SIP Working Group                               W. Marshall
Internet Draft                                  AT&T
Document: <draft-ietf-sip-manyfolks-resource-02> <draft-ietf-sip-manyfolks-resource-03>
                                                K. Ramakrishnan
                                                TeraOptic Networks

                                                E. Miller
                                                Terayon

                                                G. Russell
                                                CableLabs

                                                B. Beser
                                                Pacific Broadband

                                                M. Mannette
                                                K. Steinbrenner
                                                3Com

                                                D. Oran
                                                F. Andreasen
                                                M. Ramalho
                                                Cisco

                                                J. Pickens
                                                Com21

                                                P. Lalwaney
                                                Nokia

                                                J. Fellows
                                                Copper Mountain Networks

                                                D. Evans
                                                D. R. Evans Consulting

                                                K. Kelly
                                                NetSpeak

                                                A. Roach
                                                Ericsson

                                                J. Rosenberg
                                                D. Willis
                                                S. Donovan
                                                dynamicsoft

                                                H. Schulzrinne
                                                Columbia University

                                                February,

                                                November, 2001

                Integration of Resource Management and SIP

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Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026[1].

   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.

   The distribution of this memo is unlimited.  It is filed as <draft-
   ietf-sip-manyfolks-resource-02.txt>,
   ietf-sip-manyfolks-resource-03.txt>, and expires February 28, May 31, 2002.
   Please send comments to the authors.

1. Abstract

   This document discusses how network QoS and security establishment
   can be made a precondition to sessions initiated by the Session
   Initiation Protocol (SIP), and described by SDP. These preconditions
   require that the participant reserve network resources (or establish
   a secure media channel) before continuing with the session. We do
   not define new QoS reservation or security mechanisms; these pre-
   conditions simply require a participant to use existing resource
   reservation and security mechanisms before beginning the session.

   This results in a multi-phase call-setup mechanism, with the
   resource management protocol interleaved between two phases of call
   signaling. The objective of such a mechanism is to enable deployment
   of robust IP Telephony services, by ensuring that resources are made
   available before the phone rings and the participants of the call
   are "invited" to participate.

   This document also proposes an extension to the Session Initiation
   Protocol (SIP) to add a new COMET method, which is used to confirm
   the completion of all pre-conditions by the session originator.

2. Conventions used in this document

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   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC-2119[4].

3. Table of Contents

   Status of this Memo................................................2
   1. Abstract........................................................2
   2. Conventions used in this document...............................2
   3. Table of Contents...............................................3
   4. Introduction....................................................3
   4.1 Requirements...................................................6
   4.2 Overview.......................................................6
   5. SDP Extension...................................................8
   5.1 SDP Example....................................................9
   5.2 SDP Allowable Combinations.....................................9
   6. SIP Extension: The COMET Method................................11
   6.1 Header Field Support for COMET Method.........................12 Method.........................11
   6.2 Responses to the COMET Request Method.........................12
   6.3 Message Body Inclusion........................................13
   6.4 Behavior of SIP User Agents...................................13
   6.5 Behavior of SIP Proxy and Redirect Servers....................13
   6.5.1 Proxy Server................................................13
   6.5.2 Forking Proxy Server........................................14
   6.5.3 Redirection Server..........................................14
   7. SIP Extension: The 183-Session-Progress Response...............14
   7.1 Status Code and Reason Phrase.................................14
   7.2 Status Code Definition........................................14
   8. SIP Extension: The 580-Precondition-Failure Response...........14
   8.1 Status Code and Reason Phrase.................................14
   8.2 Status Code Definition........................................14
   9. SIP Extension: Content-Disposition header......................15
   10. Option tag for Requires and Supported headers.................16
   11. SIP Usage Rules...............................................16
   11.1 Overview.....................................................16
   11.2 Behavior of Originator (UAC).................................17
   11.3 Behavior of Destination (UAS)................................18
   12. Examples......................................................19 Examples......................................................20
   12.1 Single Media Call Flow.......................................19 Flow.......................................20
   12.2 Multiple Media Call Flow.....................................22
   13. Special considerations with Forking Proxies...................23
   14. Advantages of the Proposed Approach...........................24
   15. Security Considerations.......................................24
   16. Notice Regarding Intellectual Property Rights.................24
   17. References....................................................24
   18. Acknowledgments...............................................25
   19. Author's Addresses............................................25
   Full Copyright Statement..........................................28

4. Introduction

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   For an Internet Telephony service to be successfully used by a large
   number of subscribers, it must offer few surprises to those
   accustomed to the behavior of existing telephony services.  One
   expectation is that of connection quality, implying resources must
   be set aside for each call.

   A key contribution is a recognition of the need for coordination
   between call signaling, which controls access to telephony specific
   services, and resource management, which controls access to network-
   layer resources. This coordination is designed to meet the user
   expectations and human factors associated with telephony.

   While customers may expect, during times of heavy load, to receive a
   "fast busy" or an announcement saying "all circuits are busy now,"
   the general expectation is that once the destination phone rings
   that the connection can be made.  Blocking a call after ringing the
   destination is considered a "call defect" and is a very undesirable
   exception condition.

   This draft addresses both "QoS-Assured" and "QoS-Enabled" sessions.
   A "QoS-Assured" session will complete only if all the required
   resources are available and assigned to the session.  A provider may
   choose to block a call when adequate resources for the call are not
   available. Public policy demands that the phone system provide
   adequate quality at least in certain cases: e.g., for emergency
   communications during times of disasters.  Call blocking enables a
   provider to meet such requirements.

   A "QoS-Enabled" session allows the endpoints to complete the session
   establishment either with or without the desired resources.  Such
   session will use dedicated resources if available, and use a best-
   effort connection as an alternative if resources can not be
   dedicated.  In cases where resources are not available, the
   originating and/or terminating User Agent might consult with the
   customer to obtain guidance on whether the session should complete.

   Coordination between call signaling and resource management is also
   needed to prevent fraud and theft of service.  The coordination
   between call-signaling and QoS setup protocols ensures that users
   are authenticated and authorized before receiving access to the
   enhanced QoS associated with the telephony service.

   This coordination, referred to in this draft as "preconditions,"
   require that the participant reserve network resources (or establish
   a secure media channel) before continuing with the session. We do
   not define new QoS reservation or security mechanisms; these pre-
   conditions simply require a participant to use existing resource
   reservation and security mechanisms before beginning the session.

