Internet Engineering Task Force James M. Polk Internet Draft Cisco Systems Expiration: Aug 24th, 2003 File: draft-polk-sipping-mlpp-reqs-00.txt Multilevel Precedence and Preemption in the Session Initiation Protocol February 24th, 2003 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 proposes considerations and requirements for the extension of the Session Initiation Protocol (SIP) [1] to support an IP version of Multi-Level Precedence and Preemption functionality originally set forth in [2&3]. This document will be limited in scope to aspects having to do with the SIP Protocol. MLPP within the IETF utilizing other IETF Protocols is left to other documents, therefore is considered out of scope here. Polk Page 1 Internet Draft MLPP over IP in SIP Feb 24th, 2003 Table of Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Conventions used in this document . . . . . . . . . . . . . . . 3 2.0 Terms and Definitions . . . . . . . . . . . . . . . . . . . . . 4 3.0 MLPP Operational Functionality . . . . . . . . . . . . . . . . . 6 3.1 MLPP Precedence . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 Operational Behavior for Preemption . . . . . . . . . . . . . . 7 3.2.1 Modes of Preemption in CSN Systems . . . . . . . . . . . . . . . 7 3.3 Access Preemption Event . . . . . . . . . . . . . . . . . . . . 9 3.4 Network Preemption Event . . . . . . . . . . . . . . . . . . . . 10 4.0 MLPP over IP Basic Model . . . . . . . . . . . . . . . . . . . . 11 4.1 Components of the Basic Model . . . . . . . . . . . . . . . . . 12 5.0 SIP Multilevel Precedence and Preemption Requirements . . . . . 12 6.0 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 14 7.0 Security Considerations . . . . . . . . . . . . . . . . . . . . 15 9.0 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15 10.0 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 11.0 Author Information . . . . . . . . . . . . . . . . . . . . . . . 16 1.0 Introduction This document proposes considerations and requirements for the extension of the Session Initiation Protocol (SIP) [1]to support an IP version of Multi-Level Precedence and Preemption functionality originally set forth in [2&3]. This document will be limited in scope to aspects having to do with the SIP Protocol. MLPP within the IETF utilizing other IETF Protocols is left to other documents, therefore is considered out of scope here. MLPP was originally written to create ôa prioritized call handling serviceö in combination with ISDN supplementary services. MLPP has two very simple concepts for voice and video (Real-Time) communications: A) labeling or marking every call (at inception) with a Precedence level relative to other calls within a single administrative domain, or federation of domains; and B) during times of congestion at any point in the network, the point of congestion at the endpoint or internetworking device, having that device determine if preempting (seizing) the resources of any identifiable lower relative priority call(s) is required to properly set-up a newly signaled higher priority call This administrative control and network functionality exists today in several large deployments. It is based, or founded, in US Government Polk Page 2 Internet Draft MLPP over IP in SIP Feb 24th, 2003 network requirements. [2,3] is an augmentation service to ANSIÆs ISDN [8,9,10,11]. Several other non-US networks have been enabled with this MLPP functionality in the past decade. Most of these networks are looking to incorporate IP signaling and transport of their voice and video services and require the MLPP functionality during the transition and progression/evolution of their networks in times of government or military emergencies when congestion causes critical systems communications to falter. The applications currently run by these networks are voice and video services only. In the future, Instant Messaging and email are targets for this capability as well, but will not be further discussed within this document. This document will focus on the considerations and requirements on SIP Proxies, Gateways and User Agents, concentrating on what needs to be addressed to enable MLPP functionality. Considerations need to be met and realized in the user experience of the existing MLPP service. Because of the existing size of these networks (one network has several million end-stations), the migration of their communications over to an IP based system cannot occur quickly. With this in mind, many considerations should be kept in mind that this is not a brand new installation. Further, all new implementations with this functionality with IP endpoints will be primary line endpoints, and not in secondary