Internet Engineering Task Force Mike Pierce Internet Draft Artel draft-pierce-ieprep-assured-service-req-01.txt Don Choi June 23, 2003 DISA Expires December 2003 Requirements for Assured Service Capabilities in Voice over IP draft-pierce-ieprep-assured-service-req-01.txt Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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 To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. Copyright Copyright (C) Internet Society 2003. All rights reserved. Reproduction or translation of the complete document, but not of extracts, including this notice, is freely permitted. Abstract Assured Service refers to the set of capabilities used to ensure that critical communications are setup and remain connected. This memo describes the requirements for such capabilities in support of specific networks such as those used by government agencies, but they could also be applied in commercial environments. Table of Contents 0. Changes............................................................2 1. Introduction.......................................................3 2. Background.........................................................4 3. High Level Requirements............................................5 Mike Pierce Expires December 2003 [Page 1] Internet Draft Requirements for Assured Service June 23, 2003 4. Functional Requirements............................................5 4.1. Precedence Level Marking.......................................6 4.2. Authentication/Authorization...................................6 4.3. Preferential Treatment.........................................6 4.4. Diversion if Not Answered......................................7 4.5. Notifications to Preempted Party...............................7 4.6. Acknowledge by Preempted Party.................................7 4.7. Protection of Signaling/Routing Information from Disclosure....7 4.8. Accounting.....................................................8 4.9. Call Control Signaling Precedence..............................8 4.10. Interworking...................................................8 5. Current Situation..................................................8 6. Possible Protocol Approaches.......................................9 6.1. Precedence Level Marking.......................................9 6.2. Authentication/Authorization..................................10 6.2.1. Architecture...............................................10 6.2.2. Authentication Procedures..................................10 6.2.3. Authorization Procedures...................................11 6.3. Preferential Treatment........................................11 6.4. Diversion if Not Answered.....................................12 6.5. Notification to Preempted Party...............................12 6.6. Acknowledge by Preempted Party................................12 6.7. Protection of Signaling Information from Disclosure...........12 6.8. Accounting....................................................12 6.9. Call Control Signaling Precedence.............................13 6.10. Interworking..................................................13 7. Security Considerations...........................................14 7.1. Authentication/authorization of User Access...................14 7.2. Security of Signaling Information.............................14 7.3. Security of Routing Data......................................15 8. IANA Considerations...............................................15 9. References........................................................15 10. Authors' Addresses..............................................17 A. Overview of existing priority mechanisms...........................17 A.1 IPv4..........................................................17 A.2 DiffServ......................................................17 A.3 IntServ/RSVP..................................................18 A.4 MPLS..........................................................18 A.5 SIP...........................................................18 0. Changes This draft was originally submitted under SIPPING. This revision is being resubmitted to IEPREP in order to ensure that the Assured Service requirements are considered along with those of the related IEPS discussions (SIPPING) -00 Original draft (SIPPING) -01 Indicated informative material which would not be a part of final. Moved some to Annex. Mike Pierce Expires December 2003 [Page 2] Internet Draft Requirements for Assured Service June 23, 2003 (SIPPING) -02 Removed material to draft-pierce-sipping-pref-treat- examples-00 and draft-pierce-sipping-assured-service-arch-00. Added requirement to maintain records of use of service. (IEPREP) -00 . Updated references. . Added additional requirements related to preferential treatment in 4.3. . Added requirement in 4.8 for accounting records. . Added requirement in 4.9 that preferential treatment must be applied to call control signaling as well as to voice packets. . Added requirement in 4.10 for interworking between Assured Service and other priority schemes (e.g., IEPS) (IEPREP) -01 - Updated references - Moved informative material to Annex - Clarified requirement statements 1. Introduction Throughout many decades of evolution of the telephony network and its supporting protocols, there