Internet DRAFT - draft-foster-mgcp-redirect


Internet Engineering Task Force                              B. Foster 
Internet Draft                                            F. Andreasen 
Document: <draft-foster-mgcp-redirect-05.txt>            Cisco Systems 
Category: Informational                                      July 2003 
    Media Gateway Control Protocol (MGCP) Redirect and Reset Package 
Status of this Document 
  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 
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  The base Media Gateway Control Protocol (MGCP) specification (RFC 
  3435) allows endpoints to be re-directed one endpoint at a time.  
  This document provides extensions in the form of a new MGCP package 
  that provides mechanisms for redirecting and resetting a group of 
  endpoints.  It also includes the ability to more accurately re-direct 
  endpoints by allowing a list of Call Agents to be specified in a 
  preferred order.   
Conventions used in this document 
  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
  document are to be interpreted as described in RFC-2119 [1]. 

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                           Table of Contents 
1.  Introduction......................................................2 
2.0.  Redirect and Reset Package......................................3 
 2.1.  NotifiedEntityList Extension Parameter.........................3 
 2.2.  Endpoint Specifier.............................................4 
   2.2.1.  EndpointList and EndpointMap Extension Parameters..........4 
   2.2.2.  Application to Out-of-Service Endpoints....................5 
 2.3.  Redirect.......................................................6 
 2.4.  Reset Extension Parameter......................................7 
 2.5.  Return Codes...................................................7 
3.0.  IANA Considerations.............................................8 
4.0.  Security Considerations.........................................8 
5.0.  Normative References............................................8 
Authors' Addresses....................................................8 
Intellectual Property Statement.......................................8 
Full Copyright Statement..............................................9 
1.  Introduction 
  The base Media Gateway Control Protocol (MGCP) specification [2] 
  allows a Call Agent to specify a new NotifiedEntity parameter in 
  order to re-direct one or more endpoints to a new Call Agent.  This 
  must be done in a NotificationRequest or a connection handling 
  command.  However, because these commands affect endpoint or 
  connection state, such a request cannot typically be sent to a group 
  of endpoints with a single command.  This means that in a case where 
  a new Call Agent takes over for a failed one, the new Call Agent must 
  re-direct endpoints one at a time.  If there is a large number of 
  endpoints (e.g., within a large trunking gateway) this could take a 
  considerable amount of time.   
  This document defines a new redirect and reset package for MGCP that 
  allows the Call Agent to re-direct a group of endpoints without 
  affecting endpoint or connection state. 
  Also included is a new NotifiedEntityList parameter, which is similar 
  to the NotifiedEntity parameter but allows for multiple domain names 
  to be provided.  This allows the Call Agent to more accurately direct 
  endpoints to a preferred ordered list of alternate Call Agents. 
  A third capability contained within this package is the ability to 
  efficiently reset and re-initialize one or more groups of endpoints.  
  Such a capability is useful during Call Agent failover situations.   

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2.0.  Redirect and Reset Package 
  Package Name: RED 
  Version: 0 
  The purpose of this package is to: 
     * Define a new NotifiedEntityList extension parameter.  This works 
       the same as the NotifiedEntity parameter in [2] but allows more 
       than one domain name to be specified. 
     * Allow a Call Agent to pass a new NotifiedEntity or 
       NotifiedEntityList to a collection of endpoints specified by an 
       "all of" wildcard.  This is useful in the case where a new Call 
       Agent takes over from a previous one and wants to re-direct 
       endpoint(s) to send "Notifies" etc. to it from now on. 
     * Allow a Call Agent to request one or more groups of endpoints to 
       do a reset, which can be useful following certain types of 
2.1.  NotifiedEntityList Extension Parameter 
  The NotifiedEntityList parameter is encoded as "NL" and is followed 
  by a colon and a comma-separated list of NotifiedEntity values as 
  defined in the MGCP specification [2], e.g.: 
  The NotifiedEntityList works in a similar way to the NotifiedEntity 
  parameter, except that it allows multiple domain names to be listed.  