   In the case of SIP [2], this effectively means that the "phone won't
   ring" until the preconditions are met. These preconditions are
   described by new SDP parameters, defined in this document. The
   parameters can mandate end-to-end QoS reservations based on RSVP [5]
   or any other end-to-end reservation mechanism (such as YESSIR [6],

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   or PacketCable's Dynamic Quality of Service (D-QoS) [7]), and
   security based on IPSEC [8]. The preconditions can be defined
   independently for each media stream.

   The QoS architecture of the Internet separates QoS signaling from
   application level signaling. Application layer devices (such as web
   proxies and SIP servers) are not well suited for participation in
   network admission control or QoS management, as this is
   fundamentally a network layer issue, independent of any particular
   application. In addition, since application devices like SIP servers
   are almost never on the "bearer path" (i.e., the network path the
   RTP [9] takes), and since the RTP path and signaling paths can be
   completely different (even traversing different autonomous systems),
   these application servers are generally not capable of managing QoS
   for the media. Keeping QoS out of application signaling also means
   that there can be a single infrastructure for QoS across all
   applications. This eliminates duplication of functionality, reducing
   management and equipment costs. It also means that new applications,
   with their own unique QoS requirements, can be easily supported.

   This loose coupling works very well for a wide range of
   applications. For example, in an interactive game, one can establish
   the game using an application signaling protocol, and then later on
   use RSVP to reserve network resources. The separation is also
   effective for applications which have no explicit signaling.
   However, certain applications may require tighter coupling. In the
   case of Internet telephony, the following is an important
   requirement:

       When A calls B, B's phone should not ring unless resources
       have been reserved from A to B, and B to A.

   This could be achieved without coupling if A knew B's address, port,
   and codecs before the telephony signaling took place. However, since
   telephony signaling is used largely to obtain this information in
   the first place, the coupling cannot be avoided.

   A similar model exists for security. Rather than inventing new
   security mechanisms for each new application, common security tools
   (such as IPSEC) can be used across all applications. As with QoS, a
   means in application level protocols is needed to indicate that a
   security association is needed for the application to execute.

   To solve both of these problems, we propose an extension to SDP
   which allows indication of pre-conditions for sessions. These
   preconditions indicate that participation in the session should not
   proceed until the preconditions are met. The preconditions we define
   are (1) success of end-to-end resource reservation, and (2) success
   of end- to-end security establishment. We chose to implement these
   extensions in SDP, rather than SIP [2] or SAP [10], since they are
   fundamentally a media session issue. SIP is session agnostic;
   information about codecs, ports, and RTP [9] are outside the scope
   of SIP. Since it is the media sessions that the reservations and
   security refer to, SDP is the appropriate venue for the extensions.

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   Furthermore, placement of the extensions in SDP rather than SIP or
   SAP allows specification of preconditions for individual media
   streams. For example, a multimedia lecture might require reservation
   for the audio, but not the video (which is less important).

   Our extensions are completely backward compatible. If a recipient
   does not understand them, normal SIP or SAP processing will occur,
   at no penalty of call setup latency.

4.1 Requirements

   The basic motivation in this work is to meet and possibly exceed the
   user expectations and human factors associated with telephony.

   In this section, we briefly describe the application requirements
   that led to the set of DCS signaling design principles.  In its
   basic implementation, DCS supports a residential telephone service
   comparable to the local telephone services offered today. Some of
   the requirements for resource management, in concert with call
   signaling, are as follows:

   The system must minimize call defects.  These are situations where
   either the call never completes, or an error occurs after the
   destination is alerted.  Requirements on call defects are typically
   far more stringent than call blocking.  Note that we expect the
   provider and the endpoints to attempt to use lower bandwidth codecs
   as the first line of defense against limited network capacity, and
   to avoid blocking calls.

   The system must minimize the post-dial-delay, which is the time
   between the user dialing the last digit and receiving positive
   confirmation from the network.  This delay must be short enough that
   users do not perceive a difference with post-dial delay in the
   circuit switched network or conclude that the network connectivity
   no longer exists.

   Call signaling needs to provide enough information to the resource
   management protocol so as to enable resources to be allocated in the
   network.  This typically requires most if not all of the components
   of a packet classifier (source IP, destination IP, source port,
   destination port, protocol) to be available for resource allocation.

4.2 Overview

   For acceptable interactive voice communication it is important to
   achieve end-to-end QoS. The end-to-end QoS assurance implies
   achieving low packet delay and packet loss. End-to-end packet delay
   must be small enough that it does not interfere with normal voice
   conversations. The ITU recommends no greater than 300 ms roundtrip
   delay for telephony service.  Packet loss must be small enough to
   not perceptibly impede voice quality or the performance of fax and
   voice band modems.

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   If it is found that the network cannot guarantee end-to-end QoS
   resources, there are two alternatives: either (1) allow call
   signaling to proceed with high probability of excessive delay and
   packet loss which could impair any interactive real-time
   communication between the participants, or (2) block the call prior
   to the called party being alerted.  When calls are blocked because
   of a lack of resources in a particular segment of the network, it is
   highly desirable that such blocking occur before the called party
   picks up.

   We do expect the endpoints to attempt to use lower bandwidth codecs,
   thereby avoiding blocking calls, as the first line of defense
   against limited network capacity.

   The call signaling and resource reservation must be achieved in such
   a way that the post-dial-delay must be minimized without increasing
   the probability of call defects. This means that the number of
   round-trip messages must be kept at an absolute minimum and messages
   must be sent directly end-system to end-system if possible.

   The general idea behind the extension is simple. We define two new
   SDP attributes, "qos" and "security". The "qos" attribute indicates
   whether end-to-end resource reservation is optional or mandatory,
   and in which direction (send, recv, or sendrecv). When the attribute
   indicates mandatory, this means that the participant who has
   received the SDP does not proceed with participation in the session
   until resource reservation has completed in the direction indicated.
   In this case, "not proceeding" means that the participant behaves as
   if they had not received the SDP at all. If the attribute indicates
   that QoS for the stream is optional, then the participant proceeds
   normally with the session, but should reserve network resources in
   the direction indicated, if they are capable. Absence of the "qos"
   attribute means the participant reserves resources for this stream,
   and proceeds normally with the session. This behavior is the normal
   behavior for SDP.

