GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc3891

Network Working Group R. Mahy Request for Comments: 3891 Cisco Systems, Inc. Category: Standards Track B. Biggs

                                                               R. Dean
                                                        September 2004
      The Session Initiation Protocol (SIP) "Replaces" Header

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2004).

Abstract

 This document defines a new header for use with Session Initiation
 Protocol (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 "Call
 Pickup".  Note that the definition of these example features is non-
 normative.

Mahy, et al. Standards Track [Page 1] RFC 3891 The SIP "Replaces" Header September 2004

Table of Contents

 1.  Overview. . . . . . . . . . . . . . . . . . . . . . . . . . .   2
 2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   4
 3.  User Agent Server Behavior: Receiving a Replaces Header . . .   4
 4.  User Agent Client Behavior: Sending a Replaces Header . . . .   6
 5.  Proxy Behavior. . . . . . . . . . . . . . . . . . . . . . . .   7
 6.  Syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  The Replaces Header . . . . . . . . . . . . . . . . . .   7
     6.2.  New Option Tag for Require and Supported Headers. . . .   8
 7.  Usage Examples. . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Replacing an Early Dialog at the Originator . . . . . .   9
 8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
 9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Registration of "Replaces" SIP Header . . . . . . . . .  13
     9.2.  Registration of "replaces" SIP Option-tag . . . . . . .  13
 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
 11. References. . . . . . . . . . . . . . . . . . . . . . . . . .  13
     11.1. Normative References. . . . . . . . . . . . . . . . . .  13
     11.2. Informative References. . . . . . . . . . . . . . . . .  14
 12. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . .  15
 13. Full Copyright Statement. . . . . . . . . . . . . . . . . . .  16

1. Overview

 This document describes a SIP [1] extension header field as part of
 the SIP multiparty applications architecture framework [10].  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 [11] 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.

Mahy, et al. Standards Track [Page 2] RFC 3891 The SIP "Replaces" Header September 2004

 o  A unique call-id may be given to the replacement call.  This
    avoids dialog matching problems in any of the related User Agents.
 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 [8] method as used in a
 Transfer [12], 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
 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 mechanism.  Perhaps she subscribed to this information from the
 Parking Place (using the session dialog package [13]), 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       |
      |<--NOTIFY/200 (trying)-----------|--INVITE/200/ACK-->|
      |<--NOTIFY/200 (success)----------|<=================>|
      |------------BYE/200------------->|                   |
      |               |                 |                   |
      |               |                 |                   |
      |  Alice later retrieves call from another phone      |
      |               |                 |                   |
      |            *3 |-INV w/Replaces->|                   |
      |               |<--200-----------|                   |
      |               |---ACK---------->|----BYE/200------->|
      |               |<===============>|                   |
      |               |                 |                   |

Mahy, et al. Standards Track [Page 3] RFC 3891 The SIP "Replaces" Header September 2004

 Message *1: Bob-> Parking Place
 INVITE sip:parkingplace@example.org SIP/2.0
 To: <sip:parkingplace@example.org>
 From: <sip:bob@example.org>;tag=7743
 Call-ID: 425928@bobster.example.org
 CSeq: 1 INVITE
 Contact: <sip:bob@bobster.example.org>
 Referred-By: <sip:alice@phone1.example.org>
 Message *2: Parking Place -> Bob
 SIP/2.0 200 OK
 To: <sip:parkingplace@example.org>;tag=6472
 From: <sip:bob@example.org>;tag=7743
 Call-ID: 425928@bobster.example.org
 CSeq: 1 INVITE
 Contact: <sip:parkplace@monopoly.example.org>
 Message *3: Alice@phone2 -> Bob
 INVITE sip:bob@bobster.example.org
 To: <sip:bob@example.org>
 From: <sip:alice@phone2.example.org>;tag=8983
 Call-ID: 09870@phone2.example.org
 CSeq: 1 INVITE
 Contact: <sip:alice@phone2.example.org>
 Require: replaces
 Replaces: 425928@bobster.example.org;to-tag=7743;from-tag=6472

2. 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 BCP 14, RFC 2119 [2].
 This document refers frequently to the terms "confirmed dialog" and
 "early dialog".  These are defined in Section 12 of SIP [1].

