[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: (draft-biggs-sip-replaces) 00 01 02 03 04 05 RFC 3891

SIP WG                                                           R. Mahy
Internet-Draft                                       Cisco Systems, Inc.
Expires: September 30, 2002                                     B. Biggs
                                                                 R. Dean
                                                              April 2002


        The Session Inititation Protocol (SIP) "Replaces" Header
                     draft-ietf-sip-replaces-02.txt

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at http://
   www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on September 30, 2002.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document defines a new header for use with SIP multi-party
   applications and call control.  The Replaces header is used to
   logically replace an existing SIP dialog with a new SIP dialog.  This
   primitive can be used to enable a variety of features, for example:
   "Attended Transfer" and "Retrieve from Call Park".  Note that
   definition of these example features is non-normative.







Mahy, et al.           Expires September 30, 2002               [Page 1]

Internet-Draft                  Replaces                      April 2002


Table of Contents

   1.   Conventions  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Overview . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.   User Agent Server Behavior: Receiving a Replaces Header  . .   5
   4.   User Agent Client Behavior: Sending a Replaces header  . . .   6
   5.   Proxy behavior . . . . . . . . . . . . . . . . . . . . . . .   6
   6.   Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.1  The Replaces Header  . . . . . . . . . . . . . . . . . . . .   7
   6.2  New option tag for Require and Supported headers . . . . . .   8
   6.3  687 Response Code: "Dialog Terminated" . . . . . . . . . . .   8
   7.   Usage Examples . . . . . . . . . . . . . . . . . . . . . . .   8
   7.1  Replacing an Early Dialog at the receiver  . . . . . . . . .   8
   7.2  Replacing an Early Dialog at the originator  . . . . . . . .  10
   8.   Security Considerations  . . . . . . . . . . . . . . . . . .  12
   9.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .  13
   9.1  Registration of "Replaces" SIP header  . . . . . . . . . . .  13
   9.2  Registration of "replaces" SIP Option-tag  . . . . . . . . .  13
   9.3  Registration of "687" SIP Response code  . . . . . . . . . .  13
   10.  Changes  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   10.1 Changes Since -01  . . . . . . . . . . . . . . . . . . . . .  13
   10.2 Changes Since -00  . . . . . . . . . . . . . . . . . . . . .  14
   11.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  14
        Normative References . . . . . . . . . . . . . . . . . . . .  14
        Informational References . . . . . . . . . . . . . . . . . .  15
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  15
        Full Copyright Statement . . . . . . . . . . . . . . . . . .  17
























Mahy, et al.           Expires September 30, 2002               [Page 2]

Internet-Draft                  Replaces                      April 2002


1. Conventions

   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 [2].

   This document refers frequently to the terms "confirmed dialog" and
   "early dialog".  These are defined in Section 12 of SIP [1].

2. Overview

   This document describes a SIP [1] extension header field as part of
   the SIP multiparty applications architecture framework [6].  The
   Replaces header is used to logically replace an existing SIP dialog
   with a new SIP dialog.  This is especially useful in peer-to-peer
   call control environments.

   One use of the "Replaces" header is to replace one participant with
   another in a multimedia conversation.  While this functionality is
   already available using 3rd party call control [8] style call
   control, the 3pcc model requires a central point of control which may
   not be desirable in many environments.  As such, a method of
   performing these same call control primitives in a distributed, peer-
   to-peer fashion is very desirable.

   Use of a new INVITE with a new header for dialog matching was chosen
   over making implicit associations in an incoming INVITE based on
   call-id or other fields for the following reasons:

   o  An INVITE already has the correct semantics for a new call

   o  Using an explicit Replaces header in a new request makes the
      intent of the request obvious.

   o  A unique call-id may be given to the replacement call.  This
      avoids call-leg matching problems in any of the clients.

   o  There are no adverse effects if the header is unsupported.

   The Replaces header enables services such as attended call transfer,
   retrieve from park, and transition from locally mixed conferences to
   two party calls in a distributed peer-to-peer way.  This list of
   services is not exhaustive.  Although the Replaces header is
   frequently used in combination with the REFER [4] method as used in
   cc-transfer [7], they may be used independently.

   For example, Alice is talking to Bob from phone1.  She transfers Bob
   to a Parking Place while she goes to the lab.  When she gets there



Mahy, et al.           Expires September 30, 2002               [Page 3]

Internet-Draft                  Replaces                      April 2002


   she retrieves the "parked" call from phone2 by sending an INVITE with
   a Replaces header field to Bob with the dialog information Bob shared
   with the Parking Place.  Alice got this information using some out of
   band mechansim.  Perhaps she subscribed to this information from the
   Parking Place, or went to a website and clicked on a URI.  A short
   call flow for this example follows.  (Via and Max-Forwards headers
   are omitted for clarity.)