has been a need to provide special services to a limited subset of the users and calls within a network or domain in order to ensure completion of important calls. Examples of this need have been in support of emergency traffic for natural disasters, network restoration traffic, and high priority traffic in a private networks. Provision of the required capabilities with the signaling protocols and within the switching systems has been defined in a number of national and international standards, most notably a service referred to as Multi-Level Precedence and Preemption as defined in an American National Standard [T1.619] in the US and in corresponding ITU-T Recommendations [I.255.3, Q.735.3, and Q.955.3]. In addition, a service called High Probability of Completion (HPC) was defined in the US [T1.631] and, most recently, two ITU-T Recommendations define the requirements for the International Emergency Preference Scheme (IEPS) [E.106] and the International Preference Scheme for Multimedia Service in Support of Disaster Relief Operations [F.706]. Other drafts submitted to the IETF have addressed aspects of IEPS. Among these are the framework for IEPS for telephony over IP [Carlberg]. MLPP was the solution to providing Assured Service capabilities within the circuit switched environment. It is essential that equivalent Assured Service capabilities are defined and implemented for the packet-based, connectionless environment of the Internet, and specifically SIP. Without these capabilities, SIP can not be used for those applications which require such capabilities, and is less than optimal for many other uses. Mike Pierce Expires December 2003 [Page 3] Internet Draft Requirements for Assured Service June 23, 2003 This memo builds on these references and identifies the specific requirements for Assured Service capabilities in support of these specific types of environments. The term "Assured Service" is used to refer to the required capabilities, rather than the previous term of "MLPP" or the related but different IEPS, since the envisioned set of capabilities and protocols to achieve them are not expected to be exactly the same as those other services. Although these requirements are derived from previous government applications, many of the same requirements and capabilities may be applied for non-government networks, for example, in support of commercial network restoration efforts. A presentation in the TEWG during the August 2001 meeting demonstrated real-life situations from the past in which total network failures required extensive efforts, presumably including communication via other unaffected networks, to bring the affected network back on line. If one considered a situation in which the very network which had failed was needed to carry the network management traffic required to get it back on line, it would be hard to imagine how it could ever be brought back up in the face of overwhelming customer attempts. Capabilities would be required to give priority to the network management traffic, even to the extent of blocking all non-emergency traffic for a period of time. 2. Background In the circuit switched environment, specific circuits or channels were used for each call. These were typically 64 kbit/s channels which were normally part of a Time Division Multiplexed (TDM) transmission structure. These transmission channels were almost always interconnected and switched by Time Division Switching technology (often referred to as "TDM switching"). Later developments used packet/cell based transport instead of dedicated 64 kbit/s channels, often coupled with packet/cell-based switching, however, the effect was the same. There was still a dedicated transport capacity assigned for each call. Assured Service in the circuit switched environment may be provided by one or more of the following techniques. Note that the capabilities included within IEPS [E.106] are included here for reference but not dealt with further in this memo. . Giving priority to return of dial tone (IEPS) . Marking of signaling messages for better handling, for example, being last to be dropped in case of congestion in the signaling network (HPC) . Extra routing possibilities for higher priority calls (IEPS) - Queuing for network resources (HPC) Mike Pierce Expires December 2003 [Page 4] Internet Draft Requirements for Assured Service June 23, 2003 . Exemption from restrictive management controls (IEPS) such as hard-to-reach codes and code gapping. . Reservation of specific facilities (trunks) for higher priority traffic (IEPS) . Higher priority calls may preempt existing lower priority calls, causing the network to release the lower priority call to free up resources for immediate reuse by the higher priority call (MLPP) Identification of traffic authorized to use one or more of these techniques may be via the following methods: . Calls placed from physical lines or devices authorized for its use . Calls placed to specific telephone numbers or blocks of numbers . Entry of a special ID code and PIN from any telephone device 3. High Level Requirements While the existing requirements and capabilities have been developed with the circuit switched environment in mind, many are directly applicable to the packet environment and specifically the Voice over IP application being defined using SIP. Some of the capabilities need to be adapted or modified for application in the packet mode environment. In addition, there will likely be new techniques which can be defined specifically for the SIP case. At a high level, the Assured Service requirements can be stated as the need to ensure that mission critical voice-mode calls get set up and remain connected. (While this draft focuses on Voice over IP, there should be a consideration of the impact/solutions for other media flows which carry mission critical communication, for example, video and instant messaging. Most of the functional requirements can be equally applied to these other media.) 