   Resource reservation takes place using whatever protocols
   participants must use, based on support by their service provider.
   If the ISP's of the various participants are using differing
   resource reservation protocols, translation is necessary, but this
   is done within the network, without knowledge of the participants.

   The direction attribute indicates in which direction reservations
   should be reserved. If "send", it means reservations should be made
   in the direction of media flow from the session originator to
   participants. If "recv", it means reservations should be made in the
   direction of media flow from participants to the session originator.
   In the case of "sendrecv", it means reservations should be made in
   both directions.  If the direction attribute is "sendrecv" but the
   endpoints only support a single-direction resource reservation
   protocol, then both the originator and participants cooperate to
   ensure the agreed precondition is met.

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   In the case of security, the same attributes are defined -
   optional/mandatory, and send/recv/sendrecv. Their meaning is
   identical to the one above, except that a security association
   should be established in the given direction. The details of the
   security association are not signaled by SDP; these depend on the
   Security Policy Database of the participant.

   Either party can include a "confirm" attribute in the SDP.  When the
   "Confirm" attribute is present, the recipient sends a COMET message
   to the sender, with SDP attached, telling the status of each
   precondition as "success" or "failure."  If the "confirm" attribute
   is present in the SDP sent by the session originator to the
   participant (e.g. in the SIP INVITE message), then the participant
   sends the COMET message to the originator.  If the "confirm"
   attribute is present in the SDP sent by the recipient to the
   originator (e.g. in a SIP response message), then the originator
   sends the COMET message to the participant.

   When the "Confirm" attribute is present in both the SDP sent by the
   session originator to the participant (e.g. in the SIP INVITE
   message), and in the SDP sent by the recipient back to the
   originator (e.g. in a SIP response message), the session originator
   would wait for the COMET message with the success/failure
   notification before responding with a COMET message, and responds
   instead with a CANCEL if a mandatory precondition is not met, or if
   a sufficient combination of optional preconditions are not met.  The
   recipient does not wait for the COMET message from the originator
   before sending its COMET message.

   The "confirm" attribute is typically used if the direction attribute
   is "sendrecv" and the originator or participant only supports a
   single-direction resource reservation protocol.  In such a case, the
   originator (or participant) would reserve resources for one
   direction of media flow, and send a confirmation with a direction
   attribute of "send."  The participant (or originator) would reserve
   resources for the other direction.  On receipt of the COMET message,
   they would know that both directions have been reserved, and the
   precondition is met.

5. SDP Extension

   The formatting of the qos attribute in the Session Description
   Protocol (SDP)[3] is described by the following BNF:

      qos-attribute    = "a=qos:" strength-tag SP direction-tag
                                [SP confirmation-tag]
      strength-tag     = ("mandatory" | "optional" | "success" |
                                "failure")
      direction-tag    = ("send" | "recv" | "sendrecv")
      confirmation-tag = "confirm"

   and the security attribute:

      security-attribute = "a=secure:" SP strength-tag SP direction-tag

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                                [SP confirmation-tag]

5.1 SDP Example

   The following example shows an SDP description carried in a SIP
   INVITE message from A to B:

           v=0
           o=mhandley 2890844526 2890842807 IN IP4 126.16.64.4
           s=SDP Seminar
           i=A Seminar on the session description protocol
           u=http://www.cs.ucl.ac.uk/staff/M.Handley/sdp.03.ps
           e=mjh@isi.edu (Mark Handley)
           c=IN IP4 224.2.17.12/127
           t=2873397496 2873404696
           m=audio 49170 RTP/AVP 0
           a=qos:mandatory recv confirm
           m=video 51372 RTP/AVP 31
           a=secure:mandatory sendrecv
           m=application 32416 udp wb
           a=orient:portrait
           a=qos:optional sendrecv
           a=secure:optional sendrecv

   This SDP indicates that B should not continue its involvement in the
   session until resources for the audio are reserved from B to A, and
   a bi-directional security association is established for the video.
   B can join the sessions once these preconditions are met, but should
   reserve resources and establish a bi-directional security
   association for the whiteboard.

5.2 SDP Allowable Combinations

   If the recipient of the SDP (e.g. the UAS) is capable and willing to
   honor the precondition(s), it returns a provisional response
   containing SDP, along with the qos/security attributes, for each
   such stream. This SDP MUST be a subset of the preconditions
   indicated in the INVITE.

   Table 1 illustrates the allowed values for the direction tag in the
   response. Each row represents a value of the direction in the SIP
   INVITE, and each column the value in the response. An entry of N/A
   means that this combination is not allowed. A value of A->B (B->A)
   implies that the precondition is for resources reserved (or security
   established) from A to B (B to A). A value of A<->B means that the
   precondition is for resource reservation or security establishment
   in both directions. The value in the response is the one used by
   both parties.

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                                B: response
           A: request     send       recv  sendrecv  none
           send           N/A        A->B    N/A      --
           recv           B->A       N/A     N/A      --
           sendrecv       A<-B       B<-A   A<->B     --
           none            --         --      --      --

                Table 1: Allowed values of coupling

   Table 2 illustrates the allowed values for the strength tag in the
   request and response. A "Y" means the combination is allowed, and a
   "N" means it is not. The value in the response is the one used by
   both parties.

                                B: response
           A: request   mandatory     optional  none
           mandatory        Y            Y       Y
           optional         N            Y       Y
           none             N            N       Y

                Table 2: Allowed values of strength parameter

   Table 3 illustrates the allowed values for the direction tag in a
   confirmation message (COMET) sent from the originator to a
   participant, based on the value of the direction tag negotiated in
   the initial request and response.  A "Y" means the combination is
   allowed, and a "N" means it is not and SHOULD be ignored by the
   participant.

                         A: confirmation
           B: reponse  send   recv   sendrecv
           A->B         Y       N       N
           A<-B         N       Y       N
           A<->B        Y       Y       Y

        Table 3: Allowed values of direction in confirmation from A

   Table 4 illustrates the allowed values for the direction tag in a
   confirmation message (COMET) sent from the participant to the
   originator, based on the value of the direction tag negotiated in
   the initial request and response.  A "Y" means the combination is
   allowed, and a "N" means it is not and SHOULD be ignored by the
   originator.

                         B: confirmation
           B: reponse  send   recv   sendrecv
           A->B         N       Y       N
           A<-B         Y       N       N
           A<->B        Y       Y       Y

        Table 4: Allowed values of direction in confirmation from B

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6. SIP Extension: The COMET Method

   The COMET method is used for communicating successful completion of
   preconditions between the user agents.

   The signaling path for the COMET method is the signaling path
   established as a result of the call setup.  This can be either
   direct signaling between the calling and called user agents or a
   signaling path involving SIP proxy servers that were involved in the
   call setup and added themselves to the Record-Route header on the
   initial INVITE message.

   The precondition information is communicated in the message body,
   which MUST contain an SDP.  For every agreed precondition, the
   strength-tag MUST indicate "success" or "failure".

   If the initial request contained Record-Route headers, the
   provisional response MUST contain a copy of those headers, as if the
   response were a 200 OK to the initial request. Since provisional
   responses MAY contain Record-Route and Contact headers, the COMET
   request MUST contain Route headers headers, constructed as specified in [2],
   if the Record-Route headers were present in the provisional
   response. The Route header is constructed
   as specified in [2]. The Route header that is constructed from some
   provisional response MUST NOT be placed in any other request except
   for the COMET for that provisional response.

   A UAC MUST NOT insert a Route header into a COMET request if no
   Record-Route header was present in the response.

   If the initial request was sent with credentials, the COMET request
   SHOULD contain those credentials as well.

   The Call-ID in the COMET MUST match that of the provisional
   response. The CSeq in this request MUST be larger than the last
   request sent by this UAC for this call leg. The To, From, and Via
   headers MUST be present, and MUST be constructed as they would be
   for a re-INVITE or BYE as specified in [2]. In particular, if the
   provisional response contained a tag in the To field, this tag MUST
   be mirrored in the To field of the COMET.

   Once the COMET request is created, it is sent by the UAC. It is sent
   as would any other non-INVITE request for a call. In particular,
   when sent over UDP, the COMET request is retransmitted with an
   exponentially increasing interval, starting at 500 milliseconds and
   increasing to 4 seconds. as specified
   in [2].  Note that a UAC SHOULD NOT retransmit the COMET request
   when it receives a retransmission of the provisional response being
   acknowledged, although doing so does not create a protocol error. As
   with any other non-INVITE request, the UAC continues to retransmit
   the COMET request until it receives a final response.

   A COMET request MAY be cancelled. However, whilst allowed for
   purposes of generality, usage

   Use of CANCEL with of a COMET is NOT
   RECOMMENDED. as specified in [2].

6.1 Header Field Support for COMET Method

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6.1 Header Field Support for COMET Method

   Tables 3 5 and 4 6 are extensions of tables 4 and 5 in the SIP
   specification[2].  Refer to Section 6 of [2] for a description of
   the content of the tables.

6.2 Responses to the COMET Request Method

   If a server receives a COMET request it MUST send a final response.

   A 200 OK response MUST be sent by a UAS for a COMET request if the
   COMET request was successfully received for an existing call.
   Beyond that, no additional operations are required.

   A 481 Call Leg/Transaction Does Not Exist message MUST be sent by a
   UAS if the COMET request does not match any existing call leg.

             Header                    Where    COMET
             ------                    -----    ----
             Accept                      R       o
             Accept-Encoding             R       o
             Accept-Language             R       o
             Allow                      200      -
             Allow                      405      o
             Authorization               R       o
             Call-ID                    gc       m
             Contact                     R       o
             Contact                    1xx      -
             Contact                    2xx      -
             Contact                    3xx      -
             Contact                    485      -
             Content-Encoding            e       o
             Content-Length              e       o
             Content-Type                e       *
             CSeq                       gc       m
             Date                        g       o
             Encryption                  g       o
             Expires                     g       o
             From                       gc       m
             Hide                        R       o
             Max-Forwards                R       o
             Organization                g       o
             Table 3 5 Summary of header fields, A-0

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             Header                    Where    COMET
             ------                    -----    ----
             Priority                    R       o       -
             Proxy-Authenticate         407      o
             Proxy-Authorization         R       o
             Proxy-Require               R       o
             Record-Route                R       o
             Record-Route               2xx      o
             Require                     R       o
             Response-Key                R       o
             Retry-After                 R       -
             Retry-After            404,480,486  o
             Retry-After                503      o
             Retry-After              600,603    o
             Response-Key                R       o
             Record-Route                R       o
             Record-Route               2xx      o
             Route                       R       o
             Server                      r       o
             Subject                     R       o
             Timestamp                   g       o
             To                        gc(1)     m
             Unsupported                420      o
             User-Agent                  g       o
             Via                       gc(2)     m
             Warning                     r       o
             WWW-Authenticate           401      o

             Table 4 6 Summary of header fields, P-Z

   Other request failure (4xx), Server Failure (5xx) and Global Failure
   (6xx) responses MAY be sent for the COMET Request.

6.3 Message Body Inclusion

   The COMET request MUST contain a message body, with Content-type
   "application/sdp".

6.4 Behavior of SIP User Agents

   Unless stated otherwise, the protocol rules for the COMET request
   governing the usage of tags, Route and Record-Route, retransmission
   and reliability, CSeq incrementing and message formatting follow
   those in [2] as defined for the BYE request.

   A COMET request MAY be cancelled.  A UAS receiving a CANCEL for a
   COMET request SHOULD respond to the COMET with a "487 Request
   Cancelled" response if a final response has not been sent to the
   COMET and then behave as if the request were never received.

6.5 Behavior of SIP Proxy and Redirect Servers

6.5.1 Proxy Server

   Unless stated otherwise, the protocol rules for the COMET request at
   a proxy are identical to those for a BYE request as specified in
   [2].

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6.5.2 Forking Proxy Server

   Unless stated otherwise, the protocol rules for the COMET request at
   a proxy are identical to those for a BYE request as specified in
   [2].

6.5.3 Redirection Server

   Unless stated otherwise, the protocol rules for the COMET request at
   a proxy are identical to those for a BYE request as specified in
   [2].

7. SIP Extension: The 183-Session-Progress Response

   An additional provisional response is defined by this draft, which
   is returned by a UAS to convey information not otherwise classified.

7.1 Status Code and Reason Phrase

   The following is to be added to Figure 4 in Section 5.1.1,
   Informational and success Status codes.

        Informational = "183"  ;Session-Progress

7.2 Status Code Definition

   The following is to be added to a new section 7.1.5

   7.1.5 183 Session Progress

   The 183 (Session Progress) response is used to convey information
   about the progress of the call which is not otherwise classified.
   The Reason-Phrase MAY be used to convey more details about the call
   progress.

   The Session Progress response MAY contain a message body.  If so, it
   MUST contain a "Content-Disposition" header indicating the proper
   treatment of the message body.

8. SIP Extension: The 580-Precondition-Failure Response

   An additional error response is defined by this draft, which is
   returned by a UAS if it is unable to perform the mandatory
   preconditions for the session.

8.1 Status Code and Reason Phrase

   The following is to be added to Figure 8, Server error status codes

        Server-Error =  "580"  ;Precondition-Failure

8.2 Status Code Definition

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   The following is to be added to a new section 7.5.7.

   7.5.7 580 Precondition Failure

   The server was unable to establish the qos or security association
   mandated by the SDP precondition.

   The Precondition Failure response MUST contain a message body, with
   Content-Type "application/sdp", giving the specifics of the
   precondition that could not be met.

9. SIP Extension: Content-Disposition header

   An additional entity header is defined by this draft, which is
   returned by a UAS in a provisional response indicating preconditions
   for the session.

   The following is to be added to Table 3, SIP headers, in Section 3.

        Entity-header   = Content-Disposition   ; Section 6.14a

   The following entry is to be added to Table 4, Summary of header
   fields, A-O, in Section 6.

                                where  enc e-e  ACK BYE CAN INV OPT REG
        Content-Disposition       e         e    o   o   -   o   o   o

   The following is to be added to a new section after 6.14.

   6.14a Content-Disposition

        Content-disposition  = "Content-Disposition" ":"
                                Disposition-type *( ";" disp-param)
        Disposition-type     = "precondition" | disp-extension-token
        Disp-extension-token = token
        Disp-param           = "handling" "=" "optional" | "required"
                                | other-handling
        Other-handling       = token

   The Content-Disposition header field describes how the message body
   is to be interpreted by the UAC or UAS.

   The value "precondition" indicates the body part describes QoS
   and/or security preconditions that SHOULD be established prior to
   the start of the session.

   The handling parameter, disp-param, describes how the UAC or UAS
   should react if it receives a message body whose content type or
   disposition type it does not understand.  If the parameter has the
   value "optional" the UAS MUST ignore the message body; if it has the
   value "required" the UAS MUST return 415 (Unsupported Media Type).
   If the handling parameter is missing, the value "required" is to be
   assumed.

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10. Option tag for Requires and Supported headers

   This draft defines the option tag "precondition" for use in the
   Require and Supported headers [12].

   A UAS that supports this extension MUST respond to an OPTION request
   with a Supported header that includes the "precondition" tag.

   A UAC MAY include a "Require: precondition" in an INVITE request if
   it wants the session initiation to fail if the UAS does not support
   this feature.  A UAC that would respond to a failed session (if due
   to lack of precondition support) by immediately retrying the session
   without the preconditions, SHOULD NOT include this Require tag
   value.

   Presence of the precondition entries in the SDP message body of an
   INVITE request or response indicates support of this feature.  The
   UAC or UAS MAY in addition include a "Supported: precondition"
   header in the request or response.

11. SIP Usage Rules

11.1 Overview

   The session originator (UAC) prepares an SDP message body for the
   INVITE describing the desired QoS and security preconditions for
   each media flow, and the desired directions. The token value "send"
   means the direction of media from originator (whichever entity
   created the SDP) to recipient (whichever entity received the SDP in
   a SIP message), and "recv" is from recipient to originator. In an
   INVITE, the UAC is the originator, and the UAS is the recipient. The
   roles are reversed in the response.

   A User Agent with an active session that desires to change the media
   flows prepares an SDP message body for the re-INVITE describing the
   desired QoS and security preconditions for the revised media flows
   and the desired directions.  The procedures for the re-INVITE, and
   the subsequent message exchanges, are identical to those of an
   initial INVITE.

   The recipient of the INVITE (UAS) returns a 18x provisional response
   containing a Content-Disposition of "precondition," and SDP with the
   qos/security attribute for each stream having a precondition.  The
   preconditions in this SDP (i.e. strength tag and direction tag) are
   equal to, or a subset of, the preconditions indicated in the INVITE.
   The UAS would typically include a confirmation request in this SDP.
   Unlike normal SIP processing, the UAS MUST NOT alert the called user
   at this point.  The UAS now attempts to reserve the qos resources
   and establish the security associations.

   The 18x provisional response is received by the UAC. If the 18x
   contained SDP with mandatory qos/security parameters, the UAC does
   not let the session proceed until the mandatory preconditions are

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   met.  The UAC attempts to reserve the needed resources and establish
   the security associations.

   If either party requests a confirmation, a COMET message is sent to
   that party.  The COMET message contains the success/failure
   indication for each precondition. For a precondition with a
   direction value of "sendrecv," the COMET indicates whether the
   sender is able to confirm both directions or only one direction.
   Upon receipt of the COMET message, the UAC/UAS continues normal SIP
   call handling.  For a UAS this includes alerting the user and

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   sending a 180-Ringing or 200-OK response.  The UAC SIP transaction
   completes normally.

   Note that this extension requires usage of reliable provisional
   responses [11]. This is because the 18x contains SDP with
   information required for the session originator to initiate
   reservations towards the participant.

11.2 Behavior of Originator (UAC)

   The session originator (UAC) MAY include QoS and security
   preconditions (including the desired direction) for each media flow
   in the SDP sent with the INVITE. The token value "send" means the
   direction of media from originator (whichever entity created the
   SDP) to recipient (whichever entity received the SDP in a SIP
   message).  The token value "recv" means the direction of media from
   recipient to originator.  If preconditions are included in the
   INVITE request, the UAC MUST indicate support for reliable
   provisional responses [11].

   If the UAC receives a 18x provisional response without a Content-
   Disposition of "precondition," or without SDP, or with SDP but
   without any qos/security preconditions in any stream, UAC treats it
   as an indication that the UAS is unable or unwilling to perform the
   preconditions requested. As such, the UAC SHOULD proceed with normal
   call setup procedures.

   If the 18x provisional response contained a Content-Disposition of
   "precondition" and contained SDP with mandatory qos/security
   parameters, the UAC SHOULD NOT let the session proceed until the
   mandatory preconditions are met.

