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Internet Engineering Task Force (IETF)                          F. BakerRequest for Comments: 5865                                       J. PolkUpdates:4542,4594                                        Cisco SystemsCategory: Standards Track                                       M. DollyISSN: 2070-1721                                                AT&T Labs                                                                May 2010A Differentiated Services Code Point (DSCP)for Capacity-Admitted TrafficAbstract   This document requests one Differentiated Services Code Point (DSCP)   from the Internet Assigned Numbers Authority (IANA) for a class of   real-time traffic.  This traffic class conforms to the Expedited   Forwarding Per-Hop Behavior.  This traffic is also admitted by the   network using a Call Admission Control (CAC) procedure involving   authentication, authorization, and capacity admission.  This differs   from a real-time traffic class that conforms to the Expedited   Forwarding Per-Hop Behavior but is not subject to capacity admission   or subject to very coarse capacity admission.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5865.Baker, et al.                Standards Track                    [Page 1]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .31.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .41.2.  Problem   . . . . . . . . . . . . . . . . . . . . . . . .6   2.  Candidate Implementations of the Admitted Telephony       Service Class   . . . . . . . . . . . . . . . . . . . . . . .72.1.  Potential implementations of EF in this model . . . . . .72.2.  Capacity admission control  . . . . . . . . . . . . . . .9     2.3.  Recommendations on implementation of an Admitted           Telephony Service Class . . . . . . . . . . . . . . . . .103.  Summary: changes fromRFC 4594  . . . . . . . . . . . . . . .114.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .115.  Security Considerations . . . . . . . . . . . . . . . . . . .126.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .127.  References  . . . . . . . . . . . . . . . . . . . . . . . . .137.1.  Normative References  . . . . . . . . . . . . . . . . . .137.2.  Informative References  . . . . . . . . . . . . . . . . .13Baker, et al.                Standards Track                    [Page 2]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 20101.  Introduction   This document requests one Differentiated Services Code Point (DSCP)   from the Internet Assigned Numbers Authority (IANA) for a class of   real-time traffic.  This class conforms to the Expedited Forwarding   (EF) [RFC3246] [RFC3247] Per-Hop Behavior.  It is also admitted using   a CAC procedure involving authentication, authorization, and capacity   admission.  This differs from a real-time traffic class that conforms   to the Expedited Forwarding Per-Hop Behavior but is not subject to   capacity admission or subject to very coarse capacity admission.   In addition, this document recommends that certain classes of video   described in [RFC4594] be treated as requiring capacity admission.   Real-time traffic flows have one or more potential congestion points   between the endpoints.  Reserving capacity for these flows is   important to application performance.  All of these applications have   low tolerance to jitter (aka delay variation) and loss, as summarized   inSection 2, and most (except for multimedia conferencing) have   inelastic flow behavior from Figure 1 of [RFC4594].  Inelastic flow   behavior and low jitter/loss tolerance are the service   characteristics that define the need for admission control behavior.   One of the reasons behind the requirement for capacity admission is   the need for classes of traffic that are handled under special   policies.  Service providers need to distinguish between special-   policy traffic and other classes, particularly the existing Voice   over IP (VoIP) services that perform no capacity admission or only   very coarse capacity admission and can exceed their allocated   resources.   The requested DSCP applies to the Telephony Service Class described   in [RFC4594].   Since video classes have not had the history of mixing admitted and   non-admitted traffic in the same Per-Hop Behavior (PHB) as has   occurred for EF, an additional DSCP code point is not recommended   within this document for video.  Instead, the recommended "best   practice" is to perform admission control for all traffic in three of   the video classes from [RFC4594]:   o  The Interactive Real-Time Traffic (CS4, used for Video      conferencing and Interactive gaming),   o  The Broadcast TV (CS3) for use in a video on demand context, and   o  The AF4 Multimedia Conferencing (video conferencing).Baker, et al.                Standards Track                    [Page 3]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010   Other video classes are believed not to have the current problem of   confusion with unadmitted traffic and therefore would not benefit   from the notion of a separate DSCP for admitted traffic.  Within an   ISP and on inter-ISP links (i.e., within networks whose internal   paths are uniform at hundreds of megabits per second or faster), one   would expect all of this traffic to be carried in the Real-Time   Traffic (RTP) class described in [RFC5127].1.1.  Definitions   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 inRFC 2119 [RFC2119].   The following terms and acronyms are used in this document.   PHB:   A Per-Hop Behavior (PHB) is the externally observable          forwarding behavior applied at a Differentiated Services          compliant node to a DS behavior aggregate [RFC2475].  It may          be thought of as a program configured on the interface of an          Internet host or router, specified in terms of drop          probabilities, queuing priorities or rates, and other handling          characteristics for the traffic class.   