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 User Agent (UA) attempts to match this
 information with a confirmed or early dialog.  The User Agent Server
 (UAS) matches the to-tag and from-tag parameters as if they were tags

Mahy, et al. Standards Track [Page 4] RFC 3891 The SIP "Replaces" Header September 2004

 present in an incoming request.  In other words, the to-tag parameter
 is compared to the local tag, and the from-tag parameter 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 a 481 response.
 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 matched invitation was just terminated, the
 replacement request should fail as well.  Declining the request with
 a 600-class response prevents an irritating race-condition where the
 UA rings or alerts for a replacement call which is not wanted.)
 If the Replaces header field matches an active dialog, the UA MUST
 verify that the initiator of the new INVITE is authorized to replace
 the matched dialog.  If the initiator of the new INVITE has been
 successfully authenticated as equivalent to the user who is being
 replaced, then the replacement is authorized.  For example, if the
 user being replaced and the initiator of the replacement dialog share
 the same credentials for Digest authentication [6], or they sign the
 replacement request with S/MIME [7] with the same private key and
 present the (same) corresponding certificate used in the original
 dialog, then the replacement is authorized.
 Alternatively, the Referred-By mechanism [4] defines a mechanism that
 the UAS can use to verify that a replacement request was sent on
 behalf of the other participant in the matched dialog (in this case,
 triggered by a REFER request).  If the replacement request contains a
 Referred-By header that corresponds to the user being replaced, the
 UA SHOULD treat the replacement as if the replacement was authorized
 by the replaced party.  The Referred-By header SHOULD reference a
 corresponding, valid Refererred-By Authenticated Identity Body [5].

Mahy, et al. Standards Track [Page 5] RFC 3891 The SIP "Replaces" Header September 2004

 The UA MAY apply other local policy to authorize the remainder of the
 request.  In other words, the UAS may apply a different policy to the
 replacement dialog than was applied to the replaced dialog.
 In addition, the UA MAY use other authorization mechanisms defined
 for this purpose in standards track extensions.  Extensions could
 define other mechanisms 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 checks
 for the presence of the "early-only" flag in the Replaces header
 field.  (This flag allows the UAC to prevent a potentially
 undesirable race condition described in Section 7.1.) If the flag is
 present, the UA rejects the request with a 486 Busy response.
 Otherwise, 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 this UA, it returns a 481 (Call/Transaction Does Not
 Exist) response to the new INVITE, and leaves the matched dialog
 unchanged.  Note that since Replaces matches only a single dialog,
 the replacement dialog will not be retargeted according to the same
 forking logic as the original request which created the early dialog.
 (Currently, no use cases have been identified for replacing just a
 single dialog in this circumstance.)

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
 User Agent Client (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.  If the user agent only
 wishes to replace an early dialog (as in the Call Pickup example in
 Section 7.1), the UAC MAY also include the "early-only" parameter in

Mahy, et al. Standards Track [Page 6] RFC 3891 The SIP "Replaces" Header September 2004

 the Replaces header field.  A UAC MUST NOT send an INVITE with a
 Replaces header field that attempts to replace an early dialog which
 was not originated by the target of the INVITE with a Replaces header
 field.
 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
 Bob 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.  Although this specification takes reasonable
 precautions to prevent unexpected behavior in the face of forking,
 implementations SHOULD only address replacement requests (i.e., set
 the Request-URI of the replacement request) to the SIP Contact URI of
 the target.

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.
 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 other 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 2 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.  MESSAGE, SUBSCRIBE
 and NOTIFY, REFER, INFO, UPDATE, PRACK, and PUBLISH are defined
 respectively in [15], [16], [8], [17], [18], [19], and [20].

Mahy, et al. Standards Track [Page 7] RFC 3891 The SIP "Replaces" Header September 2004

    Header field    where   proxy   ACK  BYE  CAN  INV  OPT  REG  MSG
    ------------    -----   -----   ---  ---  ---  ---  ---  ---  ---
    Replaces          R              -    -    -    o    -    -    -
                                    SUB  NOT  REF  INF  UPD  PRA  PUB
                                    ---  ---  ---  ---  ---  ---  ---
    Replaces          R              -    -    -    -    -    -    -
 The following syntax specification uses the augmented Backus-Naur
 Form (BNF) as described in RFC 2234 [3].  The syntax below relies on
 a number of productions from SIP [1].
    Replaces        = "Replaces" HCOLON callid *(SEMI replaces-param)
    replaces-param  = to-tag / from-tag / early-flag / generic-param
    to-tag          = "to-tag" EQUAL token
    from-tag        = "from-tag" EQUAL token
    early-flag      = "early-only"
 A Replaces header field 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 RFC 2543 [9] compliant UAs, a
 tag of zero matches both tags of zero and null.  A Replaces header
 field MAY contain the early-flag.
 Examples:
    Replaces: 98732@sip.example.com
              ;from-tag=r33th4x0r
              ;to-tag=ff87ff
    Replaces: 12adf2f34456gs5;to-tag=12345;from-tag=54321;early-only
    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

Mahy, et al. Standards Track [Page 8] RFC 3891 The SIP "Replaces" Header September 2004

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 SIP
 Service Examples [14].  Via and Max-Forwards headers are omitted for
 clarity and brevity.