   If the 18x provisional response with preconditions requested an
   acknowledgement (using the methods of [11]), the UAC MUST include an
   updated SDP in the PRACK if the UAC modified the original SDP based
   on the response from the UAS.  Such a modification MAY be due to
   negotiation of compatible codecs, or MAY be due to negotiation of
   mandatory preconditions.  If the provisional response received from
   the UAS is a 180-Ringing, and the direction value of a mandatory
   precondition is "sendrecv," and the UAC uses a one-way QoS mechanism
   (such as RSVP), the updated SDP in the PRACK SHOULD request a
   confirmation from the UAS so that the bi-directional precondition
   can be satisfied before performing the requested alerting function.

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   Upon receipt of the 18x provisional response with preconditions, the
   UAC MUST initiate the qos reservations and establish the security
   associations to the best of its capabilities.

   If the UAC had requested confirmation in the initial SDP, it MAY
   wait for the COMET message from the UAS containing the
   success/failure status of each precondition.  The UAC MAY set a
   local timer to limit the time waiting for preconditions to complete.
   The UAC SHOULD merge the success/failure status in the COMET message
   with its local status.  For example, if the COMET message indicated

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   success in the "send" direction, and the UAC was also able to meet
   the precondition in the "send" direction, they combine to meet the
   precondition in the "sendrecv" direction.

   If any of the mandatory preconditions cannot be met, and a
   confirmation was not requested by the UAS, the UAC MUST send a
   CANCEL and terminate the session.  If any of the optional
   preconditions cannot be met, the UAC MAY consult with the
   originating customer for guidance on whether to complete the
   session.

   When all the preconditions have either been met or have failed, and
   the SDP received from the UAS included a confirmation request, the
   UAC MUST send a COMET message to the UAS with SDP.  Each
   precondition is updated to indicate success/failure and the
   appropriate direction tag is updated based on local operations
   performed combined with the received COMET message, if any.

   The session now completes normally, as per [2].  Any SDP included in
   subsequent requests in this transaction MUST NOT change the agreed
   media definitions (e.g. all lines in the SDP description other than
   the precondition lines).

11.3 Behavior of Destination (UAS)

   On receipt of an INVITE request containing preconditions, the UAS
   MUST generate a 18x provisional response containing a subset of the
   preconditions supported by the UAS.  In the response, the token
   value "send" means the direction of the media from the UAS to the
   UAC, and "recv" is from the UAC to the UAS.  This is reversed from
   the SDP in the initial INVITE.  The 18x provisional response MUST
   include a Content-Disposition header with parameter "precondition."
   If the "confirm" attribute is present in the SDP received from the
   UAC, or if the direction tag of a mandatory QoS precondition is
   "sendrecv" and the UAS only supports a one-way QoS reservation
   scheme (e.g. RSVP), then the UAS SHOULD include a "confirm"
   attribute. If the UAS is able to satisfy the preconditions
   immediately, and no confirmation is requested by the UAC, then a
   180-Ringing response is appropriate.  Otherwise a 183-Session-
   Progress response SHOULD be used.

   If the INVITE request did not contain any preconditions, but did
   indicate support for reliable provisional responses[11], the UAS MAY
   include preconditions in a 18x provisional response to the INVITE.

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   The 18x provisional response MUST include a Content-Disposition
   header with the parameter "precondition." The 18x provisional
   response MUST request an acknowledgement using the mechanism of
   [11].  If the PRACK includes an SDP without any preconditions, the
   UAS MAY complete the session without the preconditions, or MAY
   reject the INVITE request.

   The UAS SHOULD request an acknowledgement to the 18x provisional
   response, using the mechanism of [11].  The UAS SHOULD wait for the
   PRACK message before initiating resource reservation to allow the
   resource reservation to reflect 3-way SDP negotiation, or other
   information available only through receipt of the PRACK.

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   If the INVITE request or PRACK message contained mandatory
   preconditions, or requested a confirmation of preconditions, the UAS
   MUST NOT alert the called user.

   The UAS now attempts to reserve the qos resources and establish the
   security associations.  The UAS MAY set a local timer to limit the
   time waiting for preconditions to complete.

   If the UAS is unable to perform any mandatory precondition, and
   neither the UAC nor UAS requested a confirmation, the UAS MUST send
   a 580-Precondition-Failure response to the UAC.  If the UAS is
   unable to perform any optional precondition, it MAY consult with the
   customer to obtain guidance regarding completion of the session.

   When processing of all preconditions is complete, if a precondition
   in the initial INVITE SDP specified a confirmation request, the UAS MUST send a
   COMET message to the UAC containing SDP, along with the qos/security
   result of success/failure for each precondition.  If the direction
   tag of the precondition was "sendrecv" but the UAS was only able to
   ensure "send" or "recv," the direction tag in the COMET MUST only
   indicate what the UAS ensures.  The Request-URI, call-leg
   identification, and other headers of this COMET message are to be
   constructed identically to a BYE.

   If the UAS had requested confirmation of a precondition in the
   response SDP, it SHOULD wait for the COMET message from the
   originator containing the success/failure indication of each
   precondition from the originator's point of view.  The
   success/failure indications in the COMET message from the UAC SHOULD
   be combined with the local status to determine the overall
   success/failure of the precondition.  For example, if the COMET
   message indicated success in the "send" direction, and the UAS was
   also able to meet the precondition in the "send" direction, they
   combine to meet the precondition in the "sendrecv" direction.  If
   that combination indicates a failure for a mandatory precondition,
   the UAS MUST send a 580-Precondition-Failure response to the UAC.

   Once the preconditions are met, the UAS alerts the user, and the SIP
   transaction proceeds normally.

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   The UAS MAY send additional 18x provisional responses with Content-
   Disposition of "precondition," and the procedures described above
   are repeated sequentially for each.

   Any SDP included in subsequent requests and responses in this
   transaction MUST NOT change the agreed media definitions (e.g. all
   lines in the SDP description other than the precondition lines).

12. Examples

12.1 Single Media Call Flow

   Figure 1 presents a high-level overview of a basic end-point to end-
   point (UAC-UAS) call flow.  This example is appropriate for a
   single-media session with a mandatory quality-of-service "sendrecv"
   precondition, where both the UAC and UAS can only perform a single-
   direction ("send") resource reservation.

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   The session originator (UAC) prepares an SDP message body for the
   INVITE describing the desired QoS and security preconditions for
   each media flow, and the desired direction "sendrecv." This SDP is
   included in the INVITE message sent through the proxies, and
   includes an entry "a=qos:mandatory sendrecv."