configurations. Most of the requirements here have been taken from [2&3]. Any remaining details and concepts attained from documents came from the certification materials which all products must be tested against to achieve MLPP compliance and interoperability status in [4&5]. There are a few concepts mentioned here that were attained from interviewing users and testers of MLPP for guidance of how this MLPP-concept might be enhanced with the additional capabilities that IP and IP-based services brings to offer. This document will cover new terminology used within MLPP infrastructures. Also included will be an overview of the current decision process that exists within the MLPP enabled network. This will be followed by the SIP(PING) requirements for enabling this functionality in this working group. 1.1 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 [6]. Polk Page 3 Internet Draft MLPP over IP in SIP Feb 24th, 2003 2.0 Terms and Definitions The following is a list of definitions and conventions to used throughout this document. Note that some of the definitions are either MLPP *or* IP centric, and might not make sense to the other. Advice is taking these words in the context of the section of this document they are written in. Alternate Party Is another endstation which is configured for any call diversion if the Called device has an inbound Precedence inbound call while that Called User is actively on a call/session CSN Circuit Switched Network - public or private TDM Infrastructure; most often this will refer to the existing MLPP enabled closed network of within the same domain, and not the publicly available dial circuits Domain A network under one single administrative control entity, possibly non-adjacent geographically, meaning network islands interconnected by an intermediary (Service) Provider End Office Node EN û see EOS End Office Switch EOS û An MLPP capable PBX configured to only service that local community and its needs; it is internal network controlled; this unit connects all CPE equipment in that community Gateway Converts media provided in one type of network to the format required in another type of network; the gateway shall be capable of full duplex audio trans- lations GSTN Global or General Switched Telephone Network û world- wide circuit-switched public telephony network ISDN Integrated Services Digital Network Look ahead For Busy LFB û a feature of MLPP in which a phone can look ahead in the network to determine if a call it is about to place has available resources for call completion MLPP Multi-level Precedence and Preemption [2&3] û ANSI T1.619 and 619A specifications stipulating mechanisms for marking each voice communication with a Precedence level, and defining the requirement for the Preemption of existing lower Precedence sessions during congestion in favor of new higher Precedence Polk Page 4 Internet Draft MLPP over IP in SIP Feb 24th, 2003 session(s) MLPPoIP MLPP (functionality) over (an) IP network(s) Multifunction Switch MFS - A combination of a End Office Switch (EOS) and Tandem Switch (TS); having trunking and CPE connection capabilities within one, more economical unit Precedence The relative priority level assigned to each call by the caller at inception Precedence Call Any call that has a Precedence level higher than Routine Preempt Notification The audible notification sent to all endstations who have been preempted for any reason Preempted Any caller who has had their existing call cleared Or disconnected Preempting Call A call with a Precedence level higher than others on a specified interface at a time of congestion, including an end-station that is on a call Proxy Server SIP Server [1] that acts on behalf of other devices Registrar Server SIP Server [1] that serves as a Registration point principally for mobility Response Timer T-sub-K Is started when the network notifies the Called device of a inbound precedence call; acceptance must occur by the Called device; the timer is specified in [2] at from 4 û 30 seconds Response Timer T-sub-L Is started when an LFB information unit is sent into the network to establish an open path between the Calling endstation and the intended called end- station; the timer is expected in [2] as from 5 û 20 seconds SLA Service Level Agreement û Agreement between two adjacent networks on many aspects of how oneÆs traffic gets treated within the otherÆs network Tandem Switch TS - Only connects to EOSÆs; is the primary backbone of a circuit-switched MLPP Network User Agent UA defined in [1] as an application which can act both as a user agent client and user agent server Polk Page 5 Internet Draft MLPP over IP in SIP Feb 24th, 2003 User Agent Client UAC defined in [1] as a client application that initiates a SIP request User Agent Server UAS defined in [1] as a server application that replies to SIP requests. The response accepts, rejects or redirects the request. 