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

Mahy, et al. Standards Track [Page 9] RFC 3891 The SIP "Replaces" Header September 2004

 Message *2: Bob's desk phone -> Alice
 SIP/2.0 180 Ringing
 To: <sip:bob@example.org>;tag=6472
 From: <sip:alice@example.org>;tag=7743
 Call-ID: 425928@phone.example.org
 CSeq: 1 INVITE
 Contact: <sip:bob@bobster.example.org>
 Message *3: Bob in lab -> Alice
 INVITE sip:alice@phone.example.org
 To: <sip:alice@example.org>
 From: <sip:bob@example.org>;tag=8983
 Call-ID: 09870@labpc.example.org
 CSeq: 1 INVITE
 Contact: <sip:bob@labpc.example.org>
 Replaces: 425928@phone.example.org
  ;to-tag=7743;from-tag=6472;early-only
 Message *4: Alice -> Bob in lab
 SIP/2.0 200 OK
 To: <sip:alice@example.org>;tag=9232
 From: <sip:bob@example.org>;tag=8983
 Call-ID: 09870@labpc.example.org
 CSeq: 1 INVITE
 Contact: <sip:alice@phone.example.org>
 Message *5: Alice -> Bob's desk
 CANCEL sip:bob@example.org SIP/2.0
 To: <sip:bob@example.org>
 From: <sip:alice@example.org>;tag=7743
 Call-ID: 425928@phone.example.org
 CSeq: 1 CANCEL
 Contact: <sip:alice@phone.example.org>
 Message *6: Bob's desk -> Alice
 SIP/2.0 200 OK
 To: <sip:bob@example.org>
 From: <sip:alice@example.org>;tag=7743
 Call-ID: 425928@phone.example.org
 CSeq: 1 CANCEL
 Contact: <sip:bob@bobster.example.org>

Mahy, et al. Standards Track [Page 10] RFC 3891 The SIP "Replaces" Header September 2004

 Message *7: Bob's desk -> Alice
 SIP/2.0 487 Request Terminated
 To: <sip:bob@example.org>;tag=6472
 From: <sip:alice@example.org>;tag=7743
 Call-ID: 425928@phone.example.org
 CSeq: 1 INVITE

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 MUST only be accepted if the peer requesting
 replacement has been properly authenticated using a standard SIP
 mechanism (Digest or S/MIME), and authorized to request a replacement
 of the target dialog.  All SIP implementations are already required
 to support Digest Authentication.  In addition, implementations which
 support the Replaces header SHOULD also implement the Referred-By
 mechanism.
 How a User Agent determines which requests are legitimately
 authorized to make dialog replacements is non-trivial and depends on
 a considerable amount of local policy configuration.  In general,
 there are four cases when an authorization for a replacement is
 reasonable or warranted.
 1. Replacement made by a party considered equivalent to the replaced
    party
 2. Replacement made on behalf of the replaced party (perhaps
    transitively)
 3. Replacement made by a former participant
 4. Replacement made by a specifically authorized party
 Starting with #1 for example, if an executive and an assistant both
 receive requests for a shared address-of-record, if so configured,
 either should be able to replace dialogs of the other for the shared
 identity.  Both could even share the same keying material (Digest or
 S/MIME), or one could hold an authorization document signed by the

Mahy, et al. Standards Track [Page 11] RFC 3891 The SIP "Replaces" Header September 2004