   The recipient of the INVITE (UAS), being willing to perform the
   requested precondition, returns a 183-Session-Progress provisional
   response containing SDP, along with the qos/security attribute for
   each stream having a precondition.  Since the "sendrecv" direction
   tag required a cooperative effort of the UAC and UAS, the UAS
   requests a confirmation when the preconditions are met, with the SDP
   entry "a=qos:mandatory sendrecv confirm."  The UAS now attempts to
   reserve the qos resources and establish the security associations.

   The 183-Session-Progress provisional response is sent using the
   reliability mechanism of [11].  UAC sends the appropriate PRACK and
   UAS responds with a 200-OK to the PRACK.

   The 183-Session-Progress is received by the UAC, and the UAC
   requests the resources needed in its "send" direction, and
   establishes the security associations. Once the preconditions are
   met, the UAC sends a COMET message as requested by the confirmation
   token.  This COMET message contains an entry "a=qos:success send"

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   Originating (UAC)                            Terminating (UAS)
        |                  SIP-Proxy(s)                 |
        |  INVITE               |                       |
        |---------------------->|---------------------->|
        |                       |                       |
        |       183 w/SDP       |       183 w/SDP       |
        |<----------------------|<----------------------|
        |                                               |
        |                       PRACK                   |
        |---------------------------------------------->|
        |               200 OK (of PRACK)               |
        |<----------------------------------------------|
        | Reservation                       Reservation |
         ===========>                       <===========
        |                                               |
        |                                               |
        |               COMET                           |
        |---------------------------------------------->|
        |               200 OK (of COMET)               |
        |<----------------------------------------------|
        |
        |
        |                  SIP-Proxy(s)         User Alerted
        |                       |                       |
        |       180 Ringing     |       180 Ringing     |
        |<----------------------|<----------------------|
        |                                               |
        |                       PRACK                   |
        |---------------------------------------------->|
        |               200 OK (of PRACK)               |
        |<----------------------------------------------|
        |                                               |
        |                                       User Picks-Up
        |                  SIP-Proxy(s)         the phone
        |                       |                       |
        |       200 OK          |       200 OK          |
        |<----------------------|<----------------------|
        |                       |                       |
        |                                               |
        |                       ACK                     |
        |---------------------------------------------->|

                        Figure 1: Basic Call Flow

   The UAS successfully performs its resource reservation, in its
   "send" direction, and waits for the COMET message from the UAC.

   On receipt of the COMET message, the UAS processes the "send"
   confirmation contained in the COMET SDP.  The "send" confirmation
   from the UAC coupled with its own "send" success, allows the UAS to
   determine that all preconditions have been met.  The UAS then
   continues with session establishment.  At this point it alerts the
   user, and sends a 180-Ringing provisional response.  This

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   user, and sends a 180-Ringing provisional response.  This
   provisional response is also sent using the reliability mechanism of
   [11], resulting in a PRACK message and 200-OK of the PRACK.

   When the destination party answers, the normal SIP 200-OK final
   response is sent through the proxies to the originator, and the
   originator responds with an ACK message.

   Either party can terminate the call.  An endpoint that detects an
   "on-hook" (request to terminate the call) releases the QoS resources
   held for the connection, and sends a SIP BYE message to the remote
   endpoint, which is acknowledged with a 200-OK.

12.2 Multiple Media Call Flow

   Figure 2 presents a high-level overview of an advanced end-point to
   end-point (UAC-UAS) call flow.  This example is appropriate for a
   multiple-media session with some combination of mandatory and
   optional quality-of-service precondition.  For example, the
   originator may suggest five media streams, and be willing to
   establish the session if any three of them are satisfied.

   The use of reliable provisional responses is assumed, but not shown
   in this figure.

   The session originator (UAC) prepares an SDP message body for the
   INVITE describing the desired QoS and security preconditions for
   each media flow, and the desired directions. UAC also requests
   confirmation of the preconditions.  The UAS receiving the INVITE
   message responds with 183-Session-Progress, as in the previous
   example.

   When the UAS has completed the resource reservations and security
   session establishment, it sends a confirmation to the UAC in the
   form of a COMET message, with each precondition marked in the SDP as
   either success or failure.  Note that if UAS was not satisfied with
   the combination of successful preconditions, it could instead have
   responded with 580-Precondition-Failure, and ended the INVITE
   transaction.

   If the UAC has satisfied its preconditions, and is satisfied with
   the preconditions achieved by the UAS, it responds with the COMET
   message.  The COMET message contains the SDP with the
   success/failure results of each precondition attempted by UAC.  If
   UAC is not satisfied with the combination of successful
   preconditions, it could instead have sent a CANCEL message.

   On receipt of the COMET message, UAS examines the combination of
   satisfied preconditions reported by UAC, and makes a final decision
   whether to proceed with the session.  If sufficient preconditions
   are not satisfied, the UAS responds with 580-Precondition-Failure.
   Otherwise, the session proceeds as in the previous example.

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   Originating (UAC)                            Terminating (UAS)
        |                  SIP-Proxy(s)                 |
        |  INVITE               |                       |
        |---------------------->|---------------------->|
        |                       |                       |
        |       183 w/SDP       |       183 w/SDP       |
        |<----------------------|<----------------------|
        |                                               |
        | Reservation                       Reservation |
         ===========>                       <===========
        |                                               |
        |               COMET                           |
        |<----------------------------------------------|
        |               200 OK (of COMET)               |
        |---------------------------------------------->|
        |                                               |
        |               COMET                           |
        |---------------------------------------------->|
        |               200 OK (of COMET)               |
        |<----------------------------------------------|
        |
        |
        |                  SIP-Proxy(s)         User Alerted
        |                       |                       |
        |       180 Ringing     |       180 Ringing     |
        |<----------------------|<----------------------|
        |                                               |
        |                                               |
        |                                       User Picks-Up
        |                  SIP-Proxy(s)         the phone
        |                       |                       |
        |       200 OK          |       200 OK          |
        |<----------------------|<----------------------|
        |                       |                       |
        |                                               |
        |                       ACK                     |
        |---------------------------------------------->|

   Figure 2: Call Flow with negotiation of optional preconditions

13. Special considerations with Forking Proxies

   If a proxy along the signaling path between the UAC and UAS forks
   the INVITE request, it results in two or more UASs simultaneously
   sending provisional responses with preconditions.  The procedures
   above result in the UAC handling each independently, reserving
   resources and responding with COMET messages as required.