        Alice          Alice                             Parking
        phone1         phone2            Bob               Place
        |               |                 |                   |
        |<===============================>|                   |
        |               |                 |                   |
        |        Alice transfers Bob to Parking Place         |
        |               |                 |                   |
        |------------REFER/200----------->|    *1    *2       |
        |               |                 |--INVITE/200/ACK-->|
        |<-----------NOTIFY/200-----------|<=================>|
        |------------BYE/200------------->|                   |
        |               |                 |                   |
        |               |                 |                   |
        |  Alice later retrieves call from another phone      |
        |               |                 |                   |
        |            *3 |-INV w/Replaces->|                   |
        |               |<--200-----------|                   |
        |               |---ACK---------->|----BYE/200------->|
        |               |<===============>|                   |
        |               |                 |                   |


   Message *1: Bob-> Parking Place

   INVITE sip:parkingplace@sip.org SIP/2.0
   To: <sip:parkingplace@sip.org>
   From: <sip:bob@sip.org>;tag=7743
   Call-ID: 425928@bobster.sip.org
   CSeq: 1 INVITE
   Contact: <sip:bob@bobster.sip.org>
   Referred-By: <sip:alice@phone1.sip.org>

   Message *2: Parking Place -> Bob

   SIP/2.0 200 OK
   To: <sip:parkingplace@sip.org>;tag=6472
   From: <sip:bob@sip.org>;tag=7743
   Call-ID: 425928@bobster.sip.org
   CSeq: 1 INVITE
   Contact: <sip:parkplace@monopoly.sip.org>



Mahy, et al.           Expires September 30, 2002               [Page 4]

Internet-Draft                  Replaces                      April 2002


   Message *3: Alice@phone2 -> Bob

   INVITE sip:bob@bobster.sip.org
   To: <sip:bob@sip.org>
   From: <sip:alice@phone2.sip.org>;tag=8983
   Call-ID: 09870@phone2.sip.org
   CSeq: 1 INVITE
   Contact: <sip:alice@phone2.sip.org>
   Require: replaces
   Replaces: 425928@bobster.sip.org;to-tag=7743;from-tag=6472


3. User Agent Server Behavior: Receiving a Replaces Header

   The Replaces header contains information used to match an existing
   SIP dialog (call-id, to-tag, and from-tag).  Upon receiving an INVITE
   with a Replaces header, the UA attempts to match this information
   with a confirmed or early dialog.  The to-tag and from-tag are
   matched as if they were present in an incoming request.  In other
   words the to-tag is compared to the local tag, and the from-tag is
   compared to the remote tag.

   If more than one Replaces header field is present in an INVITE, or if
   a Replaces header field is present in a request other than INVITE,
   the UAS MUST reject the request with a 400 Bad Request response.

   The Replaces header has specific call control semantics.  If both a
   Replaces header field and another header field with contradictory
   semantics are present in a request, the request MUST be rejected with
   a 400 "Bad Request" response.

   If the Replaces header field matches more than one dialog, the UA
   MUST act as if no match is found.

   If no match is found, the UAS rejects the INVITE and returns a 481
   Call/Transaction Does Not Exist response.  Likewise, if the Replaces
   header field matches a dialog which was not created with an INVITE,
   the UAS MUST reject the request with an appropriate response (ex:
   400, 481, or 501).

   If the Replaces header field matches a dialog which has already
   terminated, the UA SHOULD decline the request with a 603 Declined
   response.

   If the Replaces header field matches a active dialog, the UA SHOULD
   verify that the initiator of the new INVITE is authorized to replace
   the matched dialog.  If the initiator of the new INVITE has
   authenticated successfully as equivalent to the user who is being



Mahy, et al.           Expires September 30, 2002               [Page 5]

Internet-Draft                  Replaces                      April 2002


   replaced, then the replacement is authorized.  In addition, the UA
   MAY use other authorization mechanisms defined for this purpose in
   standards track extensions.  For example, an extension could define a
   mechanism for transitively asserting authorization of a replacement.