DSCP:  The Differentiated Services Code Point (DSCP), as defined in          [RFC2474], is a value that is encoded in the DS field, and          that each DS Node MUST use to select the PHB that is to be          experienced by each packet it forwards [RFC3260].  It is a          6-bit number embedded into the 8-bit TOS (type of service)          field of an IPv4 datagram or the Traffic Class field of an          IPv6 datagram.   CAC:   Call Admission Control includes concepts of authorization and          capacity admission.  "Authorization" refers to any procedure          that identifies a user, verifies the authenticity of the          identification, and determines whether the user is authorized          to use the service under the relevant policy.  "Capacity          Admission" refers to any procedure that determines whether          capacity exists supporting a session's requirements under some          policy.          In the Internet, these are separate functions; while in the          Public Switched Telephone Network (PSTN), they and call          routing are carried out together.Baker, et al.                Standards Track                    [Page 4]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010   UNI:   A User/Network Interface (UNI) is the interface (often a          physical link or its virtual equivalent) that connects two          entities that do not trust each other, and in which one (the          user) purchases connectivity services from the other (the          network).          Figure 1 shows two user networks connected by what appears to          each of them to be a single network ("The Internet", access to          which is provided by their service provider) that provides          connectivity services to other users.          UNIs tend to be the bottlenecks in the Internet, where users          purchase relatively low amounts of bandwidth for cost or          service reasons, and as a result are most subject to          congestion issues and therefore issues requiring traffic          conditioning and service prioritization.   NNI:   A Network/Network Interface (NNI) is the interface (often a          physical link or its virtual equivalent) that connects two          entities that trust each other within limits, and in which the          two are seen as trading services for value.  Figure 1 shows          three service networks that together provide the connectivity          services that we call "the Internet".  They are different          administrations and are very probably in competition, but          exchange contracts for connectivity and capacity that enable          them to offer specific services to their customers.          NNIs may not be bottlenecks in the Internet if service          providers contractually agree to provision excess capacity at          them, as they commonly do.  However, NNI performance may          differ by ISP, and the performance guarantee interval may          range from a month to a much shorter period.  Furthermore, a          peering point NNI may not have contractual performance          guarantees or may become overloaded under certain conditions.          They are also policy-controlled interfaces, especially in BGP.          As a result, they may require a traffic prioritization policy.   Queue: There are multiple ways to build a multi-queue scheduler.          Weighted Round Robin (WRR) literally builds multiple lists and          visits them in a specified order, while a calendar queue          (often used to implement Weighted Fair Queuing, or WFQ) builds          a list for each time interval and queues at most a stated          amount of data in each such list for transmission during that          time interval.  While these differ dramatically in          implementation, the external difference in behavior is          generally negligible when they are properly configured.          Consistent with the definitions used in the Differentiated          Services Architecture [RFC2475], these are treated asBaker, et al.                Standards Track                    [Page 5]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010          equivalent in this document, and the lists of WRR and the          classes of a calendar queue will be referred to uniformly as          "queues".                                        _.--------.                                    ,-''           `--.                                 ,-'                   `-.           ,-------.           ,',-------.                `.         ,'         `.       ,','         `.                `.        /  User       \ UNI / /   Service   \                 \       (    Network    +-----+    Network    )                 `.        \             /  ;    \             /                    :         `.         ,'   ;     `.         .+                     :           '-------'    /        '-------'  \ NNI                 \                       ;                     \                     :                       ;     "The Internet"   \  ,-------.         :                      ;                        +'         `.        :        UNI: User/Network Interface           /   Service   \       |                     |                       (    Network    )      |        NNI: Network/Network Interface        \             /       |                      :                        +.         ,'        ;                       :                      /  '-------'         ;                       :                     /                     ;           ,-------.    \        ,-------.  / NNI                 /         ,'         `.   :     ,'         `+                     ;        /  User       \ UNI   /   Service   \                    ;       (    Network    +-----+    Network    )                 ,'        \             /     \ \             /                 /         `.         ,'       `.`.         ,'                ,'           '-------'           `.'-------'                ,'                                 `-.                   ,-'                                    `--.           _.-'                                        `--------''                      Figure 1: UNI and NNI Interfaces1.2.  Problem   In short, the Telephony Service Class, described in [RFC4594],   permits the use of capacity admission in implementing the service,   but present implementations either provide no capacity admission   services or do so in a manner that depends on specific traffic   engineering.  In the context of the Internet backbone, the two are   essentially equivalent; the edge network depends on specific   engineering by the service provider that might not be present,   especially in a mobile environment.Baker, et al.                Standards Track                    [Page 6]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010   However, services are being requested of the network that would   specifically make use of capacity admission, and would distinguish   among users or the uses of available Voice-over-IP or Video-over-IP   capacity in various ways.  Various agencies would like to provide   services as described in RFC [RFC4190] or inSection 2.6 of   [RFC4504].   This requires the use of capacity admission to differentiate among   users to provide services to them that are not afforded to non-   capacity admitted customer-to-customer IP telephony sessions.2.  Candidate Implementations of the Admitted Telephony Service Class2.1.  Potential Implementations of EF in This Model   There are at least two possible ways to implement isolation between   the Capacity Admitted PHB and the Expedited Forwarding PHB in this   model.  They are to implement separate classes as a set of   o  Multiple data plane traffic classes, each consisting of a policer      and a queue, with the queues enjoying different priorities, or   o  Multiple data plane traffic classes, each consisting of a policer      but feeding into a common queue or multiple queues at the same      priority.   We will explain the difference and describe in what way they differ   in operation.  The reason this is necessary is that there is current   confusion in the industry.   The multi-priority model is shown in Figure 2.  In this model,   traffic from each service class is placed into a separate priority   queue.  If data is present in more than one queue, traffic from one   of them will always be selected for transmission.  This has the   effect of transferring jitter from the higher-priority queue to the   lower-priority queues, and reordering traffic in a way that gives the   higher-priority traffic a smaller average queuing delay.  Each queue   must have its own policer, however, to protect the network from   errors and attacks; if a traffic class thinks it is carrying a   certain data rate but an abuse sends significantly more, the effect   of simple prioritization would not preserve the lower priorities of   traffic, which could cause routing to fail or otherwise impact a   service level agreement (SLA).Baker, et al.                Standards Track                    [Page 7]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010                                                .                        policers    priorities  |`.                Admitted EF <=> ----------||----+  `.                                            high|    `.              Unadmitted EF <=> ----------||----+     .'-----------                              .             medium  .'                 rate queues  |`.         +-----+ .' Priority              AF1------>||----+  `.      /  low |'   Scheduler                              |    `.   /              AF2------>||----+     .'-+                              |   .'              CS0------>||----+ .' Rate Scheduler                              |'   (WFQ, WRR, etc.)                Figure 2: Implementation as a Data Plane Priority   The multi-policer model is shown in Figure 3.  In this model, traffic   from each service class is policed according to its SLA requirements,   and then placed into a common priority queue.  Unlike the multi-   priority model, the jitter experienced by the traffic classes in this   case is the same, as there is only one queue, but the sum of the   traffic in this higher-priority queue experiences less average jitter   than the elastic traffic in the lower-priority.                       policers    priorities  .               Admitted EF <=> -------\        |`.                                       --||----+  `.             Unadmitted EF <=> -------/    high|    `.                             .                 |     .'--------                rate queues  |`.         +-----+   .'             AF1------>||----+  `.      /  low | .' Priority                             |    `.   /       |'   Scheduler             AF2------>||----+     .'-+                             |   .'             CS0------>||----+ .' Rate Scheduler                             |'   (WFQ, WRR, etc.)             Figure 3: Implementation as a Data Plane Policer   The difference between the two operationally is, as stated, the   issues of loss due to policing and distribution of jitter.   If the two traffic classes are, for example, voice and video,   datagrams containing video data can be relatively large (often of   variable sizes up to the path MTU), while datagrams containing voice   are relatively small, on the order of only 40 to 200 bytes, depending   on the codec.  On lower-speed links (less than 10 MBPS), the jitter   introduced by video to voice can be disruptive, while at higherBaker, et al.                Standards Track                    [Page 8]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010   speeds, the jitter is nominal compared to the jitter requirements of   voice.  