  The NotifiedEntityList thus specifies a new "notified entity" for the 
  The NotifiedEntityList parameter is optional in any command or 
  response where the NotifiedEntity parameter is allowed.  Following a 
  restart, the NotifiedEntityList is initially empty, unless 
  provisioned otherwise.  In subsequent commands, it retains its 
  current value until explicitly changed.  If both a NotifiedEntity 
  parameter and a non-empty NotifiedEntityList parameter have been set 
  (not necessarily at the same time), the NotifiedEntity parameter 
  value will be viewed as implicitly added to the beginning of the 
  NotifiedEntityList parameter.  The NotifiedEntity parameter thus 
  always defines the first domain name to contact, unless it has 
  explicitly been set to empty.  In that case, the NotifiedEntityList 
  defines the "notified entity".  If the NotifiedEntityList is also 
  empty, then the normal MGCP handling of having an empty "notified 
  entity" applies.  We will refer to the list of domain names that 
  result from the above rules as the "notified entity list". 
  When the "notified entity list" is non-empty, transmission is first 
  attempted with the first domain name in the list as in the normal 
  MGCP retransmission procedures described in [2].  Each of the IP-
  addresses for this domain name MUST first be tried as specified in 
  [2], and if this is unsuccessful, each of the IP-addresses for the 
  second domain name MUST then be attempted, etc. following the normal 
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  MGCP retransmission procedures, with "N" (the number of 
  retransmissions) set to zero for each domain name (see Section 4.3 in 
  [2]).  Whenever retransmission to a new domain name is initiated, the 
  default retransmission timer value (RTO) etc. SHOULD be used - the 
  estimator (T-DELAY) and measurements (AAD and ADEV) used for the 
  transmission to the previous domain name are considered obsolete.  
  Note however, that the maximum transaction lifetime considerations 
  apply as usual, and hence retransmission to any of the IP-addresses 
  for any of the domain names MUST NOT occur more than T-Max seconds 
  after the initial sending of the command, irrespective of where it 
  was sent.  The Max1 DNS query MAY be performed for each of the domain 
  names, or it MAY simply be performed for the first domain name.  The 
  Max2 DNS query however MUST NOT be performed for any but the last 
  domain name.  Also note, that only the last IP-address for the last 
  domain name can reach Max2 retransmissions, and hence retransmission 
  to all other IP-addresses MUST end after Max1 retransmissions.   
  The current value of the NotifiedEntityList parameter can be audited 
  via AuditEndpoint; the value of the NotifiedEntity parameter will not 
  be included here and hence must be audited separately.  Support for 
  the NotifiedEntityList in AuditConnection is permissible, but it is 
  neither required nor recommended.   
2.2.  Endpoint Specifier 
2.2.1.  EndpointList and EndpointMap Extension Parameters 
  A simple "all-of" wildcard as defined in [2] may not be sufficient to 
  accurately specify endpoints of interest.  An example of this is a 
  case where a Call Agent fails over, resulting in a state mismatch for 
  endpoints involved with transient calls.  In order to re-synchronize, 
  one Call Agent procedure involves using the reset extension parameter 
  described in section 2.4 of this document to ensure that idle 
  endpoints are in fact idle.  However, these endpoints may be randomly 
  distributed across the available endpoints in a large trunk gateway. 
  In order to satisfy this requirement, the RED package introduces some 
  new parameters that MAY be used to specify the endpoints of interest 
  for the EndpointConfiguration Command.  These are the EndpointList 
  and the EndpointMap extension parameters.  These parameters MUST only 
  be used when specifying a virtual endpoint corresponding to the 
  gateway as the LocalEndpointName i.e.: 
     EPCF 1200 MGCP 1.0 
  where "MG" is the virtual endpoint name associated with the gateway. 