   If authorization is successful, the UA attempts to accept the new
   INVITE, reassign the user interface and other resources of the
   matched dialog to the new INVITE, and shut down the replaced dialog.
   If the UA cannot accept the new INVITE (for example: it cannot
   establish required QoS or keying, or it has incompatible media), the
   UA MUST return an appropriate error response and MUST leave the
   matched dialog unchanged.

   If the Replaces header field matches a confirmed dialog, it accepts
   the new INVITE by sending a 200-class response, and shuts down the
   replaced dialog by sending a BYE.  If the Replaces header field
   matches an early dialog that was initiated by the UA, it accepts the
   new INVITE by sending a 200-class response, and shuts down the
   replaced dialog by sending a CANCEL.  If the Replaces header field
   matches an early dialog that was not initiated by the UA, the UA
   returns a provisional or final response to the new INVITE which is
   suitable for the state of the resources used by the matched dialog,
   and responds to the replaced early dialog with a 687 "Transaction
   Terminated" response (defined earlier in this document).

4. User Agent Client Behavior: Sending a Replaces header

   A User Agent that wishes to replace a single existing early or
   confirmed dialog with a new dialog of its own, MAY send the target
   User Agent an INVITE request containing a Replaces header field.  The
   UAC places the Call-ID, to-tag, and from-tag information for the
   target dialog in a single Replaces header field and sends the new
   INVITE to the target.

   Note that use of this mechanism does not provide a way to match
   multiple dialogs, nor does it provide a way to match an entire call,
   an entire transaction, or to follow a chain of proxy forking logic.
   For example, if Alice replaces Cathy in an early dialog with Bob, but
   he does not answer, Alice's replacement request will not match other
   dialogs to which Bob's UA redirects, nor other branches to which his
   proxy forwards.

5. Proxy behavior

   Proxy Servers do not require any new behavior to support this
   extension.  They simply pass the Replaces header field transparently
   as described in the SIP specification.




Mahy, et al.           Expires September 30, 2002               [Page 6]

Internet-Draft                  Replaces                      April 2002


   Note that it is possible for a proxy (especially when forking based
   on some application layer logic, such as caller screening or time-of-
   day routing) to forward an INVITE request containing a Replaces
   header field to a completely orthogonal set of Contacts than the
   original request it was intended to replace.  In this case, the
   INVITE request with the Replaces header field will fail.

6. Syntax

6.1 The Replaces Header

   The Replaces header field indicates that a single dialog identified
   by the header field is to be shut down and logically replaced by the
   incoming INVITE in which it is contained.  It is a request header
   only, and defined only for INVITE requests.  The Replaces header
   field MAY be encrypted as part of end-to-end encryption.  Only a
   single Replaces header field value may be present in a SIP request

   This document adds the following entry to Table 3 of [1].  Additions
   to this table are also provided for extension methods defined at the
   time of publication of this document.  This is provided as a courtesy
   to the reader and is not normative in any way.  SUBSCRIBE and NOTIFY,
   REFER, INFO, UPDATE, and PRACK are defined respectively in [10], [4],
   [11], [12], and [13].

        Header field    where   proxy   ACK  BYE  CAN  INV  OPT  REG
        ------------    -----   -----   ---  ---  ---  ---  ---  ---
        Replaces          R              -    -    -    o    -    -


                                        SUB  NOT  REF  INF  UPD  PRA
                                        ---  ---  ---  ---  ---  ---
        Replaces          R              -    -    -    -    -    -

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) as described in RFC-2234 [3].

      Replaces        = "Replaces" HCOLON callid *(SEMI replaces-param)
      replaces-param  = to-tag / from-tag / generic-param
      to-tag          = "to-tag" EQUAL token
      from-tag        = "from-tag" EQUAL token


   A Replaces header MUST contain exactly one to-tag and exactly one
   from-tag, as they are required for unique dialog matching.  For
   compatibility with dialogs initiated by RFC2543 [5] compliant UAs, a
   tag of zero matches both tags of zero and null tags.




Mahy, et al.           Expires September 30, 2002               [Page 7]

Internet-Draft                  Replaces                      April 2002


   Examples:

      Replaces: 98732@sip.billybiggs.com
                ;from-tag=r33th4x0r
                ;to-tag=ff87ff

      Replaces: 12adf2f34456gs5;to-tag=12345;from-tag=54321

      Replaces: 87134@171.161.34.23;to-tag=24796;from-tag=0



6.2 New option tag for Require and Supported headers

   This specification defines a new Require/Supported header option tag
   "replaces".  UAs which support the Replaces header MUST include the
   "replaces" option tag in a Supported header field.  UAs that want
   explicit failure notification if Replaces is not supported MAY
   include the "replaces" option in a Require header field.