Therefore, at access network speeds, [RFC4594] recommends the   separation of video and voice into separate queues, while at optical   speeds, [RFC5127] recommends that they use a common queue.   If, on the other hand, the two traffic classes are carrying the same   type of application with the same jitter requirements, then giving   one preference in this sense does not benefit the higher-priority   traffic and may harm the lower-priority traffic.  In such a case,   using separate policers and a common queue is a superior approach.2.2.  Capacity Admission Control   There are at least six major ways that capacity admission is done or   has been proposed to be done for real-time applications.  Each will   be described below, andSection 3 will judge which ones are likely to   meet the requirements of the Admitted Telephony service class.  These   include:   o  Drop Precedence used to force sessions to voluntarily exit,   o  Capacity admission control by assumption or engineering,   o  Capacity admission control by call counting,   o  Endpoint capacity admission performed by probing the network,   o  Centralized capacity admission control via bandwidth broker, and   o  Distributed capacity admission control using protocols such as      Resource Reservation Protocol (RSVP) or Next Steps in Signaling      (NSIS).   The problem with dropping traffic to force users to hang up is that   it affects a broad class of users -- if there is capacity for N calls   and the N+1 calls are active, data is dropped randomly from all   sessions to ensure that offered load doesn't exceed capacity.  On   very fast links, that is acceptable, but on lower speed links it can   seriously affect call quality.  There is also a behavioral issue   involved here, in which users who experience poor quality calls tend   to hang up and call again, making the problem better -- then worse.   The problem with capacity admission by assumption, which is widely   deployed in today's VoIP environment, is that it depends on the   assumptions made.  One can do careful traffic engineering to ensure   needed bandwidth, but this can also be painful, and has to be   revisited when the network is changed or network usage changes.Baker, et al.                Standards Track                    [Page 9]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010   The problem with call-counting-based admission control is that it   gets exponentially worse the farther you get from the control point   (e.g., it lacks sufficient scalability on the outskirts of the   network).   There are two fundamental problems with depending on the endpoint to   perform capacity admission: it may not be able to accurately measure   the impact of the traffic it generates on the network, and it tends   to be greedy (e.g., it doesn't care).  If the network operator is   providing a service, he must be able to guarantee the service, which   means that he cannot trust systems that are not controlled by his   network.   The problem with capacity controls via a bandwidth broker is that   centralized servers lack far away awareness, and also lack effective   real-time reaction to dynamic changes in all parts of the network at   all instances of time.   The problem with mechanisms that do not enable the association of a   policy with the request is that they do not allow for multi-policy   services, which are becoming important.   The operator's choice of admission procedure MUST, for this DSCP,   ensure the following:   o  The actual links that a session uses have enough bandwidth to      support it.   o  New sessions are refused admission if there is inadequate      bandwidth under the relevant policy.   o  A user is identified and the correct policy is applied if multiple      policies are in use in a network.   o  Under periods of network stress, the process of admission of new      sessions does not disrupt existing sessions, unless the service      explicitly allows for disruption of calls.2.3.  Recommendations on Implementation of an Admitted Telephony      Service Class   When coupled with adequate Authentication, Authorization, and   Accounting (AAA) and capacity admission procedures as described inSection 2.2, either of the two PHB implementations described inSection 2.1 is sufficient to provide the services required for an   Admitted Telephony service class.  If preemption is required,Section2.3.5.2 of [RFC4542] provides the tools for carrying out the   preemption.  If preemption is not in view, or if used in addition toBaker, et al.                Standards Track                   [Page 10]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010   preemptive services, the application of different thresholds   depending on call precedence has the effect of improving the   probability of call completion by admitting preferred calls at a time   when other calls are being refused.  Routine and priority traffic can   be admitted using the same DSCP value, as the choice of which calls   are admitted is handled in the admission procedure executed in the   control plane, not the policing of the data plane.   On the point of what protocols and procedures are required for   authentication, authorization, and capacity admission, we note that   clear standards do not exist at this time for bandwidth brokers, NSIS   has not been finalized at this time and in any event is limited to   unicast sessions, and that RSVP has been standardized and has the   relevant services.  We therefore RECOMMEND the use of a protocol,   such as RSVP, at the UNI.  Procedures at the NNI are business matters   to be discussed between the relevant networks, and are RECOMMENDED   but NOT REQUIRED.3.  Summary: Changes fromRFC 4594   To summarize, there are two changes to [RFC4594] discussed in this   document:   Telephony class: The Telephony Service Class inRFC 4594 does not                    involve capacity admission, but depends on                    application layer admission that only estimates                    capacity, and does that through static engineering.                    