  The EndPointList parameters is a list of the endpoint names which can 
  include one or more lines in the following format: 
     "RED/EL:" 0*WSP RangedLocalName 0*("," 0*WSP RangedLocalName) 

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  where RangedLocalName is a LocalEndpointName that may include the 
  ranged wildcard notation described in Appendix E (section E.5) of 
  [2], i.e.: 
    RangeWildcard  = "*" / "[" NumericalRange *("," NumericalRange)"]" 
    NumericalRange = 1*(DIGIT) [ "-" 1*(DIGIT) ] 
     RED/EL: ds/ds1-1/[1-24], ds/ds1-2/[1-24], ds/ds1-3/[1-24] 
  Including an EndpointMap parameter with the following format can 
  further specify the endpoints: 
     "RED/MP:" 0*WSP TrueOrFalse 0*(TrueOrFalse) 
     TrueOrFalse = "T" / "F" 
  where "T" indicates that the command should be applied to this 
  endpoint and "F" indicates that it should not.  This parameter can be 
  used in conjunction with the reset extension parameter described in 
  section 2.4 of this document to force arbitrarily distributed 
  endpoints to an idle state. 
  If the EndpointMap parameter is used it MUST be immediately preceded 
  (i.e. on the previous line) by an EndPointList parameter to specify 
  the endpoints that the EndpointMap is referring to.  Several 
  EndpointList and EndpointMap parameter lines MAY be provided.  It is 
  considered to be an error if the EndpointMap parameters extend beyond 
  the endpoints specified in the preceding EndPointList parameter.  In 
  that case, return code 800 MUST be used (see section 2.5).   
  The EndpointList and EndpointMap parameters MUST only be used with 
  the EndpointConfiguration command.  The EndpointList parameter MAY be 
  provided without an EndpointMap parameter.  However, as indicated 
  earlier, an EndpointMap parameter MUST be immediately preceded by an 
  EndpointList parameter.  Neither of these parameters is auditable. 
  For an example of EndpointMap parameter usage, refer to section 2.4. 
2.2.2.  Application to Out-of-Service Endpoints 
  Note that the EndpointConfiguration command is normally only valid 
  for in-service endpoints.  If an EndpointConfiguration request is 
  sent to a wild-carded LocalEndpointName [2] and any of the endpoints 
  specified are out-of-service, the command will fail with return code 
  501 (endpoint not ready). 
  However, as long as the gateway is in-service and able to respond to 
  MGCP commands, the gateway can apply the endpoint configuration 
  command to endpoints specified by the EndpointList and/or EndpointMap 
  parameters (regardless of whether those endpoints are in-service or 
  not).  The endpoint configuration information of course will not be 
  maintained over gateway restarts (i.e. the Call Agent would have to 
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  re-apply the endpoint configuration after it receives an RSIP with 
  restart method "restart"). 
  EndpointList and/or EndpointMap parameters MUST only be used with a 
  virtual endpoint name corresponding to the gateway (as indicated 
  above).  If used with any other endpoint name (whether wild-carded or 
  not), then error code 801 (section 2.5) MUST be returned.  
2.3.  Redirect 
  A new extension parameter for use with the EndpointConfiguration 
  command is defined.  A new NotifiedEntity value can be included with 
  a "RED/N" parameter as follows: 
     EPCF 1200 * MGCP 1.0 
  This changes the "notified entity" for the endpoint(s) to the value 
  specified.  If the "all of" wildcard convention is used, the 
  NotifiedEntity value replaces all of the existing "notified entities" 
  for those endpoints.  If NotifiedEntity is omitted in a subsequent 
  EndpointConfiguration command, the "notified entity" remains 
  In the case where the "notified entity" is a domain name that 
  resolves to multiple IP addresses, one of the resolved addresses MUST 
  be selected.  If one of those IP addresses is the IP address of the 
  Call Agent sending the request, that IP address SHOULD be selected 
  The NotifiedEntityList parameter can also be specified in an endpoint 
  configuration command, e.g.: 
     EPCF 1200 * MGCP 1.0 
  As indicated in section 2.2, it can also apply this to the gateway 
  virtual endpoint e.g.: 
     EPCF 1200 MGCP 1.0 
     RED/EL: * 
  As indicated in section 2.1, the NotifiedEntityList ("RED/NL") 
  parameter MAY be used with any command for which a NotifiedEntity 
  parameter is allowed.  However, the "RED/N" parameter SHOULD only be 
  used with the endpoint configuration command. 