   Example:

      Require: replaces, 100rel


6.3 687 Response Code: "Dialog Terminated"

   This specification defines a new SIP response code.  The 687 "Dialog
   Terminated" response code indicates that an early dialog has been
   completely replaced by a new dialog.  A new response code was chosen
   from the 6xx class to prevent intervening proxies from attempting to
   fork additional branches of the replaced dialog.

7. Usage Examples

   The following non-normative examples are not intended to enumerate
   all the possibilities for the usage of this extension, but rather to
   provide examples or ideas only.  For more examples, please see
   service-examples [9].  Via and Max-Forwards headers are omitted for
   clarity and brevity.

7.1 Replacing an Early Dialog at the receiver

   In this example, a Customer tries calling a call center and for some
   reason cannot get through properly.  The customer calls an Operator
   and asks for help.  The operator calls the contact center, and upon
   receiving a provisional response, assumes that everything is OK and
   transfers the Customer to the Call Center, replacing the operator's



Mahy, et al.           Expires September 30, 2002               [Page 8]

Internet-Draft                  Replaces                      April 2002


   place in the queue.

                                                       Call
      Operator               Customer                  Center
        |                       |                        |
        |<--INVITE/180/200/ACK--|                        |
        |<=====================>|  "Hello, I'm having    |
        |                       |   trouble calling ..." |
        |"OK, I'll try it and   |                        |
        | transfer you if it    |                        |
        | works for me"         |                        |
        |                       |                        |
     *1 |-----INVITE ----------------------------------->|
     *2 |<----182: You are caller number 7---------------|
        |                       |                        |
        |  completes transfer   |                        |
        |                       |                        |
        |---REFER/200---------->|                        |
        |                       |--INVITE with Replaces->| *3
        |                       |<----182: caller #7-----| *4
        |<----687 Dialog Terminated----------------------| *5
        |-----ACK--------------------------------------->|
        |<--NOTIFY/200----------|                        |
        |---BYE/200------------>|                        |
        |                       |  ...time passes..      |
        |                       |                        |
        |                       |                        |
        |                       |                        |
        |                       |<---200 OK--------------|
        |<--NOTIFY/200----------|----ACK---------------->|
        |                       |                        |
        |                       |                        |

   Message *1: Operator -> Call Center

   INVITE sip:helpdesk@clueless.org SIP/2.0
   To: <sip:helpdesk@clueless.org>
   From: <sip:operator@acme.com>;tag=7743
   Call-ID: 425928@dhcp23311.acme.com
   CSeq: 1 INVITE
   Contact: <sip:jdoe@dhcp2311.acme.com>
   Accept-Language: en

   Message *2: Call Center -> Operator

   SIP/2.0 182 You are 7th in Queue
   To: <sip:helpdesk@clueless.org>;tag=6472
   From: <sip:operator@acme.com>;tag=7743



Mahy, et al.           Expires September 30, 2002               [Page 9]

Internet-Draft                  Replaces                      April 2002


   Call-ID: 425928@dhcp23311.acme.com
   CSeq: 1 INVITE
   Contact: <sip:helpdesk@frontline.clueless.org>

   Message *3: Customer -> Call Center

   INVITE sip:helpdesk@frontline.clueless.org
   To: <sip:helpdesk@clueless.org>
   From: <sip:customer@acme.com>;tag=8983
   Call-ID: 09870@lobby12.acme.com
   CSeq: 1 INVITE
   Contact: <sip:customer@lobby12.acme.com>
   Replaces: 425928@dhcp23311.acme.com;to-tag=7743;from-tag=6472
   Accept-Language: en
   Referred-By: <sip:jdoe@dhcp2311.acme.com>

   Message *4: Call Center -> Customer

   SIP/2.0 182 You are 7th in Queue
   To: <sip:helpdesk@clueless.org>
   From: <sip:customer@acme.com>;tag=8983
   Call-ID: 09870@lobby12.acme.com
   CSeq: 1 INVITE
   Contact: <sip:helpdesk@frontline.clueless.org>

   Message *5: Call Center -> Operator

   SIP/2.0 687 Dialog Terminated
   To: <sip:helpdesk@clueless.org>;tag=6472
   From: <sip:operator@acme.com>;tag=7743
   Call-ID: 425928@dhcp23311.acme.com
   CSeq: 1 INVITE
   Contact: <sip:helpdesk@frontline.clueless.org>


7.2 Replacing an Early Dialog at the originator

   In this example, Bob just arrived in the lab and hasn't registered
   there yet.  He hears his desk phone ring.  He quickly logs into a
   software UA on a nearby computer.  Among other things, the software
   UA has access to the dialog state of his desk phone.  When it notices
   that his phone is ringing it offers him the choice to take the call
   there.  The software UA sends an INVITE with Replaces to Alice.  When
   Alice's UA receives this new INVITE, it CANCELs her original INVITE
   and connects Alice to Bob.