 other expressing this relationship.  Likewise, in a call center
 environment, each call center agent could possess credentials to
 which supervisors also have access.
 The most common use case of a replacement is on the request of the
 replaced participant (who no longer wants to be involved).  This is
 the case in many features, such as completing an Attended Transfer
 and converting a 3-way call to a point-to-point call.  Such
 replacements are typically triggered by a REFER [8] request from the
 replaced participant.  The Referred-By [4] mechanism defines one way
 to identify the apparent original requester and can point to a SIP
 Authenticated Identity Body [5] (an S/MIME-based signed assertion) to
 secure this information.
 In the example in section 1, Alice sends an INVITE with Replaces to
 Bob.  Alice was a former participant in the conversation and had a
 previous dialog relationship with Bob.  Alice can use the same Digest
 or S/MIME credentials she used to authenticate with Bob during the
 original call to prove that she was a former participant.  Note that
 this justification for replacing calls is more dangerous than the
 others, and in most cases is another way to authorize that the
 replacing participant is available.  Implementations SHOULD NOT rely
 on this method as an authorization mechanism.
 The last scenario is the easiest to secure but the least likely to be
 useful in practice.  It is unlikely that an arbitrary host in the
 Internet is aware of any special authorization relationship between
 the replaced and the replacing parties.  However, this use case may
 be useful in some environments.  Since this usage does not
 effectively degrade the security of the solution, it is still
 allowed.
 Some mechanisms for obtaining the dialog information needed by the
 Replaces header (Call-ID, to-tag, and from-tag) include URIs on a web
 page, subscriptions to an appropriate event package, and
 notifications after a REFER request.  Since manipulating this dialog
 information could cause User Agents to replace the wrong dialog, use
 of message integrity protection for this information is STRONGLY
 RECOMMENDED.  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 in standards track extensions.  In
 general, call control features benefit considerably from such work.

Mahy, et al. Standards Track [Page 12] RFC 3891 The SIP "Replaces" Header September 2004

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

10. Acknowledgments

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

11. References

11.1. Normative References

 [1]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
      Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
      Session Initiation Protocol", RFC 3261, June 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.
 [4]  Sparks, R., "The Session Initiation Protocol (SIP) Referred-By
      Mechanism", RFC 3892, September 2004.
 [5]  Peterson, J., "The Session Initiation Protocol (SIP)
      Authenticated Identity Body (AIB) Format", RFC 3893, September
      2004.

Mahy, et al. Standards Track [Page 13] RFC 3891 The SIP "Replaces" Header September 2004

 [6]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
      Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
      Basic and Digest Access Authentication", RFC 2617, June 1999.
 [7]  Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
      (S/MIME) Version 3.1 Message Specification", RFC 3851, July
      2004.

11.2. Informative References

 [8]  Sparks, R., "The Session Initiation Protocol (SIP) Refer
      Method", RFC 3515, April 2003.
 [9]  Handley, M., Schulzrinne, H., Schooler, E., and J. Rosenberg,
      "SIP: Session Initiation Protocol", RFC 2543, March 1999.
 [10] Mahy, R., "A Call Control and Multi-party usage framework for
      the Session Initiation Protocol (SIP)", Work in Progress, March
      2003.
 [11] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo,
      "Best Current Practices for Third Party Call Control (3pcc) in
      the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April
      2004.
 [12] Sparks, R. and A. Johnston, "Session Initiation Protocol Call
      Control - Transfer", Work in Progress, February 2003.
 [13] Rosenberg, J. and H. Schulzrinne, "An INVITE Initiated Dialog
      Event Package for the Session Initiation Protocol (SIP)", Work
      in Progress, March 2003.
 [14] Johnston, A. and S. Donovan, "Session Initiation Protocol
      Service Examples", Work in Progress, March 2003.
 [15] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and
      D. Gurle, "Session Initiation Protocol (SIP) Extension for
      Instant Messaging", RFC 3428, December 2002.
 [16] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
      Notification", RFC 3265, June 2002.
 [17] Donovan, S., "The SIP INFO Method", RFC 2976, October 2000.
 [18] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE
      Method", RFC 3311, October 2002.

Mahy, et al. Standards Track [Page 14] RFC 3891 The SIP "Replaces" Header September 2004

 [19] Rosenberg, J. and H. Schulzrinne, "Reliability of Provisional
      Responses in Session Initiation Protocol (SIP)", RFC 3262, June
      2002.
 [20] Campbell, B., "SIMPLE Presence Publication Mechanism", Work in
      Progress, February 2003.

12. Authors' Addresses

 Rohan Mahy
 Cisco Systems, Inc.
 5617 Scotts Valley Dr
 Scotts Valley, CA  95066
 USA
 EMail: rohan@cisco.com
 Billy Biggs
 EMail: bbiggs@dumbterm.net
 Rick Dean
 EMail: rfc@fdd.com

Mahy, et al. Standards Track [Page 15] RFC 3891 The SIP "Replaces" Header September 2004

13. Full Copyright Statement

 Copyright (C) The Internet Society (2004).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/S HE
 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
 INTERNET ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the IETF's procedures with respect to rights in IETF Documents can
 be found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at ietf-
 ipr@ietf.org.

Acknowledgement

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

Mahy, et al. Standards Track [Page 16]

/data/webs/external/dokuwiki/data/pages/rfc/rfc3891.txt · Last modified: 2004/09/09 23:40 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki