminations, subtract Terminations from a Context, 
      and audit properties of Contexts or Terminations. Commands provide 
      for complete control of the properties of Contexts and Terminations. 
      This includes specifying which events a Termination is to report, 
      which signals/actions are to be applied to a Termination and 
      specifying the topology of a Context (who hears/sees whom). 

      Most commands are for the specific use of the Media Gateway 
      Controller as command initiator in controlling Media Gateways as 
      command responders. The exceptions are the Notify and ServiceChange 
      commands: Notify is sent from Media Gateway to Media Gateway 
      Controller, and ServiceChange may be sent by either entity. Below is 
      an overview of the commands; they are explained in more detail in 
      7.2. 

      1) Add - The Add command adds a Termination to a Context. The Add 
         command on the first Termination in a Context is used to create a 
         Context. 

      2) Modify - The Modify command modifies the properties, events and 
         signals of a Termination. 

      3) Subtract - The Subtract command disconnects a Termination from its 
         Context and returns statistics on the Termination's participation 
         in the Context. The Subtract command on the last Termination in a 
         Context deletes the Context. 

      4) Move - The Move command atomically moves a Termination to another 
         Context. 

      5) AuditValue - The AuditValue command returns the current state of 
         properties, events, signals and statistics of Terminations. 

      6) AuditCapabilities - The AuditCapabilities command returns all the 
         possible values for Termination properties, events and signals 
         allowed by the Media Gateway. 



    
    
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      7) Notify - The Notify command allows the Media Gateway to inform the 
         Media Gateway Controller of the occurrence of events in the Media 
         Gateway. 

      8) ServiceChange - The ServiceChange command allows the Media Gateway 
         to notify the Media Gateway Controller that a Termination or group 
         of Terminations is about to be taken out of service or has just 
         been returned to service. ServiceChange is also used by the MG to 
         announce its availability to a MGC (registration), and to notify 
         the MGC of impending or completed restart of the MG. The MGC may 
         announce a handover to the MG by sending it a ServiceChange 
         command. The MGC may also use ServiceChange to instruct the MG to 
         take a Termination or group of Terminations in or out of service. 

      These commands are detailed in 7.2.1 through 7.2.8. 

   7.1   Descriptors 
       
      The parameters to a command are termed Descriptors. A descriptor 
      consists of a name and a list of items. Some items may have values. 
      Many Commands share common descriptors. This subclause enumerates 
      these descriptors. Descriptors may be returned as output from a 
      command. In any such return of descriptor contents, an empty 
      descriptor is represented by its name unaccompanied by any list. 
      Parameters and parameter usage specific to a given Command type are 
      described in the subclause that describes the Command. 

   7.1.1 Specifying parameters 
       
      Command parameters are structured into a number of descriptors. In 
      general, the text format of descriptors is 
      DescriptorName=<someID>{parm=value, parm=value, ...}. 

      Parameters may be fully specified, overspecified or underspecified: 

      1) Fully specified parameters have a single, unambiguous value that 
         the command initiator is instructing the command responder to use 
         for the specified parameter. 

      2) Underspecified parameters, using the CHOOSE value, allow the 
         command responder to choose any value it can support. 

      3) Overspecified parameters have a list of potential values. The list 
         order specifies the command initiator's order of preference of 
         selection. The command responder chooses one value from the 
         offered list and returns that value to the command initiator. 

      If a required descriptor other than the Audit descriptor is 
      unspecified (i.e. entirely absent) from a command, the previous 
    
    
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      values set in that descriptor for that Termination, if any, are 
      retained. In command other than Substract, a missing Audit descriptor 
      is equivalent to an empty Audit descriptor. The Behaviour of the MG 
      with respect to unspecified parameters within a descriptor varies 
      with the descriptor concerned, as indicated in succeeding subclauses. 
      Whenever a parameter is underspecified or overspecified, the 
      descriptor containing the value chosen by the responder is included 
      as output from the command. 

      Each command specifies the TerminationId the command operates on. 
      This TerminationId may be "wildcarded". When the TerminationId of a 
      command is wildcarded, the effect shall be as if the command was 
      repeated with each of the TerminationIds matched. 

   7.1.2 Modem descriptor 
       
      The Modem descriptor specifies the modem type and parameters, if any, 
      required for use in e.g. H.324 and text conversation. The descriptor 
      includes the following modem types: V.18, V.22, V.22 bis, V.32, V.32 
      bis, V.34, V.90, V.91, Synchronous ISDN, and allows for extensions. 
      By default, no Modem descriptor is present in a Termination. 

   7.1.3 Multiplex descriptor 
       
      In multimedia calls, a number of media streams are carried on a 
      (possibly different) number of bearers. The multiplex descriptor 
      associates the media and the bearers. The descriptor includes the 
      multiplex type: 

      -  H.221; 

      -  H.223; 

      -  H.226; 

      -  V.76; 

      -  possible extensions, 

      and a set of TerminationIDs representing the multiplexed bearers, in 
      order. For example: 

         Mux = H.221{ MyT3/1/2, MyT3/2/13, MyT3/3/6, MyT3/21/22} 

   7.1.4 Media descriptor 
       
      The Media descriptor specifies the parameters for all the media 
      streams. These parameters are structured into two descriptors: a 
      TerminationState descriptor, which specifies the properties of a 
    
    
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      Termination that are not stream dependent, and one or more Stream 
      descriptors each of which describes a single media stream. 

      A stream is identified by a StreamID. The StreamID is used to link 
      the streams in a Context that belong together. Multiple streams 
      exiting a Termination shall be synchronized with each other. Within 
      the Stream descriptor, there are up to three subsidiary descriptors: 
      LocalControl, Local, and Remote. The relationship between these 
      descriptors is thus: 

      Media descriptor 
         TerminationState Descriptor 
         Stream descriptor 
            LocalControl descriptor 
            Local descriptor 
            Remote descriptor 

      As a convenience, LocalControl, Local, or Remote descriptors may be 
      included in the Media descriptor without an enclosing Stream 
      descriptor. In this case, the StreamID is assumed to be 1. 

   7.1.5 TerminationState descriptor 
       
      The TerminationState descriptor contains the ServiceStates property, 
      the EventBufferControl property and properties of a Termination 
      (defined in Packages) that are not stream specific. 

      The ServiceStates property describes the overall state of the 
      Termination (not stream specific). A Termination can be in one of the 
      following states: "test", "out of service", or "in service". The 
      "test" state indicates that the Termination is being tested. The 
      state "out of service" indicates that the Termination cannot be used 
      for traffic. The state "in service" indicates that a Termination can 
      be used or is being used for normal traffic. "in service" is the 
      default state. 

        

      Values assigned to Properties may be simple values 
      (integer/string/enumeration) or may be underspecified, where more 
      than one value is supplied and the MG may make a choice: 

      -  Alternative Values - multiple values in a list, one of which must 
         be selected 

      -  Ranges - minimum and maximum values, any value between min and max 
         must be selected, boundary values included 


    
    
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      -  Greater Than/Less Than - value must be greater/less than specified 
         value 

      -  CHOOSE Wildcard - the MG chooses from the allowed values for the 
         property 

      The EventBufferControl property specifies whether events are buffered 
      following detection of an event in the Events descriptor, or 
      processed immediately. See 7.1.9 for details. 

   7.1.6 Stream descriptor 
       
      A Stream descriptor specifies the parameters of a single 
      bidirectional stream. These parameters are structured into three 
      descriptors: one that contains Termination properties specific to a 
      stream and one each for local and remote flows. The Stream Descriptor 
      includes a StreamID which identifies the stream. Streams are created 
      by specifying a new StreamID on one of the Terminations in a Context. 
      A stream is deleted by setting empty Local and Remote descriptors for 
      the stream with ReserveGroup and ReserveValue in LocalControl set to 
      "false" on all Terminations in the Context that previously supported 
      that stream. 

      StreamIDs are of local significance between MGC and MG and they are 
      assigned by the MGC. Within a Context, StreamID is a means by which 
      to indicate which media flows are interconnected: streams with the 
      same StreamID are connected. 

      If a Termination is moved from one Context to another, the effect on 
      the Context to which the Termination is moved is the same as in the 
      case that a new Termination were added with the same StreamIDs as the 
      moved Termination. 

   7.1.7 LocalControl descriptor 
       
      The LocalControl descriptor contains the Mode property, the 
      ReserveGroup and ReserveValue properties and properties of a 
      Termination (defined in Packages) that are stream specific, and are 
      of interest between the MG and the MGC. Values of properties may be 
      underspecified as in 7.1.1. 

      The allowed values for the mode property are send-only, receive-only, 
      send/receive, inactive and loop-back. "Send" and "receive" are with 
      respect to the exterior of the Context, so that, for example, a 
      stream set to mode=sendOnly does not pass received media into the 
      Context. The default value for the mode property is "Inactive". 
      Signals and Events are not affected by mode. 


    
    
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      The boolean-valued Reserve properties, ReserveValue and ReserveGroup, 
      of a Termination indicate what the MG is expected to do when it 
      receives a Local and/or Remote descriptor.  

      If the value of a Reserve property is True, the MG SHALL reserve 
      resources for all alternatives specified in the Local and/or Remote 
      descriptors for which it currently has resources available. It SHALL 
      respond with the alternatives for which it reserves resources. If it 
      cannot not support any of the alternatives, it SHALL respond with a 
      reply to the MGC that contains empty Local and/or Remote descriptors. 
      If media begins to flow while more than a single alternative is 
      reserved, media packets may be sent/received on any of the 
      alternatives and must be processed, although only a single 
      alternative may be active at any given time. 

      If the value of a Reserve property is False, the MG SHALL choose one 
      of the alternatives specified in the Local descriptor (if present) 
      and one of the alternatives specified in the Remote descriptor (if 
      present). If the MG has not yet reserved resources to support the 
      selected alternative, it SHALL reserve the resources. If, on the 
      other hand, it already reserved resources for the Termination 
      addressed (because of a prior exchange with ReserveValue and/or 
      ReserveGroup equal to True), it SHALL release any excess resources it 
      reserved previously. Finally, the MG shall send a reply to the MGC 
      containing the alternatives for the Local and/or Remote descriptor 
      that it selected. If the MG does not have sufficient resources to 
      support any of the alternatives specified, is SHALL respond with 
      error 510 (insufficient resources). 

      The default value of ReserveValue and ReserveGroup is False. More 
      information on the use of the two Reserve properties is provided in 
      7.1.8. 

      A new setting of the LocalControl Descriptor completely replaces the 
      previous setting of that descriptor in the MG. Thus, to retain 
      information from the previous setting, the MGC must include that 
      information in the new setting. If the MGC wishes to delete some 
      information from the existing descriptor, it merely resends the 
      descriptor (in a Modify command) with the unwanted information 
      stripped out. 

   7.1.8 Local and Remote descriptors 
       
      The MGC uses Local and Remote descriptors to reserve and commit MG 
      resources for media decoding and encoding for the given Stream(s) and 
      Termination to which they apply. The MG includes these descriptors in 
      its response to indicate what it is actually prepared to support. The 
      MG SHALL include additional properties and their values in its 
      response if these properties are mandatory yet not present in the 
    
    
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      requests made by the MGC (e.g. by specifying detailed video encoding 
      parameters where the MGC only specified the payload type). 

      Local refers to the media received by the MG and Remote refers to the 
      media sent by the MG. 

      When text encoding the protocol, the descriptors consist of session 
      descriptions as defined in SDP (RFC 2327). In session descriptions 
      sent from the MGC to the MG, the following exceptions to the syntax 
      of RFC 2327 are allowed: 

      -  the "s=", "t=" and "o=" lines are optional; 

      -  the use of CHOOSE is allowed in place of a single parameter value; 
         and 

      -  the use of alternatives is allowed in place of a single parameter 
         value. 

      A Stream Descriptor specifies a single bi-directional media stream 
      and so a single session description MUST NOT include more than one 
      media description ("m=" line). A Stream Descriptor may contain 
      additional session descriptions as alternatives.  Each media stream 
      for a termination must appear in distinct Stream Descriptors. When 
      multiple session descriptions are provided in one descriptor, the 
      "v=" lines are required as delimiters; otherwise they are optional in 
      session descriptions sent to the MG. Implementations shall accept 
      session descriptions that are fully conformant to RFC 2327. When 
      binary encoding the protocol the descriptor consists of groups of 
      properties (tag-value pairs) as specified in Annex C. Each such group 
      may contain the parameters of a session description. 

      Below, the semantics of the Local and Remote descriptors are 
      specified in detail. The specification consists of two parts. The 
      first part specifies the interpretation of the contents of the 
      descriptor. The second part specifies the actions the MG must take 
      upon receiving the Local and Remote descriptors. The actions to be 
      taken by the MG depend on the values of the ReserveValue and 
      ReserveGroup properties of the LocalControl descriptor. 

      Either the Local or the Remote descriptor or both may be: 

      1) unspecified (i.e. absent); 

      2) empty; 

      3) underspecified through use of CHOOSE in a property value; 

      4) fully specified; or 
    
    
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      5) overspecified through presentation of multiple groups of 
         properties and possibly multiple property values in one or more of 
         these groups. 

      Where the descriptors have been passed from the MGC to the MG, they 
      are interpreted according to the rules given in 7.1.1, with the 
      following additional comments for clarification: 

      a) An unspecified Local or Remote descriptor is considered to be a 
         missing mandatory parameter. It requires the MG to use whatever 
         was last specified for that descriptor. It is possible that there 
         was no previously specified value, in which case the descriptor 
         concerned is ignored in further processing of the command. 

      b) An empty Local (Remote) descriptor in a message from the MGC 
         signifies a request to release any resources reserved for the 
         media flow received (sent). 

      c) If multiple groups of properties are present in a Local or Remote 
         descriptor or multiple values within a group, the order of 
         preference is descending. 

      d) Underspecified or overspecified properties within a group of
         properties sent by the MGC are requests for the MG to choose one 
         or more values which it can support for each of those properties. 
         In case of an overspecified property, the list of values is in 
         descending order of preference. 

      Subject to the above rules, subsequent action depends on the values 
      of the ReserveValue and ReserveGroup properties in LocalControl. 

      If ReserveGroup is True, the MG reserves the resources required to 
      support any of the requested property group alternatives that it can 
      currently support. If ReserveValue is True, the MG reserves the 
      resources required to support any of the requested property value 
      alternatives that it can currently support. 

      NOTE - If a Local or Remote descriptor contains multiple groups of 
      properties, and ReserveGroup is True, then the MG is requested to 
      reserve resources so that it can decode or encode the media stream 
      according to any of the alternatives. For instance, if the Local 
      descriptor contains two groups of properties, one specifying 
      packetized G.711 A-law audio and the other G.723.1 audio, the MG 
      reserves resources so that it can decode one audio stream encoded in 
      either G.711 A-law format or G.723.1 format. The MG does not have to 
      reserve resources to decode two audio streams simultaneously, one 
      encoded in G.711 A-law and one in G.723.1. The intention for the use 
      of ReserveValue is analogous. 

    
    
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      If ReserveGroup is true or ReserveValue is True, then the following 
      rules apply: 

      -  If the MG has insufficient resources to support all alternatives 
         requested by the MGC and the MGC requested resources in both Local 
         and Remote, the MG should reserve resources to support at least 
         one alternative each within Local and Remote. 

      -  If the MG has insufficient resources to support at least one 
         alternative within a Local (Remote) descriptor received from the 
         MGC, it shall return an empty Local (Remote) in response. 

      -  In its response to the MGC, when the MGC included Local and Remote 
         descriptors, the MG SHALL include Local and Remote descriptors for 
         all groups of properties and property values it reserved resources 
         for. If the MG is incapable of supporting at least one of the 
         alternatives within the Local (Remote) descriptor received from 
         the MGC, it SHALL return an empty Local (Remote) descriptor. 

      -  If the Mode property of the LocalControl descriptor is RecvOnly, 
         SendRecv, or LoopBack, the MG must be prepared to receive media 
         encoded according to any of the alternatives included in its 
         response to the MGC. 

      If ReserveGroup is False and ReserveValue is False, then the MG 
      SHOULD apply the following rules to resolve Local and Remote to a 
      single alternative each: 

      -  The MG chooses the first alternative in Local for which it is able 
         to support at least one alternative in Remote. 

      -  If the MG is unable to support at least one Local and one Remote 
         alternative, it returns Error 510 (Insufficient Resources). 

      -  The MG returns its selected alternative in each of Local and 
         Remote. 

      A new setting of a Local or Remote descriptor completely replaces the 
      previous setting of that descriptor in the MG. Thus, to retain 
      information from the previous setting, the MGC must include that 
      information in the new setting. If the MGC wishes to delete some 
      information from the existing descriptor, it merely resends the 
      descriptor (in a Modify command) with the unwanted information 
      stripped out. 

   7.1.9 Events descriptor 
       
      The EventsDescriptor parameter contains a RequestIdentifier and a 
      list of events that the Media Gateway is requested to detect and 
    
    
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      report. The RequestIdentifier is used to correlate the request with 
      the notifications that it may trigger. Requested events include, for 
      example, fax tones, continuity test results, and on-hook and off-hook 
      transitions. The RequestIdentifier is omitted if the EventsDescriptor 
      is empty (i.e. no events are specified). 

      Each event in the descriptor contains the Event name, an optional 
      streamID, an optional KeepActive flag, and optional parameters. The 
      Event name consists of a Package Name (where the event is defined) 
      and an EventID. The ALL wildcard may be used for the EventID, 
      indicating that all events from the specified package have to be 
      detected. The default streamID is 0, indicating that the event to be 
      detected is not related to a particular media stream. Events can have 
      parameters. This allows a single event description to have some 
      variation in meaning without creating large numbers of individual 
      events. Further event parameters are defined in the package. 

      If a digit map completion event is present or implied in the 
      EventsDescriptor, the EventDM parameter is used to carry either the 
      name or the value of the associated digit map. See 7.1.14 for further 
      details. 

      When an event is processed against the contents of an active Events 
      Descriptor and found to be present in that descriptor ("recognized"), 
      the default action of the MG is to send a Notify command to the MGC. 
      Notification may be deferred if the event is absorbed into the 
      current dial string of an active digit map (see 7.1.14). Any other 
      action is for further study. Moreover, event recognition may cause 
      currently active signals to stop, or may cause the current Events 
      and/or Signals descriptor to be replaced, as described at the end of 
      this subclause. Unless the Events Descriptor is replaced by another 
      Events Descriptor, it remains active after an event has been 
      recognized. 

      If the value of the EventBufferControl property equals LockStep, 
      following detection of such an event, normal handling of events is 
      suspended. Any event which is subsequently detected and occurs in the 
      EventBuffer descriptor is added to the end of the EventBuffer (a FIFO 
      queue), along with the time that it was detected. The MG SHALL wait 
      for a new EventsDescriptor to be loaded. A new EventsDescriptor can 
      be loaded either as the result of receiving a command with a new 
      EventsDescriptor, or by activating an embedded EventsDescriptor. 

      If EventBufferControl equals Off, the MG continues processing based 
      on the active EventsDescriptor. 

      In the case of an embedded EventsDescriptor being activated, the MG 
      continues event processing based on the newly activated 
      EventsDescriptor. 
    
    
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        NOTE 1 - For purposes of EventBuffer handling, activation of an 
        embedded EventsDescriptor is equivalent to receipt of a new 
        EventsDescriptor. 

      When the MG receives a command with a new EventsDescriptor, one or 
      more events may have been buffered in the EventBuffer in the MG. The 
      value of EventBufferControl then determines how the MG treats such 
      buffered events. 

        

      Case 1 

      If EventBufferControl equals LockStep and the MG receives a new 
      EventsDescriptor, it will check the FIFO EventBuffer and take the 
      following actions: 

      1) If the EventBuffer is empty, the MG waits for detection of events 
         based on the new EventsDescriptor. 

      2) If the EventBuffer is non-empty, the MG processes the FIFO queue 
         starting with the first event: 

         a) If the event in the queue is in the events listed in the new 
            EventsDescriptor, the MG acts on the event and removes the 
            event from the EventBuffer. The time stamp of the Notify shall 
            be the time the event was actually detected. The MG then waits 
            for a new EventsDescriptor. While waiting for a new 
            EventsDescriptor, any events detected that appear in the 
            EventsBufferDescriptor will be placed in the EventBuffer. When 
            a new EventsDescriptor is received, the event processing will 
            repeat from step 1. 

         b) If the event is not in the new EventsDescriptor, the MG SHALL 
            discard the event and repeat from step 1. 

      Case 2 

      If EventBufferControl equals Off and the MG receives a new 
      EventsDescriptor, it processes new events with the new 
      EventsDescriptor. 

      If the MG receives a command instructing it to set the value of 
      EventBufferControl to Off, all events in the EventBuffer SHALL be 
      discarded. 

      The MG may report several events in a single Transaction as long as 
      this does not unnecessarily delay the reporting of individual events. 

    
    
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      For procedures regarding transmitting the Notify command, refer to 
      the appropriate annex or Recommendation of the H.248 sub-series for 
      specific transport considerations. 

      The default value of EventBufferControl is Off. 

        NOTE 2 - Since the EventBufferControl property is in the 
        TerminationStateDescriptor, the MG might receive a command that 
        changes the EventBufferControl property and does not include an 
        EventsDescriptor. 

      Normally, recognition of an event shall cause any active signals to 
      stop. When KeepActive is specified in the event, the MG shall not 
      interrupt any signals active on the Termination on which the event is 
      detected. 

      An event can include an Embedded Signals descriptor and/or an 
      Embedded Events descriptor which, if present, replaces the current 
      Signals/Events descriptor when the event is recognized. It is 
      possible, for example, to specify that the dial-tone Signal be 
      generated when an off-hook Event is recognized, or that the dial-tone 
      Signal be stopped when a digit is recognized. A media gateway 
      controller shall not send EventsDescriptors with an event both marked 
      KeepActive and containing an embedded SignalsDescriptor. 

      Only one level of embedding is permitted. An embedded 
      EventsDescriptor SHALL NOT contain another embedded EventsDescriptor; 
      an embedded EventsDescriptor MAY contain an embedded 
      SignalsDescriptor. 

      An EventsDescriptor received by a media gateway replaces any previous 
      Events descriptor. Event notification in process shall complete, and 
      events detected after the command containing the new EventsDescriptor 
      executes, shall be processed according to the new EventsDescriptor. 

      An empty Events Descriptor disables all event recognition and 
      reporting.  An empty EventBuffer Descriptor clears the EventBuffer 
      and disables all event accumulation in LockStep mode: the only events 
      reported will be those occurring while an Events Descriptor is 
      active.  If an empty Events Descriptor is activated while the 
      Termination is operating in LockStep mode, the events buffer is 
      immediately cleared. 

   7.1.10   EventBuffer descriptor 
       
      The EventBuffer descriptor contains a list of events, with their 
      parameters if any, that the MG is requested to detect and buffer when 
      EventBufferControl equals LockStep (see 7.1.9). 

    
    
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   7.1.11   Signals descriptor 
       
      Signals are MG generated media such as tones and announcements as 
      well as bearer-related signals such as hookswitch. More complex 
      signals may include a sequence of such simple signals interspersed 
      with and conditioned upon the receipt and analysis of media or 
      bearer-related signals. Examples include echoing of received data as 
      in Continuity Test package.  Signals may also request preparation of 
      media content for future signals. 

      A SignalsDescriptor is a parameter that contains the set of signals 
      that the Media Gateway is asked to apply to a Termination. A 
      SignalsDescriptor contains a number of signals and/or sequential 
      signal lists. A SignalsDescriptor may contain zero signals and 
      sequential signal lists. Support of sequential signal lists is 
      optional. 

      Signals are defined in packages. Signals shall be named with a 
      Package name (in which the signal is defined) and a SignalID. No 
      wildcard shall be used in the SignalID. Signals that occur in a 
      SignalsDescriptor have an optional StreamID parameter (default is 0, 
      to indicate that the signal is not related to a particular media 
      stream), an optional signal type (see below), an optional duration 
      and possibly parameters defined in the package that defines the 
      signal. This allows a single signal to have some variation in 
      meaning, obviating the need to create large numbers of individual 
      signals. 

      Finally, the optional parameter "notifyCompletion" allows a MGC to 
      indicate that it wishes to be notified when the signal finishes 
      playout. The possible cases are that the signal timed out (or 
      otherwise completed on its own), that it was interrupted by an event, 
      that it was halted when a Signals descriptor was replaced, or that it 
      stopped or never started for other reasons. If the notifyCompletion 
      parameter is not included in a Signals descriptor, notification is 
      generated only if the signal stopped or was never started for other 
      reasons. For reporting to occur, the signal completion event (see 
      E.1.2) must be enabled in the currently active Events descriptor. 

      The duration is an integer value that is expressed in hundredths of a 
      second. 

      There are three types of signals: 

      -  on/off - the signal lasts until it is turned off; 

      -  timeout - the signal lasts until it is turned off or a specific 
         period of time elapses; 

    
    
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      -  brief - the signal will stop on its own unless a new Signals 
         descriptor is applied that causes it to stop; no timeout value is 
         needed. 

      If a signal of default type other than TO has its type overridden to 
      type TO in the Signals descriptor, the duration parameter must be 
      present. 

      If the signal type is specified in a SignalsDescriptor, it overrides 
      the default signal type (see 12.1.4). If duration is specified for an 
      on/off signal, it SHALL be ignored. 

      A sequential signal list consists of a signal list identifier and a 
      sequence of signals to be played sequentially. Only the trailing 
      element of the sequence of signals in a sequential signal list may be 
      an on/off signal. The duration of a sequential signal list is the sum 
      of the durations of the signals it contains.  

      Multiple signals and sequential signal lists in the same 
      SignalsDescriptor shall be played simultaneously. 

      Signals are defined as proceeding from the Termination towards the 
      exterior of the Context unless otherwise specified in a package. When 
      the same Signal is applied to multiple Terminations within one 
      Transaction, the MG should consider using the same resource to 
      generate these Signals. 

      Production of a Signal on a Termination is stopped by application of 
      a new SignalsDescriptor, or detection of an Event on the Termination 
      (see 7.1.9). 

      A new SignalsDescriptor replaces any existing SignalsDescriptor. Any 
      signals applied to the Termination not in the replacement descriptor 
      shall be stopped, and new signals are applied, except as follows. 
      Signals present in the replacement descriptor and containing the 
      KeepActive flagshall be continued if they are currently playing and 
      have not already completed. If a replacement signal descriptor 
      contains a signal that is not currently playing and contains the 
      KeepActive flag, that signal SHALL be ignored. If the replacement 
      descriptor contains a sequential signal list with the same identifier 
      as the existing descriptor, then 

      -  the signal type and sequence of signals in the sequential signal 
         list in the replacement descriptor shall be ignored; and 

      -  the playing of the signals in the sequential signal list in the 
         existing descriptor shall not be interrupted. 


    
    
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   7.1.12   Audit descriptor 
       
      The Audit descriptor specifies what information is to be audited. The 
      Audit descriptor specifies the list of descriptors to be returned. 
      Audit may be used in any command to force the return of any 
      descriptor containing the current values of its properties, events, 
      signals and statistics even if that descriptor was not present in the 
      command, or had no underspecified parameters. Possible items in the 
      Audit descriptor are: 

         Modem  
         Mux  
         Events  
         Media 
         Signals  
         ObservedEvents 
         DigitMap 
         Statistics 
         Packages 
         EventBuffer 

      Audit may be empty, in which case, no descriptors are returned. This 
      is useful in Subtract, to inhibit return of statistics, especially 
      when using wildcard. 

   7.1.13   ServiceChange descriptor 
       
      The ServiceChangeDescriptor contains the following parameters: 

         .  ServiceChangeMethod  
         .  ServiceChangeReason  
         .  ServiceChangeAddress  
         .  ServiceChangeDelay 
         .  ServiceChangeProfile 
         .  ServiceChangeVersion  
         .  ServiceChangeMGCId 
         .  TimeStamp 
         .  Extension 

      See 7.2.8. 

   7.1.14   DigitMap descriptor 
       
   7.1.14.1 DigitMap definition, creation, modification and deletion 
       
      A DigitMap is a dialing plan resident in the Media Gateway used for 
      detecting and reporting digit events received on a Termination. The 
      DigitMap descriptor contains a DigitMap name and the DigitMap to be 
      assigned. A digit map may be preloaded into the MG by management 
    
    
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      action and referenced by name in an EventsDescriptor, may be defined 
      dynamically and subsequently referenced by name, or the actual 
      digitmap itself may be specified in the EventsDescriptor. It is 
      permissible for a digit map completion event within an Events 
      descriptor to refer by name to a DigitMap which is defined by a 
      DigitMap descriptor within the same command, regardless of the 
      transmitted order of the respective descriptors. 

      DigitMaps defined in a DigitMapDescriptor can occur in any of the 
      standard Termination manipulation Commands of the protocol. A 
      DigitMap, once defined, can be used on all Terminations specified by 
      the (possibly wildcarded) TerminationID in such a command. DigitMaps 
      defined on the root Termination are global and can be used on every 
      Termination in the MG, provided that a DigitMap with the same name 
      has not been defined on the given Termination. When a DigitMap is 
      defined dynamically in a DigitMap descriptor: 

      -  A new DigitMap is created by specifying a name that is not yet 
         defined. The value shall be present. 

      -  A DigitMap value is updated by supplying a new value for a name 
         that is already defined. Terminations presently using the digitmap 
         shall continue to use the old definition; subsequent 
         EventsDescriptors specifying the name, including any 
         EventsDescriptor in the command containing the DigitMap 
         descriptor, shall use the new one. 

      -  A DigitMap is deleted by supplying an empty value for a name that 
         is already defined. Terminations presently using the digitmap 
         shall continue to use the old definition. 

   7.1.14.2 DigitMap Timers 
       
      The collection of digits according to a DigitMap may be protected by 
      three timers, viz. a start timer (T), short timer (S), and long timer 
      (L). 

      1) The start timer (T) is used prior to any digits having been 
         dialed. If the start timer is overridden with the value set to 
         zero (T=0), then the start timer shall be disabled.  This implies 
         that the MG will wait indefinitely for digits. 

      2) If the Media Gateway can determine that at least one more digit is 
         needed for a digit string to match any of the allowed patterns in 
         the digit map, then the interdigit timer value should be set to a 
         long (L) duration (e.g. 16 seconds). 

      3) If the digit string has matched one of the patterns in a digit 
         map, but it is possible that more digits could be received which 
    
    
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         would cause a match with a different pattern, then instead of 
         reporting the match immediately, the MG must apply the short timer 
         (S) and wait for more digits. 

      The timers are configurable parameters to a DigitMap. Default values 
      of these timers should be provisioned on the MG, but can be 
      overridden by values specified within the DigitMap. 

   7.1.14.3 DigitMap Syntax 
       
      The formal syntax of the digit map is described by the DigitMap rule 
      in the formal syntax description of the protocol (see Annex A and 
      Annex B). A DigitMap, according to this syntax, is defined either by 
      a string or by a list of strings. Each string in the list is an 
      alternative event sequence, specified either as a sequence of digit 
      map symbols or as a regular expression of digit map symbols. These 
      digit map symbols, the digits "0" through "9" and letters "A" through 
      a maximum value depending on the signalling system concerned, but 
      never exceeding "K", correspond to specified events within a package 
      which has been designated in the Events descriptor on the Termination 
      to which the digit map is being applied. (The mapping between events 
      and digit map symbols is defined in the documentation for packages 
      associated with channel-associated signalling systems such as DTMF, 
      MF, or R2. Digits "0" through "9" MUST be mapped to the corresponding 
      digit events within the signalling system concerned. Letters should 
      be allocated in logical fashion, facilitating the use of range 
      notation for alternative events.) 

      The letter "x" is used as a wildcard, designating any event 
      corresponding to symbols in the range "0"-"9". The string may also 
      contain explicit ranges and, more generally, explicit sets of 
      symbols, designating alternative events any one of which satisfies 
      that position of the digit map. Finally, the dot symbol "." stands 
      for zero or more repetitions of the event selector (event, range of 
      events, set of alternative events, or wildcard) that precedes it. As 
      a consequence of the third timing rule above, inter-event timing 
      while matching a terminal dot symbol uses the short timer by default. 

      In addition to these event symbols, the string may contain "S" and 
      "L" inter-event timing specifiers and the "Z" duration modifier. "S" 
      and "L" respectively indicate that the MG should use the short (S) 
      timer or the long (L) timer for subsequent events, overriding the 
      timing rules described above. If an explicit timing specifier is in 
      effect in one alternative event sequence, but none is given in any 
      other candidate alternative, the timer value set by the explicit 
      timing specifier must be used. If all sequences with explicit timing 
      controls are dropped from the candidate set, timing reverts to the 
      default rules given above. Finally, if conflicting timing specifiers 

    
    
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      are in effect in different alternative sequences, the long timer 
      shall be used. 

      A "Z" designates a long duration event: placed in front of the 
      symbol(s) designating the event(s) which satisfy a given digit 
      position, it indicates that that position is satisfied only if the 
      duration of the event exceeds the long-duration threshold. The value 
      of this threshold is assumed to be provisioned in the MG. 

   7.1.14.4 DigitMap Completion Event 
       
      A digit map is active while the Events descriptor which invoked it is 
      active and it has not completed. A digit map completes when: 

      -  a timer has expired; or 

      -  an alternative event sequence has been matched and no other 
         alternative event sequence in the digit map could be matched 
         through detection of an additional event (unambiguous match); or 

      -  an event has been detected such that a match to a complete 
         alternative event sequence of the digit map will be impossible no 
         matter what additional events are received. 

      Upon completion, a digit map completion event as defined in the 
      package providing the events being mapped into the digit map shall be 
      generated. At that point the digit map is deactivated. Subsequent 
      events in the package are processed as per the currently active event 
      processing mechanisms. 

   7.1.14.5 DigitMap Procedures 
       
      Pending completion, successive events shall be processed according to 
      the following rules: 

      1) The "current dial string", an internal variable, is initially 
         empty. The set of candidate alternative event sequences includes 
         all of the alternatives specified in the digit map. 

      2) At each step, a timer is set to wait for the next event, based 
         either on the default timing rules given above or on explicit 
         timing specified in one or more alternative event sequences. If 
         the timer expires and a member of the candidate set of 
         alternatives is fully satisfied, a timeout completion with full 
         match is reported. If the timer expires and part or none of any 
         candidate alternative is satisfied, a timeout completion with 
         partial match is reported. 


    
    
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      3) If an event is detected before the timer expires, it is mapped to 
         a digit string symbol and provisionally added to the end of the 
         current dial string. The duration of the event (long or not long) 
         is noted if and only if this is relevant in the current symbol 
         position (because at least one of the candidate alternative event 
         sequences includes the "Z" modifier at this position in the 
         sequence). 

      4) The current dial string is compared to the candidate alternative 
         event sequences. If and only if a sequence expecting a long-
         duration event at this position is matched (i.e. the event had 
         long duration and met the specification for this position), then 
         any alternative event sequences not specifying a long duration 
         event at this position are discarded, and the current dial string 
         is modified by inserting a "Z" in front of the symbol representing 
         the latest event. Any sequence expecting a long-duration event at 
         this position but not matching the observed event is discarded 
         from the candidate set. If alternative event sequences not 
         specifying a long duration event in the given position remain in 
         the candidate set after application of the above rules, the 
         observed event duration is treated as irrelevant in assessing 
         matches to them. 

      5) If exactly one candidate remains and it has been fully matched, a 
         completion event is generated indicating an unambiguous match. If 
         no candidates remain, the latest event is removed from the current 
         dial string and a completion event is generated indicating full 
         match if one of the candidates from the previous step was fully 
         satisfied before the latest event was detected, or partial match 
         otherwise. The event removed from the current dial string will 
         then be reported as per the currently active event processing 
         mechanisms. 

      6) If no completion event is reported out of step 5, processing 
         returns to step 2. 

   7.1.14.6 DigitMap Activation 
       
      A digit map is activated whenever a new Event descriptor is applied 
      to the Termination or embedded Event descriptor is activated, that 
      Event descriptor contains a digit map completion event. The digit map 
      completion event contains an eventDM field in the requested actions 
      field. Each new activation of a digit map begins at step 1 of the 
      above procedure, with a clear current dial string. Any previous 
      contents of the current dial string from an earlier activation are 
      lost. 

      A digit map completion event that does not contain an eventDM field 
      in its requested actions field is considered an error.  Upon receipt 
    
    
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      of such an event in an EventsDescriptor, a MG shall respond with an 
      error reponse, including Error 457 - Missing parameter in signal or 
      event. 

   7.1.14.7 Interaction Of DigitMap and Event Processing 
       
      While the digit map is activated, detection is enabled for all events 
      defined in the package containing the specified digit map completion 
      event. Normal event behaviour (e.g. stopping of signals unless the 
      digit completion event has the KeepActive flag enabled) continues to 
      apply for each such event detected, except that: 

      -  the events in the package containing the specified digit map 
         completion event other than the completion event itself are not 
         individually notified and have no side-effects unless separately 
         enabled; and 

      -  an event that triggers a partial match completion event is not 
         recognized and therefore has no side effects until reprocessed 
         following the recognition of the digit map completion event. 

   7.1.14.8 Wildcards 
       
      Note that if a package contains a digit map completion event, then an 
      event specification consisting of the package name with a wildcarded 
      ItemID (Property Name) will activate a digit map; to that end, the 
      event specification must include an eventDM field according to 
      section 7.1.14.6. If the package also contains the digit events 
      themselves, this form of event specification will cause the 
      individual events to be reported to the MGC as they are detected. 

   7.1.14.9 Example 
       
      As an example, consider the following dial plan: 

      0                      Local operator 

      00                     Long-distance operator 

      xxxx                   Local extension number (starts with 1-7) 

      8xxxxxxx               Local number 

      #xxxxxxx               Off-site extension 

      *xx                    Star services 


    
    
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      91xxxxxxxxxx           Long-distance number 

      9011 + up to 15 digits International number 

       

      If the DTMF detection package described in E.6 is used to collect the 
      dialled digits, then the dialling plan shown above results in the 
      following digit map: 

       (0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.) 

   7.1.15   Statistics descriptor 
       
      The Statistics Descriptor provides information describing the status 
      and usage of a Termination during its existence within a specific 
      Context. There is a set of standard statistics kept for each 
      Termination where appropriate (number of octets sent and received for 
      example). The particular statistical properties that are reported for 
      a given Termination are determined by the Packages realized by the 
      Termination. By default, statistics are reported when the Termination 
      is Subtracted from the Context. This behaviour can be overridden by 
      including an empty AuditDescriptor in the Subtract command. 
      Statistics may also be returned from the AuditValue command, or any 
      Add/Move/Modify command using the Audit descriptor. 

      Statistics are cumulative; reporting Statistics does not reset them. 
      Statistics are reset when a Termination is Subtracted from a Context. 

   7.1.16   Packages descriptor 
       
      Used only with the AuditValue command, the PackageDescriptor returns 
      a list of Packages realized by the Termination. 

   7.1.17   ObservedEvents descriptor 
       
      ObservedEvents is supplied with the Notify command to inform the MGC 
      of which event(s) were detected. Used with the AuditValue command, 
      the ObservedEventsDescriptor returns events in the event buffer which 
      have not been Notified. ObservedEvents contains the RequestIdentifier 
      of the EventsDescriptor that triggered the notification, the event(s) 
      detected, optionally the detection time(s) and any parameters of the 
      observed event. Detection times are reported with a precision of 
      hundredths of a second. 

   7.1.18   Topology descriptor
       


    
    
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      A Topology descriptor is used to specify flow directions between 
      Terminations in a Context. Contrary to the descriptors in previous 
      subclauses, the Topology descriptor applies to a Context instead of a 
      Termination. The default topology of a Context is that each 
      Termination's transmission is received by all other Terminations. The 
      Topology descriptor is optional to implement. An MG that does not 
      support Topology descriptors, but receives a command containing one, 
      returns Error 444    Unsupported or unknown descriptor, and 
      optionally includes a string containing the name of the unsupported 
      Descriptor ("Topology") in the error text in the error descriptor. 

      The Topology descriptor occurs before the commands in an action. It 
      is possible to have an action containing only a Topology descriptor, 
      provided that the Context to which the action applies already exists. 

      A Topology descriptor consists of a sequence of triples of the form 
      (T1, T2, association). T1 and T2 specify Terminations within the 
      Context, possibly using the ALL or CHOOSE wildcard. The association 
      specifies how media flows between these two Terminations as follows. 

      -  (T1, T2, isolate) means that the Terminations matching T2 do not 
         receive media from the Terminations matching T1, nor vice versa. 

      -  (T1, T2, oneway) means that the Terminations that match T2 receive 
         media from the Terminations matching T1, but not vice versa. In 
         this case use of the ALL wildcard such that there are Terminations 
         that match both T1 and T2 is not allowed. 

      -  (T1, T2, bothway) means that the Terminations matching T2 receive 
         media from the Terminations matching T1, and vice versa. In this 
         case it is allowed to use wildcards such that there are 
         Terminations that match both T1 and T2. However, if there is a 
         Termination that matches both, no loopback is introduced. 

      CHOOSE wildcards may be used in T1 and T2 as well, under the 
      following restrictions: 

      -  the action (see clause 8) of which the topology descriptor is part 
         contains an Add command in which a CHOOSE wildcard is used; 

      -  if a CHOOSE wildcard occurs in T1 or T2, then a partial name SHALL 
         NOT be specified. 

      The CHOOSE wildcard in a Topology descriptor matches the 
      TerminationID that the MG assigns in the first Add command that uses 
      a CHOOSE wildcard in the same action. An existing Termination that 
      matches T1 or T2 in the Context to which a Termination is added, is 
      connected to the newly added Termination as specified by the Topology 
      descriptor. 
    
    
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      If a termination is not mentioned within a Topology Descriptor, any 
      topology associated with it remains unchanged. If, however, a new 
      termination is added into a context its association with the other 
      terminations within the context defaults to bothway, unless a 
      Topology Descriptor is given to change this (eg. if T3 is added to a 
      context with T1 and T2 with topology (T3,T1,oneway) it will be 
      connected bothway to T2). 

      Figure 7 and the table following it show some examples of the effect 
      of including topology descriptors in actions. In these examples it is 
      assumed that the topology descriptors are applied in sequence. 

       
        +------------------+  +------------------+  +------------------+ 
        |      +----+      |  |      +----+      |  |      +----+      | 
        |      | T2 |      |  |      | T2 |      |  |      | T2 |      | 
        |      +----+      |  |      +----+      |  |      +----+      | 
        |       ^  ^       |  |          ^       |  |          ^       | 
        |       |  |       |  |          |       |  |          |       | 
        |    +--+  +--+    |  |          +---+   |  |          +--+    | 
        |    |        |    |  |              |   |  |             |    | 
        |    v        v    |  |              v   |  |             |    | 
        | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ | 
        | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | | 
        | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ | 
        +------------------+  +------------------+  +------------------+ 
        1. No Topology Desc.   2. T1, T2, Isolate    3. T3, T2, Oneway 
       
        +------------------+  +------------------+  +------------------+ 
        |      +----+      |  |      +----+      |  |      +----+      | 
        |      | T2 |      |  |      | T2 |      |  |      | T2 |      | 
        |      +----+      |  |      +----+      |  |      +----+      | 
        |          |       |  |          ^       |  |       ^  ^       | 
        |          |       |  |          |       |  |       |  |       | 
        |          +--+    |  |          +---+   |  |    +--+  +--+    | 
        |             |    |  |              |   |  |    |        |    | 
        |             v    |  |              v   |  |    v        v    | 
        | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ | 
        | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | | 
        | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ | 
        +------------------+  +------------------+  +------------------+ 
        4. T2, T3 oneway      5. T2, T3 bothway     6. T1, T2 bothway  
       
        Note: the direction of the arrow indicates the direction of flow. 
       
                          Figure 7: Example topologies 

       

    
    
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      Topology Description 

      1 No topology descriptors    When no topology descriptors are 
                                   included, all Terminations have a 
                                   bothway connection to all other 
                                   Terminations. 

      2 T1, T2 Isolate             Removes the connection between T1 and 
                                   T2. T3 has a bothway connection with 
                                   both T1 and T2. T1 and T2 have bothway 
                                   connection to T3. 

      3 T3, T2 oneway              A oneway connection from T3 to T2 (i.e. 
                                   T2 receives media flow from T3). A 
                                   bothway connection between T1 and T3. 

      4 T2, T3 oneway              A oneway connection between T2 to T3. 
                                   T1 and T3 remain bothway connected 

      5 T2, T3 bothway             T2 is bothway connected to T3. This 
                                   results in the same as 2. 

      6 T1, T2 bothway (T2, T3     All Terminations have a bothway 
        bothway and T1, T3         connection to all other Terminations. 
        bothway may be implied or 
        explicit).  

       

      A oneway connection must be implemented in such a way that the other 
      Terminations in the Context are not aware of the change in topology. 

   7.1.19   Error Descriptor 
       
      If a responder encounters an error when processing a transaction 
      request, it must include an error descriptor in its response.  A 
      Notify request may contain an error descriptor as well. 

      An error descriptor consists of an IANA-registered error code, 
      optionally accompanied by an error text.  H.248.8 contains a list of 
      valid error codes and error descriptions. 

      An error descriptor shall be specified at the "deepest level" that is 
      semantically appropriate for the error being described and that is 
      possible given any parsing problems with the original request. An 
      error descriptor may refer to a syntactical construct other than 
      where it appears. For example, Error descriptor 422 - Syntax Error in 
      Action, could appear within a command even though it refers to the 
    
    
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      larger construct - the action - and not the particular command within 
      which it appears. 

       
   7.2   Command Application Programming Interface 
       
      Following is an Application Programming Interface (API) describing 
      the Commands of the protocol. This API is shown to illustrate the 
      Commands and their parameters and is not intended to specify 
      implementation (e.g. via use of blocking function calls). It 
      describes the input parameters in parentheses after the command name 
      and the return values in front of the Command. This is only for 
      descriptive purposes; the actual Command syntax and encoding are 
      specified in later subclauses. The order of parameters to commands is 
      not fixed. Descriptors may appear as parameters to commands in any 
      order. The descriptors SHALL be processed in the order in which they 
      appear. 

      Any reply to a command may contain an error descriptor; the API does 
      not specifically show this. 

      All parameters enclosed by square brackets ([. . .]) are considered 
      optional. 

   7.2.1 Add 
       
      The Add Command adds a Termination to a Context. 

        TerminationID 
        [,MediaDescriptor] 
        [,ModemDescriptor] 
        [,MuxDescriptor] 
        [,EventsDescriptor] 
        [,SignalsDescriptor] 
        [,DigitMapDescriptor] 
        [,ObservedEventsDescriptor] 
        [,EventBufferDescriptor] 
        [,StatisticsDescriptor]  
        [,PackagesDescriptor] 
          Add( TerminationID 
           [, MediaDescriptor] 
           [, ModemDescriptor] 
           [, MuxDescriptor] 
           [, EventsDescriptor] 
           [, EventBufferDescriptor]  
           [, SignalsDescriptor] 
           [, DigitMapDescriptor] 
           [, AuditDescriptor] 
           ) 
    
    
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      The TerminationID specifies the Termination to be added to the 
      Context. The Termination is either created, or taken from the null 
      Context. If a CHOOSE wildcard is used in the TerminationID, the 
      selected  TerminationID will be returned. Wildcards may be used in an 
      Add, but such usage would be unusual. If the wildcard matches more 
      than one TerminationID, all possible matches are attempted, with 
      results reported for each one. The order of attempts when multiple 
      TerminationIDs match is not specified. 

      The optional MediaDescriptor describes all media streams. 

      The optional ModemDescriptor and MuxDescriptor specify a modem and 
      multiplexer if applicable. For convenience, if a Multiplex descriptor 
      is present in an Add command and lists any Terminations that are not 
      currently in the Context, such Terminations are added to the Context 
      as if individual Add commands listing the Terminations were invoked. 
      If an error occurs on such an implied Add, error 471 - Implied Add 
      for Multiplex failure shall be returned and further processing of the 
      command shall cease. 

      The EventsDescriptor parameter is optional. If present, it provides 
      the list of events that should be detected on the Termination. 

      The EventBufferDescriptor parameter is optional.  If present, it 
      provides the list of events that the MG is requested to detect and 
      buffer when EventBufferControl equals LockStep. 

      The SignalsDescriptor parameter is optional. If present, it provides 
      the list of signals that should be applied to the Termination. 

      The DigitMapDescriptor parameter is optional. If present, it defines 
      a DigitMap definition that may be used in an EventsDescriptor. 

      The AuditDescriptor is optional. If present, the command will return 
      descriptors as specified in the AuditDescriptor. 

      All descriptors that can be modified could be returned by MG if a 
      parameter was underspecified or overspecified. ObservedEvents, 
      Statistics, and Packages, and the EventBuffer descriptors are 
      returned only if requested in the AuditDescriptor. 

      Add SHALL NOT be used on a Termination with a serviceState of 
      "OutofService". 

   7.2.2 Modify 
       
      The Modify Command modifies the properties of a Termination. 

        TerminationID 
    
    
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        [,MediaDescriptor] 
        [,ModemDescriptor] 
        [,MuxDescriptor] 
        [,EventsDescriptor] 
        [,SignalsDescriptor] 
        [,DigitMapDescriptor] 
        [,ObservedEventsDescriptor] 
        [,EventBufferDescriptor] 
        [,StatisticsDescriptor]  
        [,PackagesDescriptor] 
         Modify( TerminationID 
            [, MediaDescriptor] 
            [, ModemDescriptor] 
            [, MuxDescriptor] 
            [, EventsDescriptor] 
            [, EventBufferDescriptor] 
            [, SignalsDescriptor] 
            [, DigitMapDescriptor] 
            [, AuditDescriptor] 
            ) 

      The TerminationID may be specific if a single Termination in the 
      Context is to be modified. Use of wildcards in the TerminationID may 
      be appropriate for some operations. If the wildcard matches more than 
      one TerminationID, all possible matches are attempted, with results 
      reported for each one. The order of attempts when multiple 
      TerminationIDs match is not specified. The CHOOSE option is an error, 
      as the Modify command may only be used on existing Terminations. 

      For convenience, if a Multiplex Descriptor is present in a Modify 
      command, then: 

      -  if the new Multiplex Descriptor lists any Terminations that are 
         not currently in the Context, such Terminations are added to the 
         context as if individual Add commands listing the Terminations 
         were invoked. 

      -  if any Terminations listed previously in the Multiplex Descriptor 
         are no longer present in the new Multiplex Descriptor, they are 
         subtracted from the context as if individual Subtract commands 
         listing the Terminations were invoked. 

      The remaining parameters to Modify are the same as those to Add. 
      Possible return values are the same as those to Add. 

   7.2.3 Subtract 
       
      The Subtract Command disconnects a Termination from its Context and 
      returns statistics on the Termination's participation in the Context. 
    
    
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        TerminationID 
        [,MediaDescriptor] 
        [,ModemDescriptor] 
        [,MuxDescriptor] 
        [,EventsDescriptor] 
        [,SignalsDescriptor] 
        [,DigitMapDescriptor] 
        [,ObservedEventsDescriptor] 
        [,EventBufferDescriptor] 
        [,StatisticsDescriptor]  
        [,PackagesDescriptor] 
         Subtract(TerminationID 
            [, AuditDescriptor] 
            ) 

      TerminationID in the input parameters represents the Termination that 
      is being subtracted. The TerminationID may be specific or may be a 
      wildcard value indicating that all (or a set of related) Terminations 
      in the Context of the Subtract Command are to be subtracted. If the 
      wildcard matches more than one TerminationID, all possible matches 
      are attempted, with results reported for each one. The order of 
      attempts when multiple TerminationIDs match is not specified. 

      The use of CHOOSE in the TerminationID is an error, as the Subtract 
      command may only be used on existing Terminations. 

      ALL may be used as the ContextID as well as the TerminationId in a 
      Subtract, which would have the effect of deleting all Contexts, 
      deleting all ephemeral Terminations, and returning all physical 
      Terminations to Null Context. Subtract of a termination from the Null 
      Context is not allowed. 

      For convenience, if a multiplexing Termination is the object of a 
      Subtract command, then any bearer Terminations listed in its 
      Multiplex Descriptor are subtracted from the context as if individual 
      Subtract commands listing the Terminations were invoked. 

      By default, the Statistics parameter is returned to report 
      information collected on the Termination or Terminations specified in 
      the Command. The information reported applies to the Termination's or 
      Terminations' existence in the Context from which it or they are 
      being subtracted. 

      The AuditDescriptor is optional. If present, the command will return 
      only those descriptors as specified in the AuditDescriptor, which may 
      be empty. If omitted, the Statistics descriptor is returned, by 
      default. Possible return values are the same as those to Add. 


    
    
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      When a provisioned Termination is Subtracted from a Context, its 
      property values shall revert to:  

      -  the default value, if specified for the property and not 
         overridden by provisioning; 

      -  otherwise, the provisioned value. 

   7.2.4 Move 
       
      The Move Command moves a Termination to another Context from its 
      current Context in one atomic operation. The Move command is the only 
      command that refers to a Termination in a Context different from that 
      to which the command is applied. The Move command shall not be used 
      to move Terminations to or from the null Context. 

        TerminationID 
        [,MediaDescriptor] 
        [,ModemDescriptor] 
        [,MuxDescriptor] 
        [,EventsDescriptor] 
        [,SignalsDescriptor] 
        [,DigitMapDescriptor] 
        [,ObservedEventsDescriptor] 
        [,EventBufferDescriptor] 
        [,StatisticsDescriptor]  
        [,PackagesDescriptor] 
         Move( TerminationID 
            [, MediaDescriptor] 
            [, ModemDescriptor] 
            [, MuxDescriptor] 
            [, EventsDescriptor] 
            [, EventBufferDescriptor] 
            [, SignalsDescriptor] 
            [, DigitMapDescriptor] 
            [, AuditDescriptor] 
            ) 

      The TerminationID specifies the Termination to be moved. It may be 
      wildcarded, but CHOOSE shall not be used in the TerminationID. If the 
      wildcard matches more than one TerminationID, all possible matches 
      are attempted, with results reported for each one. The order of 
      attempts when multiple TerminationIDs match is not specified. The 
      Context to which the Termination is moved is indicated by the target 
      ContextId in the Action. If the last remaining Termination is moved 
      out of a Context, the Context is deleted. 

      The Move command does not affect the properties of the Termination on 
      which it operates, except those properties explicitly modified by 
    
    
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      descriptors included in the Move command. The AuditDescriptor with 
      the Statistics option, for example, would return statistics on the 
      Termination just prior to the Move. Possible descriptors returned 
      from Move are the same as for Add. 

      For convenience, if a multiplexing Termination is the object of a 
      Move command, then any bearer Terminations listed in its Multiplex 
      Descriptor are also moved as if individual Move commands listing the 
      Terminations were invoked. 

      Move SHALL NOT be used on a Termination with a serviceState of 
      "OutofService". 

   7.2.5 AuditValue 
       
      The AuditValue Command returns the current values of properties, 
      events, signals and statistics associated with Terminations. 

      TerminationID 
      [,MediaDescriptor] 
      [,ModemDescriptor] 
      [,MuxDescriptor] 
      [,EventsDescriptor] 
      [,SignalsDescriptor] 
      [,DigitMapDescriptor] 
      [,ObservedEventsDescriptor] 
      [,EventBufferDescriptor] 
      [,StatisticsDescriptor]  
      [,PackagesDescriptor] 
        AuditValue(TerminationID, 
         AuditDescriptor 
         ) 

        

      TerminationID may be specific or wildcarded. If the wildcard matches 
      more than one TerminationID, all possible matches are attempted, with 
      results reported for each one. The order of attempts when multiple 
      TerminationIDs match is not specified. If a wildcarded response is 
      requested, only one command return is generated, with the contents 
      containing the union of the values of all Terminations matching the 
      wildcard. This convention may reduce the volume of data required to 
      audit a group of Terminations. Use of CHOOSE is an error. 

      The appropriate descriptors, with the current values for the 
      Termination, are returned from AuditValue. Values appearing in 
      multiple instances of a descriptor are defined to be alternate values 
      supported, with each parameter in a descriptor considered 
      independent. 
    
    
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      ObservedEvents returns a list of events in the EventBuffer. If the 
      ObservedEventsDescriptor is audited while a DigitMap is active, the 
      returned ObservedEvents descriptor also includes a digit map 
      completion event that shows the current dial string but does not show 
      a Termination method. 

      EventBuffer returns the set of events and associated parameter values 
      currently enabled in the EventBufferDescriptor. PackagesDescriptor 
      returns a list of packages realized by the Termination. 
      DigitMapDescriptor returns the name or value of the current DigitMap 
      for the Termination. DigitMap requested in an AuditValue command with 
      TerminationID ALL returns all DigitMaps in the gateway. Statistics 
      returns the current values of all statistics being kept on the 
      Termination. Specifying an empty Audit descriptor results in only the 
      TerminationID being returned. This may be useful to get a list of 
      TerminationIDs when used with wildcard. Annexes A and B provide a 
      special syntax for presenting such a list in condensed form, such 
      that the AuditValue command tag does not have to be repeated for each 
      TerminationID. 

      AuditValue results depend on the Context, viz. specific, null, or 
      wildcarded. (Note that ContextID All does not include the null 
      Context.) The TerminationID may be specific, or wildcarded. 

      The following are examples of what is returned in case the context 
      and/or the termination is wildcarded and a wildcarded response has 
      been specified. 

      Assume that the gateway has 4 terminations: t1/1, t1/2, t2/1 and 
      t2/2. Assume that terminations t1/* have implemented packages aaa and 
      bbb and that terminations t2/* have implemented packages ccc and ddd. 
      Assume that Context 1 has t1/1 and t2/1 in it and that Context 2 has 
      t1/2 and t2/2 in it. 

      The command: 

        Context=1{AuditValue=t1/1{Audit{Packages}}} 

      Returns:  

        Context=1{AuditValue=t1/1{Packages{aaa,bbb}}} 

      The command:  

        Context=*{AuditValue=t2/*{Audit{Packages}}}  

      Returns: 

        Context=1{AuditValue=t2/1{Packages{ccc,ddd}}}, 
    
    
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        Context=2{AuditValue=t2/2{Packages{ccc,ddd}}}  

      The command: 

        Context=*{W-AuditValue=t1/*{Audit{Packages}}}  

      Returns: 

        Context=*{W-AuditValue=t1/*{Packages{aaa,bbb}}}  

      Note: A wildcard response may also be used for other commands such as 
      Subtract. 

      The following illustrates other information that can be obtained with 
      the AuditValue Command: 

       

      ContextID TerminationID Information Obtained 

      Specific  wildcard      Audit of matching Terminations in a Context 

      Specific  specific      Audit of a single Termination in a Context 

      Null      Root          Audit of Media Gateway state and events 

      Null      wildcard      Audit of all matching Terminations in the 
                               null Context 

      Null      specific      Audit of a single Termination outside of any 
                               Context 

      All       wildcard      Audit of all matching Terminations and the 
                               Context to which they are associated 

      All       Root          List of all ContextIds (the ContextID list 
                               should be returned by using multiple action 
                               replies, each containing a ContextID from 
                               the list) 

      All       Specific      (Non-null) ContextID in which the 
                               Termination currently exists 

       




    
    
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   7.2.6 AuditCapabilities 
       
      The AuditCapabilities Command returns the possible values of 
      properties, events, signals and statistics associated with 
      Terminations. 

        TerminationID 
        [,MediaDescriptor] 
        [,ModemDescriptor] 
        [,MuxDescriptor] 
        [,EventsDescriptor] 
        [,SignalsDescriptor] 
        [,ObservedEventsDescriptor] 
        [,EventBufferDescriptor] 
        [,StatisticsDescriptor]  
         AuditCapabilities(TerminationID, 
            AuditDescriptor 
            ) 

      The appropriate descriptors, with the possible values for the 
      Termination are returned from AuditCapabilities. Descriptors may be 
      repeated where there are multiple possible values. If a wildcarded 
      response is requested, only one command return is generated, with the 
      contents containing the union of the values of all Terminations 
      matching the wildcard. This convention may reduce the volume of data 
      required to audit a group of Terminations. 

      Interpretation of what capabilities are requested for various values 
      of ContextID and TerminationID is the same as in AuditValue. 

      The EventsDescriptor returns the list of possible events on the 
      Termination together with the list of all possible values for the 
      EventsDescriptor Parameters. EventBufferDescriptor returns the same 
      information as EventsDescriptor. The SignalsDescriptor returns the 
      list of possible signals that could be applied to the Termination 
      together with the list of all possible values for the Signals 
      Parameters. StatisticsDescriptor returns the names of the statistics 
      being kept on the termination. ObservedEventsDescriptor returns the 
      names of active events on the Termination. DigitMap and Packages are 
      not legal in AuditCapability. 

      The following illustrates other information that can be obtained with 
      the AuditCapabilties Command: 

      ContextID TerminationID Information Obtained 

      Specific  wildcard      Audit of matching Terminations in a Context 


    
    
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      Specific  specific      Audit of a single Termination in a Context 

      Null      Root          Audit of MG state and events 

      Null      wildcard      Audit of all matching Terminations in the 
                               Null Context 

      Null      specific      Audit of a single Termination outside of any 
                               Context 

      All       wildcard      Audit of all matching Terminations and the 
                               Context to which they are associated 

      All       Root          Same as for AuditValue 

      All       Specific      Same as for AuditValue 

       

       

   7.2.7 Notify 
       
      The Notify Command allows the Media Gateway to notify the Media 
      Gateway Controller of events occurring within the Media Gateway. 

        TerminationID 
         Notify(TerminationID, 
            ObservedEventsDescriptor, 
            [ErrorDescriptor] 
            ) 

      The TerminationID parameter specifies the Termination issuing the 
      Notify Command. The TerminationID shall be a fully qualified name. 

      The ObservedEventsDescriptor contains the RequestID and a list of 
      events that the Media Gateway detected in the order that they were 
      detected. Each event in the list is accompanied by parameters 
      associated with the event and optionally an indication of the time 
      that the event was detected. Procedures for sending Notify commands 
      with RequestID equal to 0 are for further study.  

      Notify Commands with RequestID not equal to 0 shall occur only as the 
      result of detection of an event specified by an Events descriptor 
      which is active on the Termination concerned. 

      The RequestID returns the RequestID parameter of the EventsDescriptor 
      that triggered the Notify Command. It is used to correlate the 
    
    
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      notification with the request that triggered it. The events in the 
      list must have been requested via the triggering EventsDescriptor or 
      embedded events descriptor unless the RequestID is 0 (which is for 
      further study). 

      The ErrorDescriptor may be sent in the Notify Command as a result of 
      Error 518 - Event buffer full. 

   7.2.8 ServiceChange 
       
      The ServiceChange Command allows the Media Gateway to notify the 
      Media Gateway Controller that a Termination or group of Terminations 
      is about to be taken out of service or has just been returned to 
      service. The Media Gateway Controller may indicate that 
      Termination(s) shall be taken out of or returned to service. The 
      Media Gateway may notify the MGC that the capability of a Termination 
      has changed. It also allows a MGC to hand over control of a MG to 
      another MGC. 

        

      TerminationID, 

        [ServiceChangeDescriptor] 
         ServiceChange ( TerminationID, 
            ServiceChangeDescriptor 
            ) 

      The TerminationID parameter specifies the Termination(s) that are 
      taken out of or returned to service. Wildcarding of Termination names 
      is permitted, with the exception that the CHOOSE mechanism shall not 
      be used. Use of the "Root" TerminationID indicates a ServiceChange 
      affecting the entire Media Gateway. 

      The ServiceChangeDescriptor contains the following parameters as 
      required: 

      -  ServiceChangeMethod 
      -  ServiceChangeReason 
      -  ServiceChangeDelay 
      -  ServiceChangeAddress 
      -  ServiceChangeProfile 
      -  ServiceChangeVersion 
      -  ServiceChangeMgcId 
      -  TimeStamp 

      The ServiceChangeMethod parameter specifies the type of ServiceChange 
      that will or has occurred: 

    
    
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      1) Graceful - indicates that the specified Terminations will be taken 
         out of service after the specified ServiceChangeDelay; established 
         connections are not yet affected, but the Media Gateway Controller 
         should refrain from establishing new connections and should 
         attempt to gracefully tear down existing connections on the 
         Termination(s) affected by the serviceChange command. The MG 
         should set Termination serviceState at the expiry of 
         ServiceChangeDelay or the removal of the Termination from an 
         active Context (whichever is first), to "out of service". 

      2) Forced - indicates that the specified Terminations were taken 
         abruptly out of service and any established connections associated 
         with them may be lost. For non-Root terminations, the MGC is 
         responsible for cleaning up the Context (if any) with which the 
         failed Termination is associated. At a minimum the Termination 
         shall be subtracted from the Context. The Termination serviceState 
         should be "out of service". For the root termination, the MGC can 
         assume that all connections are lost on the MG and thus can 
         consider that all the terminations have been subtracted. 

      3) Restart - indicates that service will be restored on the specified 
         Terminations after expiration of the ServiceChangeDelay. The 
         serviceState should be set to "inService" upon expiry of 
         ServiceChangeDelay. 

      4) Disconnected - always applied with the Root TerminationID, 
         indicates that the MG lost communication with the MGC, but it was 
         subsequently restored to the same MGC (possibly after trying other 
         MGCs on a pre-provisioned list). Since MG state may have changed, 
         the MGC may wish to use the Audit command to resynchronize its 
         state with the MG's. 

      5) Handoff - sent from the MGC to the MG, this reason indicates that 
         the MGC is going out of service and a new MGC association must be 
         established. Sent from the MG to the MGC, this indicates that the 
         MG is attempting to establish a new association in accordance with 
         a Handoff received from the MGC with which it was previously 
         associated. 

      6) Failover - sent from MG to MGC to indicate the primary MG is out 
         of service and a secondary MG is taking over. This serviceChange 
         method is also sent from the MG to the MGC when the MG detects 
         that MGC has failed. 

      7) Another value whose meaning is mutually understood between the MG 
         and the MGC. 



    
    
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      The ServiceChangeReason parameter specifies the reason why the 
      ServiceChange has or will occur. It consists of an alphanumeric token 
      (IANA registered) and, optionally, an explanatory string. 

      The optional ServiceChangeAddress parameter specifies the address 
      (e.g. IP port number for IP networks) to be used for subsequent 
      communications. It can be specified in the input parameter descriptor 
      or the returned result descriptor. ServiceChangeAddress and 
      ServiceChangeMgcId parameters must not both be present in the 
      ServiceChangeDescriptor or the ServiceChangeResultDescriptor. The 
      ServiceChangeAddress provides an address to be used within the 
      Context of the association currently being negotiated, while the 
      ServiceChangeMgcId provides an alternate address where the MG should 
      seek to establish another association. Note that the use of 
      ServiceChangeAddress is not encouraged.  MGCs and MGs must be able to 
      cope with the ServiceChangeAddress being either a full address or 
      just a port number in the case of TCP transports. 

      The optional ServiceChangeDelay parameter is expressed in seconds. If 
      the delay is absent or set to zero, the delay value should be 
      considered to be null. In the case of a "graceful" 
      ServiceChangeMethod, a null delay indicates that the Media Gateway 
      Controller should wait for the natural removal of existing 
      connections and should not establish new connections. For "graceful" 
      only, a null delay means the MG must not set serviceState "out of 
      service" until the Termination is in the null Context. 

      The optional ServiceChangeProfile parameter specifies the Profile (if 
      any) of the protocol supported. The ServiceChangeProfile includes the 
      version of the profile supported. 

      The optional ServiceChangeVersion parameter contains the protocol 
      version and is used if protocol version negotiation occurs (see 
      11.3). 

      The optional TimeStamp parameter specifies the actual time as kept by 
      the sender. As such, it is not necessarily absolute time according 
      to, for example, a local time zone - it merely establishes an 
      arbitrary starting time against which all future timestamps 
      transmitted by a sender during this association shall be compared. It 
      can be used by the responder to determine how its notion of time 
      differs from that of its correspondent. TimeStamp is sent with a 
      precision of hundredths of a second. 

      The optional Extension parameter may contain any value whose meaning 
      is mutually understood by the MG and MGC. 

      A ServiceChange Command specifying the "Root" for the TerminationID 
      and ServiceChangeMethod equal to Restart is a registration command by 
    
    
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      which a Media Gateway announces its existence to the Media Gateway 
      Controller. The Media Gateway may also announce a registration 
      command by specifying the "Root" for the TerminationID and 
      ServiceChangeMethod equal to Failover when the MG detects MGC 
      failures. The Media Gateway is expected to be provisioned with the 
      name of one primary and optionally some number of alternate Media 
      Gateway Controllers. Acknowledgement of the ServiceChange Command 
      completes the registration process, except when the MGC has returned 
      an alternative ServiceChangeMgcId as described in the following 
      paragraph. The MG may specify the transport ServiceChangeAddress to 
      be used by the MGC for sending messages in the ServiceChangeAddress 
      parameter in the input ServiceChangeDescriptor. The MG may specify an 
      address in the ServiceChangeAddress parameter of the ServiceChange 
      request, and the MGC may also do so in the ServiceChange reply. In 
      either case, the recipient must use the supplied address as the 
      destination for all subsequent transaction requests within the 
      association. At the same time, as indicated in clause 9, transaction 
      replies and pending indications must be sent to the address from 
      which the corresponding requests originated. This must be done even 
      if it implies extra messaging because commands and responses cannot 
      be packed together. The TimeStamp parameter shall be sent with a 
      registration command and its response. 

      The Media Gateway Controller may return a ServiceChangeMgcId 
      parameter that describes the Media Gateway Controller that should 
      preferably be contacted for further service by the Media Gateway. In 
      this case the Media Gateway shall reissue the ServiceChange command 
      to the new Media Gateway Controller. The MGC specified in a 
      ServiceChangeMgcId, if provided, shall be contacted before any 
      further alternate MGCs. On a HandOff message from MGC to MG, the 
      ServiceChangeMgcId is the new MGC that will take over from the 
      current MGC. 

      The return from ServiceChange is empty except when the Root 
      terminationID is used. In that case it includes the following 
      parameters as required: 

      -  ServiceChangeAddress, if the responding MGC wishes to specify a 
         new destination for messages from the MG for the remainder of the 
         association; 

      -  ServiceChangeMgcId, if the responding MGC does not wish to sustain 
         an association with the MG; 

      -  ServiceChangeProfile, if the responder wishes to negotiate the 
         profile to be used for the association; 

      -  ServiceChangeVersion, if the responder wishes to negotiate the 
         version of the protocol to be used for the association. 
    
    
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      The following ServiceChangeReasons are defined. This list may be 
      extended by an IANA registration as outlined in 13.3. 

         900 Service Restored 
         901 Cold Boot 
         902 Warm Boot 
         903 MGC Directed Change 
         904 Termination malfunctioning 
         905 Termination taken out of service 
         906 Loss of lower layer connectivity (e.g. downstream sync) 
         907 Transmission Failure 
         908 MG Impending Failure 
         909 MGC Impending Failure 
         910 Media Capability Failure 
         911 Modem Capability Failure 
         912 Mux Capability Failure 
         913 Signal Capability Failure 
         914 Event Capability Failure 
         915 State Loss 

   7.2.9 Manipulating and Auditing Context Attributes 
       
      The commands of the protocol as discussed in the preceding subclauses 
      apply to Terminations. This subclause specifies how Contexts are 
      manipulated and audited. 

      Commands are grouped into actions (see clause 8). An action applies 
      to one Context. In addition to commands, an action may contain 
      Context manipulation and auditing instructions. 

      An action request sent to a MG may include a request to audit 
      attributes of a Context. An action may also include a request to 
      change the attributes of a Context. 

      The Context properties that may be included in an action reply are 
      used to return information to a MGC. This can be information 
      requested by an audit of Context attributes or details of the effect 
      of manipulation of a Context. 

      If a MG receives an action which contains both a request to audit 
      context attributes and a request to manipulate those attributes, the 
      response SHALL include the values of the attributes after processing 
      the manipulation request. 

   7.2.10   Generic Command Syntax 
       
      The protocol can be encoded in a binary format or in a text format. 
      MGCs should support both encoding formats. MGs may support both 
      formats. 
    
    
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      The protocol syntax for the binary format of the protocol is defined 
      in Annex A. Annex C specifies the encoding of the Local and Remote 
      descriptors for use with the binary format. 

      A complete ABNF of the text encoding of the protocol per RFC 2234 is 
      given in Annex B. SDP is used as the encoding of the Local and Remote 
      descriptors for use with the text encoding as modified in 7.1.8. 

   7.3   Command Error Codes 
       
      Errors consist of an IANA registered error code and an explanatory 
      string. Sending the explanatory string is optional. Implementations 
      are encouraged to append diagnostic information to the end of the 
      string. 

      When a MG reports an error to a MGC, it does so in an error 
      descriptor. An error descriptor consists of an error code and 
      optionally the associated explanatory string. 

      H.248.8 contains the error codes supported by Recommendations in the 
      H.248 sub-series. 

       
   8  Transactions 
       
      Commands between the Media Gateway Controller and the Media Gateway 
      are grouped into Transactions, each of which is identified by a 
      TransactionID. Transactions consist of one or more Actions. An Action 
      consists of a non-empty series of Commands, Context property 
      modifications, or Context property audits that are limited to 
      operating within a single Context. Consequently, each Action 
      typically specifies a ContextID. However, there are two circumstances 
      where a specific ContextID is not provided with an Action. One is the 
      case of modification of a Termination outside of a Context. The other 
      is where the controller requests the gateway to create a new Context. 
      Figure 8 is a graphic representation of the Transaction, Action and 
      Command relationships. 

         +----------------------------------------------------------+ 
         | Transaction x                                            | 
         |  +----------------------------------------------------+  | 
         |  | Action 1                                           |  | 
         |  | +---------+  +---------+  +---------+  +---------+ |  | 
         |  | | Command |  | Command |  | Command |  | Command | |  | 
         |  | |    1    |  |    2    |  |    3    |  |    4    | |  | 
         |  | +---------+  +---------+  +---------+  +---------+ |  | 
         |  +----------------------------------------------------+  | 
         |                                                          | 
         |  +----------------------------------------------------+  | 
    
    
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         |  | Action 2                                           |  | 
         |  | +---------+                                        |  | 
         |  | | Command |                                        |  | 
         |  | |    1    |                                        |  | 
         |  | +---------+                                        |  | 
         |  +----------------------------------------------------+  | 
         |                                                          | 
         |  +----------------------------------------------------+  | 
         |  | Action 3                                           |  | 
         |  | +---------+  +---------+  +---------+              |  | 
         |  | | Command |  | Command |  | Command |              |  | 
         |  | |    1    |  |    2    |  |    3    |              |  | 
         |  | +---------+  +---------+  +---------+              |  | 
         |  +----------------------------------------------------+  | 
         +----------------------------------------------------------+ 
        
                  Figure 8: Transactions, Actions and Commands 
       

      Transactions are presented as TransactionRequests. Corresponding 
      responses to a TransactionRequest are received in a single reply, 
      possibly preceded by a number of TransactionPending messages (see 
      8.2.3). 

      Transactions guarantee ordered Command processing. That is, Commands 
      within a Transaction are executed sequentially. Ordering of 
      Transactions is NOT guaranteed - transactions may be executed in any 
      order, or simultaneously. 

      At the first failing Command in a Transaction, processing of the 
      remaining Commands in that Transaction stops. If a command contains a 
      wildcarded TerminationID, the command is attempted with each of the 
      actual TerminationIDs matching the wildcard. A response within the 
      TransactionReply is included for each matching TerminationID, even if 
      one or more instances generated an error. If any TerminationID 
      matching a wildcard results in an error when executed, any commands 
      following the wildcarded command are not attempted. 

      Commands may be marked as "Optional" which can override this 
      behaviour - if a command marked as Optional results in an error, 
      subsequent commands in the Transaction will be executed. If a command 
      fails, the MG shall as far as possible restore the state that existed 
      prior to the attempted execution of the command before continuing 
      with command processing. 

      A TransactionReply includes the results for all of the Commands in 
      the corresponding TransactionRequest. The TransactionReply includes 
      the return values for the Commands that were executed successfully, 
      and the Command and error descriptor for any Command that failed. 
    
    
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      TransactionPending is used to periodically notify the receiver that a 
      Transaction has not completed yet, but is actively being processed.  

      Applications SHOULD implement an application level timer per 
      transaction. Expiration of the timer should cause a retransmission of 
      the request. Receipt of a Reply should cancel the timer. Receipt of 
      Pending should restart the timer. 

   8.1   Common parameters 
       
   8.1.1 Transaction Identifiers 
       
      Transactions are identified by a TransactionID, which is assigned by 
      sender and is unique within the scope of the sender. A response 
      containing an error descriptor to indicate that the TransactionID is 
      missing in a request shall use TransactionID 0 in the corresponding 
      TransactionReply. 

   8.1.2 Context Identifiers 
       
      Contexts are identified by a ContextID, which is assigned by the 
      Media Gateway and is unique within the scope of the Media Gateway. 
      The Media Gateway Controller shall use the ContextID supplied by the 
      Media Gateway in all subsequent Transactions relating to that 
      Context. The protocol makes reference to a distinguished value that 
      may be used by the Media Gateway Controller when referring to a 
      Termination that is currently not associated with a Context, namely 
      the null ContextID. 

      The CHOOSE wildcard is used to request that the Media Gateway create 
      a new Context.  

      The MGC may use the ALL wildcard to address all Contexts on the MG. 
      The null Context is not included when the ALL wildcard is used. 

      The MGC shall not use partially specified ContextIDs containing the 
      CHOOSE or ALL wildcards. 

   8.2   Transaction Application Programming Interface 
       
      Following is an Application Programming Interface (API) describing 
      the Transactions of the protocol. This API is shown to illustrate the 
      Transactions and their parameters and is not intended to specify 
      implementation (e.g. via use of blocking function calls). It will 
      describe the input parameters and return values expected to be used 
      by the various Transactions of the protocol from a very high level. 
      Transaction syntax and encodings are specified in later subclauses. 


    
    
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   8.2.1 TransactionRequest 
       
      The TransactionRequest is invoked by the sender. There is one 
      Transaction per request invocation. A request contains one or more 
      Actions, each of which specifies its target Context and one or more 
      Commands per Context. 

        TransactionRequest(TransactionId { 
            ContextID {Command ... Command},  
               . . . 
            ContextID {Command ... Command } }) 

      The TransactionID parameter must specify a value for later 
      correlation with the TransactionReply or TransactionPending response 
      from the receiver.  

      The ContextID parameter must specify a value to pertain to all 
      Commands that follow up to either the next specification of a 
      ContextID parameter or the end of the TransactionRequest, whichever 
      comes first.  

      The Command parameter represents one of the Commands mentioned in 7.2 
      (Command Application Programming Interface). 

   8.2.2 TransactionReply 
       
      The TransactionReply is invoked by the receiver. There is one reply 
      invocation per transaction. A reply contains one or more Actions, 
      each of which must specify its target Context and one or more 
      Responses per Context. The TransactionReply is invoked by the 
      responder when it has processed the TransactionRequest. 

      A TransactionRequest has been processed: 

      -  when all actions in that TransactionRequest have been processed; 
         or 

      -  when an error is encountered in processing that 
         TransactionRequest, except when the error is in an optional 
         command. 

      A command has been processed when all descriptors in that command 
      have been processed. 

      A SignalsDescriptor is considered to have been processed when it has 
      been established that the descriptor is syntactically valid, the 
      requested signals are supported and they have been queued to be 
      applied. 

    
    
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      An EventsDescriptor or EventBufferDescriptor is considered to have 
      been processed when it has been established that the descriptor is 
      syntactically valid, the requested events can be observed, any 
      embedded signals can be generated, any embedded events can be 
      detected, and the MG has been brought into a state in which the 
      events will be detected. 

        TransactionReply(TransactionID { 
            ContextID { Response ... Response }, 
               . . . 
            ContextID { Response ... Response } }) 

      The TransactionID parameter must be the same as that of the 
      corresponding TransactionRequest. 

      The ContextID parameter must specify a value to pertain to all 
      Responses for the action. The ContextID may be specific, all or null. 

      Each of the Response parameters represents a return value as 
      mentioned in 7.2, or an error descriptor if the command execution 
      encountered an error. Commands after the point of failure are not 
      processed and, therefore, Responses are not issued for them. 

      An exception to this occurs if a command has been marked as optional 
      in the Transaction request. If the optional command generates an 
      error, the transaction still continues to execute, so the Reply 
      would, in this case, have Responses after an Error. 

      Section 7.1.19 Error Descriptor specifies the generation of error 
      descriptors.  The text below discusses several individual cases. 

      If the receiver encounters an error in processing a ContextID, the 
      requested Action response will consist of the Context ID and a single 
      error descriptor, 422 - Syntax Error in Action. 

      If the receiver encounters an error such that it cannot determine a 
      legal Action, it will return a TransactionReply consisting of the 
      TransactionID and a single error descriptor, 422 - Syntax Error in 
      Action. If the end of an action cannot be reliably determined but one 
      or more commands can be parsed, it will process them and then send 
      422 - Syntax Error in Action as the last action for the transaction. 
      If the receiver encounters an error such that is cannot determine a 
      legal Transaction, it will return a TransactionReply with a null 
      TransactionID and a single error descriptor (403 - Syntax Error in 
      Transaction). 

      If the end of a transaction cannot be reliably determined and one or 
      more Actions can be parsed, it will process them and then return 403 
      - Syntax Error in Transaction as the last action reply for the 
    
    
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      transaction. If no Actions can be parsed, it will return 403 - Syntax 
      Error in Transaction as the only reply. 

      If the terminationID cannot be reliably determined, it will send 442 
      - Syntax Error in Command as the action reply. 

      If the end of a command cannot be reliably determined, it will return 
      442 - Syntax Error in Command as the reply to the last action it can 
      parse. 

   8.2.3 TransactionPending 
       
      The receiver invokes the TransactionPending. A TransactionPending 
      indicates that the Transaction is actively being processed, but has 
      not been completed. It is used to prevent the sender from assuming 
      the TransactionRequest was lost where the Transaction will take some 
      time to complete. 

        TransactionPending(TransactionID { } ) 

      The TransactionID parameter must be the same as that of the 
      corresponding TransactionRequest. A property of root 
      (normalMGExecutionTime) is settable by the MGC to indicate the 
      interval within which the MGC expects a response to any transaction 
      from the MG. Another property (normalMGCExecutionTime) is settable by 
      the MGC to indicate the interval within which the MG should expect a 
      response to any transaction from the MGC. Senders may receive more 
      than one TransactionPending for a command. If a duplicate request is 
      received when pending, the responder may send a duplicate pending 
      immediately, or continue waiting for its timer to trigger another 
      TransactionPending. 

   8.3   Messages 
       
      Multiple Transactions can be concatenated into a Message. Messages 
      have a header, which includes the identity of the sender. The Message 
      Identifier (MID) of a message is set to a provisioned name (e.g. 
      domain address/domain name/device name) of the entity transmitting 
      the message. Domain name is a suggested default. An H.248.1 entity 
      (MG/MGC) must consistently use the same MID in all messages it 
      originates for the duration of control association with the peer 
      (MGC/MG). 

      Every Message contains a Version Number identifying the version of 
      the protocol the message conforms to. Versions consist of one or two 
      digits, beginning with version 1 for the present version of the 
      protocol. 


    
    
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      The transactions in a message are treated independently. There is no 
      order implied; there is no application or protocol acknowledgement of 
      a message. A message is essentially a transport mechanism.  For 
      example, message X containing transaction requests A, B, and C may be 
      responded to with message Y containing replies to A and C and message 
      Z containing the reply to B. Likewise, message L containing request D 
      and message M containing request E may be responded to with message N 
      containing replies to both D and E. 

       
   9  Transport 
       
      The transport mechanism for the protocol should allow the reliable 
      transport of transactions between a MGC and MG. The transport shall 
      remain independent of what particular commands are being sent and 
      shall be applicable to all application states. There are several 
      transports defined for the protocol, which are defined in Annexes to 
      this Recommendation and other Recommendations of the H.248 sub-
      series. Additional Transports may be defined as additional 
      Recommendations of the H.248 sub-series. For transport of the 
      protocol over IP, MGCs shall implement both TCP and UDP/ALF, a MG 
      shall implement TCP or UDP/ALF or both. 

      The MG is provisioned with a name or address (such as DNS name or IP 
      address) of a primary and zero or more secondary MGCs (see 7.2.8) 
      that is the address the MG uses to send messages to the MGC. If TCP 
      or UDP is used as the protocol transport and the port to which the 
      initial ServiceChange request is to be sent is not otherwise known, 
      that request should be sent to the default port number for the 
      protocol. This port number is 2944 for text-encoded operation or 2945 
      for binary-encoded operation, for either UDP or TCP. The MGC receives 
      the message containing the ServiceChange request from the MG and can 
      determine the MG's address from it. As described in 7.2.8, either the 
      MG or the MGC may supply an address in the ServiceChangeAddress 
      parameter to which subsequent transaction requests must be addressed, 
      but responses (including the response to the initial ServiceChange 
      request) must always be sent back to the address which was the source 
      of the corresponding request. For example, in IP networks, this is 
      the source address in the IP header and the source port number in the 
      TCP/UDP/SCTP header. 

   9.1   Ordering of Commands 
       
      This Recommendation does not mandate that the underlying transport 
      protocol guarantees the sequencing of transactions sent to an entity. 
      This property tends to maximize the timeliness of actions, but it has 
      a few drawbacks. For example: 


    
    
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      -  Notify commands may be delayed and arrive at the MGC after the 
         transmission of a new command changing the EventsDescriptor. 

      -  If a new command is transmitted before a previous one is 
         acknowledged, there is no guarantee that prior command will be 
         executed before the new one. 

      Media Gateway Controllers that want to guarantee consistent operation 
      of the Media Gateway may use the following rules. These rules are 
      with respect to commands that are in different transactions. Commands 
      that are in the same transaction are executed in order (see clause 
      8). 

      1) When a Media Gateway handles several Terminations, commands 
         pertaining to the different Terminations may be sent in parallel, 
         for example following a model where each Termination (or group of 
         Terminations) is controlled by its own process or its own thread. 

      2) On a Termination, there should normally be at most one outstanding 
         command (Add or Modify or Move), unless the outstanding commands 
         are in the same transaction. However, a Subtract command may be 
         issued at any time. In consequence, a Media Gateway may sometimes 
         receive a Modify command that applies to a previously subtracted 
         Termination. Such commands should be ignored, and an error code 
         should be returned. 

      3) For transports that do not guarantee in-sequence delivery of 
         messages (i.e. UDP), there should normally be on a given 
         Termination at most one outstanding Notify command at any time. 

      4) In some cases, an implicitly or explicitly wildcarded Subtract 
         command that applies to a group of Terminations may step in front 
         of a pending Add command. The Media Gateway Controller should 
         individually delete all Terminations for which an Add command was 
         pending at the time of the global Subtract command. Also, new Add 
         commands for Terminations named by the wildcarding (or implied in 
         a Multiplex descriptor) should not be sent until the wildcarded 
         Subtract command is acknowledged. 

      5) AuditValue and AuditCapability are not subject to any sequencing. 

      6) ServiceChange shall always be the first command sent by a MG as 
         defined by the restart procedure. Any other command or response 
         must be delivered after this ServiceChange command. 

      These rules do not affect the command responder, which should always 
      respond to commands. 


    
    
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   9.2   Protection against Restart Avalanche 
       
      In the event that a large number of Media Gateways are powered on 
      simultaneously and they were to all initiate a ServiceChange 
      transaction, the Media Gateway Controller would very likely be 
      swamped, leading to message losses and network congestion during the 
      critical period of service restoration. In order to prevent such 
      avalanches, the following behaviour is suggested: 

      1) When a Media Gateway is powered on, it should initiate a restart 
         timer to a random value, uniformly distributed between 0 and a 
         maximum waiting delay (MWD). Care should be taken to avoid 
         synchronicity of the random number generation between multiple 
         Media Gateways that would use the same algorithm. 

      2) The Media Gateway should then wait for either the end of this 
         timer or the detection of a local user activity, such as for 
         example an off-hook transition on a residential Media Gateway. 

      3) When the timer elapses, or when an activity is detected, the Media 
         Gateway should initiate the restart procedure. 

      The restart procedure simply requires the MG to guarantee that the 
      first message that the Media Gateway Controller sees from this MG is 
      a ServiceChange message informing the Media Gateway Controller about 
      the restart. 

        NOTE - The value of MWD is a configuration parameter that depends 
        on the type of the Media Gateway. The following reasoning may be 
        used to determine the value of this delay on residential gateways. 

      Media Gateway Controllers are typically dimensioned to handle the 
      peak hour traffic load, during which, in average, 10% of the lines 
      will be busy, placing calls whose average duration is typically 3 
      minutes. The processing of a call typically involves 5 to 6 Media 
      Gateway Controller transactions between each Media Gateway and the 
      Media Gateway Controller. This simple calculation shows that the 
      Media Gateway Controller is expected to handle 5 to 6 transactions 
      for each Termination, every 30 minutes on average, or, to put it 
      otherwise, about one transaction per Termination every 5 to 6 minutes 
      on average. This suggests that a reasonable value of MWD for a 
      residential gateway would be 10 to 12 minutes. In the absence of 
      explicit configuration, residential gateways should adopt a value of 
      600 seconds for MWD. 

      The same reasoning suggests that the value of MWD should be much 
      shorter for trunking gateways or for business gateways, because they 
      handle a large number of Terminations, and also because the usage 
      rate of these Terminations is much higher than 10% during the peak 
    
    
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      busy hour, a typical value being 60%. These Terminations, during the 
      peak hour, are this expected to contribute about one transaction per 
      minute to the Media Gateway Controller load. A reasonable algorithm 
      is to make the value of MWD per "trunk" Termination six times shorter 
      than the MWD per residential gateway, and also inversely proportional 
      to the number of Terminations that are being restarted. For example 
      MWD should be set to 2.5 seconds for a gateway that handles a T1 
      line, or to 60 milliseconds for a gateway that handles a T3 line. 

       
   10 Security considerations 
       
      This clause covers security when using the protocol in an IP 
      environment. 

   10.1  Protection of Protocol Connections 
       
      A security mechanism is clearly needed to prevent unauthorized 
      entities from using the protocol defined in this Recommendation for 
      setting up unauthorized calls or interfering with authorized calls. 
      The security mechanism for the protocol when transported over IP 
      networks is IPsec [RFC 2401 to RFC 2411]. 

      The AH header [RFC 2402] affords data origin authentication, 
      connectionless integrity and optional anti-replay protection of 
      messages passed between the MG and the MGC. The ESP header [RFC 2406] 
      provides confidentiality of messages, if desired. For instance, the 
      ESP encryption service should be requested if the session 
      descriptions are used to carry session keys, as defined in SDP. 

      Implementations of the protocol defined in this Recommendation 
      employing the ESP header SHALL comply with section 5 of [RFC 2406], 
      which defines a minimum set of algorithms for integrity checking and 
      encryption. Similarly, implementations employing the AH header SHALL 
      comply with section 5 of [RFC 2402], which defines a minimum set of 
      algorithms for integrity checking using manual keys. 

      Implementations SHOULD use IKE [RFC 2409] to permit more robust 
      keying options. Implementations employing IKE SHOULD support 
      authentication with RSA signatures and RSA public key encryption. 

   10.2  Interim AH scheme 
       
      Implementation of IPsec requires that the AH or ESP header be 
      inserted immediately after the IP header. This cannot be easily done 
      at the application level. Therefore, this presents a deployment 
      problem for the protocol defined in this Recommendation where the 
      underlying network implementation does not support IPsec. 

    
    
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      As an interim solution, an optional AH header is defined within the 
      H.248.1 protocol header. The header fields are exactly those of the 
      SPI, SEQUENCE NUMBER and DATA fields as defined in [RFC 2402]. The 
      semantics of the header fields are the same as the "transport mode" 
      of [RFC 2402], except for the calculation of the Integrity Check 
      Value (ICV). In IPsec, the ICV is calculated over the entire IP 
      packet including the IP header. This prevents spoofing of the IP 
      addresses. To retain the same functionality, the ICV calculation 
      should be performed across all the transactions (concatenated) in the 
      message prepended by a synthesized IP header consisting of a 32-bit 
      source IP address, a 32-bit destination address and a 16-bit UDP 
      destination port encoded as 20 hex digits. When the interim AH 
      mechanism is employed when TCP is the transport Layer, the UDP Port 
      above becomes the TCP port, and all other operations are the same. 

      Implementations of the H.248.1 protocol SHALL implement IPsec where 
      the underlying operating system and the transport network supports 
      IPsec. Implementations of the protocol using IPv4 SHALL implement the 
      interim AH scheme. However, this interim scheme SHALL NOT be used 
      when the underlying network layer supports IPsec. IPv6 
      implementations are assumed to support IPsec and SHALL NOT use the 
      interim AH scheme. 

      All implementations of the interim AH mechanism SHALL comply with 
      section 5 of RFC 2402 which defines a minimum set of algorithms for 
      integrity checking using manual keys.  

      The interim AH interim scheme does not provide protection against 
      eavesdropping, thus forbidding third parties from monitoring the 
      connections set up by a given Termination. Also, it does not provide 
      protection against replay attacks. These procedures do not 
      necessarily protect against denial of service attacks by misbehaving 
      MGs or misbehaving MGCs. However, they will provide an identification 
      of these misbehaving entities, which should then be deprived of their 
      authorization through maintenance procedures. 

   10.3  Protection of Media Connections 
       
      The protocol allows the MGC to provide MGs with "session keys" that 
      can be used to encrypt the audio messages, protecting against 
      eavesdropping. 

      A specific problem of packet networks is "uncontrolled barge-in". 
      This attack can be performed by directing media packets to the IP 
      address and UDP port used by a connection. If no protection is 
      implemented, the packets must be decompressed and the signals must be 
      played on the "line side". 


    
    
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      A basic protection against this attack is to only accept packets from 
      known sources, checking for example that the IP source address and 
      UDP source port match the values announced in the Remote descriptor. 
      This has two inconveniences: it slows down connection establishment 
      and it can be fooled by source spoofing: 

      -  To enable the address-based protection, the MGC must obtain the 
         remote session description of the egress MG and pass it to the 
         ingress MG. This requires at least one network round trip, and 
         leaves us with a dilemma: either allow the call to proceed without 
         waiting for the round trip to complete, and risk for example, 
         "clipping" a remote announcement, or wait for the full round trip 
         and settle for slower call-set up procedures. 

      -  Source spoofing is only effective if the attacker can obtain valid 
         pairs of source destination addresses and ports, for example by 
         listening to a fraction of the traffic. To fight source spoofing, 
         one could try to control all access points to the network. But 
         this is in practice very hard to achieve. 

      An alternative to checking the source address is to encrypt and 
      authenticate the packets, using a secret key that is conveyed during 
      the call set-up procedure. This will not slow down the call set-up, 
      and provides strong protection against address spoofing. 

       
   11 MG-MGC Control Interface  
       
      The control association between MG and MGC is initiated at MG cold 
      start, and announced by a ServiceChange message, but can be changed 
      by subsequent events, such as failures or manual service events. 
      While the protocol does not have an explicit mechanism to support 
      multiple MGCs controlling a physical MG, it has been designed to 
      support the multiple logical MG (within a single physical MG) that 
      can be associated with different MGCs. 

   11.1  Multiple Virtual MGs 
       
      A physical Media Gateway may be partitioned into one or more Virtual 
      MGs. A virtual MG consists of a set of statically partitioned 
      physical Terminations and/or sets of ephemeral Terminations. A 
      physical Termination is controlled by one MGC. The model does not 
      require that other resources be statically allocated, just 
      Terminations. The mechanism for allocating Terminations to virtual 
      MGs is a management method outside the scope of the protocol. Each of 
      the virtual MGs appears to the MGC as a complete MG client. 

      A physical MG may have only one network interface, which must be 
      shared across virtual MGs. In such a case, the packet/cell side 
    
    
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      Termination is shared. It should be noted however, that in use, such 
      interfaces require an ephemeral instance of the Termination to be 
      created per flow, and thus sharing the Termination is 
      straightforward. This mechanism does lead to a complication, namely 
      that the MG must always know which of its controlling MGCs should be 
      notified if an event occurs on the interface. 

      In normal operation, the Virtual MG will be instructed by the MGC to 
      create network flows (if it is the originating side), or to expect 
      flow requests (if it is the terminating side), and no confusion will 
      arise. However, if an unexpected event occurs, the Virtual MG must 
      know what to do with respect to the physical resources it is 
      controlling. 

      If recovering from the event requires manipulation of a physical 
      interface's state, only one MGC should do so. These issues are 
      resolved by allowing any of the MGCs to create EventsDescriptors to 
      be notified of such events, but only one MGC can have read/write 
      access to the physical interface properties; all other MGCs have 
      read-only access. The management mechanism is used to designate which 
      MGC has read/write capability, and is designated the Master MGC. 

      Each virtual MG has its own Root Termination. In most cases the 
      values for the properties of the Root Termination are independently 
      settable by each MGC. Where there can only be one value, the 
      parameter is read-only to all but the Master MGC. 

      ServiceChange may only be applied to a Termination or set of 
      Terminations partitioned to the Virtual MG or created (in the case of 
      ephemeral Terminations) by that Virtual MG. 

   11.2  Cold start 
       
      A MG is pre-provisioned by a management mechanism outside the scope 
      of this protocol with a primary and (optionally) an ordered list of 
      secondary MGCs. Upon a cold start of the MG, it will issue a 
      ServiceChange command with a "Restart" method, on the Root 
      Termination to its primary MGC. If the MGC accepts the MG, it sends a 
      Transaction Reply not including a ServiceChangeMgcId parameter. If 
      the MGC does not accept the MGs registration, it sends a Transaction 
      Reply, providing the address of an alternate MGC to be contacted by 
      including a ServiceChangeMgcId parameter. 

      If the MG receives a Transaction Reply that includes a 
      ServiceChangeMgcId parameter, it sends a ServiceChange to the MGC 
      specified in the ServiceChangeMgcId. It continues this process until 
      it gets a controlling MGC to accept its registration, or it fails to 
      get a reply. Upon failure to obtain a reply, either from the primary 
      MGC, or a designated successor, the MG tries its pre-provisioned 
    
    
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      secondary MGCs, in order. If the MG is unable to establish a control 
      relationship with any MGC, it shall wait a random amount of time as 
      described in 9.2 and then start contacting its primary, and if 
      necessary, its secondary MGCs again. 

      It is possible that the reply to a ServiceChange with Restart will be 
      lost, and a command will be received by the MG prior to the receipt 
      of the ServiceChange response. The MG shall issue Error 505 - Command 
      Received before Restart Response. 

   11.3  Negotiation of protocol version 
       
      The first ServiceChange command from a MG shall contain the version 
      number of the protocol supported by the MG in the 
      ServiceChangeVersion parameter. Upon receiving such a message, if the 
      MGC supports only a lower version, then the MGC shall send a 
      ServiceChangeReply with the lower version and thereafter all the 
      messages between MG and MGC shall conform to the lower version of the 
      protocol. If the MG is unable to comply and it has established a 
      transport connection to the MGC, it should close that connection. In 
      any event, it should reject all subsequent requests from the MGC with 
      error 406 - Version Not Supported. 

      If the MGC supports a higher version than the MG but is able to 
      support the lower version proposed by the MG, it shall send a 
      ServiceChangeReply with the lower version and thereafter all the 
      messages between MG and MGC shall conform to the lower version of the 
      protocol. If the MGC is unable to comply, it shall reject the 
      association, with error 406 - Version Not Supported. 

      Protocol version negotiation may also occur at "handoff" and 
      "failover" ServiceChanges. 

      When extending the protocol with new versions, the following rules 
      should be followed: 

      1) Existing protocol elements, i.e. procedures, parameters, 
         descriptor, property, values, should not be changed unless a 
         protocol error needs to be corrected or it becomes necessary to 
         change the operation of the service that is being supported by the 
         protocol. 

      2) The semantics of a command, a parameter, a descriptor, a property, 
         or a value should not be changed. 

      3) Established rules for formatting and encoding messages and 
         parameters should not be modified. 


    
    
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      4) When information elements are found to be obsolete they can be 
         marked as not used. However, the identifier for that information 
         element will be marked as reserved. In that way it can not be used 
         in future versions. 

   11.4  Failure of a MG 
       
      If a MG fails, but is capable of sending a message to the MGC, it 
      sends a ServiceChange with an appropriate method (graceful or forced) 
      and specifies the Root TerminationID. When it returns to service, it 
      sends a ServiceChange with a "Restart" method. 

      Allowing the MGC to send duplicate messages to both MGs accommodates 
      pairs of MGs that are capable of redundant failover of one of the 
      MGs. Only the Working MG shall accept or reject transactions. Upon 
      failover, the primary MG sends a ServiceChange command with a 
      "Failover" method and a "MG Impending Failure" reason. The MGC then 
      uses the secondary MG as the active MG. When the error condition is 
      repaired, the Working MG can send a "ServiceChange" with a "Restart" 
      method. 

        Note: Redundant failover MGs require a reliable transport, because 
        the protocol provides no means for a secondary MG running ALF to 
        acknowledge messages sent from the MGC. 

   11.5  Failure of an MGC 
       
      If the MG detects a failure of its controlling MGC, it attempts to 
      contact the next MGC on its pre  provisioned list. It starts its 
      attempts at the beginning (primary MGC), unless that was the MGC that 
      failed, in which case it starts at its first secondary MGC. It sends 
      a ServiceChange message with a "Failover" method and a " MGC 
      Impending Failure" reason. If the MG is unable to establish a control 
      relationship with any MGC, it shall wait a random amount of time as 
      described in section 9.2 and then start again contacting its primary, 
      and (if necessary) its secondary MGCs. When contacting its previously 
      controlling MGC, the MG sends the ServiceChange message with 
      "Disconnected" method. 

      In partial failure, or for manual maintenance reasons, an MGC may 
      wish to direct its controlled MGs to use a different MGC. To do so, 
      it sends a ServiceChange method to the MG with a "HandOff" method, 
      and its designated replacement in ServiceChangeMgcId. If "HandOff" is 
      supported, the MG shall send a ServiceChange message with a "Handoff" 
      method and a "MGC directed change" reason to the designated MGC. If 
      it fails to get a reply from the designated MGC, the MG shall behave 
      as if its MGC failed, and start contacting secondary MGCs as 
      specified in the previous paragraph. If the MG is unable to establish 
      a control relationship with any MGC, it shall wait a random amount of 
    
    
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      time as described in 9.2 and then start contacting its primary, and 
      if necessary, its secondary MGCs again. 

      No recommendation is made on how the MGCs involved in the Handoff 
      maintain state information; this is considered to be out of scope of 
      this Recommendation. The MGC and MG may take the following steps when 
      Handoff occurs. When the MGC initiates a HandOff, the handover should 
      be transparent to Operations on the Media Gateway. Transactions can 
      be executed in any order, and could be in progress when the 
      ServiceChange is executed. Accordingly, commands in progress continue 
      and replies to all commands from the original MGC must be sent to the 
      transport address from which they were sent. If the service 
      relationship with the sending MGC has ended, the replies should be 
      discarded. The MG may receive outstanding transaction replies from 
      the new MGC. No new messages shall be sent to the new MGC until the 
      control association is established. Repeated transaction requests 
      shall be directed to the new MGC. The MG shall maintain state on all 
      Terminations and Contexts. 

      It is possible that the MGC could be implemented in such a way that a 
      failed MGC is replaced by a working MGC where the identity of the new 
      MGC is the same as the failed one. In such a case, ServiceChangeMgcId 
      would be specified with the previous value and the MG shall behave as 
      if the value was changed, and send a ServiceChange message, as above. 

      Pairs of MGCs that are capable of redundant failover can notify the 
      controlled MGs of the failover by the above mechanism. 

       
   12 Package definition 
       
      The primary mechanism for extension is by means of Packages. Packages 
      define additional Properties, Events, Signals and Statistics that may 
      occur on Terminations. 

      Packages defined by IETF will appear in separate RFCs. 

      Packages defined by ITU-T may appear in the relevant Recommendations 
      (e.g. as Recommendations of the H.248 sub-series). 

      1) A public document or a standard forum document, which can be 
         referenced as the document that describes the package following 
         the guideline above, should be specified.  

      2) The document shall specify the version of the Package that it 
         describes. 



    
    
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      3) The document should be available on a public web server and should 
         have a stable URL. The site should provide a mechanism to provide 
         comments and appropriate responses should be returned. 

   12.1  Guidelines for defining packages 
       
      Packages define Properties, Events, Signals, and Statistics. 

      Packages may also define new error codes according to the guidelines 
      given in 13.2. This is a matter of documentary convenience: the 
      package documentation is submitted to IANA in support of the error 
      code registration. If a package is modified, it is unnecessary to 
      provide IANA with a new document reference in support of the error 
      code unless the description of the error code itself is modified. 

      Names of all such defined constructs shall consist of the PackageID 
      (which uniquely identifies the package) and the ID of the item (which 
      uniquely identifies the item in that package). In the text encoding 
      the two shall be separated by a forward slash ("/") character. 
      Example: togen/playtone is the text encoding to refer to the play 
      tone signal in the tone generation package. 

      A Package will contain the following sections: 

   12.1.1   Package 
       
      Overall description of the package, specifying: 

         Package Name: only descriptive 

         PackageID: is an identifier 

         Description:  

         Version: 

            A new version of a package can only add additional Properties, 
            Events, Signals, Statistics and new possible values for an 
            existing parameter described in the original package. No 
            deletions or modifications shall be allowed. A version is an 
            integer in the range from 1 to 99. 

         Designed to be extended only (Optional):  

            If this indication is present, it signifies that the package 
            has been expressly designed to be extended by others, not to be 
            directly referenced. For example, the package may not have any 
            function on its own or be nonsensical on its own. The MG SHOULD 
            NOT publish this PackageID when reporting packages. 
    
    
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         Extends (Optional): existing package Descriptor 

            A package may extend an existing package. The version of the 
            original package must be specified. When a package extends 
            another package it shall only add additional Properties, 
            Events, Signals, Statistics and new possible values for an 
            existing parameter described in the original package. An 
            extended package shall not redefine or overload an identifier 
            defined in the original package and packages it may have 
            extended (multiple levels of extension). Hence, if package B 
            version 1 extends package A version 1, version 2 of B will not 
            be able to extend the A version 2 if A version 2 defines a name 
            already in B version 1. 

   12.1.2   Properties 
       
      Properties defined by the package, specifying: 

         Property Name: only descriptive 

         PropertyID: is an identifier 

         Description: 

         Type: One of: 

            Boolean 

            String: UTF-8 string 

            Octet String: A number of octets.  See Annex A and Annex B.3 
            for encoding 

            Integer: 4 byte signed integer 

            Double: 8 byte signed integer 

            Character: unicode UTF-8 encoding of a single letter. Could be 
            more than one octet. 

            Enumeration: one of a list of possible unique values (see 12.3) 

            Sub-list: a list of several values from a list. The type of 
            sub-list SHALL also be specified.  The type shall be chosen 
            from the types specified in this section (with the exception of 
            sub-list). For example, Type: sub-list of enumeration.  The 
            encoding of sub-lists is specified in Annexes A and B.3. 

         Possible values: 
    
    
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            A package MUST specify either a specific set of values or a 
            description of how values are determined.  A package MUST also 
            specify a default value or the default behaviour when the value 
            is omitted from its descriptor.  For example, a package may 
            specify that procedures related to the property are suspended 
            when it value is omitted.  A default value (but not procedures) 
            may be specified as provisionable. 

         Defined in: 

            Which H.248.1 descriptor the property is defined in. 
            LocalControl is for stream dependent properties. 
            TerminationState is for stream independent properties. These 
            are expected to be the most common cases, but it is possible 
            for properties to be defined in other descriptors. 

         Characteristics: Read/Write or both, and (optionally), global:  

            Indicates whether a property is read-only, or read-write, and 
            if it is global. If Global is omitted, the property is not 
            global. If a property is declared as global, the value of the 
            property is shared by all Terminations realizing the package. 

   12.1.3   Events 
       
      Events defined by the package, specifying: 

         Event name: only descriptive 

         EventID: is an identifier 

         Description: 

         EventsDescriptor Parameters:  

            Parameters used by the MGC to configure the event, and found in 
            the EventsDescriptor. See 12.2. 

         ObservedEventsDescriptor Parameters:  

            Parameters returned to the MGC in Notify requests and in 
            replies to command requests from the MGC that audit 
            ObservedEventsDescriptor, and found in the 
            ObservedEventsDescriptor. See 12.2. 

   12.1.4   Signals 
       
      Signals defined by the package, specifying: 

    
    
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         Signal Name: only descriptive 

         SignalID: is an identifier. SignalID is used in a 
         SignalsDescriptor 

         Description 

         SignalType: one of: 

            OO (On/Off)  

            TO (TimeOut) 

            BR (Brief) 

         NOTE - SignalType may be defined such that it is dependent on the 
         value of one or more parameters. The package MUST specify a 
         default signal type.  If the default type is TO, the package MUST 
         specify a default duration which may be provisioned.  A default 
         duration is meaningless for BR.  

         Duration: in hundredths of seconds 

         Additional Parameters: see 12.2 

   12.1.5   Statistics 
       
      Statistics defined by the package, specifying: 

         Statistic name: only descriptive 

         StatisticID: is an identifier 

         StatisticID is used in a StatisticsDescriptor 

         Description: 

         Units: unit of measure, e.g. milliseconds, packets 

   12.1.6   Procedures 
       
      Additional guidance on the use of the package. 

   12.2  Guidelines to defining Parameters to Events and Signals 
       
      Parameter Name: only descriptive 

      ParameterID: is an identifier. The textual ParameterID of parameters 
      to Events and Signals shall not start with "EPA" and "SPA", 
    
    
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      respectively. The textual ParameterID shall also not be "ST", 
      "Stream", "SY", "SignalType", "DR", "Duration", "NC", 
      "NotifyCompletion", "KA", "Keepactive", "EB", "Embed", "DM" or 
      "DigitMap". 

      Type: One of: 

         Boolean 

         String: UTF-8 octet string 

         Octet String: A number of octets.  See Annex A and Annex B.3 for 
         encoding 

         Integer: 4-octet signed integer 

         Double: 8-octet signed integer 

         Character: unicode UTF-8 encoding of a single letter. Could be 
         more than one octet. 

         Enumeration: one of a list of possible unique values (see 12.3) 

         Sub-list: a list of several values from a list (not supported for 
         statistics). The type of sub-list SHALL also be specified.  The 
         type shall be chosen from the types specified in this section 
         (with the exception of sub-list). For example, Type: sub-list of 
         enumeration.  The encoding of sub-lists is specified in Annexes A 
         and B.3. 

      Possible values: 

         A package MUST specify either a specific set of values or a 
         description of how values are determined.  A package MUST also 
         specify a default value or the default behavior when the value is 
         omitted from its descriptor.  For example, a package may specify 
         that procedures related to the parameter are suspended when it 
         value is omitted.  A default value (but not procedures) may be 
         specified as provisionable. 

      Description: 

   12.3  Lists 
       
      Possible values for parameters include enumerations. Enumerations may 
      be defined in a list. It is recommended that the list be IANA 
      registered so that packages that extend the list can be defined 
      without concern for conflicting names. 

    
    
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   12.4  Identifiers 
       
      Identifiers in text encoding shall be strings of up to 64 characters, 
      containing no spaces, starting with an alphabetic character and 
      consisting of alphanumeric characters and/or digits, and possibly 
      including the special character underscore ("_"). 

      Identifiers in binary encoding are 2 octets long. 

      Both text and binary values shall be specified for each identifier, 
      including identifiers used as values in enumerated types. 

   12.5  Package registration 
       
      A package can be registered with IANA for interoperability reasons. 
      See clause 13 for IANA considerations. 

       
   13 IANA considerations 
       
   13.1  Packages 
       
      The following considerations SHALL be met to register a package with 
      IANA: 

      1) A unique string name, unique serial number and version number is 
         registered for each package. The string name is used with text 
         encoding. The serial number shall be used with binary encoding. 
         Serial Numbers 0x8000 to 0xFFFF are reserved for private use. 
         Serial number 0 is reserved. 

      2) A contact name, email and postal addresses for that contact shall 
         be specified. The contact information shall be updated by the 
         defining organization as necessary. 

      3) A reference to a document that describes the package, which should 
         be public: 
          
         The document shall specify the version of the Package that it 
         describes. 
          
         If the document is public, it should be located on a public web 
         server and should have a stable URL. The site should provide a 
         mechanism to provide comments and appropriate responses should be 
         returned. 

      4) Packages registered by other than recognized standards bodies 
         shall have a minimum package name length of 8 characters. 

    
    
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      5) All other package names are first come-first served if all other 
         conditions are met. 

   13.2  Error codes 
       
      The following considerations SHALL be met to register an error code 
      with IANA: 

      1) An error number and a one-line (80-character maximum) string is 
         registered for each error. 

      2) A complete description of the conditions under which the error is 
         detected shall be included in a publicly available document. The 
         description shall be sufficiently clear to differentiate the error 
         from all other existing error codes. 

      3) The document should be available on a public web server and should 
         have a stable URL. 

      4) Error numbers registered by recognized standards bodies shall have 
         3- or 4-character error numbers. 

      5) Error numbers registered by all other organizations or individuals 
         shall have 4-character error numbers. 

      6) An error number shall not be redefined nor modified except by the 
         organization or individual that originally defined it, or their 
         successors or assigns. 

   13.3  ServiceChange reasons 
       
      The following considerations SHALL be met to register service change 
      reason with IANA: 

      1) A one-phrase, 80-character maximum, unique reason code is 
         registered for each reason. 

      2) A complete description of the conditions under which the reason is 
         used is detected shall be included in a publicly available 
         document. The description shall be sufficiently clear to 
         differentiate the reason from all other existing reasons.  

      3) The document should be available on a public web server and should 
         have a stable URL.  





    
    
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                                   ANNEX A 
                        Binary encoding of the protocol 
       
      This annex specifies the syntax of messages using the notation 
      defined in Recommendation X.680; Information technology - Abstract 
      Syntax Notation One (ASN.1): Specification of basic notation. 
      Messages shall be encoded for transmission by applying the basic 
      encoding rules specified in Recommendation X.690, Information 
      Technology - ASN.1 Encoding Rules: Specification of Basic Encoding 
      Rules (BER), Canonical Encoding Rules (CER) and Distinguished 
      Encoding Rules. 

   A.1   Coding of wildcards 
       
      The use of wildcards ALL and CHOOSE is allowed in the protocol. This 
      allows a MGC to partially specify Termination IDs and to let the MG 
      choose from the values that conform to the partial specification. 
      Termination IDs may encode a hierarchy of names. This hierarchy is 
      provisioned. For instance, a TerminationID may consist of a trunk 
      group, a trunk within the group and a circuit. Wildcarding must be 
      possible at all levels. The following paragraphs explain how this is 
      achieved. 

      The ASN.1 description uses octet strings of up to 8 octets in length 
      for Termination IDs. This means that Termination IDs consist of at 
      most 64 bits. A fully specified Termination ID may be preceded by a 
      sequence of wildcarding fields. A wildcarding field is one octet in 
      length. Bit 7 (the most significant bit) of this octet specifies what 
      type of wildcarding is invoked: if the bit value equals 1, then the 
      ALL wildcard is used; if the bit value if 0, then the CHOOSE wildcard 
      is used. Bit 6 of the wildcarding field specifies whether the 
      wildcarding pertains to one level in the hierarchical naming scheme 
      (bit value 0) or to the level of the hierarchy specified in the 
      wildcarding field plus all lower levels (bit value 1). Bits 0 through 
      5 of the wildcarding field specify the bit position in the 
      Termination ID at which the wildcarding starts. 

      We illustrate this scheme with some examples. In these examples, the 
      most significant bit in a string of bits appears on the left hand 
      side. 

      Assume that Termination IDs are three octets long and that each octet 
      represents a level in a hierarchical naming scheme. A valid 
      Termination ID is: 

         00000001 00011110 01010101. 

      Addressing ALL names with prefix 00000001 00011110 is done as 
      follows: 
    
    
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         wildcarding field: 10000111 

         Termination ID: 00000001 00011110 xxxxxxxx. 

      The values of the bits labeled "x" is irrelevant and shall be ignored 
      by the receiver. 

      Indicating to the receiver that it must choose a name with 00011110 
      as the second octet is done as follows: 

         wildcarding fields: 00010111 followed by 00000111 

         Termination ID: xxxxxxxx 00011110 xxxxxxxx. 

      The first wildcard field indicates a CHOOSE wildcard for the level in 
      the naming hierarchy starting at bit 23, the highest level in our 
      assumed naming scheme. The second wildcard field indicates a CHOOSE 
      wildcard for the level in the naming hierarchy starting at bit 7, the 
      lowest level in our assumed naming scheme. 

      Finally, a CHOOSE-wildcarded name with the highest level of the name 
      equal to 00000001 is specified as follows: 

         wildcard field: 01001111 

         Termination ID: 0000001 xxxxxxxx xxxxxxxx . 

      Bit value 1 at bit position 6 of the first octet of the wildcard 
      field indicates that the wildcarding pertains to the specified level 
      in the naming hierarchy and all lower levels. 

      Context IDs may also be wildcarded. In the case of Context IDs, 
      however, specifying partial names is not allowed. Context ID 0x0 
      SHALL be used to indicate the NULL Context, Context ID 0xFFFFFFFE 
      SHALL be used to indicate a CHOOSE wildcard, and Context ID 
      0xFFFFFFFF SHALL be used to indicate an ALL wildcard. 

      TerminationID 0xFFFFFFFFFFFFFFFF SHALL be used to indicate the ROOT 
      Termination. 

   A.2   ASN.1 syntax specification 
       
      This subclause contains the ASN.1 specification of the H.248.1 
      protocol syntax. 

        NOTE 1 - In case a transport mechanism is used that employs 
        application level framing, the definition of Transaction below 
        changes. Refer to the annex or to the Recommendation of the H.248 

    
    
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        sub-series defining the transport mechanism for the definition that 
        applies in that case. 

        NOTE 2 - The ASN.1 specification below contains a clause defining 
        TerminationIDList as a sequence of TerminationIDs. The length of 
        this sequence SHALL be one, except possibly when used in 
        contextAuditResult. 

        NOTE 3 - This syntax specification does not enforce all 
        restrictions on element inclusions and values.  Some additional 
        restrictions are stated in comments and other restrictions appear 
        in the text of this recommendation.  These additional restrictions 
        are part of the protocol even though not enforced by this 
        specification. 

        NOTE 4 - The ASN.1 module in this Annex uses octet string types to 
        encode values for property parameter, signal parameter and event 
        parameter values and statistics. The actual types of these values 
        vary and are specified in Annex C or the relevant package 
        definition. 

      A value is first BER-encoded based on its type using the table below.  
      The result of this BER-encoding is then encoded as an ASN.1 octet 
      string, "double wrapping" the value. The format specified in Annex C 
      or the package relates to BER encoding according to the following 
      table: 

       

      Type Specified in Package   ASN.1 BER Type 

      String                      IA5String or UTF8String (Note 4) 

      Integer (4 Octet)           INTEGER 

      Double (8 octet signed int) INTEGER (Note 3) 

      Character (UTF-8, Note 1)   IA5String 

      Enumeration                 ENUMERATED 

      Boolean                     BOOLEAN 

      Unsigned Integer (Note 2)   INTEGER  (Note 3) 

      Octet (String)              OCTET STRING 

       
    
    
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        Note 1: Can be more than one byte 

        Note 2: Unsigned integer is referenced in Annex C 

        Note 3: The BER encoding of INTEGER does not imply the use of 4 
        bytes. 

        Note 4: String should be encoded as IA5String when the contents are 
        all ASCII characters, but as UTF8String if it contains any non-
        ASCII characters. 

      See ITU-T Rec. X.690, 8.7, for the definition of the encoding of an 
      octet string value. 

       

      MEDIA-GATEWAY-CONTROL DEFINITIONS AUTOMATIC TAGS::= 
      BEGIN 
       
       
      MegacoMessage ::= SEQUENCE 
      { 
         authHeader     AuthenticationHeader OPTIONAL, 
         mess           Message 
      } 
       
      AuthenticationHeader ::= SEQUENCE 
      { 
         secParmIndex   SecurityParmIndex, 
         seqNum         SequenceNum, 
         ad             AuthData 
      } 
       
      SecurityParmIndex ::= OCTET STRING(SIZE(4)) 
       
      SequenceNum       ::= OCTET STRING(SIZE(4)) 
       
      AuthData          ::= OCTET STRING (SIZE (12..32)) 
       
      Message ::= SEQUENCE 
      { 
         version           INTEGER(0..99), 
         -- The version of the protocol defined here is equal to 1. 
         mId               MId,  -- Name/address of message originator 
         messageBody       CHOICE 
         { 
            messageError      ErrorDescriptor, 
            transactions      SEQUENCE OF Transaction 
         }, 
    
    
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         ... 
      } 
       
      MId ::= CHOICE 
      { 
         ip4Address           IP4Address, 
         ip6Address           IP6Address, 
         domainName           DomainName, 
         deviceName           PathName, 
         mtpAddress           OCTET STRING(SIZE(2..4)), 
         -- Addressing structure of mtpAddress: 
         --     25 - 15           0 
         --        |  PC        | NI | 
         --      24 - 14 bits    2 bits 
         -- Note: 14 bits are defined for international use. 
         -- Two national options exist where the point code is 16 or 24   
         -- bits. 
         -- To octet align the mtpAddress, the MSBs shall be encoded as 0s. 
                ... 
      } 
       
      DomainName ::= SEQUENCE 
      { 
         name        IA5String, 
         -- The name starts with an alphanumeric digit followed by a 
         -- sequence of alphanumeric digits, hyphens and dots.  No two 
         -- dots shall occur consecutively. 
         portNumber     INTEGER(0..65535) OPTIONAL 
      } 
       
      IP4Address ::= SEQUENCE 
      { 
         address        OCTET STRING (SIZE(4)), 
         portNumber     INTEGER(0..65535) OPTIONAL 
      } 
       
      IP6Address ::= SEQUENCE 
      { 
         address        OCTET STRING (SIZE(16)), 
         portNumber     INTEGER(0..65535) OPTIONAL 
      } 
       
      PathName ::= IA5String(SIZE (1..64)) 
      -- See A.3 
       
      Transaction ::= CHOICE 
      { 
         transactionRequest   TransactionRequest, 
         transactionPending   TransactionPending, 
    
    
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         transactionReply     TransactionReply, 
         transactionResponseAck  TransactionResponseAck, 
             -- use of response acks is dependent on underlying transport 
         ... 
      } 
       
      TransactionId ::= INTEGER(0..4294967295)  -- 32-bit unsigned integer 
       
      TransactionRequest ::= SEQUENCE 
      { 
         transactionId        TransactionId, 
         actions              SEQUENCE OF ActionRequest, 
         ... 
      } 
       
      TransactionPending ::= SEQUENCE 
      { 
         transactionId        TransactionId, 
         ... 
      } 
       
      TransactionReply ::= SEQUENCE 
      { 
         transactionId        TransactionId, 
         immAckRequired       NULL OPTIONAL, 
         transactionResult    CHOICE 
         { 
              transactionError   ErrorDescriptor, 
              actionReplies      SEQUENCE OF ActionReply 
         }, 
         ... 
      } 
       
      TransactionResponseAck ::= SEQUENCE OF TransactionAck 
      TransactionAck ::= SEQUENCE 
      { 
         firstAck       TransactionId, 
         lastAck        TransactionId OPTIONAL 
      } 
       
      ErrorDescriptor ::= SEQUENCE 
      { 
         errorCode      ErrorCode, 
         errorText      ErrorText OPTIONAL 
      } 
       
      ErrorCode ::= INTEGER(0..65535) 
      -- See clause 13 for IANA considerations with respect to error codes 
       
    
    
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      ErrorText ::= IA5String 
       
      ContextID ::= INTEGER(0..4294967295) 
       
      -- Context   NULL Value: 0 
      -- Context CHOOSE Value: 4294967294 (0xFFFFFFFE)  
      -- Context    ALL Value: 4294967295 (0xFFFFFFFF) 
       
       
      ActionRequest ::= SEQUENCE 
      { 
         contextId         ContextID, 
         contextRequest       ContextRequest OPTIONAL, 
         contextAttrAuditReq  ContextAttrAuditRequest OPTIONAL, 
         commandRequests   SEQUENCE OF CommandRequest 
      } 
       
      ActionReply ::= SEQUENCE 
      { 
         contextId         ContextID, 
         errorDescriptor   ErrorDescriptor OPTIONAL, 
         contextReply      ContextRequest OPTIONAL, 
         commandReply      SEQUENCE OF CommandReply 
      } 
       
      ContextRequest ::= SEQUENCE 
      { 
         priority       INTEGER(0..15) OPTIONAL, 
         emergency      BOOLEAN OPTIONAL, 
         topologyReq    SEQUENCE OF TopologyRequest OPTIONAL, 
         ... 
      } 
       
      ContextAttrAuditRequest ::= SEQUENCE 
      { 
         topology    NULL OPTIONAL, 
         emergency   NULL OPTIONAL, 
         priority    NULL OPTIONAL, 
         ... 
      } 
       
      CommandRequest ::= SEQUENCE 
      { 
         command           Command, 
         optional          NULL OPTIONAL, 
         wildcardReturn    NULL OPTIONAL, 
         ... 
      } 
       
    
    
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      Command ::= CHOICE 
      { 
         addReq               AmmRequest, 
         moveReq              AmmRequest, 
         modReq               AmmRequest, 
         -- Add, Move, Modify requests have the same parameters 
         subtractReq          SubtractRequest, 
         auditCapRequest      AuditRequest, 
         auditValueRequest    AuditRequest, 
         notifyReq            NotifyRequest, 
         serviceChangeReq     ServiceChangeRequest, 
         ... 
      } 
       
      CommandReply ::= CHOICE 
      { 
         addReply                AmmsReply, 
         moveReply               AmmsReply, 
         modReply                AmmsReply, 
         subtractReply           AmmsReply, 
         -- Add, Move, Modify, Subtract replies have the same parameters 
         auditCapReply           AuditReply, 
         auditValueReply         AuditReply, 
         notifyReply             NotifyReply, 
         serviceChangeReply      ServiceChangeReply, 
         ... 
      } 
       
      TopologyRequest ::= SEQUENCE 
      { 
         terminationFrom         TerminationID, 
         terminationTo           TerminationID, 
         topologyDirection       ENUMERATED 
         { 
            bothway(0), 
            isolate(1), 
            oneway(2) 
         }, 
         ... 
      } 
       
      AmmRequest ::= SEQUENCE 
      { 
         terminationID        TerminationIDList, 
         descriptors          SEQUENCE OF AmmDescriptor, 
         -- At most one descriptor of each type (see AmmDescriptor) 
         -- allowed in the sequence. 
         ... 
      } 
    
    
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      AmmDescriptor ::= CHOICE 
      { 
         mediaDescriptor         MediaDescriptor, 
         modemDescriptor         ModemDescriptor, 
         muxDescriptor           MuxDescriptor, 
         eventsDescriptor        EventsDescriptor, 
         eventBufferDescriptor   EventBufferDescriptor, 
         signalsDescriptor       SignalsDescriptor, 
         digitMapDescriptor      DigitMapDescriptor, 
         auditDescriptor         AuditDescriptor, 
         ... 
      } 
       
       
      AmmsReply ::= SEQUENCE 
      { 
         terminationID        TerminationIDList, 
         terminationAudit     TerminationAudit OPTIONAL, 
         ... 
      } 
       
      SubtractRequest ::= SEQUENCE 
      { 
         terminationID        TerminationIDList, 
         auditDescriptor      AuditDescriptor OPTIONAL, 
         ... 
      } 
       
      AuditRequest ::= SEQUENCE 
      { 
         terminationID        TerminationID, 
         auditDescriptor      AuditDescriptor, 
         ... 
      } 
       
      AuditReply ::= CHOICE 
      { 
         contextAuditResult   TerminationIDList, 
         error                ErrorDescriptor, 
         auditResult          AuditResult, 
         ... 
      } 
       
      AuditResult ::= SEQUENCE 
      { 
       
         terminationID           TerminationID, 
         terminationAuditResult  TerminationAudit 
    
    
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      } 
       
       
       
      TerminationAudit ::= SEQUENCE OF AuditReturnParameter 
       
      AuditReturnParameter ::= CHOICE 
      { 
         errorDescriptor         ErrorDescriptor, 
         mediaDescriptor         MediaDescriptor, 
         modemDescriptor         ModemDescriptor, 
         muxDescriptor           MuxDescriptor, 
         eventsDescriptor        EventsDescriptor, 
         eventBufferDescriptor   EventBufferDescriptor, 
         signalsDescriptor       SignalsDescriptor, 
         digitMapDescriptor      DigitMapDescriptor, 
         observedEventsDescriptor   ObservedEventsDescriptor, 
         statisticsDescriptor    StatisticsDescriptor, 
         packagesDescriptor      PackagesDescriptor, 
         emptyDescriptors        AuditDescriptor, 
         ... 
      } 
       
      AuditDescriptor ::= SEQUENCE 
      { 
         auditToken  BIT STRING 
            { 
               muxToken(0), modemToken(1), mediaToken(2), 
               eventsToken(3), signalsToken(4), 
               digitMapToken(5), statsToken(6), 
               observedEventsToken(7), 
               packagesToken(8), eventBufferToken(9) 
            } OPTIONAL, 
         ... 
      } 
       
      NotifyRequest ::= SEQUENCE 
      { 
         terminationID              TerminationIDList, 
         observedEventsDescriptor   ObservedEventsDescriptor, 
         errorDescriptor            ErrorDescriptor OPTIONAL, 
         ... 
      } 
       
      NotifyReply ::= SEQUENCE 
      { 
         terminationID           TerminationIDList, 
         errorDescriptor         ErrorDescriptor OPTIONAL, 
         ... 
    
    
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      } 
       
      ObservedEventsDescriptor ::= SEQUENCE 
      { 
         requestId               RequestID, 
         observedEventLst        SEQUENCE OF ObservedEvent 
      } 
       
      ObservedEvent ::= SEQUENCE 
      { 
         eventName            EventName, 
         streamID             StreamID OPTIONAL, 
         eventParList         SEQUENCE OF EventParameter, 
         timeNotation         TimeNotation OPTIONAL, 
         ... 
      } 
       
      EventName ::= PkgdName 
       
      EventParameter ::= SEQUENCE 
      { 
         eventParameterName      Name, 
         value                   Value, 
      -- For use of extraInfo see the comment related to PropertyParm 
         extraInfo CHOICE 
         { 
            relation Relation, 
            range    BOOLEAN, 
            sublist  BOOLEAN 
         } OPTIONAL, 
         ... 
       
      } 
       
      ServiceChangeRequest ::= SEQUENCE 
      { 
         terminationID           TerminationIDList, 
         serviceChangeParms      ServiceChangeParm, 
         ... 
      } 
       
      ServiceChangeReply ::= SEQUENCE 
      { 
         terminationID           TerminationIDList, 
         serviceChangeResult     ServiceChangeResult, 
         ... 
      } 
       
      -- For ServiceChangeResult, no parameters are mandatory.  Hence the 
    
    
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      -- distinction between ServiceChangeParm and ServiceChangeResParm. 
       
      ServiceChangeResult ::= CHOICE 
      { 
         errorDescriptor            ErrorDescriptor, 
         serviceChangeResParms      ServiceChangeResParm 
      } 
       
      WildcardField ::= OCTET STRING(SIZE(1)) 
       
      TerminationID ::= SEQUENCE 
      { 
         wildcard SEQUENCE OF WildcardField,  
         id    OCTET STRING(SIZE(1..8)), 
         ... 
      } 
      -- See A.1 for explanation of wildcarding mechanism. 
      -- Termination ID 0xFFFFFFFFFFFFFFFF indicates the ROOT Termination. 
       
      TerminationIDList ::= SEQUENCE OF TerminationID 
       
      MediaDescriptor ::= SEQUENCE 
      { 
          
         termStateDescr TerminationStateDescriptor OPTIONAL, 
         streams     CHOICE 
         { 
            oneStream      StreamParms, 
            multiStream    SEQUENCE OF StreamDescriptor 
         } OPTIONAL, 
         ... 
      } 
       
      StreamDescriptor ::= SEQUENCE 
      { 
         streamID          StreamID, 
         streamParms       StreamParms 
      } 
       
      StreamParms ::= SEQUENCE 
      { 
         localControlDescriptor     LocalControlDescriptor OPTIONAL, 
         localDescriptor            LocalRemoteDescriptor OPTIONAL, 
         remoteDescriptor           LocalRemoteDescriptor OPTIONAL, 
         ... 
      } 
       
      LocalControlDescriptor ::= SEQUENCE 
      { 
    
    
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         streamMode        StreamMode OPTIONAL, 
         reserveValue      BOOLEAN OPTIONAL, 
         reserveGroup      BOOLEAN OPTIONAL, 
         propertyParms     SEQUENCE OF PropertyParm, 
         ... 
      } 
       
      StreamMode ::= ENUMERATED  
      { 
         sendOnly(0), 
         recvOnly(1), 
         sendRecv(2), 
         inactive(3), 
         loopBack(4), 
            ... 
      } 
       
      -- In PropertyParm, value is a SEQUENCE OF octet string.  When sent 
      -- by an MGC the interpretation is as follows: 
      -- empty sequence means CHOOSE 
      -- one element sequence specifies value 
      -- If the sublist field is not selected, a longer sequence means 
      -- "choose one of the values" (i.e. value1 OR value2 OR ...) 
      -- If the sublist field is selected, 
      -- a sequence with more than one element encodes the value of a 
      -- list-valued property (i.e. value1 AND value2 AND ...). 
      -- The relation field may only be selected if the value sequence 
      -- has length 1.  It indicates that the MG has to choose a value 
      -- for the property. E.g. x > 3 (using the greaterThan 
      -- value for relation) instructs the MG to choose any value larger 
      -- than 3 for property x. 
      -- The range field may only be selected if the value sequence 
      -- has length 2.  It indicates that the MG has to choose a value 
      -- in the range between the first octet in the value sequence and 
      -- the trailing octet in the value sequence, including the 
      -- boundary values. 
      -- When sent by the MG, only responses to an AuditCapability request 
      -- may contain multiple values, a range, or a relation field. 
       
      PropertyParm ::= SEQUENCE 
      { 
         name        PkgdName, 
         value       SEQUENCE OF OCTET STRING, 
         extraInfo   CHOICE 
         { 
            relation    Relation, 
            range       BOOLEAN, 
            sublist     BOOLEAN 
         } OPTIONAL, 
    
    
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         ... 
      } 
       
      Name ::= OCTET STRING(SIZE(2)) 
       
      PkgdName ::= OCTET STRING(SIZE(4)) 
      -- represents Package Name (2 octets) plus Property, Event, 
      -- Signal Names or Statistics ID. (2 octets) 
      -- To wildcard a package use 0xFFFF for first two octets, choose 
      -- is not allowed. To reference native property tag specified in 
      -- Annex C, use 0x0000 as first two octets. 
      -- To wildcard a Property, Event, Signal, or Statistics ID, use 
      -- 0xFFFF for last two octets, choose is not allowed. 
      -- Wildcarding of Package Name is permitted only if Property, 
      -- Event, Signal, or Statistics ID are 
      -- also wildcarded. 
       
      Relation ::= ENUMERATED 
      { 
         greaterThan(0), 
         smallerThan(1), 
         unequalTo(2), 
         ... 
      } 
       
      LocalRemoteDescriptor ::= SEQUENCE 
      { 
         propGrps SEQUENCE OF PropertyGroup, 
         ... 
      } 
       
      PropertyGroup ::= SEQUENCE OF PropertyParm 
       
      TerminationStateDescriptor ::= SEQUENCE  
      { 
         propertyParms        SEQUENCE OF PropertyParm, 
         eventBufferControl   EventBufferControl OPTIONAL, 
         serviceState         ServiceState OPTIONAL, 
         ... 
      } 
       
      EventBufferControl ::= ENUMERATED 
      { 
         off(0), 
         lockStep(1), 
         ... 
      } 
       
      ServiceState ::= ENUMERATED 
    
    
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      { 
         test(0), 
         outOfSvc(1), 
         inSvc(2), 
            ... 
      } 
       
      MuxDescriptor   ::= SEQUENCE 
      { 
         muxType           MuxType, 
         termList          SEQUENCE OF TerminationID, 
         nonStandardData   NonStandardData OPTIONAL, 
         ... 
      } 
       
      MuxType ::= ENUMERATED 
      { 
         h221(0), 
         h223(1), 
         h226(2), 
         v76(3), 
         ... 
      } 
       
      StreamID ::= INTEGER(0..65535)   -- 16-bit unsigned integer 
       
      EventsDescriptor ::= SEQUENCE 
      { 
         requestID      RequestID OPTIONAL, 
                     -- RequestID must be present if eventList 
                     -- is non empty 
         eventList      SEQUENCE OF RequestedEvent, 
         ... 
      } 
       
      RequestedEvent ::= SEQUENCE 
      { 
         pkgdName       PkgdName, 
         streamID       StreamID OPTIONAL, 
         eventAction    RequestedActions OPTIONAL, 
         evParList      SEQUENCE OF EventParameter, 
         ... 
      } 
       
      RequestedActions ::= SEQUENCE 
      { 
         keepActive        BOOLEAN OPTIONAL, 
         eventDM           EventDM OPTIONAL, 
         secondEvent          SecondEventsDescriptor OPTIONAL, 
    
    
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         signalsDescriptor    SignalsDescriptor OPTIONAL, 
         ... 
      } 
       
       
      EventDM ::= CHOICE 
      {  digitMapName   DigitMapName, 
         digitMapValue  DigitMapValue 
      } 
       
      SecondEventsDescriptor ::= SEQUENCE 
      { 
         requestID         RequestID OPTIONAL, 
         eventList         SEQUENCE OF SecondRequestedEvent, 
         ... 
      } 
       
      SecondRequestedEvent ::= SEQUENCE 
      { 
         pkgdName          PkgdName, 
         streamID          StreamID OPTIONAL, 
         eventAction       SecondRequestedActions OPTIONAL, 
         evParList         SEQUENCE OF EventParameter, 
         ... 
      } 
       
      SecondRequestedActions ::= SEQUENCE 
      { 
         keepActive           BOOLEAN OPTIONAL, 
         eventDM              EventDM OPTIONAL, 
         signalsDescriptor    SignalsDescriptor OPTIONAL, 
         ... 
      } 
       
      EventBufferDescriptor ::= SEQUENCE OF EventSpec 
       
      EventSpec ::= SEQUENCE 
      { 
         eventName      EventName, 
         streamID       StreamID OPTIONAL, 
         eventParList   SEQUENCE OF EventParameter, 
         ... 
      } 
       
       
      SignalsDescriptor ::= SEQUENCE OF SignalRequest 
       
      SignalRequest ::=CHOICE 
      { 
    
    
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         signal         Signal, 
         seqSigList     SeqSigList, 
         ... 
      } 
       
      SeqSigList ::= SEQUENCE 
      { 
         id                INTEGER(0..65535), 
         signalList        SEQUENCE OF Signal 
      } 
       
      Signal ::= SEQUENCE 
      { 
         signalName        SignalName, 
         streamID          StreamID OPTIONAL, 
         sigType           SignalType OPTIONAL, 
         duration          INTEGER (0..65535) OPTIONAL, 
         notifyCompletion  NotifyCompletion OPTIONAL, 
         keepActive        BOOLEAN OPTIONAL, 
         sigParList        SEQUENCE OF SigParameter, 
         ... 
      } 
       
      SignalType ::= ENUMERATED 
      { 
         brief(0), 
         onOff(1), 
         timeOut(2), 
         ... 
      } 
       
      SignalName ::= PkgdName 
       
      NotifyCompletion ::= BIT STRING 
      { 
         onTimeOut(0), onInterruptByEvent(1), 
         onInterruptByNewSignalDescr(2), otherReason(3) 
      } 
       
      SigParameter ::= SEQUENCE 
      { 
         sigParameterName     Name, 
         value                Value, 
         -- For use of extraInfo see the comment related to PropertyParm 
         extraInfo CHOICE 
         { 
            relation Relation, 
            range    BOOLEAN, 
            sublist  BOOLEAN 
    
    
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         } OPTIONAL, 
         ... 
      } 
       
      -- For an AuditCapReply with all events, the RequestID SHALL be ALL. 
      -- ALL is represented by 0xffffffff. 
       
      RequestID ::= INTEGER(0..4294967295)   -- 32-bit unsigned integer 
       
      ModemDescriptor ::= SEQUENCE 
      { 
         mtl               SEQUENCE OF ModemType,  
         mpl               SEQUENCE OF PropertyParm, 
         nonStandardData   NonStandardData OPTIONAL 
      } 
       
      ModemType ::= ENUMERATED 
      { 
         v18(0), 
         v22(1), 
         v22bis(2), 
         v32(3), 
         v32bis(4), 
         v34(5), 
         v90(6), 
         v91(7), 
         synchISDN(8), 
         ... 
      } 
       
      DigitMapDescriptor ::= SEQUENCE 
      { 
         digitMapName   DigitMapName   OPTIONAL, 
         digitMapValue  DigitMapValue  OPTIONAL 
      } 
       
      DigitMapName ::= Name 
       
      DigitMapValue ::= SEQUENCE 
      { 
         startTimer     INTEGER(0..99) OPTIONAL, 
         shortTimer     INTEGER(0..99) OPTIONAL, 
         longTimer      INTEGER(0..99) OPTIONAL, 
         digitMapBody      IA5String, 
      -- Units are seconds for start, short and long timers, and 
      -- hundreds of milliseconds for duration timer. Thus start, 
      -- short, and long range from 1 to 99 seconds and duration 
      -- from 100 ms to 9.9 s 
         -- See A.3 for explanation of digit map syntax 
    
    
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         ... 
      } 
       
      ServiceChangeParm ::= SEQUENCE 
      { 
         serviceChangeMethod     ServiceChangeMethod, 
         serviceChangeAddress    ServiceChangeAddress OPTIONAL, 
         serviceChangeVersion    INTEGER(0..99) OPTIONAL, 
         serviceChangeProfile    ServiceChangeProfile OPTIONAL, 
         serviceChangeReason     Value, 
      -- A serviceChangeReason consists of a numeric reason code 
      -- and an optional text description. 
      -- The serviceChangeReason SHALL be a string consisting of  
      -- a decimal reason code, optionally followed by a single  
      -- space character and a textual description string. 
      -- This string is first BER-encoded as an IA5String. 
      -- The result of this BER-encoding is then encoded as 
      -- an ASN.1 OCTET STRING type, "double wrapping" the  
      -- value as was done for package elements. 
         serviceChangeDelay      INTEGER(0..4294967295) OPTIONAL, 
                                           -- 32-bit unsigned integer 
         serviceChangeMgcId      MId OPTIONAL, 
         timeStamp               TimeNotation OPTIONAL, 
         nonStandardData         NonStandardData OPTIONAL, 
         ... 
      } 
       
      ServiceChangeAddress ::= CHOICE 
      { 
         portNumber        INTEGER(0..65535),    -- TCP/UDP port number 
         ip4Address        IP4Address, 
         ip6Address        IP6Address, 
         domainName        DomainName, 
         deviceName        PathName, 
         mtpAddress        OCTET STRING(SIZE(2..4)), 
         ... 
      } 
       
      ServiceChangeResParm ::= SEQUENCE 
      { 
         serviceChangeMgcId      MId OPTIONAL, 
         serviceChangeAddress    ServiceChangeAddress OPTIONAL, 
         serviceChangeVersion    INTEGER(0..99) OPTIONAL, 
         serviceChangeProfile    ServiceChangeProfile OPTIONAL, 
         timestamp               TimeNotation OPTIONAL, 
         ... 
      } 
       
      ServiceChangeMethod ::= ENUMERATED 
    
    
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      { 
         failover(0), 
         forced(1), 
         graceful(2), 
         restart(3), 
         disconnected(4), 
         handOff(5), 
         ... 
      } 
       
      ServiceChangeProfile ::= SEQUENCE 
      { 
         profileName    IA5String(SIZE (1..67)) 
         -- 64 characters for name, 1 for "/", 2 for version to match ABNF 
      } 
       
      PackagesDescriptor ::= SEQUENCE OF PackagesItem 
       
      PackagesItem ::= SEQUENCE 
      { 
         packageName       Name, 
         packageVersion    INTEGER(0..99), 
         ... 
      } 
       
      StatisticsDescriptor ::= SEQUENCE OF StatisticsParameter 
       
      StatisticsParameter ::= SEQUENCE 
      { 
         statName       PkgdName, 
         statValue      Value OPTIONAL 
      } 
       
      NonStandardData ::= SEQUENCE 
      { 
         nonStandardIdentifier   NonStandardIdentifier, 
         data                    OCTET STRING 
      } 
       
      NonStandardIdentifier ::= CHOICE 
      { 
         object            OBJECT IDENTIFIER, 
         h221NonStandard   H221NonStandard, 
         experimental      IA5String(SIZE(8)),  
             -- first two characters should be "X-" or "X+" 
         ... 
      } 
       
      H221NonStandard ::= SEQUENCE 
    
    
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      {  t35CountryCode1   INTEGER(0..255), 
         t35CountryCode2   INTEGER(0..255),      -- country, as per T.35 
         t35Extension      INTEGER(0..255),      -- assigned nationally 
         manufacturerCode     INTEGER(0..65535), -- assigned nationally 
         ... 
      } 
       
      TimeNotation ::= SEQUENCE 
      { 
         date     IA5String(SIZE(8)),  -- yyyymmdd format 
         time     IA5String(SIZE(8))   -- hhmmssss format 
         -- per ISO 8601:1988 
      } 
       
      Value ::= SEQUENCE OF OCTET STRING 
       
       
      END 
       
       
   A.3   Digit maps and path names 
       
      From a syntactic viewpoint, digit maps are strings with syntactic 
      restrictions imposed upon them. The syntax of valid digit maps is 
      specified in ABNF [RFC 2234].  The syntax for digit maps presented in 
      this subclause is for illustrative purposes only. The definition of 
      digitMap in Annex B takes precedence in the case of differences 
      between the two. 

        digitMap = (digitString / LWSP "(" LWSP digitStringList LWSP ")"  
                  LWSP) 
         
        digitStringList = digitString *( LWSP "|" LWSP digitString ) 
        digitString = 1*(digitStringElement) 
        digitStringElement = digitPosition [DOT] 
        digitPosition = digitMapLetter / digitMapRange 
        digitMapRange = ("x" / (LWSP "[" LWSP digitLetter LWSP "]" LWSP)) 
        digitLetter = *((DIGIT "-" DIGIT) /digitMapLetter) 
        digitMapLetter = DIGIT           ;digits 0-9 
                / %x41-4B / %x61-6B    ;a-k and A-K 
                / "L"/ "S"       ;Inter-event timers 
                                    ;(long, short) 
                / "Z"            ;Long duration event 
        DOT = %x2E ; "." 
        LWSP = *(WSP / COMMENT / EOL) 
        WSP = SP / HTAB 
        COMMENT = ";" *(SafeChar / RestChar / WSP) EOL 
        EOL = (CR [LF]) / LF 
        SP = %x20 
    
    
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        HTAB = %x09 
        CR = %x0D 
        LF = %x0A 
        SafeChar = DIGIT / ALPHA / "+" / "-" / "&" / "!" / "_" / "/" / 
            "'" / "?" / "@" / "^" / "`" / "~" / "*" / "$" / "\" / 
            "(" / ")" / "%" / "." 
        RestChar = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#" / 
            "<" / ">" / "=" / %x22 
        DIGIT = %x30-39       ; digits 0 through 9 
        ALPHA = %x41-5A / %x61-7A; A-Z, a-z 
       
      A path name is also a string with syntactic restrictions imposed upon 
      it.  The ABNF production defining it is copied from Annex B. 
       
        ; Total length of pathNAME must not exceed 64 chars. 
        pathNAME = ["*"] NAME *("/" / "*"/ ALPHA / DIGIT /"_" / "$" )  
                               ["@" pathDomainName ] 
         
        ; ABNF allows two or more consecutive "." although it is  
        ; meaningless in a path domain name.  
        pathDomainName       = (ALPHA / DIGIT / "*" )  
                               *63(ALPHA / DIGIT / "-"  
        NAME = ALPHA *63(ALPHA / DIGIT / "_" ) 
       

























    
    
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                                   ANNEX B 
                        Text encoding of the protocol 
       
   B.1   Coding of wildcards 
       
      In a text encoding of the protocol, while TerminationIDs are 
      arbitrary, by judicious choice of names, the wildcard character, "*" 
      may be made more useful. When the wildcard character is encountered, 
      it will "match" all TerminationIDs having the same previous and 
      following characters (if appropriate). For example, if there were 
      TerminationIDs of R13/3/1, R13/3/2 and R13/3/3, the TerminationID 
      R13/3/* would match all of them. There are some circumstances where 
      ALL Terminations must be referred to. The TerminationID "*" suffices, 
      and is referred to as ALL. The CHOOSE TerminationID "$" may be used 
      to signal to the MG that it has to create an ephemeral Termination or 
      select an idle physical Termination. 

   B.2   ABNF specification 
       
      The protocol syntax is presented in ABNF according to RFC 2234. 

        Note 1 - This syntax specification does not enforce all 
        restrictions on element inclusions and values.  Some additional 
        restrictions are stated in comments and other restrictions appear 
        in the text of this recommendation.  These additional restrictions 
        are part of the protocol even though not enforced by this 
        specification. 

        Note 2 - The syntax is context-dependent. For example, "Add" can be 
        the AddToken or a NAME depending on the context in which it occurs. 

      Everything in the ABNF and text encoding is case insensitive. This 
      includes TerminationIDs, digitmap Ids etc. SDP is case sensitive as 
      per RFC 2327. 
       
      ; NOTE -- The ABNF in this section uses the VALUE construct (or lists  
      ; of VALUE constructs) to encode various package element values  
      ; (properties, signal parameters, etc.).  The types of these values  
      ; vary and are specified the relevant package definition.  Several  
      ; such types are described in section 12.2. 
      ; 
      ; The ABNF specification for VALUE allows a quotedString form or a 
      ; collection of SafeChars.  The encoding of package element values  
      ; into ABNF VALUES is specified below.  If a type's encoding allows  
      ; characters other than SafeChars, the quotedString form MUST be used  
      ; for all values of that type, even for specific values that consist  
      ; only of SafeChars. 
      ; 
      ; String:  A string MUST use the quotedString form of VALUE and can 
    
    
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      ; contain anything allowable in the quotedString form. 
      ; 
      ; Integer, Double, and Unsigned Integer:  Decimal values can be  
      ; encoded using characters 0-9.  Hexadecimal values must be prefixed  
      ; with '0x' and can use characters 0-9,a-f,A-F.  An octal format is  
      ; not supported.  Negative integers start with '-' and MUST be  
      ; Decimal.  The SafeChar form of VALUE MUST be used. 
      ;  
      ; Character:  A UTF-8 encoding of a single letter surrounded by  
      ; double quotes. 
      ; 
      ; Enumeration:  An enumeration MUST use the SafeChar form of VALUE 
      ; and can contain anything allowable in the SafeChar form. 
      ; 
      ; Boolean:  Boolean values are encoded as "on" and "off" and are 
      ; case insensitive.  The SafeChar form of VALUE MUST be used. 
      ; 
      ; Future types:  Any defined types MUST fit within 
      ; the ABNF specification of VALUE.  Specifically, if a type's  
      ; encoding allows characters other than SafeChars, the quotedString  
      ; form MUST be used for all values of that type, even for specific  
      ; values that consist only of SafeChars.  
      ; 
      ; Note that there is no way to use the double quote character within 
      ; a value. 
      ; 
      ; Note that SDP disallows whitespace at the beginning of a line,  
      ; Megaco ABNF allows whitespace before the beginning of the SDP in  
      ; the Local/Remote descriptor.  Parsers should accept whitespace  
      ; between the LBRKT following the Local/Remote token and the  
      ; beginning of the SDP. 
       
      megacoMessage        = LWSP [authenticationHeader SEP ] message  
       
      authenticationHeader = AuthToken EQUAL SecurityParmIndex COLON  
                             SequenceNum COLON AuthData  
                              
      SecurityParmIndex    = "0x" 8(HEXDIG) 
      SequenceNum          = "0x" 8(HEXDIG) 
      AuthData             = "0x" 24*64(HEXDIG) 
       
      message            = MegacopToken SLASH Version SEP mId SEP 
      messageBody 
      ; The version of the protocol defined here is equal to 1. 
                            
      messageBody          = ( errorDescriptor / transactionList ) 
       
      transactionList      = 1*( transactionRequest / transactionReply /  
                             transactionPending / transactionResponseAck ) 
    
    
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      ;Use of response acks is dependent on underlying transport 
        
       
      transactionPending   = PendingToken EQUAL TransactionID LBRKT                   
      RBRKT 
       
      transactionResponseAck = ResponseAckToken LBRKT transactionAck 
                     *(COMMA transactionAck) RBRKT 
      transactionAck = transactionID / (transactionID "-" transactionID) 
       
      transactionRequest   = TransToken EQUAL TransactionID LBRKT 
                             actionRequest *(COMMA actionRequest) RBRKT 
       
      actionRequest        = CtxToken EQUAL ContextID LBRKT (( 
                             contextRequest [COMMA  commandRequestList])  
                             / commandRequestList) RBRKT 
       
      contextRequest    = ((contextProperties [COMMA contextAudit]) 
                  / contextAudit) 
       
      contextProperties    = contextProperty *(COMMA contextProperty) 
       
      ; at-most-once 
      contextProperty    = (topologyDescriptor / priority / EmergencyToken) 
       
      contextAudit   = ContextAuditToken LBRKT contextAuditProperties 
                            *(COMMA contextAuditProperties) RBRKT 
       
      ; at-most-once 
      contextAuditProperties = ( TopologyToken / EmergencyToken /  
                                 PriorityToken ) 
       
      ; "O-" indicates an optional command 
      ; "W-" indicates a wildcarded response to a command  
      commandRequestList = ["O-"] ["W-"] commandRequest  
                           *(COMMA ["O-"] ["W-"]commandRequest) 
       
      commandRequest      = ( ammRequest / subtractRequest / auditRequest /  
                              notifyRequest / serviceChangeRequest)  
       
      transactionReply     = ReplyToken EQUAL TransactionID LBRKT  
                        [ ImmAckRequiredToken COMMA]  
                      ( errorDescriptor / actionReplyList ) RBRKT  
                              
      actionReplyList      = actionReply *(COMMA actionReply )  
       
      actionReply          = CtxToken EQUAL ContextID LBRKT  
                        ( errorDescriptor / commandReply ) / 
               (commandReply COMMA errorDescriptor) ) RBRKT 
    
    
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      commandReply      = (( contextProperties [COMMA commandReplyList] ) /  
                              commandReplyList ) 
       
       
      commandReplyList     = commandReplys *(COMMA commandReplys ) 
       
      commandReplys        = (serviceChangeReply / auditReply / ammsReply /  
                              notifyReply ) 
       
      ;Add Move and Modify have the same request parameters 
      ammRequest           = (AddToken / MoveToken / ModifyToken ) EQUAL  
                             TerminationID [LBRKT ammParameter *(COMMA  
                             ammParameter) RBRKT] 
       
      ;at-most-once 
      ammParameter         = (mediaDescriptor / modemDescriptor /  
                              muxDescriptor / eventsDescriptor /  
                              signalsDescriptor / digitMapDescriptor / 
                              eventBufferDescriptor / auditDescriptor) 
       
      ammsReply            = (AddToken / MoveToken / ModifyToken /  
                              SubtractToken ) EQUAL TerminationID [ LBRKT  
                              terminationAudit RBRKT ] 
                               
      subtractRequest      =  SubtractToken EQUAL TerminationID  
                              [ LBRKT auditDescriptor RBRKT] 
       
      auditRequest         =  (AuditValueToken / AuditCapToken ) EQUAL 
                              TerminationID LBRKT auditDescriptor RBRKT 
       
      auditReply           = (AuditValueToken / AuditCapToken )  
                             ( contextTerminationAudit  / auditOther)  
       
      auditOther           = EQUAL TerminationID [LBRKT  
                             terminationAudit RBRKT] 
       
      terminationAudit = auditReturnParameter *(COMMA auditReturnParameter)  
       
      contextTerminationAudit = EQUAL CtxToken ( terminationIDList /  
                             LBRKT errorDescriptor RBRKT ) 
       
      auditReturnParameter = (mediaDescriptor / modemDescriptor /   
                              muxDescriptor / eventsDescriptor /  
                              signalsDescriptor / digitMapDescriptor /  
                         observedEventsDescriptor / eventBufferDescriptor / 
                              statisticsDescriptor / packagesDescriptor /  
                               errorDescriptor / auditItem) 
       
    
    
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      auditDescriptor      = AuditToken LBRKT [ auditItem  
                             *(COMMA auditItem) ] RBRKT 
       
      notifyRequest        = NotifyToken EQUAL TerminationID  
                             LBRKT ( observedEventsDescriptor  
                                   [ COMMA errorDescriptor ] ) RBRKT 
       
      notifyReply          = NotifyToken EQUAL TerminationID  
                             [ LBRKT errorDescriptor RBRKT ] 
       
      serviceChangeRequest = ServiceChangeToken EQUAL TerminationID 
                             LBRKT serviceChangeDescriptor RBRKT  
       
      serviceChangeReply   = ServiceChangeToken EQUAL TerminationID 
                             [LBRKT (errorDescriptor /  
                             serviceChangeReplyDescriptor) RBRKT] 
                              
      errorDescriptor   = ErrorToken EQUAL ErrorCode 
                          LBRKT [quotedString] RBRKT 
       
      ErrorCode            = 1*4(DIGIT) ; could be extended 
       
      TransactionID        = UINT32 
       
      mId                  = (( domainAddress / domainName )  
                             [":" portNumber]) / mtpAddress / deviceName 
       
      ; ABNF allows two or more consecutive "." although it is meaningless  
      ; in a domain name.  
      domainName           = "<" (ALPHA / DIGIT) *63(ALPHA / DIGIT / "-" /  
                             ".") ">" 
      deviceName           = pathNAME 
       
      ;The values 0x0, 0xFFFFFFFE and 0xFFFFFFFF are reserved. 
      ContextID            = (UINT32 / "*" / "-" / "$") 
       
      domainAddress        = "[" (IPv4address / IPv6address) "]" 
      ;RFC2373 contains the definition of IP6Addresses. 
      IPv6address          = hexpart [ ":" IPv4address ] 
      IPv4address          = V4hex DOT V4hex DOT V4hex DOT V4hex 
      V4hex                = 1*3(DIGIT) ; "0".."255" 
      ; this production, while occurring in RFC2373, is not referenced 
      ; IPv6prefix           = hexpart SLASH 1*2DIGIT 
      hexpart           = hexseq "::" [ hexseq ] / "::" [ hexseq ] / hexseq
      hexseq               = hex4 *( ":" hex4) 
      hex4                 = 1*4HEXDIG 
       
      portNumber           = UINT16 
       
    
    
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      ; Addressing structure of mtpAddress: 
      ; 25 - 15            0 
      ;    |  PC        | NI | 
      ;    24 - 14 bits    2 bits 
      ; Note: 14 bits are defined for international use. 
      ; Two national options exist where the point code is 16 or 24 bits. 
      ; To octet align the mtpAddress the MSBs shall be encoded as 0s.  
      ; An octet shall be represented by 2 hex digits. 
      mtpAddress           = MTPToken LBRKT 4*8 (HEXDIG) RBRKT 
       
      terminationIDList  = LBRKT TerminationID *(COMMA TerminationID) RBRKT 
       
      ; Total length of pathNAME must not exceed 64 chars. 
      pathNAME      = ["*"] NAME *("/" / "*"/ ALPHA / DIGIT /"_" / "$" )  
                             ["@" pathDomainName ] 
       
      ; ABNF allows two or more consecutive "." although it is meaningless  
      ; in a path domain name.  
      pathDomainName       = (ALPHA / DIGIT / "*" )  
                             *63(ALPHA / DIGIT / "-" / "*" / ".") 
                              
      TerminationID        = "ROOT" / pathNAME / "$" / "*" 
       
      mediaDescriptor = MediaToken LBRKT mediaParm *(COMMA mediaParm) RBRKT 
       
      ; at-most one terminationStateDescriptor 
      ; and either streamParm(s) or streamDescriptor(s) but not both 
      mediaParm            = (streamParm / streamDescriptor /  
                              terminationStateDescriptor) 
       
      ; at-most-once per item 
      streamParm           = ( localDescriptor / remoteDescriptor /  
                              localControlDescriptor ) 
       
      streamDescriptor     = StreamToken EQUAL StreamID LBRKT streamParm  
                             *(COMMA streamParm) RBRKT 
       
      localControlDescriptor = LocalControlToken LBRKT localParm  
                               *(COMMA localParm) RBRKT 
       
      ; at-most-once per item except for propertyParm 
      localParm = ( streamMode / propertyParm / reservedValueMode 
                     / reservedGroupMode ) 
       
      reservedValueMode    = ReservedValueToken EQUAL ( "ON" / "OFF" ) 
      reservedGroupMode    = ReservedGroupToken EQUAL ( "ON" / "OFF" ) 
       
      streamMode           = ModeToken EQUAL streamModes 
       
    
    
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      streamModes     = (SendonlyToken / RecvonlyToken / SendrecvToken /  
                             InactiveToken / LoopbackToken ) 
       
      propertyParm         = pkgdName parmValue 
      parmValue            = (EQUAL alternativeValue/ INEQUAL VALUE) 
      alternativeValue     = ( VALUE  
                     / LSBRKT VALUE *(COMMA VALUE) RSBRKT  
                      ; sublist (i.e. A AND B AND ...) 
                     / LBRKT VALUE *(COMMA VALUE) RBRKT 
                      ; alternatives (i.e. A OR B OR ...)   
                     /  LSBRKT VALUE COLON VALUE RSBRKT ) 
                      ; range 
                             
       
      INEQUAL              = LWSP (">" / "<" / "#" ) LWSP 
      LSBRKT               = LWSP "[" LWSP 
      RSBRKT               = LWSP "]" LWSP 
       
      ; Note - The octet zero is not among the permitted characters in  
      ; octet string. As the current definition is limited to SDP, and a  
      ; zero octet would not be a legal character in SDP, this is not a  
      ; concern. 
       
      localDescriptor      = LocalToken LBRKT octetString RBRKT 
       
      remoteDescriptor     = RemoteToken LBRKT octetString RBRKT 
       
      eventBufferDescriptor= EventBufferToken [ LBRKT eventSpec 
                             *( COMMA eventSpec) RBRKT ] 
       
      eventSpec      = pkgdName [ LBRKT eventSpecParameter 
                   *(COMMA eventSpecParameter) RBRKT ] 
      eventSpecParameter   = (eventStream / eventOther) 
       
      eventBufferControl     = BufferToken EQUAL ( "OFF" / LockStepToken ) 
       
      terminationStateDescriptor = TerminationStateToken LBRKT  
                 terminationStateParm *( COMMA terminationStateParm ) RBRKT 
       
      ; at-most-once per item except for propertyParm 
      terminationStateParm = (propertyParm / serviceStates /  
                              eventBufferControl ) 
       
      serviceStates        = ServiceStatesToken EQUAL ( TestToken / 
                             OutOfSvcToken / InSvcToken ) 
       
      muxDescriptor        = MuxToken EQUAL MuxType  terminationIDList 
       
      MuxType              = ( H221Token / H223Token / H226Token / V76Token 
    
    
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                              / extensionParameter ) 
       
      StreamID             = UINT16 
      pkgdName     = (PackageName SLASH ItemID) ;specific item 
                   / (PackageName SLASH "*") ;all items in package 
                   / ("*" SLASH "*") ; all items supported by the MG 
      PackageName          = NAME 
      ItemID               = NAME 
       
      eventsDescriptor     = EventsToken [ EQUAL RequestID LBRKT  
                           requestedEvent *( COMMA requestedEvent ) RBRKT ] 
       
      requestedEvent       = pkgdName [ LBRKT eventParameter 
                             *( COMMA eventParameter ) RBRKT ] 
       
      ; at-most-once each of KeepActiveToken , eventDM and eventStream 
      ;at most one of either embedWithSig or embedNoSig but not both 
      ;KeepActiveToken and embedWithSig must not both be present 
      eventParameter       = ( embedWithSig / embedNoSig / KeepActiveToken  
                               /eventDM / eventStream / eventOther ) 
       
      embedWithSig         = EmbedToken LBRKT signalsDescriptor 
                               [COMMA embedFirst ] RBRKT 
      embedNoSig        = EmbedToken LBRKT embedFirst RBRKT 
       
      ; at-most-once of each 
      embedFirst      = EventsToken [ EQUAL RequestID LBRKT 
                 secondRequestedEvent *(COMMA secondRequestedEvent) RBRKT ] 
       
      secondRequestedEvent = pkgdName [ LBRKT secondEventParameter 
                             *( COMMA secondEventParameter ) RBRKT ] 
       
      ; at-most-once each of embedSig , KeepActiveToken, eventDM or 
      ; eventStream 
      ; KeepActiveToken and embedSig must not both be present 
      secondEventParameter = ( embedSig / KeepActiveToken / eventDM /  
                               eventStream / eventOther ) 
       
      embedSig  = EmbedToken LBRKT signalsDescriptor RBRKT 
       
      eventStream          = StreamToken EQUAL StreamID 
       
      eventOther           = eventParameterName parmValue 
       
      eventParameterName   = NAME 
       
      eventDM              = DigitMapToken EQUAL(( digitMapName ) /  
                             (LBRKT digitMapValue RBRKT ))  
       
    
    
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      signalsDescriptor    = SignalsToken LBRKT [ signalParm  
                             *(COMMA signalParm)] RBRKT 
       
      signalParm           = signalList / signalRequest 
       
      signalRequest        = signalName [ LBRKT sigParameter  
                             *(COMMA sigParameter) RBRKT ] 
       
      signalList           = SignalListToken EQUAL signalListId LBRKT  
                             signalListParm *(COMMA signalListParm) RBRKT 
                              
      signalListId         = UINT16 
       
      ;exactly once signalType, at most once duration and every signal 
      ;parameter 
      signalListParm       = signalRequest 
       
      signalName           = pkgdName 
      ;at-most-once sigStream, at-most-once sigSignalType, 
      ;at-most-once sigDuration, every signalParameterName at most once 
      sigParameter = sigStream / sigSignalType / sigDuration / sigOther 
                  / notifyCompletion / KeepActiveToken 
      sigStream            = StreamToken EQUAL StreamID 
      sigOther             = sigParameterName parmValue 
      sigParameterName     = NAME 
      sigSignalType        = SignalTypeToken EQUAL signalType 
      signalType           = (OnOffToken / TimeOutToken / BriefToken) 
      sigDuration          = DurationToken EQUAL UINT16 
      notifyCompletion     = NotifyCompletionToken EQUAL (LBRKT 
               notificationReason *(COMMA notificationReason) RBRKT) 
       
      notificationReason   = ( TimeOutToken / InterruptByEventToken 
                           / InterruptByNewSignalsDescrToken 
                           / OtherReasonToken ) 
      observedEventsDescriptor = ObservedEventsToken EQUAL RequestID 
                         LBRKT observedEvent *(COMMA observedEvent) RBRKT 
       
      ;time per event, because it might be buffered 
      observedEvent        = [ TimeStamp LWSP COLON] LWSP  
                             pkgdName [ LBRKT observedEventParameter 
                             *(COMMA observedEventParameter) RBRKT ] 
       
      ;at-most-once eventStream, every eventParameterName at most once 
      observedEventParameter = eventStream / eventOther 
       
      ; For an AuditCapReply with all events, the RequestID should be ALL. 
      RequestID            = ( UINT32 / "*" ) 
       
      modemDescriptor      = ModemToken (( EQUAL modemType) /  
    
    
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                         (LSBRKT modemType *(COMMA modemType) RSBRKT)) 
                        [ LBRKT propertyParm *(COMMA propertyParm) RBRKT ] 
                            
       
      ; at-most-once except for extensionParameter 
      modemType            = (V32bisToken / V22bisToken / V18Token /  
                              V22Token / V32Token / V34Token / V90Token /  
                            V91Token / SynchISDNToken / extensionParameter) 
       
      digitMapDescriptor  = DigitMapToken EQUAL  
                           ( ( LBRKT digitMapValue RBRKT ) / 
                           (digitMapName [ LBRKT digitMapValue RBRKT ]) ) 
      digitMapName        = NAME 
      digitMapValue       = ["T" COLON Timer COMMA] ["S" COLON Timer COMMA] 
                            ["L" COLON Timer COMMA] digitMap  
      Timer               = 1*2DIGIT 
      ; Units are seconds for T, S, and L timers, and hundreds of  
      ; milliseconds for Z timer. Thus T, S, and L range from 1 to 99 
      ; seconds and Z from 100 ms to 9.9 s 
      digitMap = (digitString /  
                  LWSP "(" LWSP digitStringList LWSP ")" LWSP) 
      digitStringList   = digitString *( LWSP "|" LWSP digitString ) 
      digitString       = 1*(digitStringElement) 
      digitStringElement = digitPosition [DOT] 
      digitPosition     = digitMapLetter / digitMapRange 
      digitMapRange     = ("x" / (LWSP "[" LWSP digitLetter LWSP "]" LWSP)) 
      digitLetter       = *((DIGIT "-" DIGIT ) / digitMapLetter) 
      digitMapLetter    = DIGIT   ;Basic event symbols 
                  / %x41-4B / %x61-6B ; a-k, A-K 
                  / "L" / "S"   ;Inter-event timers (long, short) 
                  / "Z"         ;Long duration modifier 
       
      ;at-most-once, and DigitMapToken and PackagesToken are not allowed 
      ;in AuditCapabilities command 
      auditItem            = ( MuxToken / ModemToken / MediaToken /  
                              SignalsToken / EventBufferToken / 
                              DigitMapToken / StatsToken / EventsToken / 
                              ObservedEventsToken / PackagesToken ) 
       
      serviceChangeDescriptor = ServicesToken LBRKT serviceChangeParm  
                               *(COMMA serviceChangeParm) RBRKT 
       
      ; each parameter at-most-once 
      ; at most one of either serviceChangeAddress or serviceChangeMgcId  
      ; but not both 
      ; serviceChangeMethod and serviceChangeReason are REQUIRED 
      serviceChangeParm    = (serviceChangeMethod / serviceChangeReason / 
                             serviceChangeDelay / serviceChangeAddress /   
                             serviceChangeProfile / extension / TimeStamp / 
    
    
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                             serviceChangeMgcId / serviceChangeVersion ) 
                            
      serviceChangeReplyDescriptor = ServicesToken LBRKT 
                           servChgReplyParm *(COMMA servChgReplyParm) RBRKT 
       
      ; at-most-once. Version is REQUIRED on first ServiceChange response 
      ; at most one of either serviceChangeAddress or serviceChangeMgcId  
      ; but not both 
      servChgReplyParm     = (serviceChangeAddress / serviceChangeMgcId / 
                             serviceChangeProfile / serviceChangeVersion /  
                             TimeStamp) 
      serviceChangeMethod  = MethodToken EQUAL (FailoverToken /  
                             ForcedToken / GracefulToken / RestartToken /  
                             DisconnectedToken / HandOffToken /  
                             extensionParameter) 
      ; A serviceChangeReason consists of a numeric reason code 
      ; and an optional text description. 
      ; A serviceChangeReason MUST be encoded using the quotedString  
      ; form of VALUE. 
      ; The quotedString SHALL contain a decimal reason code, 
      ; optionally followed by a single space character and a  
      ; textual description string. 
                              
                              
      serviceChangeReason  = ReasonToken  EQUAL VALUE 
      serviceChangeDelay   = DelayToken   EQUAL UINT32 
      serviceChangeAddress = ServiceChangeAddressToken EQUAL ( mId / 
                             portNumber ) 
      serviceChangeMgcId   = MgcIdToken   EQUAL mId 
      serviceChangeProfile = ProfileToken EQUAL NAME SLASH Version 
      serviceChangeVersion = VersionToken EQUAL Version 
      extension            = extensionParameter parmValue 
       
      packagesDescriptor   = PackagesToken LBRKT packagesItem   
                             *(COMMA packagesItem) RBRKT 
       
      Version              = 1*2(DIGIT) 
      packagesItem         = NAME "-" UINT16 
       
      TimeStamp            = Date "T" Time ; per ISO 8601:1988  
      ; Date = yyyymmdd 
      Date                 = 8(DIGIT) 
      ; Time = hhmmssss 
      Time                 = 8(DIGIT) 
      statisticsDescriptor = StatsToken LBRKT statisticsParameter 
                            *(COMMA statisticsParameter ) RBRKT 
       
      ;at-most-once per item  
      statisticsParameter  = pkgdName [EQUAL VALUE]  
    
    
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      topologyDescriptor   = TopologyToken LBRKT topologyTriple 
                             *(COMMA topologyTriple) RBRKT 
      topologyTriple       = terminationA COMMA  
                             terminationB COMMA topologyDirection 
      terminationA         = TerminationID 
      terminationB         = TerminationID 
      topologyDirection    = BothwayToken / IsolateToken / OnewayToken 
       
      priority             = PriorityToken EQUAL UINT16 
       
      extensionParameter   = "X"  ("-" / "+") 1*6(ALPHA / DIGIT) 
       
      ; octetString is used to describe SDP defined in RFC2327. 
      ; Caution should be taken if CRLF in RFC2327 is used. 
      ; To be safe, use EOL in this ABNF. 
      ; Whenever "}" appears in SDP, it is escaped by "\", e.g. "\}" 
      octetString          = *(nonEscapeChar) 
      nonEscapeChar        = ( "\}" / %x01-7C / %x7E-FF ) 
      ; Note - The double-quote character is not allowed in quotedString. 
      quotedString         = DQUOTE *(SafeChar / RestChar/ WSP) DQUOTE 
       
      UINT16               = 1*5(DIGIT)  ; %x0-FFFF  
      UINT32               = 1*10(DIGIT) ; %x0-FFFFFFFF  
       
      NAME                 = ALPHA *63(ALPHA / DIGIT / "_" ) 
      VALUE                = quotedString / 1*(SafeChar) 
      SafeChar             = DIGIT / ALPHA / "+" / "-" / "&" /  
                             "!" / "_" / "/" / "'" / "?" / "@" /  
                             "^" / "`" / "~" / "*" / "$" / "\" /  
                             "(" / ")" / "%" / "|" / "." 
       
      EQUAL                = LWSP %x3D LWSP ; "=" 
      COLON                = %x3A           ; ":" 
      LBRKT                = LWSP %x7B LWSP ; "{" 
      RBRKT                = LWSP %x7D LWSP ; "}" 
      COMMA                = LWSP %x2C LWSP ; "," 
      DOT                  = %x2E           ; "." 
      SLASH                = %x2F           ; "/" 
      ALPHA                = %x41-5A / %x61-7A ; A-Z / a-z 
      DIGIT                = %x30-39         ; 0-9 
      DQUOTE               = %x22            ; " (Double Quote) 
      HEXDIG               = ( DIGIT / "A" / "B" / "C" / "D" / "E" / "F" ) 
      SP                   = %x20        ; space 
      HTAB                 = %x09        ; horizontal tab 
      CR                   = %x0D        ; Carriage return 
      LF                   = %x0A        ; linefeed 
      LWSP                 = *( WSP / COMMENT / EOL ) 
      EOL                  = (CR [LF] / LF ) 
    
    
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      WSP                  = SP / HTAB ; white space 
      SEP                  = ( WSP / EOL / COMMENT) LWSP 
      COMMENT              = ";" *(SafeChar/ RestChar / WSP / %x22) EOL 
      RestChar            = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#" /  
                             "<" / ">" / "="  
       
      ; New Tokens added to sigParameter must take the format of SPA* 
      ; * may be of any form i.e. SPAM 
      ; New Tokens added to eventParameter must take the form of EPA* 
      ; * may be of any form i.e. EPAD 
       
      AddToken                   = ("Add"                   / "A") 
      AuditToken                 = ("Audit"                 / "AT") 
      AuditCapToken              = ("AuditCapability"       / "AC") 
      AuditValueToken            = ("AuditValue"            / "AV") 
      AuthToken                  = ("Authentication"        / "AU") 
      BothwayToken               = ("Bothway"               / "BW") 
      BriefToken                 = ("Brief"                 / "BR") 
      BufferToken                = ("Buffer"                / "BF") 
      CtxToken                   = ("Context"               / "C") 
      ContextAuditToken       = ("ContextAudit"    / "CA") 
      DigitMapToken              = ("DigitMap"              / "DM") 
      DisconnectedToken          = ("Disconnected"          / "DC") 
      DelayToken                 = ("Delay"                 / "DL") 
      DurationToken              = ("Duration"              / "DR") 
      EmbedToken                 = ("Embed"                 / "EM") 
      EmergencyToken             = ("Emergency"             / "EG") 
      ErrorToken                 = ("Error"                 / "ER") 
      EventBufferToken           = ("EventBuffer"           / "EB") 
      EventsToken                = ("Events"                / "E") 
      FailoverToken              = ("Failover"              / "FL") 
      ForcedToken                = ("Forced"                / "FO") 
      GracefulToken              = ("Graceful"              / "GR") 
      H221Token                  = ("H221" ) 
      H223Token                  = ("H223" ) 
      H226Token                  = ("H226" ) 
      HandOffToken               = ("HandOff"               / "HO") 
      ImmAckRequiredToken        = ("ImmAckRequired"        / "IA") 
      InactiveToken              = ("Inactive"              / "IN") 
      IsolateToken               = ("Isolate"               / "IS") 
      InSvcToken                 = ("InService"             / "IV") 
      InterruptByEventToken      = ("IntByEvent"            / "IBE") 
      InterruptByNewSignalsDescrToken 
                                 = ("IntBySigDescr"         / "IBS") 
      KeepActiveToken            = ("KeepActive"            / "KA") 
      LocalToken                 = ("Local"                 / "L") 
      LocalControlToken          = ("LocalControl"          / "O") 
      LockStepToken              = ("LockStep"              / "SP") 
      LoopbackToken              = ("Loopback"              / "LB") 
    
    
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      MediaToken                 = ("Media"                 / "M") 
      MegacopToken               = ("MEGACO"                / "!") 
      MethodToken                = ("Method"                / "MT") 
      MgcIdToken                 = ("MgcIdToTry"            / "MG") 
      ModeToken                  = ("Mode"                  / "MO") 
      ModifyToken                = ("Modify"                / "MF") 
      ModemToken                 = ("Modem"                 / "MD") 
      MoveToken                  = ("Move"                  / "MV") 
      MTPToken                   = ("MTP") 
      MuxToken                   = ("Mux"                   / "MX") 
      NotifyToken                = ("Notify"                / "N") 
      NotifyCompletionToken      = ("NotifyCompletion"      / "NC") 
      ObservedEventsToken        = ("ObservedEvents"        / "OE") 
      OnewayToken                = ("Oneway"                / "OW") 
      OnOffToken                 = ("OnOff"                 / "OO") 
      OtherReasonToken           = ("OtherReason"           / "OR") 
      OutOfSvcToken              = ("OutOfService"          / "OS") 
      PackagesToken              = ("Packages"              / "PG") 
      PendingToken               = ("Pending"               / "PN") 
      PriorityToken              = ("Priority"              / "PR") 
      ProfileToken               = ("Profile"               / "PF") 
      ReasonToken                = ("Reason"                / "RE") 
      RecvonlyToken              = ("ReceiveOnly"           / "RC") 
      ReplyToken                 = ("Reply"                 / "P") 
      RestartToken               = ("Restart"               / "RS") 
      RemoteToken                = ("Remote"                / "R") 
      ReservedGroupToken         = ("ReservedGroup"         / "RG") 
      ReservedValueToken         = ("ReservedValue"         / "RV") 
      SendonlyToken              = ("SendOnly"              / "SO") 
      SendrecvToken              = ("SendReceive"           / "SR") 
      ServicesToken              = ("Services"              / "SV") 
      ServiceStatesToken         = ("ServiceStates"         / "SI") 
      ServiceChangeToken         = ("ServiceChange"         / "SC") 
      ServiceChangeAddressToken  = ("ServiceChangeAddress"  / "AD") 
      SignalListToken            = ("SignalList"            / "SL") 
      SignalsToken               = ("Signals"               / "SG") 
      SignalTypeToken            = ("SignalType"            / "SY") 
      StatsToken                 = ("Statistics"            / "SA") 
      StreamToken                = ("Stream"                / "ST") 
      SubtractToken              = ("Subtract"              / "S") 
      SynchISDNToken             = ("SynchISDN"             / "SN") 
      TerminationStateToken      = ("TerminationState"      / "TS") 
      TestToken                  = ("Test"                  / "TE") 
      TimeOutToken               = ("TimeOut"               / "TO") 
      TopologyToken              = ("Topology"              / "TP") 
      TransToken                 = ("Transaction"           / "T") 
      ResponseAckToken           = ("TransactionResponseAck" / "K") 
      V18Token                   = ("V18") 
      V22Token                   = ("V22") 
    
    
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      V22bisToken                = ("V22b") 
      V32Token                   = ("V32") 
      V32bisToken                = ("V32b") 
      V34Token                   = ("V34") 
      V76Token                   = ("V76") 
      V90Token                   = ("V90") 
      V91Token                   = ("V91") 
      VersionToken               = ("Version"               / "V") 
       
   B.3   Hexadecimal octet coding 
       
      Hexadecimal octet coding is a means for representing a string of 
      octets as a string of hexadecimal digits, with two digits 
      representing each octet. This octet encoding should be used when 
      encoding octet strings in the text version of the protocol. 
      For each octet, the 8-bit sequence is encoded as two hexadecimal 
      digits. Bit 0 is the first transmitted; bit 7 is the last. 
      Bits 7-4 are encoded as the first hexadecimal digit, with Bit 7 as 
      MSB and Bit 4 as LSB. Bits 3-0 are encoded as the second hexadecimal 
      digit, with Bit 3 as MSB and Bit 0 as LSB. 
      Examples: 
       
           Octet bit pattern                   Hexadecimal coding 
           00011011                            D8 
           11100100                            27 
           10000011 10100010 11001000 00001001 C1451390 
       
   B.4   Hexadecimal octet sequence 
       
      A hexadecimal octet sequence is an even number of hexadecimal digits, 
      terminated by a <CR> character. 

        















    
    
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                                   ANNEX C 
                       Tags for media stream properties 
       
      Parameters for Local, Remote and LocalControl descriptors are 
      specified as tag-value pairs if binary encoding is used for the 
      protocol. This annex contains the property names (PropertyID), the 
      tags (Property tag), type of the property (Type) and the values 
      (Value). Values presented in the Value field when the field contains 
      references shall be regarded as "information". The reference contains 
      the normative values. If a value field does not contain a reference, 
      then the values in that field can be considered as "normative". 

      Tags are given as hexadecimal numbers in this annex. When setting the 
      value of a property, a MGC may underspecify the value according to 
      one of the mechanisms specified in 7.1.1. 

      It is optional to support the properties in this Annex or any of its 
      sub-sections. For example, only three properties from C.3 and only 
      five properties from C.8 might be implemented. 

      For type "enumeration" the value is represented by the value in 
      brackets, e.g. Send(0), Receive(1). Annex C properties with the types 
      "N bits" or "M Octets" should be treated as octet strings when 
      encoding the protocol. Properties with "N bit integer" shall be 
      treated as an integers. "String" shall be treated as an IA5String 
      when encoding the protocol. 

      When a type is smaller than one octet, the value shall be stored in 
      the low-order bits of an octet string of size 1. 

   C.1   General media attributes 
       

      PropertyID    Property Type          Value 
                    tag 

      Media         1001     Enumeration   Audio(0), Video(1), Data(2) 

      Transmission  1002     Enumeration   Send(0), Receive(1), 
      mode                                 Send&Receive(2) 

      Number of     1003     Unsigned      0-255 
      Channels               integer 

      Sampling      1004     Unsigned      0-2^32 
      rate                   integer 


    
    
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      Bitrate       1005     Integer       (0..4294967295)NOTE - Units of 
                                           100 bit/s. 

      ACodec        1006     Octet string  Audio Codec Type: 
                                           Ref.: ITU-T Q.765  
                                           Non-ITU-T codecs are defined 
                                           with the appropriate standards 
                                           organization under a defined 
                                           Organizational Identitifier. 

      Samplepp      1007     Unsigned      Maximum samples or frames per 
                             integer       packet: 0..65535 

      Silencesupp   1008     Boolean       Silence Suppression: True/False 

      Encrypttype   1009     Octet string  Ref.: ITU-T H.245 

      Encryptkey    100A     Octet string  Encryption key 
                             size          Ref.: ITU-T H.235 
                             (0..65535) 

      Echocanc      100B                    Not Used. See H.248.1 E.13 for 
                                           an example of possible Echo 
                                           Control properties. 

      Gain          100C     Unsigned      Gain in dB: 0..65535 
                             integer 

      Jitterbuff    100D     Unsigned      Jitter buffer size in ms: 
                             integer       0..65535 

      PropDelay     100E     Unsigned      Propagation Delay: 0..65535 
                             integer       Maximum propagation delay in 
                                           milliseconds for the bearer 
                                           connection between two media 
                                           gateways. The maximum delay 
                                           will be dependent on the bearer 
                                           technology. 

      RTPpayload    100F     Integer       Payload type in RTP Profile for 
                                           Audio and Video Conferences 
                                           with Minimal Control 
                                           Ref.: RFC 1890 

       
       


    
    
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   C.2   Mux properties 
       

      PropertyID Property tag Type         Value 

      H222       2001         Octet string H222LogicalChannelParameters 
                                            Ref.: ITU-T H.245 

      H223       2002         Octet string H223LogicalChannelParameters 
                                            Ref.: ITU-T H.245 

      V76        2003         Octet string V76LogicalChannelParameters 
                                            Ref.: ITU-T H.245 

      H2250      2004         Octet string H2250LogicalChannelParameters 
                                            Ref.: ITU-T H.245 

       

       
   C.3   General bearer properties 
       
      PropertyID Property   Type        Value 
                 tag 

      Mediatx    3001       Enumeration Media Transport TypeTDM 
                                         Circuit(0), ATM(1), FR(2), 
                                         Ipv4(3), Ipv6(4), ... 

      BIR        3002       4 octets    Value depends on transport 
                                         technology 

      NSAP       3003       1-20 octets See NSAP. 
                                         Ref.: Annex A/X.213 

       

       
   C.4   General ATM properties 
       

      PropertyID Property Type              Value 
                 tag  

      AESA       4001     20 octets         ATM End System Address 

      VPVC       4002     4 octets: VPCI    VPCI/VCI 
                           in first two 
    
    
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                           least             Ref.: ITU-T Q.2931 
                           significant 
                           octets, VCI in 
                           second two 
                           octets 

      SC         4003     Enumeration       Service Category: CBR(0), 
                                             nrt-VBR1(1), nrt  VBR2(2), 
                                             nrt-VBR3(3), rt-VBR1(4), 
                                             rt  VBR2(5), rt-VBR3(6), 
                                             UBR1(7), UBR2(8), ABR(9). 
                                             Ref.: ATM Forum UNI 4.0 

      BCOB       4004     5-bit integer     Broadband Bearer Class 
                                             Ref.: ITU-T Q.2961.2 

      BBTC       4005     7-bit integer     Broadband Transfer Capability 
                                             Ref.: ITU-T Q.2961.1 

      ATC        4006     Enumeration       I.371 ATM Traffic 
                                             CapabilityDBR(0), SBR1(1), 
                                             SBR2(2), SBR3(3), ABT/IT(4), 
                                             ABT/DT(5), ABR(6) 
                                             Ref.: ITU-T I.371 

      STC        4007     2 bits            Susceptibility to clipping: 
                                             Bits 
                                             2 1 
                                             --- 
                                             0 0     not susceptible to 
                                                     clipping 
                                             0 1     susceptible to  
                                                     clipping 
                                             Ref.: ITU-T Q.2931 

      UPCC       4008     2 bits            User Plane Connection 
                                             configuration: 
                                             Bits 
                                             2 1 
                                             --- 
                                             0 0     point-to-point 
                                             0 1     point-to-multipoint 
                                             Ref.: ITU-T Q.2931 

      PCR0       4009     24-bit integer    Peak Cell Rate (For CLP = 0) 
                                             Ref.: ITU-T Q.2931 


    
    
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      SCR0       400A     24-bit integer    Sustainable Cell Rate (For 
                                             CLP = 0) 
                                             Ref.: ITU-T Q.2961.1 

      MBS0       400B     24-bit integer    Maximum Burst Size (For CLP = 
                                             0) 
                                             Ref.: ITU-T Q.2961.1 

      PCR1       400C     24-bit integer    Peak Cell Rate (For CLP = 0 + 
                                             1) 
                                             Ref.: ITU-T Q.2931 

      SCR1       400D     24-bit integer    Sustainable Cell Rate (For 
                                             CLP = 0 + 1) 
                                             Ref.: ITU-T Q.2961.1 

      MBS1       400E     24-bit integer    Maximum Burst Size (For CLP = 
                                             0 + 1) 
                                             Ref.: ITU-T Q.2961.1 

      BEI        400F     Boolean           Best Effort Indicator 
                                             Value 1 indicates that BEI is 
                                             to be included in the ATM 
                                             signaling; value 0 indicates 
                                             that BEI is not to be 
                                             included in the ATM 
                                             signaling. 
                                             Ref.: ATM Forum UNI 4.0 

      TI         4010     Boolean           Tagging Indicator 
                                             Value 0 indicates that 
                                             tagging is not allowed; value 
                                             1 indicates that tagging is 
                                             requested. 
                                             Ref.: ITU-T Q.2961.1 

      FD         4011     Boolean           Frame Discard 
                                             Value 0 indicates that no 
                                             frame discard is allowed; 
                                             value 1 indicates that frame 
                                             discard is allowed. 
                                             Ref.: ATM Forum UNI 4.0 

      A2PCDV     4012     24-bit integer    Acceptable 2-point CDV 
                                             Ref.: ITU-T Q.2965.2 

      C2PCDV     4013     24-bit integer    Cumulative 2-point CDV 

    
    
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                                             Ref.: ITU-T Q.2965.2 

      APPCDV     4014     24-bit integer    Acceptable P-P CDV 
                                             Ref.: ATM Forum UNI 4.0 

      CPPCDV     4015     24-bit integer    Cumulative P-P CDV 
                                             Ref.: ATM Forum UNI 4.0 

      ACLR       4016     8-bit integer     Acceptable Cell Loss Ratio 
                                             Ref.: ITU-T Q.2965.2, ATM 
                                             Forum UNI 4.0 

      MEETD      4017     16-bit integer    Maximum End-to-end transit 
                                             delay 
                                             Ref.: ITU-T Q.2965.2, ATM 
                                             Forum UNI 4.0 

      CEETD      4018     16-bit integer    Cumulative End-to-end transit 
                                             delay 
                                             Ref.: ITU-T Q.2965.2, ATM 
                                             Forum UNI 4.0 

      QosClass   4019     Integer 0-5          QoS Class 

                                               QoS Class     Meaning 

                                               0             Default QoS 
                                                              associated 
                                                              with the ATC 
                                                              as defined 
                                                              in ITU-T 
                                                              Q.2961.2 

                                               1             Stringent 

                                               2             Tolerant 

                                               3             Bi-level 

                                               4             Unbounded 

                                               5             Stringent 
                                                              Bi-level 

                                                 

                                             Ref.: ITU-T Q.2965.1 

    
    
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      AALtype    401A     1 octet           AAL Type 
                                             Bits  
                                             8 7 6 5 4 3 2 1 
                                             --------------- 
                                             0 0 0 0 0 0 0 0   AAL for 
                                                               voice 
                                             0 0 0 0 0 0 0 1   AAL type 1 
                                             0 0 0 0 0 0 1 0   AAL type 2 
                                             0 0 0 0 0 0 1 1   AAL type  
                                                               3/4 
                                             0 0 0 0 0 1 0 1   AAL type 5 
                                             0 0 0 1 0 0 0 0   user- 
                                                               defined AAL 
                                             Ref.: ITU-T Q.2931 

       

   C.5   Frame Relay 
       
      PropertyID         Property    Type          Value 
                         tag 

      DLCI               5001        Unsigned      Data link connection 
                                     integer       id 

      CID                5002        Unsigned      sub-channel id 
                                     integer 

      SID/Noiselevel     5003        Unsigned      silence insertion 
                                     integer       descriptor  

      Primary Payload    5004        Unsigned      Primary Payload Type 
      type                           integer       Covers FAX and codecs 

        

   C.6   IP 
       
      PropertyID Property tag Type                Value 

      IPv4       6001         32 bits Ipv4Address Ipv4Address 
                                                   Ref.: IETF RFC 791 

      IPv6       6002         128 bits            IPv6 Address 
                                                   Ref.: IETF RFC 2460 

      Port       6003         Unsigned integer    0..65535 

    
    
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      Porttype   6004         Enumerated          TCP(0), UDP(1), SCTP(2) 

       

   C.7   ATM AAL2 
       
      PropertyID Property Type                   Value 
                 tag 

      AESA       7001     20 octets              AAL2 service endpoint 
                                                   address as defined in 
                                                   the referenced 
                                                   Recommendation. 
                                                   ESEANSEA 
                                                   Ref.: ITU-T Q.2630.1 

      BIR        See C.3  4 octets               Served user generated 
                                                   reference as defined in 
                                                   the referenced 
                                                   Recommendation. 
                                                   SUGR 
                                                   Ref.: ITU-T Q.2630.1 

      ALC        7002     12 octets              AAL2 link 
                                                   characteristics as 
                                                   defined in the 
                                                   referenced 
                                                   Recommendation. 
                                                   Maximum/Average CPS-SDU 
                                                   bit rate; 
                                                   Maximum/Average CPS-SDU 
                                                   size 
                                                   Ref.: ITU-T Q.2630.1 

      SSCS       7003     I.366.2: Audio (8      Service specific 
                           octets); Multirate (3  convergence sublayer 
                           octets), or I.366.1:   information as defined 
                           SAR-assured (14        in: 
                           octets);SAR-unassured  - ITU-T Q.2630.1,and 
                           (7 octets).            used in: 
                                                   - ITU-T I.366.2: 
                                                   Audio/Multirate; 
                                                   - ITU-T I.366.1: SAR-
                                                   assured/unassured. 
                                                   Ref.: ITU-T Q.2630.1, 
                                                   I.366.1 and I.366.2 


    
    
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      SUT        7004     1..254 octets          Served user transport 
                                                   parameter as defined in 
                                                   the referenced 
                                                   Recommendation. 
                                                   Ref.: ITU-T Q.2630.1 

      TCI        7005     Boolean                Test connection 
                                                   indicator as defined in 
                                                   the referenced 
                                                   Recommendation. 
                                                   Ref.: ITU-T Q.2630.1 

      Timer_CU   7006     32-bit integer         Timer-CU 
                                                   Milliseconds to hold 
                                                   partially filled cell 
                                                   before sending. 

      MaxCPSSDU  7007     8-bit integer          Maximum Common Part 
                                                   Sublayer Service Data 
                                                   Unit 
                                                   Ref.: ITU-T Q.2630.1 

      CID        7008     8 bits                 subchannel id: 0-255 
                                                   Ref.: ITU-T I.363.2 

       

   C.8   ATM AAL1 
       

      PropertyID Property   Type        Value 
                 tag  

      BIR        See table  4-29 octets GIT (Generic Identifier 
                 in C.3                 Transport) 
                                         Ref.: ITU-T Q.2941.1 

      AAL1ST     8001       1 octet     AAL1 Subtype 
                                         Bits 
                                         8 7 6 5 4 3 2 1 
                                         --------------- 
                                         0 0 0 0 0 0 0 0     null 
                                         0 0 0 0 0 0 0 1     voiceband
                                         signal transport on 64 kbit/s 
                                         0 0 0 0 0 0 1 0     circuit 
                                         transport 
                                         0 0 0 0 0 1 0 0     high-quality 
                                         audio signal transport 
    
    
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                                         0 0 0 0 0 1 0 1     video signal 
                                         transport 
                                         Ref.: ITU-T Q.2931 

      CBRR       8002       1 octet     CBR Rate 
                                         Bits 
                                         8 7 6 5 4 3 2 1 
                                         --------------- 
                                         0 0 0 0 0 0 0 1       64 kbit/s 
                                         0 0 0 0 0 1 0 0     1544 kbit/s 
                                         0 0 0 0 0 1 0 1     6312 kbit/s 
                                         0 0 0 0 0 1 1 0   32 064 kbit/s 
                                         0 0 0 0 0 1 1 1   44 736 kbit/s 
                                         0 0 0 0 1 0 0 0   97 728 kbit/s 
                                         0 0 0 1 0 0 0 0     2048 kbit/s 
                                         0 0 0 1 0 0 0 1     8448 kbit/s 
                                         0 0 0 1 0 0 1 0   34 368 kbit/s 
                                         0 0 0 1 0 0 1 1  139 264 kbit/s 
                                         0 1 0 0 0 0 0 0   n x 64 kbit/s 
                                         0 1 0 0 0 0 0 1    n x 8 kbit/s 
                                         Ref.: ITU-T Q.2931 

      MULT       See table              Multiplier, or n x 64k/8k/300 
                 in C.9                 Ref.: ITU-T Q.2931 

      SCRI       8003       1 octet     Source Clock Frequency Recovery 
                                         Method 
                                         Bits 
                                         8 7 6 5 4 3 2 1 
                                         --------------- 
                                         0 0 0 0 0 0 0 0     null 
                                         0 0 0 0 0 0 0 1     SRTS 
                                         0 0 0 0 0 0 1 0     ACM 
                                         Ref.: ITU-T Q.2931 

      ECM        8004       1 octet     Error Correction Method 
                                         Bits 
                                         8 7 6 5 4 3 2 1 
                                         --------------- 
                                         0 0 0 0 0 0 0 0     null 
                                         0 0 0 0 0 0 0 1     FEC - Loss 
                                         0 0 0 0 0 0 1 0     FEC - Delay 
                                         Ref.: ITU-T Q.2931 

      SDTB       8005       16-bit      Structured Data Transfer 
                            integer     Blocksize 
                                         Block size of SDT CBR service 

    
    
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                                         Ref.: ITU-T I.363.1 

      PFCI       8006       8-bit       Partially filled cells identifier 
                            integer     1-47 
                                         Ref.: ITU-T I.363.1 

       

   C.9   Bearer capabilities 
       
      The table entries referencing Recommendation Q.931 refer to the 
      encoding in the bearer capability information element of Q.931, not 
      to the low layer information element. 

      PropertyID    Tag    Type      Value 

      TMR           9001   1 octet   Transmission Medium 
                                     Requirement (Q.763) 
                                     Bits 
                                     87654321 
                                     -------- 
                                     00000000  speech 
                                     00000001  spare 
                                     00000010  64 kbit/s 
                                     unrestricted 
                                     00000011  3.1 kHz audio 
                                     00000100  reserved for 
                                     alternate speech (service 
                                     2)/64 kbit/s unrestricted 
                                     (service 1) 
                                     00000101  reserved for 
                                     alternate 64 kbit/s 
                                     unrestricted (service 
                                     1)/speech (service 2)  
                                     00000110  64 kbit/s preferred 
                                      
                                     The assigned codepoints 
                                     listed below are all for 
                                     unrestricted service. 
                                     00000111  2  64 kbit/s  
                                     00001000  384 kbit/s  
                                     00001001  1536 kbit/s  
                                     00001010  1920 kbit/s  
                                     00001011 
                                      through  
                                     00001111  spare 
                                     00010000 
                                      through  
    
    
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                                     00101010: 
                                        3 x 64 kbit/s through 
                                       29 x 64 kbit/s 
                                     except 
                                     00010011  spare 
                                     00100101  spare 
                                       
                                     00101011 
                                      through  
                                     11111111  spare 
                                     Ref.: ITU-T Q.763 
                                      
      TMRSR         9002   1 octet   Transmission Medium 
                                     Requirement Subrate 
                                     0     unspecified 
                                     1      8 kbit/s 
                                     2     16 kbit/s 
                                     3     32 kbit/s 
                                      
      Contcheck     9003   Boolean   Continuity Check 
                                     0     continuity check not 
                                     required on this circuit 
                                     1     continuity check 
                                     required on this circuit 
                                     Ref.: ITU-T Q.763 
                                      
      ITC           9004   5 bits    Information Transfer 
                                     Capability 
                                     Bits 
                                     5 4 3 2 1 
                                     --------- 
                                     0 0 0 0 0     Speech 
                                     0 1 0 0 0     Unrestricted 
                                     digital information 
                                     0 1 0 0 1     Restricted 
                                     digital information 
                                     1 0 0 0 0     3.1 kHz audio 
                                     1 0 0 0 1     Unrestricted 
                                     digital information with 
                                     tones/announcements 
                                     1 1 0 0 0     Video 
                                     All other values are 
                                     reserved. 
                                     Ref.: ITU-T Q.763 
                                      
      TransMode     9005   2 bits    Transfer Mode 
                                     Bits 
                                     2 1 
    
    
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                                     --- 
                                     0 0     Circuit mode 
                                     1 0     Packet mode 
                                     Ref.: ITU-T Q.931 
                                      
      TransRate     9006   5 bits    Transfer Rate 
                                     Bits 
                                     5 4 3 2 1 
                                     --------- 
                                     0 0 0 0 0     This code shall 
                                     be used for packet mode calls 
                                     1 0 0 0 0      64 kbit/s 
                                     1 0 0 0 1  2 x 64 kbit/s 
                                     1 0 0 1 1     384 kbit/s 
                                     1 0 1 0 1    1536 kbit/s 
                                     1 0 1 1 1    1920 kbit/s 
                                     1 1 0 0 0  Multirate (64 
                                     kbit/s base rate) 
                                     Ref.: ITU-T Q.931 
                                      
      MULT          9007   7 bits    Rate Multiplier 
                                     Any value from 2 to n 
                                     (maximum number of B-
                                     channels) 
                                     Ref.: ITU-T Q.931 
                                      
      layer1prot    9008   5 bits    User Information Layer 1 
                                     Protocol 
                                     Bits 
                                     5 4 3 2 1 
                                     --------- 
                                     0 0 0 0 1     ITU-T 
                                     standardized rate adaption 
                                     V.110 and X.30. 
                                     0 0 0 1 0     Recommendation 
                                     G.711 m-law 
                                     0 0 0 1 1     Recommendation 
                                     G.711 A-law 
                                     0 0 1 0 0     Recommendation 
                                     G.721 32 kbit/s ADPCM and 
                                     Recommendation I.460 
                                     0 0 1 0 1     Recommendations 
                                     H.221 and H.242 
                                     0 0 1 1 0     Recommendations 
                                     H.223 and H.245 
                                     0 0 1 1 1     Non-ITU-T 
                                     standardized rate adaption. 
                                     0 1 0 0 0     ITU-T 

    
    
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                                     standardized rate adaption 
                                     V.120. 
                                     0 1 0 0 1     ITU-T 
                                     standardized rate adaption 
                                     X.31 HDLC flag stuffing 
                                     All other values are 
                                     reserved. 
                                     Ref.: ITU Recommendation 
                                     Q.931 
                                      
      syncasync     9009   Boolean   Synchronous/Asynchronous 
                                     0     Synchronous data 
                                     1     Asynchronous data 
                                     Ref.: ITU-T Q.931 
                                      
      negotiation   900A   Boolean   Negotiation 
                                     0     In-band negotiation 
                                     possible 
                                     1     In-band negotiation not 
                                     possible 
                                     Ref.: ITU-T Q.931 
                                      
      Userrate      900B   5 bits    User Rate 
                                     Bits 
                                     5 4 3 2 1 
                                     --------- 
                                     0 0 0 0 0     Rate is 
                                     indicated by E-bits specified 
                                     in Recommendation I.460 or 
                                     may be negotiated in-band 
                                     0 0 0 0 1     0.6 kbit/s 
                                     Recommendations V.6 and X.1 
                                     0 0 0 1 0     1.2 kbit/s 
                                     Recommendation V.6 
                                     0 0 0 1 1     2.4 kbit/s 
                                     Recommendations V.6 and X.1 
                                     0 0 1 0 0     3.6 kbit/s 
                                     Recommendation V.6 
                                     0 0 1 0 1     4.8 kbit/s 
                                     Recommendations V.6 and X.1 
                                     0 0 1 1 0     7.2 kbit/s 
                                     Recommendation V.6 
                                     0 0 1 1 1     8 kbit/s 
                                     Recommendation I.460 
                                     0 1 0 0 0     9.6 kbit/s 
                                     Recommendations V.6 and X.1 
                                     0 1 0 0 1     14.4 kbit/s 
                                     Recommendation V.6 

    
    
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                                     0 1 0 1 0     16 kbit/s 
                                     Recommendation I.460 
                                     0 1 0 1 1     19.2 kbit/s 
                                     Recommendation V.6 
                                     0 1 1 0 0     32 kbit/s 
                                     Recommendation I.460 
                                     0 1 1 0 1     38.4 kbit/s 
                                     Recommendation V.110 
                                     0 1 1 1 0     48 kbit/s 
                                     Recommendations V.6 and X.1 
                                     0 1 1 1 1     56 kbit/s 
                                     Recommendation V.6 
                                     1 0 0 1 0     57.6 kbit/s 
                                     Recommendation V.14 extended 
                                     1 0 0 1 1     28.8 kbit/s 
                                     Recommendation V.110 
                                     1 0 1 0 0     24 kbit/s 
                                     Recommendation V.110 
                                     1 0 1 0 1     0.1345 kbit/s 
                                     Recommendation X.1 
                                     1 0 1 1 0     0.100 kbit/s 
                                     Recommendation X.1 
                                     1 0 1 1 1     0.075/1.2 
                                     kbit/s Recommendations V.6 
                                     and X.1 
                                     1 1 0 0 0     1.2/0.075 
                                     kbit/s Recommendations V.6 
                                     and X.1 
                                     1 1 0 0 1     0.050 kbit/s 
                                     Recommendations V.6 and X.1 
                                     1 1 0 1 0     0.075 kbit/s 
                                     Recommendations V.6 and X.1 
                                     1 1 0 1 1     0.110 kbit/s 
                                     Recommendations V.6 and X.1 
                                     1 1 1 0 0     0.150 kbit/s 
                                     Recommendations V.6 and X.1 
                                     1 1 1 0 1     0.200 kbit/s 
                                     Recommendations V.6 and X.1 
                                     1 1 1 1 0     0.300 kbit/s 
                                     Recommendations V.6 and X.1 
                                     1 1 1 1 1     12 kbit/s 
                                     Recommendation V.6 
                                     All other values are 
                                     reserved. 
                                     Ref.: ITU-T Q.931 
      INTRATE       900C   2 bits    Intermediate Rate 
                                     Bits 
                                     2 1 

    
    
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                                     --- 
                                     0 0     Not used 
                                     0 1     8 kbit/s 
                                     1 0     16 kbit/s 
                                     1 1     32 kbit/s 
                                     Ref.: ITU-T Q.931 
                                      
      nictx         900D   Boolean   Network Independent Clock 
                                     (NIC) on transmission 
                                     0     Not required to send 
                                     data with network independent 
                                     clock 
                                     1     Required to send data 
                                     with network independent 
                                     clock 
                                     Ref.: ITU-T Q.931 
                                      
      nicrx         900E   Boolean   Network independent clock 
                                     (NIC) on reception 
                                     0     Cannot accept data with 
                                     network independent clock 
                                     (i.e. sender does not support 
                                     this optional procedure) 
                                     1     Can accept data with 
                                     network independent clock 
                                     (i.e. sender does support 
                                     this optional procedure) 
                                     Ref.: ITU-T Q.931 
                                      
      flowconttx    900F   Boolean   Flow Control on transmission 
                                     (Tx) 
                                     0     Not required to send 
                                     data with flow control 
                                     mechanism 
                                     1     Required to send data 
                                     with flow control mechanism 
                                     Ref.: ITU-T Q.931 
                                      
      flowcontrx    9010   Boolean   Flow control on reception 
                                     (Rx) 
                                     0     Cannot accept data with 
                                     flow control mechanism (i.e. 
                                     sender does not support this 
                                     optional procedure) 
                                     1     Can accept data with 
                                     flow control mechanism (i.e. 
                                     sender does support this 
                                     optional procedure) 
    
    
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                                     Ref.: ITU-T Q.931 
                                      
      rateadapthdr  9011   Boolean   Rate adaption header/no 
                                     header 
                                     0     Rate adaption header 
                                     not included 
                                     1     Rate adaption header 
                                     included 
                                     Ref.: ITU-T Q.931 
                                      
      multiframe    9012   Boolean   Multiple frame establishment 
                                     support in data link 
                                     0     Multiple frame 
                                     establishment not supported. 
                                     Only UI frames allowed 
                                     1     Multiple frame 
                                     establishment supported 
                                     Ref.: ITU-T Q.931 
                                      
      OPMODE        9013   Boolean   Mode of operation 
                                     0     Bit transparent mode of 
                                     operation 
                                     1     Protocol sensitive mode 
                                     of operation 
                                     Ref.: ITU-T Q.931 
                                      
      llidnegot     9014   Boolean   Logical link identifier 
                                     negotiation 
                                     0     Default, LLI = 256 only 
                                     1     Full protocol 
                                     negotiation 
                                     Ref.: ITU-T Q.931 
                                      
      assign        9015   Boolean   Assignor/assignee 
                                     0     Message originator is 
                                     "default assignee" 
                                     1     Message originator is 
                                     "assignor only" 
                                     Ref.: ITU-T Q.931 
                                      
      inbandneg     9016   Boolean   In-band/out-band negotiation 
                                     0     Negotiation is done 
                                     with USER INFORMATION 
                                     messages on a temporary 
                                     signalling connection 
                                     1     Negotiation is done in-
                                     band using logical link zero 
                                     Ref.: ITU-T Q.931 
    
    
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      stopbits      9017   2 bits    Number of stop bits 
                                     Bits 
                                     2 1 
                                     --- 
                                     0 0     Not used 
                                     0 1     1 bit 
                                     1 0     1.5 bits 
                                     1 1     2 bits 
                                     Ref.: ITU-T Q.931 
                                      
      databits      9018   2 bits    Number of data bits excluding 
                                     parity bit if present 
                                     Bits 
                                     2 1 
                                     --- 
                                     0 0     Not used 
                                     0 1     5 bits 
                                     1 0     7 bits 
                                     1 1     8 bits 
                                     Ref.: ITU-T Q.931 
                                      
      parity        9019   3 bits    Parity information 
                                     Bits 
                                     3 2 1 
                                     ------ 
                                     0 0 0     Odd 
                                     0 1 0     Even 
                                     0 1 1     None 
                                     1 0 0     Forced to 0 
                                     1 0 1     Forced to 1 
                                     All other values are 
                                     reserved. 
                                     Ref.: ITU-T Q.931 
                                      
      duplexmode    901A   Boolean   Mode duplex 
                                     0     Half duplex 
                                     1     Full duplex 
                                     Ref.: ITU-T Q.931 
                                      
      modem         901B   6 bits    Modem Type 
                                     Bits 
                                     6 5 4 3 2 1 
                                     ----------- 
                                     0 0 0 0 0 0 through      
                                     0 0 0 1 0 1   National use 
                                     0 1 0 0 0 1   Rec. V.21 
                                     0 1 0 0 1 0     Rec. V.22 
    
    
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                                     0 1 0 0 1 1     Rec. V.22 bis 
                                     0 1 0 1 0 0     Rec. V.23 
                                     0 1 0 1 0 1     Rec. V.26 
                                     0 1 1 0 0 1     Rec. V.26 bis 
                                     0 1 0 1 1 1     Rec. V.26 ter 
                                     0 1 1 0 0 0     Rec. V.27 
                                     0 1 1 0 0 1     Rec. V.27 bis 
                                     0 1 1 0 1 0     Rec. V.27 ter 
                                     0 1 1 0 1 1     Rec. V.29 
                                     0 1 1 1 0 1     Rec. V.32 
                                     0 1 1 1 1 0     Rec. V.34 
                                     1 0 0 0 0 0  through  
                                     1 0 1 1 1 1    National use 
                                     1 1 0 0 0 0  through  
                                     1 1 1 1 1 1    User specified 
                                     Ref.: ITU-T Q.931 
                                      
      layer2prot    901C   5 bits    User information layer 2 
                                     protocol 
                                     Bits 
                                     5 4 3 2 1 
                                     --------- 
                                     0 0 0 1 0    Rec. Q.921/I.441 
                                     0 0 1 1 0    Rec. X.25, link 
                                     layer 
                                     0 1 1 0 0    LAN logical link 
                                     control (ISO/IEC 8802  2) 
                                     All other values are 
                                     reserved. 
                                     Ref.: ITU-T Q.931 
                                      
      layer3prot    901D   5 bits    User information layer 3 
                                     protocol 
                                     Bits 
                                     5 4 3 2 1 
                                     --------- 
                                     0 0 0 1 0     ITU-T Q.931 
                                     0 0 1 1 0     ITU-T X.25, 
                                     packet layer 
                                     0 1 0 1 1     ISO/IEC TR 9577 
                                     (Protocol identification in 
                                     the network layer) 
                                     All other values are 
                                     reserved. 
                                     Ref.: ITU-T Q.931 
                                      
      addlayer3prot 901E   Octet     Additional User Information 
                                     layer 3 protocol 

    
    
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                                     Bits        Bits 
                                     4 3 2 1     4 3 2 1 
                                     -------     ------- 
                                     1 1 0 0     1 1 0 0     
                                     Internet Protocol (RFC 791) 
                                     (ISO/IEC TR 9577) 
                                     1 1 0 0     1 1 1 1     
                                     Point-to-point Protocol (RFC 
                                     1661) 
                                     Ref.: ITU-T Q.931 
                                      
      DialledN      901F   30        Dialled Number 
                           octets 
                            
      DiallingN     9020   30        Dialling Number 
                           octets 
                            
      ECHOCI        9021             Not Used. See H.248.1 E.13 
                                     for an example of possible 
                                     Echo Control properties. 
                                      
      NCI           9022   1 octet   Nature of Connection 
                                     Indicators 
                                     Bits 
                                     2 1     Satellite Indicator 
                                     --- 
                                     0 0     no satellite circuit 
                                     in the connection 
                                     0 1     one satellite circuit 
                                     in the connection 
                                     1 0     two satellite 
                                     circuits in the connection 
                                     1 1     spare 
                                      
                                     Bits 
                                     4 3     Continuity check  
                                     ---     indicator 
                                     0 0     continuity check not 
                                     required 
                                     0 1     continuity check 
                                     required on this circuit 
                                     1 0     continuity check 
                                     performed on a previous 
                                     circuit 
                                     1 1     spare 
                                      
                                     Bit 
                                     5     Echo control device  
    
    
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                                     -     indicator  
                                     0     outgoing echo control 
                                     device not included 
                                     1     outgoing echo control 
                                     device included 
                                      
                                     Bits 
                                     8 7 6     Spare 
                                     Ref.: ITU-T Q.763 
                                      
      USI           9023   Octet     User Service Information 
                           string    Ref.: ITU-T Q.763 Clause 3.57 
       
       
   C.10  AAL5 properties 
       
      PropertyID Property    Type       Value 
                 tag 

      FMSDU      A001        32-bit     Forward Maximum CPCS-SDU Size: 
                             integer    Maximum CPCS-SDU size sent in the 
                                        direction from the calling user to 
                                        the called user. 
                                        Ref.: ITU-T Q.2931 

      BMSDU      A002        32-bit     Backwards Maximum CPCS-SDU Size: 
                             integer    Maximum CPCS-SDU size sent in the 
                                        direction from the called user to 
                                        the calling user. 
                                        Ref.: ITU-T Q.2931 

      SSCS       See table   See table  See table in C.7 
                 in C.7      in C.7     Additional values: 
                                        VPI/VCI 

       

   C.11  SDP equivalents 
       
      PropertyID Property    Type   Value 
                 tag  

      SDP_V      B001        String Protocol Version 
                                     Ref.: RFC 2327 

      SDP_O      B002        String Owner/creator and session ID 
                                     Ref.: RFC 2327 

    
    
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      SDP_S      B003        String Session name 
                                     Ref.: RFC 2327 

      SDP_I      B004        String Session identifier 
                                     Ref.: RFC 2327 

      SDP_U      B005        String URI of descriptor 
                                     Ref.: RFC 2327 

      SDC_E      B006        String email address 
                                     Ref.: RFC 2327 

      SDP_P      B007        String phone number 
                                     Ref.: RFC 2327 

      SDP_C      B008        String Connection information 
                                     Ref.: RFC 2327 

      SDP_B      B009        String Bandwidth Information 
                                     Ref.: RFC 2327 

      SDP_Z      B00A        String Time zone adjustment 
                                     Ref.: RFC 2327 

      SDP_K      B00B        String Encryption Key 
                                     Ref.: RFC 2327 

      SDP_A      B00C        String Zero or more session attributes 
                                     Ref.: RFC 2327 

      SDP_T      B00D        String Active Session Time 
                                     Ref.: RFC 2327 

      SDP_R      B00E        String Zero or more repeat times 
                                     Reference: RFC 2327 

      SDP_M      B00F        String Media type, port, transport and format 
                                     Ref.: RFC 2327 

       

   C.12  H.245 
       
      PropertyID Property   Type     Value 
                 tag  

      OLC        C001       Octet    The value of H.245 
                                      OpenLogicalChannel structure. 
    
    
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                            string   Ref.: ITU-T H.245 

      OLCack     C002       Octet    The value of H.245 
                            string   OpenLogicalChannelAck structure. 
                                      Ref.: ITU-T H.245 

      OLCcnf     C003       Octet    The value of H.245 
                            string   OpenLogicalChannelConfirm structure. 
                                      Ref.: ITU-T H.245 

      OLCrej     C004       Octet    The value of H.245 
                            string   OpenLogicalChannelReject structure. 
                                      Ref.: ITU-T H.245 

      CLC        C005       Octet    The value of H.245 
                            string   CloseLogicalChannel structure. 
                                      Ref.: ITU-T H.245 

      CLCack     C006       Octet    The value of H.245 
                            string   CloseLogicalChannelAck structure. 
                                      Ref.: ITU-T H.245 



























    
    
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                                   ANNEX D 
                              Transport over IP 
       

   D.1   Transport over IP/UDP using Application Level Framing (ALF) 
       
      Protocol messages defined in this Recommendation may be transmitted 
      over UDP. When no port is provided by the peer (see 7.2.8), commands 
      should be sent to the default port number: 2944 for text-encoded 
      operation, or 2945 for binary-encoded operation. Responses must be 
      sent to the address and port from which the corresponding commands 
      were sent. 

      ALF is a set of techniques that allows an application, as opposed to 
      a stack, to affect how messages are sent to the other side. A typical 
      ALF technique is to allow an application to change the order of 
      messages sent when there is a queue after it has queued them.  There 
      is no formal specification for ALF. The procedures in Annex D.1 
      contain a minimum suggested set of ALF behaviours 

      Implementors using IP/UDP with ALF should be aware of the 
      restrictions of the MTU on the maximum message size. 

   D.1.1 Providing At-Most-Once functionality 
       
      Messages, being carried over UDP, may be subject to losses. In the 
      absence of a timely response, commands are repeated. Most commands 
      are not idempotent. The state of the MG would become unpredictable 
      if, for example, Add commands were executed several times. The 
      transmission procedures shall thus provide an "At-Most-Once" 
      functionality. 

      Peer protocol entities are expected to keep in memory a list of the 
      responses that they sent to recent transactions and a list of the 
      transactions that are currently outstanding. The transaction 
      identifier of each incoming message is compared to the transaction 
      identifiers of the recent responses sent to the same MId. If a match 
      is found, the entity does not execute the transaction, but simply 
      repeats the response. If no match is found, the message will be 
      compared to the list of currently outstanding transactions. If a 
      match is found in that list, indicating a duplicate transaction, the 
      entity does not execute the transaction (see D.1.4 for procedures on 
      sending TransactionPending). 

      The procedure uses a long timer value, noted LONG-TIMER in the 
      following. The timer should be set larger than the maximum duration 
      of a transaction, which should take into account the maximum number 
      of repetitions, the maximum value of the repetition timer and the 

    
    
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      maximum propagation delay of a packet in the network. A suggested 
      value is 30 seconds. 

      The copy of the responses may be destroyed either LONG-TIMER seconds 
      after the response is issued, or when the entity receives a 
      confirmation that the response has been received, through the 
      "Response Acknowledgement parameter". For transactions that are 
      acknowledged through this parameter, the entity shall keep a copy of 
      the transaction-id for LONG-TIMER seconds after the response is 
      issued, in order to detect and ignore duplicate copies of the 
      transaction request that could be produced by the network. 

   D.1.2 Transaction identifiers and three-way handshake 
       
   D.1.2.1  Transaction identifiers  
       
      Transaction identifiers are 32-bit integer numbers. A Media Gateway 
      Controller may decide to use a specific number space for each of the 
      MGs that they manage, or to use the same number space for all MGs 
      that belong to some arbitrary group. MGCs may decide to share the 
      load of managing a large MG between several independent processes. 
      These processes will share the same transaction number space. There 
      are multiple possible implementations of this sharing, such as having 
      a centralized allocation of transaction identifiers, or pre-
      allocating non-overlapping ranges of identifiers to different 
      processes. The implementations shall guarantee that unique 
      transaction identifiers are allocated to all transactions that 
      originate from a logical MGC (identical mId). MGs can simply detect 
      duplicate transactions by looking at the transaction identifier and 
      mId only. 

   D.1.2.2  Three-way handshake 
       
      The TransactionResponse Acknowledgement parameter can be found in any 
      message. It carries a set of "confirmed transaction-id ranges". 
      Entities may choose to delete the copies of the responses to 
      transactions whose id is included in "confirmed transaction-id 
      ranges" received in the transaction response messages. They should 
      silently discard further commands when the transaction-id falls 
      within these ranges. 

      The "confirmed transaction-id ranges" values shall not be used if 
      more than LONG-TIMER seconds have elapsed since the MG issued its 
      last response to that MGC, or when a MG resumes operation. In this 
      situation, transactions should be accepted and processed, without any 
      test on the transaction-id. 

      Messages that carry the "Transaction Response Acknowledgement" 
      parameter may be transmitted in any order. The entity shall retain 
    
    
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      the "confirmed transaction-id ranges" received for LONG-TIMER 
      seconds. 

      In the binary encoding, if only the firstAck is present in a response 
      acknowledgement (see A.2), only one transaction is acknowledged. If 
      both firstAck and lastAck are present, then the range of transactions 
      from firstAck to lastAck is acknowledged. In the text encoding, a 
      horizontal dash is used to indicate a range of transactions being 
      acknowledged (see B.2). 

   D.1.3 Computing retransmission timers 
       
      It is the responsibility of the requesting entity to provide suitable 
      timeouts for all outstanding transactions, and to retry transactions 
      when timeouts have been exceeded. Furthermore, when repeated 
      transactions fail to be acknowledged, it is the responsibility of the 
      requesting entity to seek redundant services and/or clear existing or 
      pending connections. 

      The specification purposely avoids specifying any value for the 
      retransmission timers. These values are typically network dependent. 
      The retransmission timers should normally estimate the timer value by 
      measuring the time spent between the sending of a command and the 
      return of a response. Implementations SHALL ensure that the algorithm 
      used to calculate retransmission timing performs an exponentially 
      increasing backoff of the retransmission timeout for each 
      retransmission or repetition after the first one. 

        NOTE - One possibility is to use the algorithm implemented in TCP-
        IP, which uses two variables: 

      -  The average acknowledgement delay (AAD), estimated through an 
         exponentially smoothed average of the observed delays. 

      -  The average deviation (ADEV), estimated through an exponentially 
         smoothed average of the absolute value of the difference between 
         the observed delay and the current average. The retransmission 
         timer, in TCP, is set to the sum of the average delay plus N times 
         the average deviation. The maximum value of the timer should 
         however be bounded for the protocol defined in this 
         Recommendation, in order to guarantee that no repeated packet 
         would be received by the gateways after LONG-TIMER seconds. A 
         suggested maximum value is 4 seconds. 

      After any retransmission, the entity SHOULD do the following: 

      -  It should double the estimated value of the average delay, AAD. 


    
    
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      -  It should compute a random value, uniformly distributed between 
         0.5 AAD and AAD. 

      -  It should set the retransmission timer to the sum of that random 
         value and N times the average deviation. 

      This procedure has two effects. Because it includes an exponentially 
      increasing component, it will automatically slow down the stream of 
      messages in case of congestion. Because it includes a random 
      component, it will break the potential synchronization between 
      notifications triggered by the same external event. 

   D.1.4 Provisional responses 
       
      Executing some transactions may require a long time. Long execution 
      times may interact with the timer-based retransmission procedure. 
      This may result either in an inordinate number of retransmissions, or 
      in timer values that become too long to be efficient. Entities that 
      can predict that a transaction will require a long execution time may 
      send a provisional response, "Transaction Pending". They SHOULD send 
      this response if they receive a repetition of a transaction that is 
      still being executed. 

      Entities that receive a Transaction Pending shall switch to a 
      different repetition timer for repeating requests. The root 
      Termination has a property (ProvisionalResponseTimerValue), which can 
      be set to the requested maximum number of milliseconds between 
      receipt of a command and transmission of the TransactionPending 
      response. Upon receipt of a final response following receipt of 
      provisional responses, an immediate confirmation shall be sent, and 
      normal repetition timers shall be used thereafter. An entity that 
      sends a provisional response, SHALL include the immAckRequired field 
      in the ensuing final response, indicating that an immediate 
      confirmation is expected. Receipt of a Transaction Pending after 
      receipt of a reply shall be ignored. 

   D.1.5 Repeating Requests, Responses and Acknowledgements 
       
      The protocol is organized as a set of transactions, each of which is 
      composed request and a response, commonly referred to as an 
      acknowledgement. The protocol messages, being carried over UDP, may 
      be subject to losses. In the absence of a timely response, 
      transactions are repeated. Entities are expected to keep in memory a 
      list of the responses that they sent to recent transactions, i.e. a 
      list of all the responses they sent over the last LONG-TIMER seconds, 
      and a list of the transactions that are currently being executed. 

      The repetition mechanism is used to guard against three types of 
      possible errors: 
    
    
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      -  transmission errors, when for example a packet is lost due to 
         noise on a line or congestion in a queue; 

      -  component failure, when for example an interface to a entity 
         becomes unavailable; 

      -  entity failure, when for example an entire entity become 
         unavailable. 

      The entities should be able to derive from the past history an 
      estimate of the packet loss rate due to transmission errors. In a 
      properly configured system, this loss rate should be kept very low, 
      typically less than 1%. If a Media Gateway Controller or a Media 
      Gateway has to repeat a message more than a few times, it is very 
      legitimate to assume that something else than a transmission error is 
      occurring. For example, given a loss rate of 1%, the probability that 
      five consecutive transmission attempts fail is 1 in 100 billion, an 
      event that should occur less than once every 10 days for a Media 
      Gateway Controller that processes 1000 transactions per second. 
      (Indeed, the number of repetition that is considered excessive should 
      be a function of the prevailing packet loss rate.) We should note 
      that the "suspicion threshold", which we will call "Max1", is 
      normally lower than the "disconnection threshold", which should be 
      set to a larger value. 

      A classic retransmission algorithm would simply count the number of 
      successive repetitions, and conclude that the association is broken 
      after retransmitting the packet an excessive number of times 
      (typically between 7 and 11 times.) In order to account for the 
      possibility of an undetected or in  progress "failover", we modify 
      the classic algorithm so that if the Media Gateway receives a valid 
      ServiceChange message announcing a failover, it will start 
      transmitting outstanding commands to that new MGC. Responses to 
      commands are still transmitted to the source address of the command. 

      In order to automatically adapt to network load, this Recommendation 
      specifies exponentially increasing timers. If the initial timer is 
      set to 200 milliseconds, the loss of a fifth retransmission will be 
      detected after about 6 seconds. This is probably an acceptable 
      waiting delay to detect a failover. The repetitions should continue 
      after that delay not only in order to perhaps overcome a transient 
      connectivity problem, but also in order to allow some more time for 
      the execution of a failover  (waiting a total delay of 30 seconds is 
      probably acceptable). 

      It is, however, important that the maximum delay of retransmissions 
      be bounded. Prior to any retransmission, it is checked that the time 
      elapsed since the sending of the initial datagram is no greater than 
      T-MAX. If more than T-MAX time has elapsed, the MG concludes that the 
    
    
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      MGC has failed, and it begins its recovery process as described in 
      section 11.5. If the MG retries to connect to the current MGC it 
      shall use a ServiceChange with ServiceChangeMethod set to 
      Disconnected so that the new MGC will be aware that the MG lost one 
      or more transactions. The value T-MAX is related to the LONG-TIMER 
      value: the LONG-TIMER value is obtained by adding to T  MAX the 
      maximum propagation delay in the network. 

   D.2   Using TCP 
       
      Protocol messages as defined in this Recommendation may be 
      transmitted over TCP. When no port is specified by the other side 
      (see 7.2.8), the commands should be sent to the default port. The 
      defined protocol has messages as the unit of transfer, while TCP is a 
      stream-oriented protocol. TPKT, according to RFC 1006, SHALL be used 
      to delineate messages within the TCP stream. 

      In a transaction-oriented protocol, there are still ways for 
      transaction requests or responses to be lost. As such, it is 
      recommended that entities using TCP transport implement application 
      level timers for each request and each response, similar to those 
      specified for application level framing over UDP. 

   D.2.1 Providing the At-Most-Once functionality 
       
      Messages, being carried over TCP, are not subject to transport 
      losses, but loss of a transaction request or its reply may 
      nonetheless be noted in real implementations. In the absence of a 
      timely response, commands are repeated. Most commands are not 
      idempotent. The state of the MG would become unpredictable if, for 
      example, Add commands were executed several times.  

      To guard against such losses, it is recommended that entities follow 
      the procedures in D.1.1. 

   D.2.2 Transaction identifiers and three-way handshake 
       
      For the same reasons, it is possible that transaction replies may be 
      lost even with a reliable delivery protocol such as TCP. It is 
      recommended that entities follow the procedures in D.1.2.2. 

   D.2.3 Computing retransmission timers 
       
      With reliable delivery, the incidence of loss of a transaction 
      request or reply is expected to be very low. Therefore, only simple 
      timer mechanisms are required. Exponential back-off algorithms should 
      not be necessary, although they could be employed where, as in an 
      MGC, the code to do so is already required, since MGCs must implement 
      ALF/UDP as well as TCP. 
    