   This results in multiple resource reservations from the UAC, only
   one of which will be utilized for the final session.  While
   functionally correct, this has the unfortunate side-effect of
   increasing the call blocking probability.

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   Customized resource allocation protocols may be used by the UAC to
   reduce this duplicate allocation and prevent excess blocking of
   calls.  For one such example, see [8].

   Other procedures which the UAC has available to handle multiple
   simultaneously active transactions (e.g. CANCEL, and BYE) are as
   given in [2].

14. Advantages of the Proposed Approach

   The use of two-phase call signaling makes it possible for SIP to
   meet user expectations that come from the telephony services.

   The reservation of resources before the user is alerted makes sure
   that the network resources are assured before the destination end-
   point is informed about the call.

   The number of messages and the total delay introduced by these
   messages is kept to a minimum without sacrificing compatibility with
   SIP servers that do not implement preconditions.

15. Security Considerations

   If the contents of the SDP contained in the 183-Session-Progress are
   private then end-to-end encryption of the message body can be used
   to prevent unauthorized access to the content.

   The security considerations given in the SIP specification apply to
   the COMET method.  No additional security considerations specific to
   the COMET method are necessary.

16. Notice Regarding Intellectual Property Rights

   The IETF has been notified of intellectual property rights claimed
   in regard to some or all of the specification contained in this
   document.  For more information consult the online list of claimed
   rights.

17. References

   1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP
     9, RFC 2026, October 1996.

   2. M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
     Session Initiation Protocol," RFC 2543, March 1999.

   3. M. Handley and V. Jacobson, "SDP: Session Description Protocol,"
     RFC 2327, April 1998.

   4. Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997

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   5. R. Braden, Ed., L. Zhang, S. Berson, S. Herzog, and S. Jamin,
     "Resource ReSerVation protocol (RSVP) -- version 1 functional
     specification," RFC 2205, September, 1997.

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   6. P. P. Pan and H. Schulzrinne, "YESSIR: A simple reservation
     mechanism for the Internet," in Proc. International Workshop on
     Network and Operating System Support for Digital Audio and Video
     (NOSSDAV), (Cambridge, England), July 1998.  Also IBM Research
     Technical Report TC20967.  Available at
     http://www.cs.columbia.edu/~hgs/papers/Pan98_YESSIR.ps.gz.

   7. PacketCable, Dynamic Quality of Service Specification, pkt-sp-
     dqos-i01-991201, December 1, 1999.  Available at
     http://www.packetcable.com/specs/pkt-sp-dqos-i01-991202.pdf.

   8. S. Kent and R. Atkinson, "Security architecture for the internet
     protocol," RFC 2401, November 1998.

   9. H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP: a
     Transport Protocol for Real-Time Applications," RFC 1889, January
     1996.

   10.  M. Handley, C. Perkins, and E. Whelan, "Session Announcement
     Protocol," RFC2974, October, 2000.

   11.  "Reliability of Provisional Responses in SIP," RFC pending.

   12.  "The SIP Supported Header,"  RFC pending.

18. Acknowledgments

   The Distributed Call Signaling work in the PacketCable project is
   the work of a large number of people, representing many different
   companies.  The authors would like to recognize and thank the
   following for their assistance: John Wheeler, Motorola; David
   Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jay Strater,
   Jeff Ollis, Clive Holborow, General Instruments; Doug Newlin, Guido
   Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks; Farzi
   Khazai, Nortel; John Chapman, Bill Guckel, Cisco; Chuck Kalmanek,
   Doug Nortz, John Lawser, James Cheng, Tung-Hai Hsiao, Partho Mishra,
   AT&T; Telcordia Technologies; and Lucent Cable Communications.

19. Author's Addresses

   Bill Marshall
   AT&T
   Florham Park, NJ  07932
   Email: wtm@research.att.com

   K. K. Ramakrishnan
   TeraOptic Networks
   Sunnyvale, CA
   Email: kk@teraoptic.com

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   TeraOptic Networks
   Sunnyvale, CA
   Email: kk@teraoptic.com

   Ed Miller
   Terayon
   Louisville, CO  80027
   Email: E.Miller@terayon.com

   Glenn Russell
   CableLabs
   Louisville, CO  80027
   Email: G.Russell@Cablelabs.com

   Burcak Beser
   Pacific Broadband Communications
   San Jose, CA
   Email: Burcak@pacband.com

   Mike Mannette
   3Com
   Rolling Meadows, IL  60008
   Email: Michael_Mannette@3com.com

   Kurt Steinbrenner
   3Com
   Rolling Meadows, IL  60008
   Email: Kurt_Steinbrenner@3com.com

   Dave Oran
   Cisco
   Acton, MA  01720
   Email: oran@cisco.com

   Flemming Andreasen
   Cisco
   Edison, NJ
   Email: fandreas@cisco.com

   Michael Ramalho
   Cisco
   Wall Township, NJ
   Email: mramalho@cisco.com

   John Pickens
   Com21
   San Jose, CA
   Email: jpickens@com21.com

   Poornima Lalwaney
   Nokia
   San Diego, CA  92121
   Email: poornima.lalwaney@nokia.com

   Jon Fellows
   Copper Mountain Networks
   San Diego, CA  92121
   Email: jfellows@coppermountain.com

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   Jon Fellows
   Copper Mountain Networks
   San Diego, CA  92121
   Email: jfellows@coppermountain.com

   Doc Evans
   D. R. Evans Consulting
   Boulder, CO  80303
   Email: n7dr@arrl.net

   Keith Kelly
   NetSpeak
   Boca Raton, FL  33587
   Email: keith@netspeak.com

   Adam Roach
   Ericsson
   Richardson, TX  75081
   Email: adam.roach@ericsson.com

   Jonathan Rosenberg
   dynamicsoft
   West Orange, NJ  07052
   Email: jdrosen@dynamicsoft.com

   Dean Willis
   dynamicsoft
   West Orange, NJ  07052
   Email: dwillis@dynamicsoft.com

   Steve Donovan
   dynamicsoft
   West Orange, NJ  07052
   Email: sdonovan@dynamicsoft.com

   Henning Schulzrinne
   Columbia University
   New York, NY
   Email: schulzrinne@cs.columbia.edu

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