                              Bob                      Bob
       Alice                  desk                     lab



Mahy, et al.           Expires September 30, 2002              [Page 10]

Internet-Draft                  Replaces                      April 2002


        |                       |                        |
    *1  |-----INVITE----------->|                        |
    *2  |<----180---------------|  Bob hears desk phone  |
        |                       |  ringing from lab but  |
        |                       |  isn't REGISTERed yet  |
        |                       |                        |
        |                       |<--fetch dialog state --|
        |                       |---response ----------->|
   *3/4 |<-----INVITE with Replaces/200/ACK--------------|
   *5/6 |------CANCEL/200------>|                        |
   *7   |<-----487--------------|                        |
        |------ACK------------->|                        |
        |                       |                        |
        |                       |                        |

   Message *1: Alice -> Bob's desk phone

   INVITE sip:bob@sip.org SIP/2.0
   To: <sip:bob@sip.org>
   From: <sip:alice@sip.org>;tag=7743
   Call-ID: 425928@phone.sip.org
   CSeq: 1 INVITE
   Contact: <sip:alice@phone.sip.org>

   Message *2: Bob's desk phone -> Alice

   SIP/2.0 180 Ringing
   To: <sip:bob@sip.org>;tag=6472
   From: <sip:alice@sip.org>;tag=7743
   Call-ID: 425928@phone.sip.org
   CSeq: 1 INVITE
   Contact: <sip:bob@bobster.sip.org>

   Message *3: Bob in lab -> Alice

   INVITE sip:alice@phone.sip.org
   To: <sip:alice@sip.org>
   From: <sip:bob@sip.org>;tag=8983
   Call-ID: 09870@labpc.sip.org
   CSeq: 1 INVITE
   Contact: <sip:bob@labpc.sip.org>
   Replaces: 425928@phone.sip.org;to-tag=7743;from-tag=6472

   Message *4: Alice -> Bob in lab

   SIP/2.0 200 OK
   To: <sip:alice@sip.org>;tag=9232
   From: <sip:bob@sip.org>;tag=8983



Mahy, et al.           Expires September 30, 2002              [Page 11]

Internet-Draft                  Replaces                      April 2002


   Call-ID: 09870@labpc.sip.org
   CSeq: 1 INVITE
   Contact: <sip:alice@phone.sip.org>

   Message *5: Alice -> Bob's desk

   CANCEL sip:bob@sip.org SIP/2.0
   To: <sip:bob@sip.org>
   From: <sip:alice@sip.org>;tag=7743
   Call-ID: 425928@phone.sip.org
   CSeq: 1 CANCEL
   Contact: <sip:alice@phone.sip.org>

   Message *6: Bob's desk -> Alice

   SIP/2.0 200 OK
   To: <sip:bob@sip.org>
   From: <sip:alice@sip.org>;tag=7743
   Call-ID: 425928@phone.sip.org
   CSeq: 1 CANCEL
   Contact: <sip:bob@bobster.sip.org>

   Message *7: Bob's desk -> Alice

   SIP/2.0 487 Request Terminated
   To: <sip:bob@sip.org>;tag=6472
   From: <sip:alice@sip.org>;tag=7743
   Call-ID: 425928@phone.sip.org
   CSeq: 1 INVITE
   Contact: <sip:bob@bobster.sip.org>


8. Security Considerations

   The extension specified in this document significantly changes the
   relative security of SIP devices.  Currently in SIP, even if an
   eavesdropper learns the Call-ID, To, and From headers of a dialog,
   they cannot easily modify or destroy that dialog if Digest
   authentication or end-to-end message integrity are used.

   This extension can be used to disconnect participants or replace
   participants in a multimedia conversation.  As such, invitations with
   the Replaces header SHOULD only be accepted if the peer requesting
   replacement has been properly authenticated using a standard SIP
   mechanism, and authorized to request a replacement of the target
   dialog.