4. Functional Requirements The functional requirements for Assured Service being detailed here are specifically those needed to support the US government requirements. This memo concentrates on those portions mentioned in Section 2 which are derived from the requirements for MLPP as defined in the American National Standard [T1.619]. The basic requirements can be defined as follows; Mike Pierce Expires December 2003 [Page 5] Internet Draft Requirements for Assured Service June 23, 2003 4.1. Precedence Level Marking It MUST be possible to assign each authorized user the highest precedence level they are entitled to use. It MUST be possible for the originator of a call to select and signal one of five precedence levels for the call, with the call defaulting to the lowest level if none is specified. It MUST be possible to carry this call associated precedence level though the IP network. It MUST be possible to deliver the originally signaled precedence level to the called party. 4.2. Authentication/Authorization It MUST be possible to verify that the calling party is authorized to use the Assured Service and the requested precedence level value and to take the appropriate action if the calling party attempts to use a higher level. The preferred action is to reject the call, and send an indication of the reason to the caller. 4.3. Preferential Treatment It MUST be possible to provide preferential treatment to higher precedence calls in relation to lower precedence calls. Examples of preferential treatments are: . reservation of network resources for precedence calls . usage of higher Call Acceptance limits for higher precedence calls . preferential queuing of signaling messages based on precedence level . preferential queuing of user data packets based on precedence level . discarding of packets of lower precedence call . preemption of one or more existing calls of lower precedence level . preemption of some of the resources being used by a call of lower precedence level . preemption of the reservation of resources being held for other traffic The provision of preferential treatment MUST be in place before the need to use it occurs. That is, initiation of the appropriate measures MUST NOT require manual intervention or configuration of network entities, for example, establishment of dedicated bandwidth for high priority traffic. Further, application of preferential treatment MUST NOT require a significant time delay, even if such procedures are automatic. A "significant time delay" is considered Mike Pierce Expires December 2003 [Page 6] Internet Draft Requirements for Assured Service June 23, 2003 to be any delay noticeable to the calling priority party, for example, more than a couple of seconds. Preferential treatment SHOULD NOT be provided through any scheme of dedicated or pre- reserved bandwidth or resources. In those cases in which such dedicated bandwidth or resources are used, when such dedicated or pre-reserved bandwidth or resources have been consumed by the high priority traffic, further traffic of that same high priority MUST NOT be provided worse treatment than any of the lower priority levels. Possible methods of providing Preferential Treatment using the provisions of this memo, as well as other existing IETF protocols, are described in [Pierce1]. 4.4. Diversion if Not Answered If a precedence call (one higher that the lowest level) does not answer within a designated time or the called party is busy with a call of equal or higher precedence such that an indication of the new call can not be given to the intended called party, the call MUST be diverted to a predetermined alternate party. In general, this SHOULD operate similar to a normal "Call Forwarding on No Answer" service. 4.5. Notifications to Preempted Party All preempted parties MUST be provided with a distinct notification informing them that their call has been preempted. 4.6. Acknowledge by Preempted Party When an existing call is preempted for delivery of a higher precedence call to the same party, after the party is notified that a new call is being presented, the party MUST acknowledge the preemption before the new call is connected. That is, there MUST be a positive acknowledgement before any audio information is transferred in either direction. 4.7. Protection of Signaling/Routing Information from Disclosure Although protection is not actually an integral part of the Assured Service functionality, it is specifically identified here since this capability is generally required in those networks which are assumed to be the primary users of Assured Service. Sensitive information MUST NOT be made available to non-secure portions of the network or to any non-secure network through which the traffic passes. It MUST NOT be accessible by users connected to the network. This non-disclosure requirement especially applies to information which is used to control link state routing protocols based on knowledge of the current traffic load at each precedence level on each route or through each router. Mike Pierce Expires December 2003 [Page 7] Internet Draft Requirements for Assured Service June 23, 2003 Further, the precedence information regarding each call (as well as the other information such as calling/called party identity) SHOULD be protected from disclosure to the greatest extent possible. 4.8. Accounting Proper administration of the Assured Service capability requires that use of the service can be reviewed after the fact for potential abuse. Therefore, it MUST be possible for the appropriate records to be kept of calls made, including the calling and called parties' identity, time of the call, and the precedence level used. This is similar to the requirements for Call Detail Recording (CDR) for billing purposes for other services in a commercial environment. 4.9. Call Control Signaling Precedence It MUST be possible to apply preferential treatment to the call control signaling, since it competes for the same transport resources as the voice packets. It is essential that: . the call control signaling does not adversely affect the voice (e.g., by introducing excessive packet delay variation due to extremely long messages). . the voice traffic does not significantly delay important call control signaling (e.g., by preventing release messages from getting through). 4.10. Interworking Assured Service calls MUST interwork with other priority schemes which are being provided within the same network, such as the one defined for IEPS [Carlberg]. This includes the following two cases: - both types of traffic may exist in a single network, for example, an IEPS call may be originated from within a network which also supports "Assured Service" calls. Procedures to determine the relative priority and the resulting preferential treatment are required. - a network which provides "Assured Service" needs to support interworking of calls to and from a network which provides another scheme such as IEPS as well as another network which provides "Assured Service". Mapping between the priority values must be supported. 5. Current Situation Annex A provides an informative overview of existing mechanisms within IETF defined protocols for providing various types of priority. Mike Pierce Expires December 2003 [Page 8] Internet Draft Requirements for Assured Service June 23, 2003 6. Possible Protocol Approaches The following identify possible approaches to meeting the requirements stated above. This section is included in the draft to stimulate discussion on ways of meeting the requirements, but is not expected to be included in the final version when it is advanced toward RFC status. 6.1. Precedence Level Marking The approaches to be used for precedence level marking are different for each of the following cases: A. Individual call setup: There needs to be a definition of a field to be carried in SIP which identifies the precedence levels of 0-4 for the call (session) setup. Currently, MLPP uses five values which have specific meanings as currently defined in applicable standard [T1.619, I.225.3]) and the definition of the field in SIP may reflect these meanings. However, it is preferable to provide easy support for other network applications which utilize a different number of levels or different meanings. The specification may allow more than 5 levels. There is no need for the 65k levels defined in [RFC2751] nor is there currently a requirement to carry separate preemption and defending priorities [RFC2751] or separate setup and holding priorities [RFC3212, RFC3209]. The proposed Resource Priority Header [Resource] is expected to satisfy this requirement. B. Packet forwarding: To support preferential treatment on the packet transfer level, the current lack of any priority mechanism within the single Expedited Forwarding class of DiffServ will need additional capabilities to provide the required functionality. Just as Assured Forwarding includes multiple drop precedences for each class, there should be multiple drop precedences for EF, which is intended for voice. In fact, voice transport is more tolerable to dropped packets than many of the intended uses of AF classes. (It should be emphasized again that such multiple "drop precedence" levels for EF would not provide an actual priority forwarding mechanisms per packet, e.g., priority queuing of some packets ahead of other within that EF class, just as there is no such capability included within the AF PHB definition.) In order to provide the required preferential treatments for the five call precedence levels, it is required to provide five corresponding drop precedence levels for the voice packet handling. The proposed MLEF PHB [Silverman] provides this capability. Mike Pierce Expires December 2003 [Page 9] Internet Draft Requirements for Assured Service June 23, 2003 C. Trunk group establishment: For MPLS, RFC 2702 defines the idea of a "traffic trunk" for which a priority may be signaled by the label distribution protocol in order to establish telephony "trunk groups". If LDP is used for label distribution, the priority defined in [RFC3212] should be used. If RSVP is used for label distribution, the priority defined in [RFC3209] should be used. It should be noted that the traditional definition of a "trunk group" does not include the notion of a "priority" associated with a trunk group. The priority is only associated with individual calls placed on that trunk group. It is possible that the routing logic could reserve a trunk group for higher priority traffic, but this is also not the normal application, since it wastes facilities during periods when very little high priority traffic exists and it can not support the heavier load of high priority traffic when conditions cause such a high volume. 6.2. Authentication/Authorization This draft uses the following definitions from draft-ietf-aaa- transport-12 [Aboda]: . Authentication: The act of verifying a claimed identity, in the form of a pre-existing label from a mutually known name space, as the originator of a message (message authentication) or as the end-point of a channel (entity authentication). . Authorization: The act of determining if a particular right, such as access to some resource, can be granted to the presenter of a particular credential. 6.2.1. Architecture In many other cases besides call setup for Assured Service it is also necessary to perform authentication and authorization. Appropriate security mechanisms have already been defined which may be used. Refer to [pierce2] for a discussion of the architecture required to support the authentication/authorization requirements in a network providing the Assured Service capability. 6.2.2. Authentication Procedures It is essential that a framework for security for SIP be established that allows a security association to be established between a user's terminal and their dedicated SIP proxy at the time of an initial registration. This initial registration, which includes authentication, may require an extensive number of messages and interactions with numerous network elements, including a Policy Mike Pierce Expires December 2003 [Page 10] Internet Draft Requirements for Assured Service June 23, 2003 Server, and may require a rather large time as a password is verified. This registration and authentication would normally be done when a terminal is turned on, activated, or places the first call. It is not performed for each call. This reduces the need to apply preferential treatment procedures to the authentication process. For the purpose of Assured Service provision, as with other SIP- based services, it is expected that Authentication may be performed based on the entry of an ID and password or the use of terminal resident biometrics (e.g., iris scan) so that permission to use the services can be associated with an individual, not a device. Once registration is done, this permission is then associated with the device. 6.2.3. Authorization Procedures The procedures for authorization per call MUST consist only of added fields/information within the normal messages used for basic call setup as defined for SIP [RFC3261]. It MUST NOT require additional messages to be added to the call setup sequence. 6.3. Preferential Treatment The preferential treatments would not be standardized unless they require signaling between network elements. Currently, most treatments envisioned are local matters within a proxy or router. Consideration of preferential treatments depends on the case: A. Per call: Preemption of existing calls, if done, would require coordination between network elements, and therefore protocol standards, especially if distinct actions are expected to reserve the preempted resources for setup of the higher precedence call. It is not expected that network initiated preemption of calls (sessions) within the IP environment will be necessary. Instead, sufficient preferential treatment can be provided by applying higher call admission control limits and lower drop precedence procedures to higher precedence calls. Examples of these procedures are shown in [Pierce1]. B. Packet Level: Current capabilities of DiffServ, with additional code points for drop precedences within an EF-type class, will provide the necessary preferential treatments regarding voice packet transfer, including indications of discard priority. It will also be necessary to define new capabilities to provide the necessary preferential treatment for call control signaling. C. MPLS/RSVP Paths: Mike Pierce Expires December 2003 [Page 11] Internet Draft Requirements for Assured Service June 23, 2003 There should be no need for preemption of MPLS/RSVP established traffic trunks (trunk groups) as described in [RFC2702] and [RFC2205]. The required capability should be provided by mechanisms to reduce the traffic engineering limits placed on lower priority trunk groups (even by reducing to zero) to allow the capacity to be used for the establishment of higher priority calls in other traffic engineered traffic trunks. 6.4. Diversion if Not Answered It is expected that Diversion would be based on procedures that are developed for a Call Forwarding on No Answer type service. However, it MUST NOT be dependent on a timing performed by the original calling or called parties' devices. It MUST be the function of a proxy serving the called party as shown in the proposed Service Examples [Johnston]. 6.5. Notification to Preempted Party Notification to the preempted party should follow whatever is done for notifications for any network-initiated release. Since it is expected that actual call preemption will only be needed in the circuit mode environment, the gateway between it and the IP environment should deal with such preemption by application of the required notification (in-band) to party on the IP side. 6.6. Acknowledge by Preempted Party Acknowledge by the preempted party (before connection of a new call) should follow the same general procedures as used for normal call presentation, that is, the new call must be acknowledged (answered) before any audio is transferred in either direction between end users. (Note that this does not refer to the transfer of "media" between the terminals, only the transfer of actual audio between the persons using the terminals.) 6.7. Protection of Signaling Information from Disclosure See Section 7. 6.8. Accounting This draft uses the following definition from draft-ietf-aaa- transport-12 [Aboda]: Accounting: The act of collecting information on resource usage for the purpose of trend analysis, auditing, billing, or cost allocation. Call detail records (CDR) can be maintained by the proxy, since it knows which users are authorized to place Assured Service calls and knows when they do. Since not actually done to support billing functions, it is not expected that a record of call duration is required. Mike Pierce Expires December 2003 [Page 12] Internet Draft Requirements for Assured Service June 23, 2003 6.9. Call Control Signaling Precedence Adequate precedence (and preferential treatment) can be provided to call control signaling, with respect to user data carried by EF, by utilization of a single AF class (single queue) for all call control signaling. A weighted queue serving algorithm is then required to guarantee that this queue receives a minimum percentage of the bandwidth of the outgoing facility, if it needs it, regardless of the volume of "higher priority" packers (such as voice in an "EF" queue). It is expected that this percentage for call control signaling would be less than 5% of the total bandwidth. To address the situation in which the signaling traffic exceeds the minimum guaranteed and there is excessive traffic, thereby blocking some call control messages, the multiple drop precedence capability of AF must be available. Relative drop precedences for SIP messages can be modeled on those use in ISUP. In order to address the other side of the problem - preventing long call control messages from adversely affecting the performance of the voice packets - it may be necessary to utilize a packet segmentation scheme. 6.10. Interworking Interworking requirements can be met in the following manner: Within a single network which supports two or more priority schemes, the network operator MUST determine the relative priority and preferential treatments to apply. For example, the operator may decide that the IEPS priority for "Authorized Emergency" will fall between the Assured Service levels of Immediate and Flash. At the gateway between two networks which support two different priority schemes, the operator of the gateway MUST determine and perform the mapping between the two schemes. For example, for the priority schemes defined for Assured Service (in the Defense Switched Network or DSN) and assuming 3 levels (normal, public emergency, and authorized emergency) for IEPS (in the public network), the mappings could be: From DSN To public network ------------ --------------------- Routine --> Normal Priority --> Normal Immediate --> Normal Flash --> Authorized Emergency Flash Override --> Authorized Emergency and Mike Pierce Expires December 2003 [Page 13] Internet Draft Requirements for Assured Service June 23, 2003 From Public network TO DSN -------------------- ------- Normal --> Routine Public Emergency --> Immediate Authorized Emergency --> Flash 7. Security Considerations 7.1. Authentication/authorization of User Access Discussions within SIP continue to identify the need to authenticate/authorize all access to capabilities, since virtually any function could be misused, resulting in harm to the network or to other users. Because Assured Service is intended to provide an authorized user with better service than other users, including the potential of actually preempting resources, it is even more important to authenticate/authorize the user's access to the Assured Service capabilities. However, the requirement definitely exists for all cases, not just Assured Service, therefore the solution is not unique to Assured Service. [RFC3261] describes the use of a stateless challenged-based mechanism for authentication in which a proxy server or user agent may challenge the initiator of a request to provide assurance of their identity. For real-time needs such as placing telephone calls, especially those for which Assured Service capabilities are being applied, such a challenge-based system will likely be too slow, or would itself be hampered by the very network condition which requires Assured Service to be applied. Pre-establishment of security associations is required, in order to allow for the timely exchange of security information needed to perform authentication/ authorization of individual actions. 