3.0 MLPP Operational Functionality This section will provide the operational functionality of an MLPP infrastructure. The requirements section later in this document will be based on this section (and subsections) for its operational requirements in SIP(PING). The following from the core MLPP documents [2,3] must be referenced in detail, as well as the documents involving the actual testing of any component for certification of MLPP compliance [4,5,7]. The root specification [2] states that there are two conceptual parts to MLPP: Precedence and Preemption. 3.1 MLPP Precedence Precedence means Priority. It is the relative priority of a call to all other calls within that domain (or federation of domains if applicable) when traversing any interface, including an endstation. It is set or assigned by the calling party at the beginning of a call, on a per call basis. Once the precedence level is chosen by a caller, it cannot be changed for the duration of that call. The next call being independent of the first call, can be made at another authorized level, also chosen by the calling party. The table below from [2] specifies the precedence values as: Priority ISDN Text Level Sequence Sequence --- ---- -------- 1 "0000" = "Flash Override" (highest level) 2 "0001" = "Flash" 3 "0010" = "Immediate" 4 "0011" = "Priority" 5 "0100" = "Routine" (lowest level) "0101 û 1111" are unspecified The possible levels the call can be assigned, in CSN MLPP infrastructures, is bound to the allowable levels set on the switch (or EOS) for that circuit. Each line in this infrastructure is configured to only allow certain levels to be chosen by anyone accessing that phone. Someone with personal access to higher levels than that of the phone they're in front Polk Page 6 Internet Draft MLPP over IP in SIP Feb 24th, 2003 of, needs to go to a phone with access to those higher precedence levels in order to make a higher precedence call. Because the precedence level chosen for a (or any) call is used solely in the determination of which call or calls are preempted (should congestion occur at any point or interface this call traverses) as explained in the next section, the user of that phone cannot use a level above what they are authorized to gain access to. Since UAs aren't bound by any physical connection to a switch, this restraint no longer will exist. Thus, another means will be required by SIP to restrict the unauthorized use of higher precedence calls by those that are not allowed to signal these precedence values in their INVITE messages. An important background note, the determination of who is granted permission to make precedence calls (meaning any call with a precedence level higher than routine - the lowest level) is by job function in most MLPP networks, and not by who they are, or how long they've been with that organization. This is the case within the US "DSN" network. This means that if there is a job related rank to each person's employment, higher ranking employees don't necessarily dictate access to higher precedence call privileges, but in practice, this is generally close to alignment. 3.2 Operational Behavior for Preemption Preemption (in a CSN case) is the seizing of otherwise used resources of one or more calls in order to complete another call in a congestion situation. The nodes that determine preemption are EOSs or TNs in the CSN infrastructure. The decision is based on the precedence values assigned to each circuit with the trunk groups on those nodes. When a call is placed, the transiting node maintains state as to the precedence value of that call assigned to a inbound and outbound port on that node. When a new call is signaled (via SS7) into that CSN node, the node looks for available resources to route that call through. If the node determines that it has no more outbound (egress) resources available (for example on a T1 interface) for this new call, a comparison is performed of this new call's precedence value to that of all the other calls existing on that outbound interface. If this new call has a higher precedence value than any one of the other calls, one or more calls (in fact all that are necessary) are cleared to complete this new call. 3.2.1 Modes of Preemption in CSN Systems There are two modes of Preemption: preemption of the called device with another inbound higher precedence call (Access Preemption Event), and preemption within the network not involving either party of the preempted