    
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   D.2.4 Provisional responses 
       
      As with UDP, executing some transactions may require a long time. 
      Entities that can predict that a transaction will require a long 
      execution time may send a provisional response, "Transaction 
      Pending". They should send this response if they receive a repetition 
      of a transaction that is still being executed. 

      Entities that receive a Transaction Pending shall switch to a longer 
      repetition timer for that transaction. 

      Entities shall retain Transactions and replies until they are 
      confirmed. The basic procedure of D.1.4 should be followed, but 
      simple timer values should be sufficient. There is no need to send an 
      immediate confirmation upon receipt of a final response. 

   D.2.5 Ordering of commands 
       
      TCP provides ordered delivery of transactions. No special procedures 
      are required. It should be noted that ALF/UDP allows sending entity 
      to modify its behaviour under congestion, and in particular, could 
      reorder transactions when congestion is encountered. TCP could not 
      achieve the same results. 


























    
    
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                                   ANNEX E  
                                Basic packages 
       
      This annex contains definitions of some packages for use with 
      Recommendation H.248.1. 

   E.1   Generic 
       
      PackageID: g (0x0001) 
      Version: 1 
      Extends: None 

      Description: 
         Generic package for commonly encountered items. 

   E.1.1 Properties 
       
      None. 

   E.1.2 Events 
       
      Cause 

         EventID: cause (0x0001) 
         Generic error event 

         EventsDescriptor parameters:  None 

         ObservedEvents Descriptor Parameters: 

            General Cause 
            ParameterID: Generalcause (0x0001) 

               This parameter groups the failures into six groups, which 
               the MGC may act upon. 

               Type: enumeration 

               Possible values: 
                        "NR" Normal Release (0x0001) 
                        "UR" Unavailable Resources (0x0002) 
                        "FT" Failure, Temporary (0x0003) 
                        "FP" Failure, Permanent (0x0004) 
                        "IW" Interworking Error (0x0005) 
                        "UN" Unsupported (0x0006) 




    
    
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            Failure Cause 
            ParameterID: Failurecause (0x0002) 

               Possible values:  OCTET STRING 

               Description: The Failure Cause is the value generated by the 
               Released equipment, i.e. a released network connection. The 
               concerned value is defined in the appropriate bearer control 
               protocol. 

      Signal Completion 

         EventID: sc (0x0002) 

         Indicates the termination of a signal for which the 
         notifyCompletion parameter was set to enable reporting of a 
         completion event. For further procedural description, see 7.1.1, 
         7.1.17 and 7.2.7. 

         EventsDescriptor parameters:  None 

         ObservedEvents Descriptor parameters: 

            Signal Identity 
            ParameterID: SigID (0x0001) 

               This parameter identifies the signal which has terminated. 
               For a signal that is contained in a signal list, the signal 
               list identity parameter should also be returned indicating 
               the appropriate list. 

               Type: Binary: octet (string), Text: string 

               Possible values: a signal which has terminated. A signal 
               shall be identified using the pkgdName syntax without 
               wildcarding. 

            Termination Method 
            ParameterID: Meth (0x0002) 

               Indicates the means by which the signal terminated. 

               Type: enumeration 

               Possible values: 
                  "TO" (0x0001) Signal timed out or otherwise completed on 
                  its own 
                  "EV" (0x0002) Interrupted by event 
                  "SD" (0x0003) Halted by new Signals descriptor 
    
    
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                  "NC" (0x0004) Not completed, other cause 

            Signal List ID 
            ParameterID:  SLID (0x0003) 

               Indicates to which signal list a signal belongs. The 
               SignalList ID is only returned in cases where the signal 
               resides in a signal list. 

               Type: integer 

               Possible values: any integer 

   E.1.3 Signals 
       
      None. 

   E.1.4 Statistics 
       
      None. 

       
   E.2   Base Root Package 
       
      PackageID: root (0x0002) 
      Version: 1 
      Extends: None 

      Description: 
         This package defines Gateway wide properties. 

   E.2.1 Properties 
       
      MaxNrOfContexts 
      PropertyID: maxNumberOfContexts (0x0001) 

         The value of this property gives the maximum number of contexts 
         that can exist at any time. The NULL context is not included in 
         this number. 

         Type: double 

         Possible values: 1 and up 

         Defined in: TerminationState 

         Characteristics: read only 


    
    
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      MaxTerminationsPerContext 
      PropertyID: maxTerminationsPerContext (0x0002) 

         The maximum number of allowed terminations in a context, see 6.1 

         Type: integer 

         Possible values: any integer 

         Defined in: TerminationState 

         Characteristics: read only 

      normalMGExecutionTime 
      PropertyId: normalMGExecutionTime (0x0003) 

         Settable by the MGC to indicate the interval within which the MGC 
         expects a response to any transaction from the MG (exclusive of 
         network delay) 

         Type: integer 

         Possible values: any integer, represents milliseconds 

         Defined in: TerminationState 

         Characteristics: read / write 

      normalMGCExecutionTime 
      PropertyId: normalMGCExecutionTime (0x0004) 

         Settable by the MGC to indicate the interval within which the MG 
         should expects a response to any transaction from the MGC 
         (exclusive of network delay) 

         Type: integer 

         Possible values: any integer, represents milliseconds 

         Defined in: TerminationState 

         Characteristics: read / write 

      MGProvisionalResponseTimerValue 
      PropertyId: MGProvisionalResponseTimerValue (0x0005) 

         Indicates the time within which the MGC should expect a Pending 
         Response from the MG if a Transaction cannot be completed. 

    
    
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         Initially set to normalMGExecutionTime plus network delay, but may 
         be lowered. 

         Type: Integer 

         Possible Values: any integer, represents milliseconds 

         Defined in: TerminationState 

         Characteristics: read / write  

      MGCProvisionalResponseTimerValue 
      PropertyId: MGCProvisionalResponseTimerValue (0x0006) 

         Indicates the time within which the MG should expect a Pending 
         Response from the MGC if a Transaction cannot be completed.  
         Initially set to normalMGCExecutionTime plus network delay, but 
         may be lowered. 

         Type: Integer 

         Possible Values: any integer, represents milliseconds 

         Defined in: TerminationState 

         Characteristics: read / write 

   E.2.2 Events 
       
      None. 

   E.2.3 Signals 
       
      None. 

   E.2.4 Statistics 
       
      None. 

   E.2.5 Procedures 
       
      None. 

       
   E.3   Tone Generator Package 
       
      PackageID: tonegen (0x0003) 
      Version: 1 
      Extends: None 
    
    
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      Description: 

         This package defines signals to generate audio tones. This package 
         does not specify parameter values. It is intended to be 
         extendable. Generally, tones are defined as an individual signal 
         with a parameter, ind, representing "interdigit" time delay, and a 
         tone id to be used with playtones. A tone id should be kept 
         consistent with any tone generation for the same tone. MGs are 
         expected to be provisioned with the characteristics of appropriate 
         tones for the country in which the MG is located. 

      Designed to be extended only.  

   E.3.1 Properties 
       
      None. 

   E.3.2 Events 
       
      None. 

   E.3.3 Signals 
       
      Play tone 
      SignalID: pt (0x0001) 

         Plays audio tone over an audio channel 

         Signal Type: Brief 

         Duration: Provisioned 

         Additional parameters: 

            Tone id list 
            ParameterID: tl (0x0001) 

               Type: list of tone ids 

               List of tones to be played in sequence. The list SHALL 
               contain one or more tone ids. 

            Inter signal duration 
            ParameterID: ind (0x0002) 

               Type: integer 

               Timeout between two consecutive tones in milliseconds 

    
    
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      No tone ids are specified in this package. Packages that extend this 
      package can add possible values for tone id as well as adding 
      individual tone signals. 

   E.3.4 Statistics 
       
      None. 

   E.3.5 Procedures 
       
      None. 

       
   E.4   Tone Detection Package 
       
      PackageID: tonedet (0x0004) 
      Version: 1 
      Extends: None 

      This Package defines events for audio tone detection. Tones are 
      selected by name (tone id). MGs are expected to be provisioned with 
      the characteristics of appropriate tones for the country in which the 
      MG is located.  

      Designed to be extended only: 
         This package does not specify parameter values. It is intended to 
         be extendable.  

   E.4.1 Properties 
       
      None. 

   E.4.2 Events 
       
      Start tone detected 
      EventID: std, 0x0001 

         Detects the start of a tone. The characteristics of positive tone 
         detection are implementation dependent. 

         EventsDescriptor parameters: 

            Tone id list 
            ParameterID: tl (0x0001) 

               Type: list of tone ids 

               Possible values: The only tone id defined in this package is 
               "wild card" which is "*" in text encoding and 0x0000 in 
    
    
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               binary. Extensions to this package would add possible values 
               for tone id. If tl is "wild card", any tone id is detected. 

         ObservedEventsDescriptor parameters: 

            Tone id  
            ParameterID: tid (0x0003) 

               Type: enumeration 

               Possible values: "wildcard" as defined above is the only 
               value defined in this package. Extensions to this package 
               would add additional possible values for tone id. 

      End tone detected 
      EventID: etd, 0x0002 

         Detects the end of a tone. 

         EventDescriptor parameters: 

            Tone id list 
            ParameterID: tl (0x0001) 

               Type: enumeration or list of enumerated types 

               Possible values: No possible values are specified in this 
               package. Extensions to this package would add possible 
               values for tone id. 

         ObservedEventsDescriptor parameters: 

            Tone id 
            ParameterID: tid (0x0003) 

               Type: enumeration 

               Possible values: "wildcard" as defined above is the only 
               value defined in this package. Extensions to this package 
               would add possible values for tone id. 

            Duration 
            ParameterId: dur (0x0002) 

               Type: integer, in milliseconds 

               This parameter contains the duration of the tone from first 
               detection until it stopped. 

    
    
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      Long tone detected 
      EventID: ltd, 0x0003 

         Detects that a tone has been playing for at least a certain amount 
         of time. 

         EventDescriptor parameters: 

            Tone id list 
            ParameterID: tl (0x0001) 

               Type: enumeration or list 

               Possible values: "wildcard" as defined above is the only 
               value defined in this package. Extensions to this package 
               would add possible values for tone id. 

            Duration 
            ParameterID: dur (0x0002) 

               Type: integer, duration to test against 

               Possible values: any legal integer, expressed in 
               milliseconds 

         ObservedEventsDescriptor parameters: 

            Tone id  
            ParameterID: tid (0x0003) 

               Type: Enumeration 

               Possible values: No possible values are specified in this 
               package. Extensions to this package would add possible 
               values for tone id. 

   E.4.3 Signals 
       
      None. 

   E.4.4 Statistics 
       
      None. 

   E.4.5 Procedures 
       
      None. 

       
    
    
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   E.5   Basic DTMF Generator Package 
       
      PackageID: dg (0x0005) 
      Version: 1 
      Extends: tonegen version 1 

      This package defines the basic DTMF tones as signals and extends the 
      allowed values of parameter tl of playtone in tonegen.  

   E.5.1 Properties 
       
      None. 

   E.5.2 Events 
       
      None. 

   E.5.3 Signals 
       
      DTMF character 0 
      SignalID: d0 (0x0010) 

         Generate DTMF 0 tone. The physical characteristic of DTMF 0 is 
         defined in the gateway.  

         Signal Type: Brief 

         Duration: Provisioned 

         Additional parameters: 

            None.  

      Additional values: 

         d0 (0x0010) is defined as a tone id for playtone 

      The other DTMF characters are specified in exactly the same way. A 
      table with all signal names and signal IDs is included. Note that 
      each DTMF character is defined as both a signal and a tone id, thus 
      extending the basic tone generation package. Also note that DTMF 
      SignalIds are different from the names used in a digit map. 

       





    
    
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                        Signal name     Signal ID/Tone id 

                       DTMF character 0    d0 (0x0010) 
                       DTMF character 1    d1 (0x0011) 
                       DTMF character 2    d2 (0x0012) 
                       DTMF character 3    d3 (0x0013) 
                       DTMF character 4    d4 (0x0014) 
                       DTMF character 5    d5 (0x0015) 
                       DTMF character 6    d6 (0x0016) 
                       DTMF character 7    d7 (0x0017) 
                       DTMF character 8    d8 (0x0018) 
                       DTMF character 9    d9 (0x0019) 
                       DTMF character *    ds (0x0020) 
                       DTMF character #    do (0x0021) 
                       DTMF character A    da (0x001a) 
                       DTMF character B    db (0x001b) 
                       DTMF character C    dc (0x001c) 
                       DTMF character D    dd (0x001d) 

       

   E.5.4 Statistics 
       
      None. 

   E.5.5 Procedures 
       
      None. 

       
   E.6   DTMF detection Package 
       
      PackageID: dd (0x0006) 
      Version: 1 
      Extends: tonedet version 1 

      This package defines the basic DTMF tones detection. This Package 
      extends the possible values of tone id in the "start tone detected" 
      "end tone detected" and "long tone detected" events. 

      Additional tone id values are all tone ids described in package dg 
      (basic DTMF generator package).  

      The following table maps DTMF events to digit map symbols as 
      described in 7.1.14. 

       

    
    
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                              DTMF Event Symbol 

                              d0   "0" 
                              d1   "1" 
                              d2   "2" 
                              d3   "3" 
                              d4   "4" 
                              d5   "5" 
                              d6   "6" 
                              d7   "7" 
                              d8   "8" 
                              d9   "9" 
                              da   "A" or "a" 
                              db   "B" or "b" 
                              dc   "C" or "c" 
                              dd   "D" or "d" 
                              ds   "E" or "e" 
                              do   "F" or "f" 
       
       

   E.6.1 Properties 
       
      None. 

   E.6.2 Events 
       
      DTMF digits 

         EventIds are defined with the same names as the SignalIds defined 
         in the table found in E.5.3. 

      DigitMap Completion Event 
      EventID: ce, 0x0004 

         Generated when a digit map completes as described in 7.1.14. 

         EventsDescriptor parameters: None. 

         ObservedEventsDescriptor parameters: 

            DigitString 
            ParameterID: ds (0x0001) 

               Type: string of digit map symbols (possibly empty) returned 
               as a quotedString 


    
    
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               Possible values: a sequence of the characters "0" through 
               "9", "A" through "F", and the long duration modifier "Z". 

               Description: the portion of the current dial string as 
               described in 7.1.14 which matched part or all of an 
               alternative event sequence specified in the digit map. 

            Termination Method 
            ParameterID: Meth (0x0003) 

               Type: enumeration 

               Possible values: 

                  "UM" (0x0001) Unambiguous match 

                  "PM" (0x0002) Partial match, completion by timer expiry 
                  or unmatched event 

                  "FM" (0x0003) Full match, completion by timer expiry or 
                  unmatched event 

               Description: indicates the reason for generation of the 
               event. See the procedures in 7.1.14. 

   E.6.3 Signals 
       
      None. 

   E.6.4 Statistics 
       
      None. 

   E.6.5 Procedures 
       
      Digit map processing is activated only if an events descriptor is 
      activated that contains a digit map completion event as defined in 
      Section E.6.2 and that digit map completion event contains an eventDM 
      field in the requested actions as defined in Section 7.1.9.  Other 
      parameters such as KeepActive or embedded events of signals 
      descriptors may also be present in the events descriptor and do not 
      affect the activation of digit map processing. 

       
   E.7   Call Progress Tones Generator Package 

      PackageID: cg, 0x0007 
      Version: 1 
      Extends: tonegen version 1 
    
    
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      This package defines the basic call progress tones as signals and 
      extends the allowed values of the tl parameter of playtone in 
      tonegen. 

   E.7.1 Properties 
       
      None. 

   E.7.2 Events 
       
      None. 

   E.7.3 Signals 
       
      Dial Tone 
      SignalID: dt (0x0030) 

         Generate dial tone. The physical characteristic of dial tone is 
         available in the gateway. 

         Signal Type: TimeOut 

         Duration: Provisioned 

         Additional parameters: 

            None. 

      Additional values: 

         dt (0x0030) is defined as a tone id for playtone 

      The other tones of this package are defined in exactly the same way. 
      A table with all signal names and signal IDs is included. Note that 
      each tone is defined as both a signal and a tone id, thus extending 
      the basic tone generation package. 

        Signal Name                 Signal ID/tone id 

        Dial Tone                   dt (0x0030) 
        Ringing Tone                rt (0x0031) 
        Busy Tone                   bt (0x0032) 
        Congestion Tone             ct (0x0033) 
        Special Information Tone    sit(0x0034) 
        Warning Tone                wt (0x0035) 
        Payphone Recognition Tone   prt (0x0036) 
        Call Waiting Tone           cw (0x0037) 
        Caller Waiting Tone         cr (0x0038) 
    
    
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   E.7.4 Statistics 
       
      None. 

   E.7.5 Procedures 
       
         NOTE - The required set of tone ids corresponds to those defined 
         in Recommendation E.180/Q.35. See Recommendation E.180/Q.35 for 
         definition of the meanings of these tones. 

       
   E.8   Call Progress Tones Detection Package 
       
      PackageID: cd (0x0008) 
      Version: 1 
      Extends: tonedet version 1 

      This package defines the basic call progress detection tones. This 
      package extends the possible values of tone id in the "start tone 
      detected", "end tone detected" and "long tone detected" events. 

      Additional values 

         toneID values are defined for start tone detected, end tone 
         detected and long tone detected with the same values as those in 
         package cg (call progress tones generation package). 

      The required set of tone ids corresponds to Recommendation 
      E.180/Q.35. See Recommendation E.180/Q.35 for definition of the 
      meanings of these tones. 

   E.8.1 Properties 
       
      None. 

   E.8.2 Events 
       
      Events are defined as in the call progress tones generator package 
      (cg) for the tones listed in the table of E.7.3. 

   E.8.3 Signals 
       
      None. 

   E.8.4 Statistics 
       
    
    
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      None. 

   E.8.5 Procedures 
       
      None. 

       
   E.9   Analog Line Supervision Package 
       
      PackageID: al, 0x0009 
      Version: 1 
      Extends: None 

      This package defines events and signals for an analog line.  

   E.9.1 Properties 
       
      None. 

   E.9.2 Events 
       
      onhook 
      EventID: on (0x0004) 

         Detects handset going on hook. Whenever an events descriptor is 
         activated that requests monitoring for an on-hook event and the 
         line is already on-hook, then the MG shall behave according to the
         setting of the "strict" parameter. 

         EventDescriptor parameters: 

            Strict Transition 
            ParameterID: strict (0x0001) 

               Type: enumeration 

               Possible values: "exact" (0x00), "state" (0x01), "failWrong" 
               (0x02) 

                 "exact" means that only an actual hook state transition to 
                 on-hook is to be recognized; 

                 "state" means that the event is to be recognized either if 
                 the hook state transition is detected or if the hook state 
                 is already on-hook; 

                 "failWrong" means that if the hook state is already on-
                 hook, the command fails and an error is reported. 

    
    
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         ObservedEventsDescriptor parameters: 

            Initial State 
            ParameterID: init (0x0002) 

               Type: Boolean 

               Possible values: 

                  "True" means that the event was reported because the line 
                  was already on-hook when the events descriptor containing 
                  this event was activated; 

                  "False" means that the event represents an actual state 
                  transition to on-hook. 

      offhook 
      EventID: of (0x0005) 

         Detects handset going off hook. Whenever an events descriptor is 
         activated that requests monitoring for an off-hook event and the 
         line is already off-hook, then the MG shall behave according to 
         the setting of the "strict" parameter. 

         EventDescriptor parameters: 

            Strict Transition 
            ParameterID: strict (0x0001) 

               Type: enumeration 

               Possible values: "exact" (0x00), "state" (0x01), "failWrong" 
               (0x02) 

                  "exact" means that only an actual hook state transition 
                  to off-hook is to be recognized; 

                  "state" means that the event is to be recognized either 
                  if the hook state transition is detected or if the hook 
                  state is already off-hook; 

                  "failWrong" means that if the hook state is already off-
                  hook, the command fails and an error is reported. 

         ObservedEventsDescriptor parameters 

            Initial State 
            ParameterID: init (0x0002) 

    
    
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               Type: Boolean 

               Possible values:  

                  "True" means that the event was reported because the line 
                  was already off-hook when the events descriptor 
                  containing this event was activated; 

                  "False" means that the event represents an actual state 
                  transition to off-hook. 

      flashhook 
      EventID: fl, 0x0006 

         Detects handset flash. A flash occurs when an onhook is followed 
         by an offhook between a minimum and maximum duration. 

         EventDescriptor parameters: 

            Minimum duration 
            ParameterID: mindur (0x0004) 

               Type: integer in milliseconds 

               Default value is provisioned. 

            Maximum duration 
            ParameterID: maxdur (0x0005) 

               Type: integer in milliseconds 

               Default value is provisioned. 

         ObservedEventsDescriptor parameters: 

            None 

   E.9.3 Signals 
       
      ring 
      SignalID: ri, 0x0002 

         Applies ringing on the line 

         Signal Type: TimeOut 

         Duration: Provisioned 

         Additional parameters: 
    
    
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            Cadence 
            ParameterID: cad (0x0006) 

               Type: list of integers representing durations of alternating 
               on and off segments, constituting a complete ringing cycle 
               starting with an on. Units in milliseconds 

               Default is fixed or provisioned. Restricted function MGs may 
               ignore cadence values they are incapable of generating. 

            Frequency 
            ParameterID: freq (0x0007) 

               Type: integer in Hz 

               Default is fixed or provisioned. Restricted function MGs may 
               ignore frequency values they are incapable of generating. 

   E.9.4 Statistics 
       
      None. 

   E.9.5 Procedures 
       
      If the MGC sets an EventsDescriptor containing a hook state 
      transition event (on-hook or off-hook) with the "strict" (0x0001) 
      parameter set to "failWrong", and the hook state is already what the 
      transition implies, the execution of the command containing that 
      EventsDescriptor fails. The MG SHALL include error code 540 
      "Unexpected initial hook state" in its reponse. 

   E.9.6 Error code 
       
      This package defines a new error code: 

         540 - Unexpected initial hook state 

      The procedure for use of this code is given in E.9.5. 

       
   E.10  Basic Continuity Package 
       
      PackageID: ct (0x000a) 
      Version: 1 
      Extends: None 

      This package defines events and signals for continuity test. The 
      continuity test includes provision of either a loopback or 
      transceiver functionality. 
    
    
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   E.10.1   Properties 
       
      None. 

   E.10.2   Events 
       
      Completion 
      EventID: cmp, 0x0005 

         This event detects test completion of continuity test. 

         EventDescriptor parameters 

            None. 

         ObservedEventsDescriptor parameters 

            Result 
            ParameterID: res (0x0008) 

               Type: enumeration 

               Possible values: success (0x0001), failure (0x0000) 

   E.10.3   Signals 
       
      Continuity test 
      SignalID: ct (0x0003) 

         Initiates sending of continuity test tone on the termination to 
         which it is applied. 

         Signal Type: TimeOut 

         Default value is provisioned 

         Additional parameters: 

            None. 

      Respond 
      SignalID: rsp (0x0004) 

         The signal is used to respond to a continuity test. See E.10.5 for 
         further explanation. 

         Signal Type: On/Off 

         Default duration is provisioned 
    
    
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         Additional parameters: 

            None. 

   E.10.4   Statistics 
       
      None. 

   E.10.5   Procedures 
       
      When a MGC wants to initiate a continuity test, it sends a command to 
      the MG containing: 

        a signals descriptor with the ct signal; and 

        an events descriptor containing the cmp event. 

      Upon reception of a command containing the ct signal and cmp event, 
      the MG initiates the continuity test tone for the specified 
      Termination. If the return tone is detected and any other required 
      conditions are satisfied before the signal times out, the cmp event 
      shall be generated with the value of the result parameter equal to 
      success. In all other cases, the cmp event shall be generated with 
      the value of the result parameter equal to failure. 

      When a MGC wants the MG to respond to a continuity test, it sends a 
      command to the MG containing a signals descriptor with the rsp 
      signal. Upon reception of a command with the rsp signal, the MG 
      either applies a loopback or (for 2-wire circuits) awaits reception 
      of a continuity test tone. In the loopback case, any incoming 
      information shall be reflected back as outgoing information. In the 
      2-wire case, any time the appropriate test tone is received, the 
      appropriate response tone should be sent. The MGC determines when to 
      remove the rsp signal. 

      When a continuity test is performed on a Termination, no echo devices 
      or codecs shall be active on that Termination. 

      Performing voice path assurance as part of continuity testing is 
      provisioned by bilateral agreement between network operators. 

         (Informative Note) Example tones and test procedure details are 
         given in Q.724 sections 7 and 8, Q.764 section 2.1.8 and Q.1902.4. 

       




    
    
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   E.11  Network Package 
       
      PackageID: nt (0x000b) 
      Version: 1 
      Extends: None 

      This package defines properties of network terminations independent 
      of network type. 

   E.11.1   Properties 
       
      Maximum Jitter Buffer 
      PropertyID: jit (0x0007) 

         This property puts a maximum size on the jitter buffer. 

         Type: integer in milliseconds 

         Possible values: This property is specified in milliseconds. 

         Defined in: LocalControlDescriptor 

         Characteristics: read/write 

   E.11.2   Events 
       
      network failure 
      EventID: netfail, 0x0005 

         The termination generates this event upon detection of a failure 
         due to external or internal network reasons. 

         EventDescriptor parameters 

            None. 

         ObservedEventsDescriptor parameters 

            cause 
            ParameterID: cs (0x0001) 

               Type: string 

               Possible values: any text string 

               This parameter may be included with the failure event to 
               provide diagnostic information on the reason of failure. 


    
    
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      quality alert 
      EventID: qualert, 0x0006 

         This property allows the MG to indicate a loss of quality of the 
         network connection. The MG may do this by measuring packet loss, 
         interarrival jitter, propogation delay and then indicating this 
         using a percentage of quality loss.  

         EventDescriptor parameters 

            Threshold 
            ParameterId: th (0x0001) 

               Type: integer 

               Possible values: 0 to 99 

               Description: threshold for percent of quality loss measured, 
               calculated based on a provisioned method, that could take 
               into consideration packet loss, jitter, and delay for 
               example. Event is triggered when calculation exceeds the 
               threshold. 

         ObservedEventsDescriptor parameters 

            Threshold 
            ParameterId: th (0x0001) 

               Type: integer 

               Possible values: 0 to 99 

               Description: percent of quality loss measured, calculated 
               based on a provisioned method, that could take into 
               consideration packet loss, jitter, and delay for example. 

   E.11.3   Signals 
       
      None. 

   E.11.4   Statistics 
       
      Duration 
      StatisticsID: dur (0x0001) 

         Description: provides duration of time the termination has been in 
         the Context. 

         Type: double, in milliseconds  
    
    
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      Octets Sent 
      StatisticID: os (0x0002) 

         Type: double 

         Possible values: any 64-bit integer 

      Octets Received 
      StatisticID: or (0x0003) 

         Type: double 

         Possible values: any 64-bit integer  

   E.11.5   Procedures 
       
      None. 

       
   E.12  RTP Package 
       
      PackageID: rtp (0x000c) 
      Version: 1 
      Extends: Network Package version 1 

      This package is used to support packet-based multimedia data transfer 
      by means of the Real-time Transport Protocol (RTP) [RFC 1889]. 

   E.12.1   Properties 
       
      None. 

   E.12.2   Events 
       
      Payload Transition 
      EventID: pltrans, 0x0001 

         This event detects and notifies when there is a transition of the 
         RTP payload format from one format to another. 

         EventDescriptor parameters 

            None. 

         ObservedEventsDescriptor parameters 

            ParameterName: rtppayload 
            ParameterID: rtppltype, 0x01 

    
    
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            Type: list of enumerated types. 

            Possible values: The encoding method shall be specified by 
            using one or several valid encoding names, as defined in the 
            RTP AV Profile or registered with IANA. 

   E.12.3   Signals 
       
      None. 

   E.12.4   Statistics 
       
      Packets Sent 
      StatisticID: ps (0x0004) 

         Type: double 

         Possible values: any 64-bit integer 

      Packets Received 
      StatisticID: pr (0x0005) 

         Type: double 

         Possible values: any 64-bit integer 

      Packet Loss 
      StatisticID: pl (0x0006) 

         Describes the current rate of packet loss on an RTP stream, as 
         defined in IETF RFC 1889. Packet loss is expressed as percentage 
         value: number of packets lost in the interval between two 
         reception reports, divided by the number of packets expected 
         during that interval. 

         Type: double 

         Possible values: a 32-bit whole number and a 32-bit fraction. 

      Jitter 
      StatisticID: jit (0x0007) 

         Requests the current value of the interarrival jitter on an RTP 
         stream as defined in IETF RFC 1889. Jitter measures the variation 
         in interarrival time for RTP data packets. 




    
    
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      Delay 
      StatisticID:delay (0x0008) 

         Requests the current value of packet propagation delay expressed 
         in timestamp units. Same as average latency. 

   E.12.5   Procedures 
       
      None. 

       
   E.13  TDM Circuit Package 
       
      PackageID: tdmc (0x000d) 
      Version: 1 
      Extends: Network Package version 1 

      This package may be used by any termination that supports gain and 
      echo control.  It was originally intended for use on TDM circuits but 
      may be more widely used. 

      New versions or extensions of this package should take non-TDM use 
      into account. 

   E.13.1   Properties 
       
      Echo Cancellation 
      PropertyID: ec (0x0008) 

         Type: boolean 

         Possible values: 

            "on" (when the echo cancellation is requested) and 

            "off" (when it is turned off.) 

            The default is provisioned. 

         Defined in: LocalControlDescriptor 

         Characteristics: read/write 

      Gain Control 
      PropertyID: gain (0x000a) 

         Gain control, or usage of of signal level adaptation and noise 
         level reduction is used to adapt the level of the signal. However, 

    
    
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         it is necessary, for example for modem calls, to turn off this 
         function. 

         Type: integer 

         Possible values: 

            The gain control parameter may either be specified as 
            "automatic" (0xffffffff), or as an explicit number of decibels 
            of gain (any other integer value). The default is provisioned 
            in the MG. 

         Defined in: LocalControlDescriptor 

         Characteristics: read/write 

   E.13.2   Events 
       
      None. 

   E.13.3   Signals 
       
      None. 

   E.13.4   Statistics 
       
      None. 

   E.13.5   Procedures 
       
      None. 


















    
    
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                 APPENDIX I  EXAMPLE CALL FLOWS (INFORMATIVE) 
       

      All H.248 implementors must read the normative part of this document 
      carefully before implementing from it. No one should use the examples 
      in this section as stand-alone explanations of how to create protocol 
      messages. 

      The examples in this section use SDP for encoding of the Local and 
      Remote stream descriptors. SDP is defined in RFC 2327. If there is 
      any discrepancy between the SDP in the examples, and RFC 2327, the 
      RFC should be consulted for correctness. Audio profiles used are 
      those defined in RFC 1890, and others registered with IANA. For 
      example, G.711 A-law is called PCMA in the SDP, and is assigned 
      profile 0. G.723 is profile 4, and H263 is profile 34.  

   A.1   Residential Gateway to Residential Gateway Call 
       
      This example scenario illustrates the use of the elements of the 
      protocol to set up a Residential Gateway to Residential Gateway call 
      over an IP-based network.  For simplicity, this example assumes that 
      both Residential Gateways involved in the call are controlled by the 
      same Media Gateway Controller. 

   A.1.1 Programming Residential GW Analog Line Terminations for Idle 
   Behavior 
       
      The following illustrates the API invocations from the Media Gateway 
      Controller and Media Gateways to get the Terminations in this 
      scenario programmed for idle behavior.  Both the originating and 
      terminating Media Gateways have idle AnalogLine Terminations 
      programmed to look for call initiation events (i.e.-offhook) by using 
      the Modify Command with the appropriate parameters.  The null Context 
      is used to indicate that the Terminations are not yet involved in a 
      Context. The ROOT termination is used to indicate the entire MG 
      instead of a termination within the MG. 

      In this example, MG1 has the IP address 124.124.124.222, MG2 is 
      125.125.125.111, and the MGC is 123.123.123.4. The default Megaco 
      port is 55555 for all three. 

      1. An MG registers with an MGC using the ServiceChange command: 

      MG1 to MGC: 

      MEGACO/1 [124.124.124.222] 
      Transaction = 9998 { 
          Context = - { 
              ServiceChange = ROOT {Services { 
    
    
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                  Method=Restart,  
                  ServiceChangeAddress=55555, Profile=ResGW/1} 
              } 
          } 
      } 
       

      2. The MGC sends a reply: 

      MGC to MG1: 

      MEGACO/1 [123.123.123.4]:55555 
      Reply = 9998 { 
         Context = - {ServiceChange = ROOT {  
           Services {ServiceChangeAddress=55555, Profile=ResGW/1} } } 
      } 
       

      3. The MGC programs a Termination in the NULL context. The 
      terminationId is A4444, the streamId is 1, the requestId in the 
      Events descriptor is 2222. The   mId is the identifier of the sender 
      of this message, in this case, it is the IP address and port 
      [123.123.123.4]:55555. Mode for this stream is set to SendReceive. 
      "al" is the analog line supervision package. Local and Remote are 
      assumed to be provisioned. 

      MGC to MG1: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 9999 { 
          Context = - { 
              Modify = A4444 { 
                  Media { Stream = 1 {  
                           LocalControl { 
                               Mode = SendReceive,  
                               tdmc/gain=2,  ; in dB,  
                               tdmc/ec=on 
                           }, 
                            
                       } 
                  }, 
                  Events = 2222 {al/of(strict=state)}          
              } 
          } 
      } 
       

      The dialplan script could have been loaded into the MG previously.  
      Its function would be to wait for the OffHook, turn on dialtone and 
    
    
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      start collecting DTMF digits. However in this example, we use the 
      digit map, which is put into place after the offhook is detected 
      (step 5 below).  

      Note that the embedded EventsDescriptor could have been used to 
      combine steps 3 and 4 with steps 8 and 9, eliminating steps 6 and 7. 

      4. The MG1 accepts the Modify with this reply: 

      MG1 to MGC: 

      MEGACO/1 [124.124.124.222]:55555 

      Reply = 9999 { 
         Context = - {Modify = A4444} 
      } 
       

      5. A similar exchange happens between MG2 and the MGC, resulting in 
      an idle Termination called A5555. 

   A.1.2 Collecting Originator Digits and Initiating Termination 
       
      The following builds upon the previously shown conditions.  It 
      illustrates the transactions from the Media Gateway Controller and 
      originating Media Gateway (MG1) to get the originating Termination 
      (A4444) through the stages of digit collection required to initiate a 
      connection to the terminating Media Gateway (MG2).  

      6. MG1 detects an offhook event from User 1 and reports it to the 
      Media Gateway Controller via the Notify Command.  

      MG1 to MGC: 

      MEGACO/1 [124.124.124.222]:55555 
      Transaction = 10000 { 
         Context = - { 
             Notify = A4444 {ObservedEvents =2222 { 
               19990729T22000000:al/of(init=false)}} 
         }  
      } 
       

      7. And the Notify is acknowledged. 

      MGC to MG1: 

      MEGACO/1 [123.123.123.4]:55555 
      Reply = 10000 { 
    
    
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          Context = - {Notify = A4444} 
      } 
       

      8. The MGC Modifies the termination to play dial tone, to look for 
      digits according to Dialplan0 and to look for the on-hook event now.  

      MGC to MG1: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 10001 { 
          Context = - { 
              Modify = A4444 { 
                  Events = 2223 { 
                      al/on(strict=state), dd/ce {DigitMap=Dialplan0}            
                  }, 
                  Signals {cg/dt},  
                  DigitMap= Dialplan0{ 
      (0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)}    
              } 
          } 
      }  
       

      9. And the Modify is acknowledged. 

      MG1 to MGC: 

      MEGACO/1 [124.124.124.222]:55555 
      Reply = 10001 { 
          Context = - {Modify = A4444} 
      } 
       

      10.   Next, digits are accumulated by MG1 as they are dialed by User 
      1.  Dialtone is stopped upon detection of the first digit. When an 
      appropriate match is made of collected digits against the currently 
      programmed Dialplan for A4444, another Notify is sent to the Media 
      Gateway Controller.  

      MG1 to MGC: 

      MEGACO/1 [124.124.124.222]:55555 
      Transaction = 10002 { 
         Context = - { 
             Notify = A4444 {ObservedEvents =2223 { 
               19990729T22010001:dd/ce{ds="916135551212",Meth=UM}}} 
         }  
      } 
    
    
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      11.   And the Notify is acknowledged. 

      MGC to MG1: 

      MEGACO/1 [123.123.123.4]:55555 
      Reply = 10002 { 
          Context = - {Notify = A4444} 
      } 
       

      12.   The controller then analyses the digits and determines that a 
      connection needs to be made from MG1 to MG2. Both the TDM termination 
      A4444, and an RTP termination are added to a new context in MG1. Mode 
      is ReceiveOnly since Remote descriptor values are not yet specified. 
      Preferred codecs are in the MGC's preferred order of choice. 

      MGC to MG1: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 10003 { 
          Context = $ { 
             Add = A4444,  
             Add = $ { 
                 Media {  
                   Stream = 1 {  
                        LocalControl {                            
                            Mode = ReceiveOnly,  
       
                            nt/jit=40 ; in ms 
                        }, 
                        Local { 
      v=0                                
      c=IN IP4 $                                
      m=audio $ RTP/AVP 4 
      a=ptime:30 
      v=0                                
      c=IN IP4 $                                
      m=audio $ RTP/AVP 0 
                        } 
                   } 
                }     
             } 
          } 
      }   
       


    
    
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         NOTE - The MGC states its preferred parameter values as a series 
         of SDP blocks in  Local. The MG fills in the Local Descriptor in 
         the Reply. 

      13.   MG1 acknowledges the new Termination and fills in the Local IP 
      address and UDP port. It also makes a choice for the codec based on 
      the MGC preferences in Local. MG1 sets the RTP port to 2222. 

      MG1 -> MGC: 

      MEGACO/1 [124.124.124.222]:55555 
      Reply = 10003 { 
         Context = 2000 {  
            Add = A4444, 
            Add=A4445{ 
               Media {  
                   Stream = 1 { 
                       Local { 
      v=0  
      o=- 2890844526 2890842807 IN IP4 124.124.124.222 
      s=- 
      t= 0 0                               
      c=IN IP4 124.124.124.222                                
      m=audio 2222 RTP/AVP 4 
      a=ptime:30 
      a=recvonly 
                       } ; RTP profile for G.723.1 is 4 
                   } 
               } 
            } 
         } 
      } 
       

      14.   The MGC will now associate A5555 with a new Context on MG2, and 
      establish an RTP Stream (i.e, A5556 will be assigned), SendReceive 
      connection through to the originating user, User 1. The MGC also sets 
      ring on A5555. 