7.2. Security of Signaling Information The need to protect signaling information from disclosure is independent from the provision of Assured Service. Many networks have long been built on the premise that such information needs to be protected. Bulk encryption of signaling links (as well as the user data channels) between secure switches provided much of this protection. In addition, the Signal Transfer Points of the SS#7 network could be secured against unauthorized access. It should be noted that commercial networks have recognized the need for the same level of protection previously only applied to various government networks. In the IP environment, the signaling packets as well as the user data traverse many routers and could be accessed by unauthorized persons at any one of them. While the contents of the individual signaling messages could be hidden by encryption of the request and response for end-to-end protection of information, the header must be visible to intermediate routers. It is preferable to not require decryption/ encryption at each router. The approach has been to Mike Pierce Expires December 2003 [Page 14] Internet Draft Requirements for Assured Service June 23, 2003 encrypt the contents of the signaling message but not the headers which are needed by the routers. However, the headers themselves may contain sensitive information such as precedence level and called party identification. [RFC3261] describes the transport and network layer security methods which may be used to protect signaling traffic. 7.3. Security of Routing Data Of more concern than the information about an individual call is the information normally needed by Link State routing logic used by an originating device to select a route though an entire network. Such a routing function requires knowledge of the state (busy or not) of various portions of the network. When Assured Service based on precedence levels is added, this requires that the routing point also know the current loading of various precedence levels for each portion of the network. Especially in a large network, this is highly sensitive information and must not be revealed to unauthorized network elements. It should be noted that the constraint-based LSP setup proposed in [RFC3212] depends on the routing point knowing this information. 8. IANA Considerations It is not expected that there will be any IANA involvement in support of Assured Service beyond what is described for the Resource Priority Header [Resource]. 9. References [T1.523] ANSI T1.523-2001, "Telecommunications Glossary". [T1.619] ANSI T1.619-1992 (R1999), "Multi-Level Precedence and Preemption (MLPP) Service, ISDN Supplementary Service Description". [T1.619a] ANSI T1.619a-1994 (R1999), "Addendum to MLPP". [T1.631] ANSI T1.631-1993 (R1999), "Telecommunications - Signalling System No. 7 (SS7) - High Probability of Completion (HPC) Network Capability". [E.106] ITU-T Recommendation E.106 (2000), "International Emergency Preference Scheme (IEPS)". [F.706] ITU-T Recommendation F.706 (draft), "International Preference Scheme for Multimedia Service in Support of Disaster Relief Operations and Mitigation". [I.255.3] ITU-T Recommendation I.255.3 (1990), "Multilevel precedence and preemption service (MLPP)". Mike Pierce Expires December 2003 [Page 15] Internet Draft Requirements for Assured Service June 23, 2003 [Q.735.3] ITU-T Recommendation Q.735.3 (1993), "Description for community of interest supplementary services using SS No. 7 - Multilevel precedence and preemption (MLPP)". [Q.955.3] ITU-T Recommendation Q.955.3 (1993), "Description for community of interest supplementary services using DSS1 - Multilevel precedence and preemption (MLPP)". [RFC2205] RFC 2205, "Resource ReSerVation Protocol (RSVP)", R. Braden, et al, September 1997 [RFC2597] RFC 2597, "Assured Forwarding PHB Group", J. Heinanen, et al, June 1999. [RFC2702] RFC 2702, "Requirements for Traffic Engineering Over MPLS", D. Awduche, et al, September 1999. [RFC2751] RFC 2751, "Signaled Preemption Priority Policy Element", S. Herzog, January 2000. [RFC3209] RFC 3209, "RSVP-TE: Extensions to RSVP for LSP Tunnels", D. Awduche, et al, December 2001. [RFC3212] RFC 3212, "CR-LDP: Constraint-based LSP Setup using LDP", B. Jamoussi, et al, January 2002. [RFC3246] RFC 3246, "An Expedited Forwarding PHB", B. Davie, et al, March 2002. [RFC3261] RFC 3261, "SIP: Session Initiation Protocol", J. Rosenberg, et al, June 2002. [RFC3313] RFC 3313, "Private SIP Extensions for Media Authorization", W. Marshall, May 2002. [Aboda] draft-ietf-aaa-transport-12, "Authentication, Authorization and Accounting (AAA) Transport Profile", Bernard Aboda, January 2003. (in editor's queue) [Carlberg] draft-ietf-ieprep-framework-04, "Framework for Supporting IEPS in IP Telephony", Ken Carlberg, et al, March 2003. [Johnston] draft-ietf-sipping-service-examples-04, "Session Initiation Protocol Service Examples", A. Johnston, et al, February 2003. [Pierce1] draft-pierce-ieprep-pref-treat-examples-01, "Examples for Provision of Preferential Treatment in Voice over IP", Mike Pierce, et al, June 2003. [Pierce2] draft-pierce-ieprep-assured-service-arch-01, "Architecture for Assured Service Capabilities in Voice over IP", Mike Pierce, et al, June 2003. Mike Pierce Expires December 2003 [Page 16] Internet Draft Requirements for Assured Service June 23, 2003 [Resource] draft-ietf-sip-resource-priority-00, "SIP Communications Resource Priority Header", Henning Schulzrinne and James Polk, June 2003. [Silverman] draft-silverman-diffserv-mlefphb-01, "Multi-Level Expedited Forwarding Per Hop Behavior (MLEF PHB", Steve Silverman, et al, April 2003. 