   Some mechanisms for obtaining the dialog information needed by the



Mahy, et al.           Expires September 30, 2002              [Page 12]

Internet-Draft                  Replaces                      April 2002


   Replaces header (Call-ID, to-tag, and from-tag) include URIs on a web
   page, subscriptions to an appropriate event package, and notifcations
   after a REFER request.  Use of end-to-end security mechanisms to
   encrypt this information is also RECOMMENDED.

   This extension was designed to take advantage of future signature or
   authorization schemes defined by the SIP Working Group.  In general,
   call control features would benefit considerably from such work.

9. IANA Considerations

9.1 Registration of "Replaces" SIP header

   Name of Header:          Replaces

   Short form:              none

   Normative description:   section 6.1 of this document


9.2 Registration of "replaces" SIP Option-tag

   Name of option:          replaces

   Description:             Support for the SIP Replaces header

   SIP headers defined:     Replaces

   Normative description:   This document



9.3 Registration of "687" SIP Response code

   Number of response code: 687

   Default reason phrase:   Dialog Terminated

   Normative description:   section 6.3 of this document


10. Changes

10.1 Changes Since -01

   o  Removed the to-tag=* matching mechanism, and related proxy
      requirements and examples based on WG consensus at interim meeting
      and on the mailing list.



Mahy, et al.           Expires September 30, 2002              [Page 13]

Internet-Draft                  Replaces                      April 2002


   o  Reorganized motivational overview material

   o  Moved extra examples to service-flows

   o  Added authorization language in UAS behavior section

   o  Removed allowance to match on one of multiple matching dialogs
      with no tags

   o  Updated references


10.2 Changes Since -00

   o  When no dialog matches the Call-ID and tags in a Replaces header,
      the UAS now returns a 481 instead of silently accepting the
      INVITE.

   o  Changed the BNF to match the explicit whitespace BNF now used by
      SIP.

   o  Added the to-tag=* matching mechanism.

   o  Added requirements for forking proxies and a discussion of the
      consequences if forking proxies do not support Replaces.

   o  Added last two examples.

   o  Split normative and non-normative references


11. Acknowledgments

   Thanks to Robert Sparks, Alan Johnston, and Ben Campbell and many
   other members of the SIP WG for their continued support of the cause
   of distributed call control in SIP.

Normative References

   [1]  Rosenberg, J. and H. Schulzrinne, "SIP: Session Initiation
        Protocol", draft-ietf-sip-rfc2543bis-09 (work in progress),
        February 2002.

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

   [3]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.



Mahy, et al.           Expires September 30, 2002              [Page 14]

Internet-Draft                  Replaces                      April 2002


Informational References

   [4]   Sparks, R., "The Refer Method", draft-ietf-sip-refer-04 (work
         in progress), May 2002.

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

   [6]   Mahy, R., "A Multi-party Application Framework for SIP", draft-
         ietf-sipping-cc-framework-00 (work in progress), March 2002.

   [7]   Sparks, R., "SIP Call Control - Transfer", draft-ietf-sip-cc-
         transfer-05.txt (work in progress), July 2001.

   [8]   Rosenberg, J., Schulzrinne, H., Camarillo, G. and J. Peterson,
         "Best Current Practices for Third Party Call Control in the
         Session  Initiation Protocol", draft-ietf-sipping-3pcc-00 (work
         in progress), May 2002.

   [9]   Johnston, A., "SIP Service Examples", draft-ietf-sipping-
         service-examples-01 (work in progress), April 2002.

   [10]  Roach, A., "SIP-Specific Event Notification", draft-ietf-sip-
         events-05 (work in progress), March 2002.

   [11]  Donovan, S., "The SIP INFO Method", RFC 2976, October 2000.

   [12]  Rosenberg, J., "The Session Initiation Protocol UPDATE Method",
         draft-ietf-sip-update-02 (work in progress), May 2002.

   [13]  Rosenberg, J. and H. Schulzrinne, "Reliability of Provisional
         Responses in SIP", draft-ietf-sip-100rel-06 (work in progress),
         February 2002.


Authors' Addresses

   Rohan Mahy
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   EMail: rohan@cisco.com







Mahy, et al.           Expires September 30, 2002              [Page 15]

Internet-Draft                  Replaces                      April 2002


   Billy Biggs

   EMail: bbiggs@dumbterm.net


   Rick Dean

   EMail: rfc@fdd.com











































Mahy, et al.           Expires September 30, 2002              [Page 16]

Internet-Draft                  Replaces                      April 2002


Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















Mahy, et al.           Expires September 30, 2002              [Page 17]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/