In addition to that class, a separate Admitted                    Telephony Class is added that performs capacity                    admission dynamically.   Video classes:   Capacity admission is added to three video classes.                    These are the Interactive Real-Time Traffic class,                    Broadcast TV class when used for video on demand,                    and the Multimedia Conferencing class.4.  IANA Considerations   IANA assigned a DSCP value to a second EF traffic class consistent   with [RFC3246] and [RFC3247] in the "Differentiated Services Field   Codepoints" registry.  It implements the Telephony Service Class   described in [RFC4594] at lower speeds and is included in the Real-   Time Treatment Aggregate [RFC5127] at higher speeds.  The code point   value should be from pool 1 within the dscp-registry.  The value is   parallel with the existing EF code point (101110), as IANA assignedBaker, et al.                Standards Track                   [Page 11]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010   the code point 101100 -- keeping the (left-to-right) first 4 binary   values the same in both.  The code point described in this document   is referred to as VOICE-ADMIT and has been registered as follows:   Sub-registry: Pool 1 Codepoints   Reference: [RFC2474]   Registration Procedures: Standards Action      Registry:      Name         Space    Reference      ---------    -------  ---------      VOICE-ADMIT  101100   [RFC5865]   This traffic class REQUIRES the use of capacity admission, such as   RSVP services together with AAA services, at the User/Network   Interface (UNI); the use of such services at the NNI is at the option   of the interconnected networks.5.  Security Considerations   A major requirement of this service is effective use of a signaling   protocol, such as RSVP, with the capabilities to identify its user as   either an individual or a member of some corporate entity, and assert   a policy such as "normal", "routine", or some level of "priority".   This capability, one has to believe, will be abused by script kiddies   and others if the proof of identity is not adequately strong or if   policies are written or implemented improperly by the carriers.  This   goes without saying, but this section is here for it to be said.   Many of the security considerations fromRFC 3246 [RFC3246] apply to   this document, as well as the security considerations inRFC 2474 andRFC 4542.RFC 4230 [RFC4230] analyzes RSVP, providing some gap   analysis to the NSIS WG as they started their work.  Keep in mind   that this document is advocating RSVP at the UNI only, whileRFC 4230   discusses (mostly) RSVP from a more complete point of view (i.e., e2e   and edge2edge).  When considering the RSVP aspect of this document,   understandingSection 6 of RFC 4230 is a good source of information.6.  Acknowledgements   Kwok Ho Chan, Georgios Karagiannis, Dan Voce, and Bob Briscoe   commented and offered text.  The impetus for including video in the   discussion, which initially only targeted voice, is from Dave   McDysan.Baker, et al.                Standards Track                   [Page 12]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 20107.  References7.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,              "Definition of the Differentiated Services Field (DS              Field) in the IPv4 and IPv6 Headers",RFC 2474, December              1998.   [RFC3246]  Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,              J., Courtney, W., Davari, S., Firoiu, V., and D.              Stiliadis, "An Expedited Forwarding PHB (Per-Hop              Behavior)",RFC 3246, March 2002.7.2.  Informative References   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,              and W. Weiss, "An Architecture for Differentiated              Service",RFC 2475, December 1998.   [RFC3247]  Charny, A., Bennet, J., Benson, K., Boudec, J., Chiu, A.,              Courtney, W., Davari, S., Firoiu, V., Kalmanek, C., and K.              Ramakrishnan, "Supplemental Information for the New              Definition of the EF PHB (Expedited Forwarding Per-Hop              Behavior)",RFC 3247, March 2002.   [RFC3260]   Grossman, D., "New Terminology and Clarifications for              Diffserv",RFC 3260, April 2002.   [RFC4190]  Carlberg, K., Brown, I., and C. Beard, "Framework for              Supporting Emergency Telecommunications Service (ETS) in              IP Telephony",RFC 4190, November 2005.   [RFC4504]  Sinnreich, H., Ed., Lass, S., and C. Stredicke, "SIP              Telephony Device Requirements and Configuration",RFC4504, May 2006.   [RFC4542]  Baker, F. and J. Polk, "Implementing an Emergency              Telecommunications Service (ETS) for Real-Time Services in              the Internet Protocol Suite",RFC 4542, May 2006.   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration              Guidelines for DiffServ Service Classes",RFC 4594, August              2006.Baker, et al.                Standards Track                   [Page 13]

RFC 5865           DSCP for Capacity-Admitted Traffic           May 2010   [RFC5127]  Chan, K., Babiarz, J., and F. Baker, "Aggregation of              DiffServ Service Classes",RFC 5127, February 2008.   [RFC4230]  Tschofenig, H. and R. Graveman, "RSVP Security              Properties",RFC 4230, December 2005.Authors' Addresses   Fred Baker   Cisco Systems   Santa Barbara, California  93117   USA   Phone: +1-408-526-4257   EMail: fred@cisco.com   James Polk   Cisco Systems   Richardson, Texas  75082   USA   Phone: +1-817-271-3552   EMail: jmpolk@cisco.com   Martin Dolly   AT&T Labs   Middletown Township, New Jersey  07748   USA   Phone: +1-732-420-4574   EMail: mdolly@att.comBaker, et al.                Standards Track                   [Page 14]