10. Authors' Addresses Michael Pierce Artel 1893 Preston White Drive Reston, VA 20191 Phone: +1 410.817.4795 Email: pierce1m@ncr.disa.mil Don Choi DISA 5600 Columbia Pike Falls Church, VA 22041-2717 Phone: +1 703.681.2312 Email: choid@ncr.disa.mil A. Overview of existing priority mechanisms Current support within various IETF defined protocols and ongoing initiatives is not considered to be sufficient for Assured Services requirements. This informative Annex details some of these. A.1 IPv4 Although support for the traditional five precedence levels was included in the TOS field of IPv4 from the earliest days, support for this field is not universal, and it only provides packet level priority. It does not provide call setup priority or control of call retention. A.2 DiffServ Within DiffServ, Assured Forwarding defined in RFC 2597 provides four classes and three drop precedences for each class. One of these classes could be used for the signaling messages for session establishment and release. The multiple drop precedences could be used for various signaling messages, as is being done with the equivalent call control messages in ISUP for SS#7. However, AF is not considered to be appropriate for voice. Expedited Forwarding defined in RFC 3246 is intended for voice, but it treats all such voice packets the same. It does not define multiple drop precedences as AF does so there is no way to provide Mike Pierce Expires December 2003 [Page 17] Internet Draft Requirements for Assured Service June 23, 2003 preferential treatment to packets associated with higher priority calls. A.3 IntServ/RSVP Although RSVP includes mention of preemption of existing reservations in favor of other higher priority ones, it does not provide detailed procedures for doing so. In principle, it should be straightforward to do so. However, it is not believed that the procedures required for establishment of a path using RSVP, and the additional procedures that would be necessary for preemption of an existing path, would allow this to be useful for the provision of Assured Service capabilities to individual calls. A.4 MPLS Since MPLS is fundamentally a means to emulate circuit-mode operation by establishment of a "path" which then functions like a "connection", the principles of priority and preemption could be applied to the setup and retention of this path the same as they are in the circuit-mode environment. RFC 2702 describes the requirements for such capabilities as applied to "traffic trunks". However, it uses the term "traffic trunk" to refer to a facility which is established to carry an aggregate of traffic, i.e., many telephone calls. This is the equivalent of a "trunk group" in standard telephony terminology [T1.523]. Because of the extensive procedures that are required to establish and remove such a Label Switched Path, it is believed that this prevents MPLS from being used to setup paths for individual calls. MPLS may be applicable for the establishment of the equivalent of dedicated trunk groups between switching entities. Each of these "trunk groups" or "traffic trunks" could exist to support a specific precedence level of traffic between two points and could be setup using the procedures defined in [RFC3212] or those in [RFC3209]. These documents allow the signaling of the required five levels of precedence as well as separate setup and holding priorities. A.5 SIP SIP [RFC3261] defines four tokens for priority levels (non-urgent, normal, urgent, and emergency), however, they are not intended to be used to control call setup nor do they equate to the levels required for Assured Service. The proposed Resource Priority Header [Resource] provides for the five precedence levels required for per call marking. Security is discussed in [RFC3261] and many drafts, but it has been recognized in various Working Group discussions that security for all aspects of call control needs to be considered in a unified manner. Security for each individual component of call setup and release can not be designed separately. Mike Pierce Expires December 2003 [Page 18] Internet Draft Requirements for Assured Service June 23, 2003 The procedure being proposed for authorization of call set-up and media allocation [RFC3313] appears to be too time consuming to expect it to occur each time a user attempts to place a telephone call, especially a high-priority one. The probable delay in establishing this authorization would be contrary to the goals and requirements for Assured Service. Use of this type of procedure would require that preferential treatments also be applied to all message interactions and proxy processing of the sequence of messages required for the authorization. Overloads of the proxies responsible for the Call Authorization would prevent or unacceptably delay setup of the high precedence call. Full Copyright Statement Copyright (c) The Internet Society (2003). 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 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. Mike Pierce Expires December 2003 [Page 19]