call at all, but at a point of congestion (Network Preemption Event) Polk Page 7 Internet Draft MLPP over IP in SIP Feb 24th, 2003 between CSN nodes. MLPP is mandated in [2] as having call handling influence with a single domain based implementation only. The precedence value set in one MLPP Domain SHOULD NOT cross domain boundaries into another domain and have any preferential treatment applied to that call. The MLPP Domain-Identifier [2] was included in the ISDN and SS7 for this reason. MLPP compliant Tandems (TNÆs) are to look at the Precedence level set within the call set-up signaling as well as the domain identifier within that same call set-up to ensure validity within that network. This prevented leaking of one domainÆs call behavior into anotherÆs. In other words, no preemption of any resources shall occur within a domain as a result of a call into that domain from outside the domain, even if both domains are MLPP compliant networks. Here are the three preemption conditions: o A distinctive preemption notification (tone) shall be introduced into any connection(s) that is to be cleared due to either a Access or network Preemption event; (this is not a SIP protocol issue, but an implementation one, yet worth noting here) o The party on the inbound end of a preempting call MUST acknowledge that inbound call before connection to that call; o Upon determination of no available resources and calls existing on an interface of lower precedence, the lowest level call(s) MUST be cleared in order to complete the higher precedence call; A call can be preempted at any time after the precedence level has been determined to be lower than the existing call and before call clearing has begun. However, no preemption of any resources shall occur within a domain as a result of a call into that domain from another domain, even if both domains are MLPP compliant networks. A clarification must be stated: higher precedence provides preferential call handling throughout an MLPP domain, regardless of how much higher a call is relative to others. For example, a "Routine" call is equally lower in precedence level than "Priority", "Immediate", "Flash" and "Flash Override" as far as preferential treatment in the network is concern. Having stated that, currently there is no recognized/Standardized method or mechanism in the case of which one of several lower precedence calls gets disconnected, where such a condition exists. Only such that the lowest level call are the first to get disconnected. But if there are more than one such lower level call existing at a congested interface and a higher precedence call comes through, determining which lowest level call gets preempted first is left to the implementer. An example, if there is a saturated interface with 6 equal bandwidth connections existing, 1 "Flash" call, 1 "Immediate" and 4 "Routine" calls, Polk Page 8 Internet Draft MLPP over IP in SIP Feb 24th, 2003 when another "Flash" level attempts to gain resources out that interface; if that new "Flash" call is the same bandwidth as the others (all are equal in this situation), then a "Routine" is preempted, being the lowest level on that interface. Which one is up to that vendor's product algorithm. At some point, the IETF might suggest a common mechanism for this choice for consistency. MLPP [2] also established the Alternative Party, and the Non-Preemptable Resources options. The Alternative Party option is pre-configured to a secondary phone to ring in the times where the original phone is being used. This can prevent a preemption event, even when that new inbound MLPP call is of higher precedence. The Alternative Party must answer before the Timer T sub K expires. Additionally, a party of a phone can preset their phone with the option of æNon-Preemptable ResourcesÆ. This prevents Access Preemption events, but does not prevent Network Preemption events. The Alternative Party redirect MUST be to a valid domain address and is RECOMMENDED to a location which always answers the phone, such as a operator or ACD pool of personnel. A limit in [12] set the maximum number of call diversions to 5. An additional benefit to the Timer T sub K is that it limits the time of these diversions when it expires for a call. The example below give this mechanism more clarity. 3.3 Access Preemption Event The following is a CSN example from [2] of the MLPP mandated process for how Access-based Preemption events MUST occur, similar to a flow chart: Scenario #1: Caller A and D are on an MLPP call when Caller C calls D IP Phone A \ \ EOS =====> IP Phone D / / IP Phone C Figure 1. Call A-D exists when C calls D If there is an existing call between two parties (A & D), and a third party (C) calls into D (provided there is no congestion between C & D), D (at the EOS) first checks the Precedence of this new inbound call. If the Precedence value is equal to or less than that of the existing call between D & A, then C either is returned a Disconnect (user busy), or is diverted to an alternate party (another phone) if there is one specified; C is Disconnect (Precedence Call Blocked indication) if one isn't specified. Polk Page 9 Internet Draft MLPP over IP in SIP Feb 24th, 2003 If the MLPP call from C has a greater Precedence value than the A to D call, then a determination is made at D (at the EOS) whether D is Preemptable. If D is not Preemptable, then an alternate party is looked for. If there is identified, the call is diverted. If it is not, C is returned a Disconnect (Not Equipped for Preemption). If D is Preemptable, the user and device of D is notified. So is the Device A. The device at D is offered with Call Setup information, while also starting the T sub K timer (defined as being between 4-30 seconds). A Disconnect is sent to A now, placing it in the Idle state for at least the moment. The device at D is waiting for the user at D to determine 1 of 3 possible paths to take: Path #1 is when nothing occurs until the T sub K timer expires. This results in a determination if an alternate party was specified by D. If there is, C is then connected to this alternate party. [12] stipulates a maximum number of 5 call diversions can occur. If not, C's call is normally set-up into D. Path #2 is if there is a request from C to Clear the call. This results in A, C, and D being idle now. Path #3 is when D acknowledges the inbound Preemption by C, thereby accepting the call from C. This stops the T sub K timer. The Call is set-up between C to D. 3.4 Network Preemption Event The following is a CSN example from [2] of the MLPP mandated process for how Network-based Preemption events MUST occur, similar to a flow chart: Scenario #2: Caller A and B are on an MLPP call when Caller C initiates a higher precedence call to Caller D (than the existing one between A and B) IP Phone A IP Phone B \ / EOS 1 EOS 2 \ / TS 1 <=========> TS 2 / \ EOS 3 EOS 4 / \ IP Phone C IP Phone D Figure 2. Call A-B exists when C calls D If there is an existing MLPP call between two parties (A & B), and a new MLPP call (C-D) has a higher Precedence level than the A-B call (shown between TSÆs 1 and 2 in Figure 2 above), the network first checks to see Polk Page 10 Internet Draft MLPP over IP in SIP Feb 24th, 2003 if there are available resources for that new call between the two new parties (C & D); if there is, everything works as if both calls were on the same Precedence level with no congestion. But if there is congestion at any common interface between the calls A-B this new call C-D, there is now a search at that interface for Preemptable resources (any call with a lower Precedence level than this new C-D call attempt). If there is not, a determination is made whether the Call from C is a Precedence call. If the call from C is not, C is returned from the network a "Disconnect: Network Resources Unavailable" indication. If the call from C is a Precedence Call, C is returned a "Disconnect: Precedence Call Blocked" indication. The call remains between A and B through both cases. If, there are preemptable resources available at the shared interface for calls A-B and C-D (with C-D having a higher Precedence level than A-B), A is notified of Preemption (without knowing where from). At the same time B is notified of Preemption (also without knowing where from). The network now releases (disconnects, clears) the amount of resources in order to have the C-D call be set-up normally. Under this Network Preemption scenario within MLPP, the amount of resources necessary for this call C-D, even if it requires more than one other call to be preempted, MUST be made to satisfy the higher precedence call completion. All necessary lower Precedence level resources MUST be cleared for any higher Precedence Call. 4.0 MLPP over IP Basic Model Figure 3 (below) is a basic model of an MLPP over IP (MLPPoIP) domain connected to both an MLPP CSN domain where the above requirements MUST be extended throughout, and to the public GSTN where the above requirements cease at the edge of the MLPPoIP network at GW#1. Additionally, Phone A will start an MLPPoIP aware call at GW#1, likely with a minimum precedence value, just as is deployed today within existing MLPP networks where the entrance to an MLPP network is precedence marked "routine", with no possibility of upgrading or requesting higher precedence values for that call. GW#1--GSTN Circuit network -- Phone / A UA#1 ----- MLPPoIP Domain (or federation of domains) / | \ Proxy UA#2 GW#2-- MLPP CSN --- Phone Server B Figure 3. Generic MLPP-MLPPoIP-GSTN Interworking model Polk Page 11 Internet Draft MLPP over IP in SIP Feb 24th, 2003 4.1 Components of the Basic Model Figure 1 shows several components in the diagram. The generic scope of each is as follows: UA's 1 & 2 SIP user agents; Phone A MLPP-based phone that exists within and adheres to the MLPP specifications as written in [2&3] and those connected directly to EOSÆs; Phone B TDM-based phone which could be one from a corporate network, private network or residential Gateway#1 Seamless translator between the GSTN communications methods and the MLPPoIP domain Gateway#2 Seamless translator between the MLPP communications methods specified in [2&3] and the MLPPoIP domain Proxy Server SIP-based Server serving the functions defined in [1] There is not mention of the details within each network-type (MLPPoIP or GSTN) for the purposes of keeping this explanation a simple a possible; the burden should mostly fall on the Gateways to seamlessly translate the communications from one type of network to the adjacent type. 5.0 SIP Multilevel Precedence and Preemption Requirements The previous section explained the operational conditions needed in an MLPP circuit-switched infrastructure. The following are the requirements SIP for the interoperating with existing MLPP CSN infrastructures, as well as on SIP for operating within a IP based domain or federation of domains with MLPP functionality: REQ# - There MUST be a means by which the user of a UAC can select a precedence level for a session. This is not to be a user priority, but a priority that will influence behaviors of User Agent and gateway resources [2] specifies the precedence values as: Priority ISDN Text Level Sequence Sequence --- ---- -------- 1 "0000" = "Flash Override" (highest level) 2 "0001" = "Flash" 3 "0010" = "Immediate" Polk Page 12 Internet Draft MLPP over IP in SIP Feb 24th, 2003 4 "0011" = "Priority" 5 "0100" = "Routine" (lowest level) "0101 û 1111" are unspecified However SIP or SIPPING chooses to actually solve this binding between MLPP in ISDN and SIP message (Headers or something else), at least 5 distinct and relative precedence levels MUST be maintained to ensure interoperability. Further, if more relative levels are chosen within SIP, a binding of these 5 ISDN levels to the higher precedence or priority levels MUST be maintained throughout a domain (or federation of domains) to ensure interoperability. REQ#1 - This precedence choice by the UAC SHOULD be able to influence Proxy Server behavior. The choice of whether this function is utilized should be a matter of local policy. REQ#2 - The precedence levels available to the user of a SIP entity should be limited to only those levels granted that user within that domain (or federation of domains). Each MLPP over IP infrastructure SHOULD have an mechanism to authenticate and then authorize the use of precedence levels other than the "routine" (or default "normal" level for everyday voice communications). This might be mandatory in some domains, but that assignment is policy, and should be left for local administration (and not part of this document). REQ#3 - Once a precedence level has been chosen and the SIP Request transmitted, the precedence level (however signified within the message) MUST be maintain for the duration of that session. The UAS cannot reset this precedence level within the SIP response. REQ#4 - User migration from a CSN infrastructure to an IP infrastructure should not impact user behavior with reduced capabilities. SIP GWs MUST maintain the precedence level chosen that originate within a MLPP enabled MLPP CSN network. This configuration will be from a CSN to IP transition, and the users shouldn't expect a loss in preferential treatment. REQ#5 - SIP GWs SHOULD set all there GSTN side received calls to the minimum precedence setting, for that is no way of authenticating a GSTN call is from a user authorized for higher precedence levels REQ#6 - Any session SHOULD be considered independent to the session initiated before it and the one after it from a precedence setting point of view. REQ#7 - There MUST be some means of identifying each domain within the SIP message. Polk Page 13 Internet Draft MLPP over IP in SIP Feb 24th, 2003 This is to ensure those SIP entities that are enabled for preferential treatment based on the precedence level present within the SIP message have a means of easily differentiating those requests that are from their domain and those that are not. REQ#8 - There SHOULD be a means in which a UAS can authenticate the included precedence level within a SIP Request. This should not burden the UAS to authenticate each and every UAC possible of sending SIP Requests. This is specifically to address Access Preemption Events in which local policy could mandate the preemption of an existing session in lieu of a higher precedence level in this new SIP Request REQ#9 - The User of a UAC SHOULD be able to remain anonymous, therefore there MUST be a means by which an anonymous SIP Request can be authenticated by the UAS receiving the request. This requirement should also apply to Proxies. REQ#10 - There SHOULD be a means by which a UAC can use there precedence level to signal QOS, or that the UAC can react to an error which was sent by a UAS requiring QOS for that session, with the indication within that error of which QOS (perhaps a level within itself) to use. REQ#11 - The SIP and SIPPING WGs should investigate how SIP can help in providing Network Preemption Events, but this is not a direct requirement here. REQ#12 - All SIP entities that do not recognize the means in which a SIP message indicates precedence, or which domain the precedence level is from, MUST ignore the means but not fail the SIP Request based solely on that criteria. This applies to SIP UAs, SIP GWs and SIP servers. REQ#13 - There SHOULD be a mechanism in which any MLPP over IP domain can determine the functional and configuration capabilities for Registering UAs to ensure each can behave as the domain MIGHT mandate. REQ#14 - An SLA SHOULD solve all interoperability decisions regarding a federation of domains internetworking. 6.0 IANA Considerations There are no IANA considerations requested with this document Polk Page 14 Internet Draft MLPP over IP in SIP Feb 24th, 2003 7.0 Security Considerations This topic is chalk full of security concerns. However, this document is not requesting capabilities that are to be implemented on the open Internet. The intention for SIP to extend itself to meet these requirements is for interoperation and transition with existing closed networks that are MLPP enabled; which are few, yet very large (in the millions of endpoints). The current safeguard for MLPP signaling leaking into other networks is the domain identifier. Further, some requirements stated here call for the authentication abilities of the receiving UAS (or Proxy) of a SIP message with a precedence level indication to the UAC. If this authentication, or more accurately authenticated authorization doesnÆt pass, the precedence level request should be ignored. Existing MLPP enabled domains will likely fail the session for many reasons, this one being only one of them. User authentication to their networks will be mandated, and policed heavily. Properly build infrastructures with these capabilities should not influence the Internet or stray SIP Proxies that process non-MLPP over IP transactions. Certain domains will likely mandate that all UAs conform to this functionality in order to communicate, with appropriate challenges configured at each SIP entity to prevent unwanted or disallowed SIP communications. 8.0 Acknowledgements Your name here 9.0 References [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "Session Initiation Protocol", RFC 3261, June 2002 [2] ANSI specification ANSI T1.619-1992. [3] ANSI specification ANSI T1.619A-1994. [4] "Generic Switching Center Requirements" (GSCR), JIEO Technical Report 8249, March 1997 [5] Defense Switched Network "Generic Switching Test Plan" (GSTP), June 1999 [6] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Polk Page 15 Internet Draft MLPP over IP in SIP Feb 24th, 2003 [7] ITU-T Recommendation Q.735.3 (1993), "Description for Community of Interest Supplementary Services using SS7 - Multilevel precedence and preemption" [8] ANSI T1.604-1990 "Integrated Services Digital Network (ISDN)", [9] T1.113-1988 "Signaling System Number 7 (SS7) û ISDN User Part" [10] ANSI T1.604-1990 "ISDN û Layer 3 Signaling Specification for Circuit-Switched Bearer service for Digital Subscriber System Number 1 (DSS1)" [11] ANSI T1.610-1990 "DSS1 û Generic Procedures for the Control of ISDN Supplementary Services" [12] ITU-T Recommendation I.255.3 (1990), "Multilevel precedence and preemption service (MLPP)". 10.0 Author Information James M. Polk Cisco Systems 2200 East President George Bush Turnpike Richardson, Texas 75082 USA jmpolk@cisco.com "Copyright (C) The Internet Society (February 23rd, 2001). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS Polk Page 16 Internet Draft MLPP over IP in SIP Feb 24th, 2003 IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." The Expiration date for this Internet Draft is: August 24th, 2003 Polk Page 17