      MGC to MG2: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 50003 { 
          Context = $ {  
             Add = A5555  { Media {  
                  Stream = 1 {  
                       LocalControl {Mode = SendReceive} }}, 
            Events=1234{al/of(strict=state)},  
                  Signals {al/ri} 
    
    
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                  }, 
             Add  = $ {Media {  
                  Stream = 1 {  
                       LocalControl {   
                          Mode = SendReceive, 
                          nt/jit=40 ; in ms 
                       }, 
                       Local { 
      v=0 
      c=IN IP4 $  
      m=audio $ RTP/AVP 4  
      a=ptime:30 
                       }, 
                       Remote { 
      v=0 
      c=IN IP4 124.124.124.222  
      m=audio 2222 RTP/AVP 4  
      a=ptime:30 
                       } ; RTP profile for G.723.1 is 4  
                   } 
                } 
            } 
         } 
      } 
       

      15.   This is acknowledged. The stream port number is different from 
      the control port number. In this case it is 1111 (in the SDP). 

      MG2 to MGC: 

      MEGACO/1 [125.125.125.111]:55555 
      Reply = 50003 { 
         Context = 5000 { 
         Add = A5555, 
            Add = A5556{ 
               Media {  
                  Stream = 1 {  
                      Local { 
      v=0 
      o=- 7736844526 7736842807 IN IP4 125.125.125.111 
      s=- 
      t= 0 0 
      c=IN IP4 125.125.125.111  
      m=audio 1111 RTP/AVP 4 
      }  
                  } ; RTP profile for G723.1 is 4 
               } 
             } 
    
    
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         } 
      } 
       

      16.   The above IPAddr and UDPport need to be given to MG1 now.  

      MGC to MG1: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 10005 { 
        Context = 2000 { 
          Modify = A4444 { 
            Signals {cg/rt} 
          }, 
          Modify = A4445 { 
             Media {  
                  Stream = 1 {  
                      Remote { 
      v=0 
      o=- 7736844526 7736842807 IN IP4 125.125.125.111 
      s=- 
      t= 0 0 
      c=IN IP4 125.125.125.111  
      m=audio 1111 RTP/AVP 4 
                      }  
                  } ; RTP profile for G723.1 is 4 
              } 
          } 
        } 
      } 
       

      MG1 to MGC: 

      MEGACO/1 [124.124.124.222]:55555 
      Reply = 10005 { 
         Context = 2000 {Modify = A4444, Modify = A4445} 
      } 
       

      17.   The two gateways are now connected and User 1 hears the 
      RingBack. The MG2 now waits until User2 picks up the receiver and 
      then the two-way call is established. 

      From MG2 to MGC: 

      MEGACO/1 [125.125.125.111]:55555 
      Transaction = 50005 { 
         Context = 5000 { 
    
    
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             Notify = A5555 {ObservedEvents =1234 { 
               19990729T22020002:al/of(init=false)}} 
         }  
      } 
       

      From MGC to MG2: 

      MEGACO/1 [123.123.123.4]:55555 
      Reply = 50005 { 
          Context = - {Notify = A5555} 
      } 
       

      From MGC to MG2: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 50006 { 
         Context = 5000 { 
            Modify = A5555 { 
               Events = 1235 {al/on(strict=state)}, 
               Signals { } ; to turn off ringing  
            } 
         } 
      } 
       

      From MG2 to MGC: 

      MEGACO/1 [125.125.125.111]:55555 
      Reply = 50006 { 
       Context = 5000 {Modify = A4445} 
      } 
       

      18.   Change mode on MG1 to SendReceive, and stop the ringback. 

       

      MGC to MG1: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 10006 { 
         Context = 2000 { 
            Modify = A4445 { 
               Media {  
                  Stream = 1 {  
                     LocalControl { 
                        Mode=SendReceive 
    
    
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                     }  
                  } 
               } 
            }, 
            Modify = A4444 { 
               Signals { } 
            }         
         } 
      } 
       

      from MG1 to MGC: 

      MEGACO/1 [124.124.124.222]:55555 
      Reply = 10006 { 
         Context = 2000 {Modify = A4445, Modify = A4444}} 
       

      19.   The MGC decides to Audit the RTP termination on MG2. 

      MGC -> MG2: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 50007 { 
         Context = - {AuditValue = A5556{  
            Audit{Media, DigitMap, Events, Signals, Packages, Statistics }} 
         }   
      } 
       

      20.   The MG2 replies. 

      MG2 -> MGC: 

      MEGACO/1 [125.125.125.111]:55555 
      Reply = 50007 { 
         Context = - { 
      AuditValue = A5556 { 
                Media {  
                   TerminationState { ServiceStates = InService, 
               Buffer = OFF },  
             Stream = 1 {  
                       LocalControl { Mode = SendReceive, 
                          nt/jit=40 }, 
                       Local { 
      v=0 
      o=- 7736844526 7736842807 IN IP4 125.125.125.111 
      s=- 
      t= 0 0 
    
    
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      c=IN IP4 125.125.125.111  
      m=audio 1111 RTP/AVP  4  
      a=ptime:30 
                      }, 
                       Remote { 
      v=0 
      o=- 2890844526 2890842807 IN IP4 124.124.124.222 
      s=- 
      t= 0 0 
      c=IN IP4 124.124.124.222  
      m=audio 2222 RTP/AVP  4 
      a=ptime:30   
                       } } }, 
                 Events, 
              Signals, 
              DigitMap, 
             Packages {nt-1, rtp-1}, 
                Statistics { rtp/ps=1200,  ; packets sent 
                             nt/os=62300, ; octets sent 
                             rtp/pr=700, ; packets received 
                             nt/or=45100, ; octets received 
                             rtp/pl=0.2,  ; % packet loss  
                             rtp/jit=20, 
                             rtp/delay=40 } ; avg latency  
             } 
          }     
      } 
       

      21.   When the MGC receives an onhook signal from one of the MGs, it 
      brings down the call. In this example, the user at MG2 hangs up 
      first. 

      From MG2 to MGC: 

      MEGACO/1 [125.125.125.111]:55555 
      Transaction = 50008 { 
         Context = 5000 { 
             Notify = A5555 {ObservedEvents =1235 { 
                19990729T24020002:al/on(init=false)} 
             } 
         }  
      } 
       

      From MGC to MG2: 

      MEGACO/1 [123.123.123.4]:55555 
      Reply = 50008 { 
    
    
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          Context = - {Notify = A5555} 
      } 
       

      22.   The MGC now sends both MGs a Subtract to take down the call. 
      Only the subtracts to MG2 are shown here. Each termination has its 
      own set of statistics that it gathers. An MGC may not need to request 
      both to be returned. A5555 is a physical termination, and A5556 is an 
      RTP termination. 

      From MGC to MG2: 

      MEGACO/1 [123.123.123.4]:55555 
      Transaction = 50009 { 
         Context = 5000 { 
            Subtract = A5555 {Audit{Statistics}}, 
            Subtract = A5556 {Audit{Statistics}} 
         } 
      } 
       

      From MG2 to MGC: 

      MEGACO/1 [125.125.125.111]:55555 
      Reply = 50009 { 
         Context = 5000 { 
           Subtract = A5555 { 
                Statistics {  
                   nt/os=45123, ; Octets Sent 
                   nt/dur=40 ; in seconds 
                   } 
             }, 
             Subtract = A5556 { 
                Statistics { 
                   rtp/ps=1245, ; packets sent 
                   nt/os=62345, ; octets sent 
                   rtp/pr=780, ; packets received 
                   nt/or=45123, ; octets received 
                   rtp/pl=10, ;  % packets lost 
                   rtp/jit=27, 
                   rtp/delay=48 ; average latency 
                } 
             } 
         } 
      } 
       

      23.   The MGC now sets up both MG1 and MG2 to be ready to detect the 
      next off-hook event. See step 1. Note that this could be the default 
    
    
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      state of a termination in the null context, and if this were the 
      case, no message need be sent from the MGC to the MG. Once a 
      termination returns to the null context, it goes back to the default 
      termination values for that termination. 













































    
    
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                      APPENDIX II  Changes From RFC 3015 
       
      In the following table, "source" indicates when the change was first 
      approved.  It has the following values: 
       
      IG1100: H.248 Implementor's Guide approved in November, 2000 (as TD 
      Plen-39, Christian Groves, editor). 
       
      IG0601: H.248 Implementor's Guide approved in June, 2001 (as  TD 
      Plen-15, Christian Groves, editor). 
       
      IGDUB: Draft H.248 Implementor's Guide approved at the Q.3 
      Rapporteur's meeting held near Dublin, October 2001 (as TD-28, Terry 
      Anderson, editor). 
       
      GEN0202: added at the Geneva meeting, February 2002, which consented 
      to H.248 v1 Amendment 1 (as TD Plen-36r1, Marcello Pantaleo, editor). 
       
      ITUPOST: added in post-Geneva editing by the ITU-T. 
       
      TTPOST: added in post-approval editing by the Megaco Chair, Tom 
      Taylor, who assembled this document for submission. 
       
       
       
      Section    Source                       Change 
                                                   
      1          ITUPOST   Reference changed from H.248 to H.248.1. 
                            
      2.1        ITUPOST   Reference added for error codes, changed from 
                           H.248 Annex L to H.248.8 (2002). 
                            
      2.1        IG1100   Corrected Q.765 reference to Q.765.5. 
                            
      2.1        GEN0202   Added reference to X.690. 
                            
      2.2        GEN0202   Added reference to H.226. 
                            
      2.2         IGDUB    Added informative references to Q.724, Q.764, 
                           and Q.1902.4. 
                            
      4          IG0601   Added expansion of ALF. 
                            
      5          TTPOST   Gave priority to IETF conventions (added at 
                           start of document). 
                            
      6.1.1      IG0601   Added text regarding use of wildcards for 
                           context identifiers.  (This information 
    
    
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                           already appeared in section 8.1.2.  The IG 
                           change subsequently disappeared.) 
                            
      6.1.1      IG1100   Added ranking of priority values. 
                            
      6.2         IGDUB    Deleted definition of signals. 
                            
      6.2        GEN0202   Expanded text and diagrams describing 
                           multiplexing terminations. 
                            
      6.2        TTPOST   Added asterisks to multiplexing diagrams to 
                           indicate centre of context.  Added Figure 6a 
                           showing cascading of multiplexes. 
                            
      6.2.2      IG0601   Added text indicating that ALL does not 
                           include ROOT. 
                            
      6.2.3      IG1100   Added text clarifying what must be supported 
                           to claim support of a package. 
                            
      6.2.3      IG1100   Added text indicating what packages a peer can 
                           indicate support for, when some of them are 
                           extensions of others. 
                            
      6.2.4      IG0601   Added text on ability of provisioning to 
                           override default values, and need for MGC to 
                           audit to learn the provisioned defaults. 
                            
      6.2.4      IG0601   Added text indicating effect of omitting 
                           specific properties from Descriptors in 
                           commands modifying a termination.  
                           Contradicted original text saying that omitted 
                           properties retain their prior values (still 
                           true for entirely-omitted Descriptors). 
                            
      6.2.4      GEN0202   Modified above text to restrict it to 
                           read/write properties, allow for default 
                           behaviour in place of default values if so 
                           specified in the property definition. 
                            
      6.2.4       IGDUB    Trimmed definition of signals Descriptor in 
                           table and inserted cross-reference to section 
                           7.1.11. 
                            
      6.2.4      IG1100   Added Topology and Error Descriptors to table. 
                            
      6.2.5       IGDUB    Specified error code to return if ROOT used 
                           inappropriately. 
    
    
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      7.1.1      IG1100   Added qualification to explanation of effect 
                           of missing Audit Descriptor, excepting 
                           Subtract. 
                            
      7.1.3      GEN0202   Changed "inputs" to "bearers" to be consistent 
                           with terminology in 6.2. 
                            
      7.1.4      IG0601   Small change to make clear that more than one 
                           of Local, Remote, and LocalControl can be 
                           included in the default streamId. 
                            
      7.1.7      IG0601   Default value for Mode specified to be 
                           Inactive. 
                            
      7.1.7      GEN0202   Added text requiring processing of media in 
                           any of the reserved formats, where more than 
                           one has been reserved in a given stream. 
                            
      7.1.8       IGDUB    Added restriction to at most one m= line per 
                           session description. 
                            
      7.1.9      IG0601   Text added to omit request identifier if the 
                           EventsDescriptor is empty.  Further text added 
                           at end to indicate the effects of an empty 
                           EventsDescriptor and an empty 
                           EventBufferDescriptor. 
                            
      7.1.9      IG0601   Fixed typo for destination of a Notify. 
                            
      7.1.9      IG1100   Added note to say event remains active after 
                           it has been notified, so long as it is still 
                           present in the active Events Descriptor. 
                            
      7.1.11      IGDUB    Added definition of signals. 
                            
      7.1.11     GEN0202   Modified definition to include example of more 
                           complex signal, and added role of signal in 
                           media preparation for future signals. 
                            
      7.1.11      IGDUB    The timeout completion reason was broadened to 
                           include other circumstances where the signal 
                           completed on its own.  Text added to indicate 
                           that if default signal type changed to TO, 
                           duration parameter must be provided. 
                            
      7.1.11     GEN0202   Removed reference to BR signal being "so 
                           short" it will stop on its own.  Added text 
    
    
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                           indicating that if the type of a signal is 
                           changed to TO, the Duration parameter must be 
                           supplied. 
                            
      7.1.11     IG1100   Deleted text discussing type of Signals List. 
                            
      7.1.12     GEN0202   Improved wording of introductory paragraph and 
                           added text making content of returned 
                           Descriptor clear. 
                            
      7.1.14.2   GEN0202   Added text indicating that when the start 
                           timer is set to 0, initial digit timing is 
                           disabled and the MG waits indefinitely for 
                           digits. 
                            
      7.1.14.2   GEN0202   Added text pointing out that default digit 
                           timer values should be provisioned, but can be 
                           overridden in the digit map. 
                            
      7.1.14.3   GEN0202   Changed result of long-short digit timer 
                           conflict from undefined to long. 
                            
      7.1.14.6   IG1100   Clarified that the digit map is provided by 
                           the eventDM parameter, which must be present. 
                            
      7.1.14.7   GEN0202   Added text clarifying that events covered by 
                           the digit map completion event have no side-
                           effects unless separately enabled. 
                            
      7.1.14.8   IG0601   Added requirement that the event specification 
                           include the eventDM parameter. 
                            
      7.1.17      IGDUB    Added text to indicate timestamp is optional 
                           and to include observed event parameters in 
                           reported content. 
                            
      7.1.17     GEN0202   Deleted provision that time is expressed in 
                           UTC (since intention was to use format, not 
                           time zone). 
                            
      7.1.18      IGDUB    Added text indicating error to return if 
                           topology option not supported. 
                            
      7.1.18     IG1100   Added text clarifying effect of not mentioning 
                 TTPOST   a termination in a topology Descriptor, and 
                           default topology for a new termination.  (This 
                           text got lost between the Dublin meeting and 
                           the production of H.248 Amendment 1 out of the 
    
    
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                           Geneva 02/02 meeting.  It has been added back 
                           to the present document.) 
                            
      7.1.19     IG1100   New section to describe Error Descriptor.  
                 GEN0202   Slightly edited in Geneva 02/02 meeting.  
                 ITUPOST   Reference for error code documentation updated 
                          to H.248.8. 
                            
      7.1.19     IG0601   Added paragraph giving guidance on level at 
                           which errors should be reported. 
                            
      7.2        IG1100   Noted possibility of Error Descriptor in reply 
                           to any command. 
                            
      7.2.1      IG1100   Added EventBufferDescriptor as Add parameter. 
                            
      7.2.1      IG1100   Removed restriction on use of CHOOSE wildcard. 
                            
      7.2.2      IG1100   Added EventBufferDescriptor as Modify 
                           parameter. 
                            
      7.2.2      GEN0202   Added text on side-effects of Modify of a 
                           multiplexing termination. 
                            
      7.2.3      IG1100   Added prohibition against subtracting from the 
                           NULL context. 
                            
      7.2.3      GEN0202   Added text on side-effects of Subtract of a 
                           multiplexing termination. 
                            
      7.2.3       IGDUB    Added text clarifying effect of empty 
                           AuditDescriptor in Subtract. 
                            
      7.2.4      IG1100   Added EventBufferDescriptor as Move parameter. 
                            
      7.2.4      GEN0202   Removed misleading statement that Move acts as 
                           subtract from original context. 
                            
      7.2.4      IG1100   Clarified effect of Move on properties of the 
                           moved termination. 
                            
      7.2.4      GEN0202   Added text on side-effects of Move of a 
                           multiplexing termination. 
                            
      7.2.5      IG1100   Added examples showing W- wildcard usage. 
                            
      7.2.5      IG1100   Noted that returning a list of all contextIDs 
                           requires that they be returned one per 
    
    
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                           ActionReply. 
                            
      7.2.5      IG1100   Added table entry (ALL, specific) to determine 
                           context in which termination currently 
                           resides. 
                            
      7.2.6      GEN0202   Added table similar to that in 7.2.5. 
                            
      7.2.7      IG0601   Added TerminationID to API. 
                            
      7.2.7       IGDUB    Indicated timestamp was optional in Notify, to 
                           accord with syntax. 
                            
      7.2.7      IG1100   Noted possibility of sending Error Descriptor 
                           in Notify. 
                            
      7.2.8      IG0601   Added text to description of Forced method to 
                           indicate that Forced on ROOT indicates a cold 
                           restart (all context state lost). 
                            
      7.2.8       IGDUB    Amplified explanation of Disconnected method 
                           to emphasize return to the previously 
                           controlling MGC. 
                            
      7.2.8      IG0601   Added text for MG use of Failover method when 
                           it detects MGC failure. 
                            
      7.2.8      IG1100   Added notes discouraging use of 
                           ServiceChangeAddress and warning that it could 
                           be either a full address or just a port 
                           number. 
                            
      7.2.8      IG0601   Added text indicating that timestamp does not 
                           necessarily represent absolute time, only 
                           local clock reading. 
                            
      7.2.8       IGDUB    Corrected "gateway" to "MGC" in discussion of 
                           returned ServiceChangeMgcId parameter. 
                            
      7.3        IG0601   Removed error code documentation to Annex L 
                 ITUPOST   (now H.248.8). 
                            
      8          IG1100   Added requirement that an Action be non-empty. 
                            
      8          GEN0202   Added context properties and context property 
                           audit requests to commands as potential 
                           contents of actions. 
                            
    
    
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      8.1.2      GEN0202   Added prohibition on using partial contextIDs 
                           with ALL wildcards. 
                            
      8.2.2      IG1100   Added text clarifying when in transaction 
                           processing the requested actions have been 
                           completed and a reply can be sent. 
                            
      8.2.2      IG1100   Added ALL as allowed contextID in 
                           TransactionReply. 
                            
      8.2.2      GEN0202   Provided general reference to section 7.1.19 
                           for generation of error Descriptors. 
                            
      8.2.2      IG0601   Corrected Actions to Commands when discussing 
                           partially-understood action. 
                            
      8.3        IG0601   Added text specifying that the same MId value 
                           must be used by a given entity throughout the 
                           life of a control association. 
                            
      8.3        IG0601   Added text expanding on independence of 
                           transactions from messages. 
                            
      9          ITUPOST   Indicated that additional transports may be 
                           defined in separate Recommendations as well as 
                           annexes to the primary specification. 
                            
      9          IG0601   Gave specific example of "request source 
                           address" for IP. 
                            
      9.1        IG1100   Deleted restriction to one outstanding Notify 
                           command on a termination at one time, since 
                           this is transport-specific. 
                            
      9.1        IG0601   Restored restriction, but noted that it 
                           applied only to transport not guaranteeing 
                           ordered delivery. 
                            
      10.2       IG1100   Corrected length of synthesized address field 
                           from 10 to 20 hex digits and indicated that 
                           calculation should be over entire message, not 
                           just one transaction. 
                            
      11.2       IG1100   Corrected text in first two paragraphs 
                           describing use of ServiceChangeMgcId 
                           parameter. 
                            
      11.2       IG1100   Corrected "Transaction Accept" to "Transaction 
    
    
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                           Reply". 
                            
      11.4       IG0601   Noted that support of redundant MGs requires 
                 GEN0202   use of a reliable transport and support in the 
                           MGC.  Added more explanation in Geneva. 
                            
      11.5       IG0601   Added text clarifying procedure if MG unable 
                           to establish a control relationship with any 
                           of its eligible MGCs. 
                            
      11.5        IGDUB    Added text indicating that when trying to 
                           reestablish contact with the previously 
                           controlling MGC the MG uses the Disconnected 
                           method. 
                            
      11.5       IG1100   Clarified handoff procedure. 
                            
      11.5       GEN0202   Changed text on replies to transactions in 
                           progress during handoff.  Replies now 
                           discarded when the service relationship with 
                           the old MGC has ended, rather than sent to the 
                           new MGC.  The new MGC could still send replies 
                           to requests sent to the old MGC. 
                            
      12.1.1     GEN0202   Added optional package designation as 
                           "designed to be extended only". 
                            
      12.1.1     IG1100   Made prohibition on overloading of identifiers 
                           in extended packages transitive through all 
                           ancestors of the extended package. 
                            
      12.1.2      IGDUB    Clarified the set of types allowed for 
                           properties. 
                            
      12.1.2     GEN0202   Added requirement to specify the base type of 
                           a sub-list. 
                            
      12.1.2     GEN0202   Provided requirements for content of the 
                           "Possible Values" template item, including 
                           specification of default values or behaviour. 
                            
      12.1.4     GEN0202   Added requirement to specify the default 
                           signal type, and specify a default duration 
                           for TO signals.  Also noted that duration is 
                           meaningless for BR, and that the signal type 
                           might be dependent on the values of other 
                           signal parameters. 
                            
    
    
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      12.2       GEN0202   Fixed section title (covers only event and 
                           signal parameters, not properties or 
                           statistics). 
                            
      12.2       IG1100   Reserved SPA and EPA prefixes, so they are not 
                           to be used for signal and event parameter 
                           tokens. 
                            
      12.2       IG0601   Expanded list of reserved prefixes. 
                            
      12.2        IGDUB    Clarified the set of types allowed for signal 
                           and event parameters. 
                            
      12.2       GEN0202   Added requirement to specify the base type of 
                           a sub-list. 
                            
      12.2       GEN0202   Provided requirements for content of the 
                           "Possible Values" template item, including 
                           specification of default values or behaviour. 
                            
      12.4        IGDUB    Corrected to indicate identifiers must start 
                           with alphabetic rather than aphanumeric 
                           character. 
                            
      13.1       IG0601   Changed private range of binary package 
                           identifiers to convenient hex values. 
                            
      A          GEN0202   Removed versions from X.680 and X.690 
                           references. 
                            
      A.2         IGDUB    Added note warning that the syntax alone does 
                           not provide a complete description of the 
                           constraints, but must be supplemented by a 
                           reading of the text and comments. 
                            
      A.2        IG0601   Added description of double wrapping of 
                           parameters declared as OCTET STRING. 
                            
      A.2        GEN0202   Some editing of double wrapping description to 
                           use ASN.1, BER in their proper places.  Added 
                           possibility of encoding strings as UTF8String, 
                           but only if they contain non-ASCII characters. 
                            
      A.2         IGDUB    Added line in table on double wrapping of true 
                           octet strings. 
                            
      A.2        IG1100   Corrected and expanded comments describing 
                           mtpAddress form of MId.  Fixed maximum length 
    
    
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                           of mtpAddress both here and in 
                           ServiceChangeAddress. 
                            
      A.2        IG0601   Inserted missing lines in IP4Address 
                           production. 
                            
      A.2        IG0601   Modified TransactionResponseAck to allow 
                           acknowledgement of multiple ranges of 
                           transactionIds. 
                            
      A.2        IG0601   Corrected numerical value of CHOOSE as a 
                           context identifier. 
                            
      A.2         IGDUB    Added missing extension marker in 
                           TopologyRequest. 
                            
      A.2        IG1100   AuditReply and AuditResult modified to bring 
                           binary functionality into line with text 
                           functionality.
                            
      A.2        IG0601   Removed OPTIONAL tag from terminationID in 
                           NotifyReply. 
                            
      A.2        IG0601   Added extraInfo substructure to EventParameter 
                           and SigParameter. 
                            
      A.2        IG0601   Modified MediaDescriptor to make it optional 
                           to specify a stream. 
                            
      A.2        IG0601   Added OPTIONAL tags to reserveValue and 
                           reserveGroup. 
                            
      A.2         IGDUB    Added to comments for pkgdName to indicate 
                           applicability to event names, signal names, 
                           and statisticIds as well as property. 
                            
      A.2        IG0601   RequestID made optional in EventsDescriptor 
                           and SecondEventsDescriptor and comment added 
                           saying it must be present if events are 
                           present. 
                            
      A.2        IG1100   Added OPTIONAL tags on RequestActions and 
                           SecondRequestedActions keepActive BOOLEANs. 
                            
      A.2        IG1100   Added comment to indicate requestID value to 
                           use in an AuditCapReply. 
                            
      A.2        GEN0202   Added comment to DigitMapValue indicating time 
    
    
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                           units for timers. 
                            
      A.2        IG0601   Added comment indicating coding of Value for 
                 GEN0202   ServiceChangeReason.  Cleaned up in Geneva to 
                           use ASN.1 and BER in their proper places. 
                            
      A.2        IG0601   Inserted missing extension marker in 
                           ServiceChangeParm production. 
                            
      A.2        IG0601   Aligned definition of mtpAddress in 
                           ServiceChangeAddress with that in MId. 
                            
      A.2        IG0601   Added timestamp to ServiceChangeResParm. 
                            
      A.2         IGDUB    Changed type of profileName in 
                           ServiceChangeProfile to IA5String. 
                            
      A.2        IG0601   Made returned value optional in 
                           statisticsParameter, to support 
                           auditCapability result. 
                            
      A.2        GEN0202   Added reference to ISO 8601:1988 for 
                           TimeNotation. 
                            
      A.2        IG1100   Value production modified to support the 
                           sublist parameter type. 
                            
      A.3        IG1100   Corrected ABNF for digitStringlisT, replacing 
                           "/" with "|". 
                            
      A.3        IG1100   Added parentheses to digitMapRange production. 
                            
      A.3        IG1100   Replaced more abbreviated syntax for pathName 
                           with fuller definition and constraints copied 
                           from B.2. 
                            
      B.2         IGDUB    Added note warning that the syntax alone does 
                           not provide a complete description of the 
                           constraints, but must be supplemented by a 
                           reading of the text and comments. 
                            
      B.2        IG0601   Added note warning that the interpretation of 
                           symbols is context-dependent. 
                            
      B.2        IG1100   Added comment to indicate case insensitivity 
                           of protocol (excepting SDP) and ABNF. 
                            
      B.2        IG0601   Expanded upon and capitalized this comment. 
    
    
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      B.2        IG0601   Lengthy note added on the coding of the VALUE 
                           construct. 
                            
      B.2         IGDUB    Deleted sentence in note suggesting that 
                           packages could add new types for properties, 
                           parameters, or statistics. 
                            
      B.2        IG0601   Added note indicating that parsers should 
                           allow for white space preceding the first line 
                           of SDP in Local or Remote. 
                            
      B.2         IGDUB    Added comments identifying the O- and W- tags. 
                            
      B.2        IG1100   Moved wildcard tag up from individual commands 
                           to commandRequestList. 
                            
      B.2        GEN0202   Added additional error case to actionReply. 
                            
      B.2        IG0601   Modified syntax of auditOther to allow return 
                           of terminationID only. 
                            
      B.2         IGDUB    Corrected upper limit for V4hex. 
                            
      B.2        IG1100   Corrected and expanded comments describing 
                           mtpAddress form of MId. 
                            
      B.2        IG0601   Modified comment to mediaParm to make 
                           streamParms and StreamDescriptor mutually 
                           exclusive. 
                            
      B.2        GEN0202   Modified comment further to indicate at most 
                           one instance of terminationStateDescriptor. 
                            
      B.2        GEN0202   Expanded comment for streamParm to indicate 
                           the restriction on repetition is per item. 
                            
      B.2        IG0601   Modified "at most once" comments to localParm, 
                           terminationStateParm, and modemType, to allow 
                           multiple instances of propertyParm in the 
                           first two cases and extensionParameter in the 
                           last one. 
                            
      B.2        IG0601   Added note before description of Local and 
                           Remote, pointing out that the octet value x00 
                           is not allowed in octetString. 
                            
      B.2        IG0601   Syntax for eventsDescriptor, embedFirst, and 
    
    
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                           eventBufferDescriptor modified to make 
                           contents beyond token optional. 
                            
      B.2         IGDUB    Replaced "event" by "item" in comment to 
                           pkgdName because pkgdName applies to 
                           properties, signals, and statistics as well. 
                            
      B.2        IG0601   Corrected placement of EQUAL in eventDM 
                           production. 
                            
      B.2        IG1100   Added comment and syntax to indicate requestID 
                           value to use in an AuditCapReply. 
                            
      B.2        IG1100   Corrected Modem Descriptor to allow package 
                           items as properties. 
                            
      B.2        IG0601   Comment to modemType changed to allow multiple 
                           instances of extensionParameter. 
                            
      B.2        GEN0202   Comment added to indicate units for Timer. 
                            
      B.2        IG1100   Added parentheses to digitMapRange production. 
                            
      B.2        IG1100   Added comment to serviceChangeParm, 
                           restricting each parameter to one appearance. 
                            
      B.2        IG0601   Added comments making serviceChangeMgcId and 
                           serviceChangeAddress mutually exclusive in 
                           ServiceChangeParm and servChgReplyParm. 
                            
      B.2         IGDUB    Added comment to serviceChangeParm indicating 
                           that ServiceChangeMethod and 
                           ServiceChangeReason are required. 
                            
      B.2        IG0601   Added Timestamp to servChgReplyParm. 
                            
      B.2        IG0601   Added comment indicating coding of Value for 
                           ServiceChangeReason. 
                            
      B.2        IG0601   Modified ServiceChangeAddress to use MId 
                           definition for full address. 
                            
      B.2        IG1100   Made returned value optional in 
                           statisticsParameter, to support 
                           auditCapability result. 
                            
      B.2        IG1100   Changed topologyDescriptor to allow multiple 
                           triples. 
    
    
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      B.2        IG0601   Added comment forbidding use of a double quote 
                           within a quotedString value. 
                            
      B.2        IG1100   Reserved prefixes for new tokens added to 
                           signalParameter and eventParameter, to avoid 
                           collision with package names. 
                            
      B.2        IG1100   EmbedToken and EmergencyToken changed to 
                           remove clash with EventBufferToken. 
                            
      B.3        IG1100   New section describing hexadecimal octet 
                           encoding. 
                            
      B.4        IG1100   New section describing hex octet sequence. 
                            
      C          IG1100   Added permission to use Annex C properties in 
                           LocalControl as well as in Local and Remote. 
                            
      C          IG0601   Added text making support of all properties of 
                           Annex C optional. 
                            
      C           IGDUB    Added directions to reconcile tabulated 
                           formats with allowed types for properties. 
                            
      C.1        IG1100   Corrected Q.765 reference to Q.765.5 for 
                           ACodec. 
                            
      C.1        IG1100   Deprecated Echocanc codepoint in favour of 
                           package-defined property. 
                            
      C.4        ITUPOST   Updated references from Q.2961 to Q.2961.1. 
                            
      C.4         IGDUB    Added details on format of VPVC. 
                            
      C.9        IG1100   Renamed USI to layer1prot. 
                            
      C.9        IG1100   Deprecated ECHOCI codepoint in favour of 
                           package-defined property. 
                            
      C.9        IG1100   Added new USI property. 
                            
      C.11       IG1100   Added m= line tag. 
                            
      D.1        IG0601   Added explanation of ALF. 
                            
      D.1.5       IGDUB    Expanded text indicating that when trying to 
                           reestablish contact with the previously 
    
    
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                           controlling MGC the MG uses the Disconnected 
                           method. 
                            
      E.1.2      GEN0202   Added missing EventsDescriptor parameters 
                           lines.   
                            
      E.1.2      GEN0202   For the Signal Completion event:  
                           - corrected the description of how it is 
                           enabled 
                           - heavily edited the description of the Signal 
                           Identity observed event parameter and added a 
                           type. 
                            
      E.1.2       IGDUB    The timeout completion reason for the Signal 
                           Completion event was broadened to include 
                           other circumstances where the signal completed 
                           on its own. 
                            
      E.1.2      IG1100   Added signal list ID observed event parameter 
                           to the Signal Completion event. 
                            
      E.2.1      IG0601   Added missing read only, read-write 
                           specifications. 
                            
      E.2.1      IG0601   Split ProvisionalResponseTimer properties into 
                           one for MG, one for MGC. 
                            
      E.3        GEN0202   Added "Designed to be extended only" to 
                           tonegen package description. 
                            
      E.4        GEN0202   Added "Designed to be extended only" to 
                           tonedet package description. 
                            
      E.4.2      GEN0202   Added type for tone ID observed parameter for 
                           Long Tone Detected event. 
                            
      E.6.2      IG1100   Corrected binary identifier for digit map 
                           completion event to avoid clash with base 
                           package. 
                            
      E.6.2      IG1100   Removed procedural text. 
                            
      E.6.5      IG1100   Added procedural text indicating where to find 
                           the applicable digit map and indicating the 
                           error to return if the parameter is missing. 
                            
      E.6.5      IG0601   Further modified procedural text. 
                            
    
    
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      E.7.3      IG1100   Corrected text identifier for payphone 
                           recognition tone to avoid clash with base 
                           package. 
                            
      E.10.5      IGDUB    Provided informative references for tones and 
                           procedures for continuity check. 
                            
      E.13       GEN0202   Added note that TDM package could also apply 
                           to other transports. 
                            
      E.13.1     IG1100   Changed default for echo cancellation from 
                           "on" to provisioned. 
                            
      E.13.1     IG0601   Corrected type for gain property. 
                            
      Appendix   TTPOST   Included a number of corrections which were 
         I                not picked up in H.248.1 Amendment 1 but which 
                           do appear in H.248.1 v2. 
       





























    
    
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   INTELLECTUAL PROPERTY RIGHTS 
       
      The ITU draws attention to the possibility that the practice or 
      implementation of this Recommendation may involve the use of a 
      claimed Intellectual Property Right. The ITU takes no position 
      concerning the evidence, validity or applicability of claimed 
      Intellectual Property Rights, whether asserted by ITU members or 
      others outside of the Recommendation development process. 

      As of the date of approval of this Recommendation, the ITU had 
      received notice of intellectual property, protected by patents, which 
      may be required to implement this Recommendation. However, 
      implementors are cautioned that this may not represent the latest 
      information and are therefore strongly urged to consult the TSB 
      patent database. 

      The IETF has also received notice of intellectual property claims 
      relating to Megaco/H.248.1.  Please consult the IETF IPR 
      announcements at http://www.ietf.org/ipr.html. 

   Acknowledgments 
       
      Megaco/H.248.1 is the result of hard work by many people in both the 
      IETF and in ITU-T Study Group 16.  This section records those who 
      played a prominent role in ITU-T meetings, on the Megaco list, or 
      both. 
       
      Megaco/H.248 owes a large initial debt to the MGCP protocol (RFC 
      2705), and thus to its authors, Mauricio Arango, Andrew Dugan, Ike 
      Elliott, Christian Huitema, and Scott Pickett.  Flemming Andreasen 
      does not appear on this list of authors, but was a major contributor 
      to the development of both MGCP and Megaco/H.248.1.  draft-andreasen-
      mgcp-rfc2705bis-04.txt has an extensive acknowledgement of many other 
      people who worked on media gateway control before Megaco got started. 
       
      The authors of the first Megaco RFCs (2885, then 3015) were Fernando 
      Cuervo, Nancy Greene, Abdallah Rayhan, Christian Huitema, Brian 
      Rosen, and John Segers.  Christian Groves conceived and was editor of 
      Annex C.  The people most active on the Megaco list in the period 
      leading up to the completion of RFC 2885 were Brian Rosen, Tom 
      Taylor, Nancy Greene, Christian Huitema, Matt Holdrege, Chip Sharp, 
      John Segers, Michael Thomas, Henry Sinnreich, and Paul Sijben.  The 
      people who sacrificed sleep and meals to complete the massive amount 
      of work required in the decisive Study Group 16 meeting of February, 
      2000, were Michael Brown, Ranga Dendi, Larry Forni, Glen Freundlich, 
      Christian Groves, Alf Heidemark, Steve Magnell, Selvam Rengasami, 
      Rich Rubin, Klaus Sambor, John Segers, Chip Sharp, Tom Taylor, and 
      Stephen Terrill. 
       
    
    
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      The most active people on the Megaco list in the period since the 
      February 2000 have been Tom Taylor, Brian Rosen, Christian Groves, 
      Madhu Babu Brahmanapally, Troy Cauble, Terry Anderson, Chuong Nguyen, 
      and Kevin Boyle, but many other people have been regular 
      contributors.  Brian Rosen did tremendous service in putting together 
      the Megaco interoperability tests.  On the Study Group 16 side, the 
      editorial team for the final revised document in February, 2002 
      included Christian Groves, Marcello Pantaleo, Terry Anderson, Peter 
      Leis, Kevin Boyle, and Tom Taylor. 
       
      Tom Taylor as Megaco Chair managed the day to day operation of the 
      Megaco list, with Brian Rosen taking an equal share of the burden for 
      most of the last three years.  Glen Freundlich as the Study Group 16 
      Rapporteur ran the ITU-T meetings and ensured that all of the work at 
      hand was completed.  Without Glen's determination the Megaco/H.248 
      standard would have taken at least half a year longer to produce.  
      Christian Groves filled in ably as Rapporteur when Glen could no 
      longer take part. 
       
       
   Authors' Addresses 
       
      Terry L Anderson 
      Lucent Technologies/INS/Voice Over IP Access Networks 
      Rm 2G-219A, 101 Crawfords Corner Rd, Holmdel, NJ 07733-3030 
      Phone: +1.732.949.5628 
      Email: tla@lucent.com 
       
      Christian Groves 
      Ericsson AsiaPacificLab Australia 
      37/360 Elizabeth St 
      Melbourne, Victoria 3000 
      Australia 
      Email: Christian.Groves@ericsson.com.au 
       
      Marcello Pantaleo 
      Ericsson Eurolab Deuschland 
      Ericsson Allee 1 
      52134 Herzogenrath, Germany 
      e-mail: Marcello.Pantaleo@eed.ericsson.se 
       
      Tom Taylor 
      Nortel Networks 
      1852 Lorraine Ave, 
      Ottawa, Ontario 
      Canada K1H 6Z8 
      Phone: +1 613 736 0961 
      E-mail: taylor@nortelnetworks.com 
        
    
    
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