  The "RED/N" parameter does not have a default value, and the auditing 
  behavior for auditing the "NotifiedEntity" is unchanged from that 
  specified in [2], regardless of how the "NotifiedEntity" was set 
  (i.e. there is no specific audit associated with the "RED/N" 
  parameter and hence the "RED/N" parameter cannot be audited). 
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2.4.  Reset Extension Parameter 
  Another EndpointConfiguration parameter ("RED/R"), allows the Call 
  Agent to reset one or more endpoints.  The ABNF syntax for the 
  parameter line is as follows: 
     "RED/R:" 0*WSP "reset" 
  This has the effect of re-setting and re-initializing the specified 
  endpoints (i.e. any connections on the endpoint will be deleted, and 
  the endpoint will be returned to its clean default state without any 
  active signals, etc.). 
     EPCF 1200 MGCP 1.0 
     RED/EL: ds/e1-3/[1-30] 
     RED/EL: ds/e1-5/[1-30] 
     RED/R: reset 
  In this case, the particular endpoints specified by "T" by the 
  EndpointMap parameter in the E1 spans ds/e1-3 and ds/e1-5 are reset. 
  The "RED/R" parameter MUST NOT be used with any command other than 
  the endpoint configuration parameter.  There is no default value for 
  the parameter and hence when omitted, it does not affect operation.  
  There is no specific audit behavior associated with this parameter, 
  i.e. it cannot be audited.   
2.5.  Return Codes 
  The following package specific return codes are defined for the "RED" 
     Code   Text                     Explanation  
     800    EndpointMap              Either the EndpointMap parameters  
            Out of Range             are outside the range specified by  
                                     the EndpointList parameter or the  
                                     EndpointList Parameter was not  
                                     included when an EndpointMap  
                                     parameter was included. 
     801    Incorrect Usage          Incorrect usage of parameters such  
            Of Parameters            as EndpointList parameter used  
                                     where the endpoint name was not 
                                     the virtual endpoint name  
                                     corresponding to the gateway. 
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3.0.  IANA Considerations 
  The MGCP package title "Redirect and Reset" with the name "RED" and 
  version number 0 should be registered with IANA as indicated in 
  Appendix C.1 in [2]. 
4.0.  Security Considerations 
  Section 5 of the base MGCP specification [2] discusses security 
  requirements for the base protocol, which apply equally to the 
  package defined in this document. Use of a security Protocol such as 
  IPsec (RFC 2401, RFC 2406) that provides per message authentication 
  and integrity services is required in order to ensure that requests 
  and responses are obtained from authenticated sources and that 
  messages have not been modified.  Without such services, gateways and 
  Call Agents are open to attacks. 
  For example, without such security services an attacker could 
  masquerade as a Call Agent and initiate a denial of service attack by 
  resetting endpoints that were involved in valid calls. Another attack 
  using the package described in this document could involve re-
  directing endpoints to itself so that it now acts as the Call Agent 
  for those endpoints. 
5.0.  Normative References 
  [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement  
      Levels", BCP 14, RFC 2119, March 1997. 
  [2] F.  Andreasen, B.  Foster "Media Gateway Control Protocol (MGCP)  
      Version 1.0", RFC 3435, January 2003 
Authors' Addresses 
  Flemming Andreasen 
  Cisco Systems 
  499 Thornall Street, 8th Floor 
  Edison, NJ 08837 
  Bill Foster 
  Cisco Systems 
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