One document matched: draft-ietf-sipping-transc-conf-00.txt
SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: December 3, 2005 June 1, 2005
The Session Initiation Protocol (SIP) Conference Bridge Transcoding
Model
draft-ietf-sipping-transc-conf-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
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 December 3, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document describes how to invoke transcoding services using the
conference bridge model. This way of invocation meets the
requirements for SIP regarding transcoding services invocation to
support deaf, hard of hearing and speech-impaired individuals.
Camarillo Expires December 3, 2005 [Page 1]
Internet-Draft Conference Transcoding Model June 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Caller's Invocation . . . . . . . . . . . . . . . . . . . . . 4
3.1 Unsuccessful Session Establishment . . . . . . . . . . . . 6
4. Callee's Invocation . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1 Normative References . . . . . . . . . . . . . . . . . . . 8
8.2 Informational References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 10
Camarillo Expires December 3, 2005 [Page 2]
Internet-Draft Conference Transcoding Model June 2005
1. Introduction
The Framework for Transcoding with SIP [6] describes how two SIP [4]
UAs (User Agents) can discover imcompatibilities that prevent them
from establishing a session (e.g., lack of support for a common codec
or for a common media type). When such incompatibilities are found,
the UAs need to invoke transcoding services to successfully establish
the session. The transcoding framework introduces two models to
invoke transcoding services: the 3pcc (third-party call control)
model [7] and the conference bridge model. This document specifies
the conference bridge model.
In the conference bridge model for transcoding invocation, a
transcoding server that provides a particular transcoding service
(e.g., speech-to-text) behaves as a B2BUA (Back-to-Back User Agent)
between both UAs and is identified by a URI. As shown in Figure 1,
both UAs, A and B, exchange signalling and media with the transcoder
T. The UAs do not exchange any traffic (signalling or media) directly
between them.
+-------+
| |**
| T | **
| |\ **
+-------+ \\ **
^ * \\ **
| * \\ **
| * SIP **
SIP * \\ **
| * \\ **
| * \\ **
v * \ **
+-------+ +-------+
| | | |
| A | | B |
| | | |
+-------+ +-------+
<-SIP-> Signalling
******* Media
Figure 1: Conference bridge model
Section 3 and Section 4 specify how the caller A or the callee B,
respectively, can use the conference bridge model to invoke
transcoding services from T.
Camarillo Expires December 3, 2005 [Page 3]
Internet-Draft Conference Transcoding Model June 2005
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [3] and indicate requirement levels for
compliant implementations.
3. Caller's Invocation
A needs to perform two operations to invoke transcoding services from
T for a session between A and B. A needs to establish a session with
T and provide T with B's URI so that T can generate an INVITE towards
B. A uses the procedures for Conference Establishment Using Request-
Contained Lists in SIP [9] to provide T with B's URI using the same
INVITE that establishes the session between A and T.
Figure 2 shows the message flow for the caller's invocation of a
transcoder T. The caller (A) sends an INVITE (1) to the transcoder
(T) to establish the session A-T. Following the procedures in [9], A
adds a body part whose disposition type is recipient-list [8]. This
body part consists of a URI-list that MUST contain a single URI: B's
URI.
If a trancoder receives a URI-list with more than one URI, it SHOULD
return a 488 (Max 1 URI allowed in URI-list) response.
A T B
| | |
|-----(1) INVITE SDP A----->| |
| | |
|<-(2) 183 Session Progress-| |
| |-----(3) INVITE SDP TB---->|
| | |
| |<-----(4) 200 OK SDP B-----|
| | |
| |---------(5) ACK---------->|
|<----(6) 200 OK SDP TA-----| |
| | |
|---------(7) ACK---------->| |
| | |
| ************************* | ************************* |
|** Media **|** Media **|
| ************************* | ************************* |
| | |
Figure 2: Successful invocation of a transcoder by the caller
Camarillo Expires December 3, 2005 [Page 4]
Internet-Draft Conference Transcoding Model June 2005
The following example shows an INVITE with two body parts: an SDP
[10] session description and a URI-list.
INVITE sip:transcoder@example.com SIP/2.0
Via: SIP/2.0/TCP client.chicago.example.com
;branch=z9hG4bKhjhs8ass83
Max-Forwards: 70
To: Transcoder <sip:transcoder@example.org>
From: A <sip:A@chicago.example.com>;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 1 INVITE
Contact: <sip:A@client.chicago.example.com>
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER,
SUBSCRIBE, NOTIFY
Allow-Events: dialog
Accept: application/sdp, message/sipfrag
Require: recipient-list-invite
Conten-Type: multipart/mixed;boundary="boundary1"
Content-Length: xxx
--boundary1
Content-Type: application/sdp
v=0
o=example 2890844526 2890842807 IN IP4 chicago.example.com
s=-
c=IN IP4 192.0.2.1
t=0 0
m=audio 20000 RTP/AVP 0
a=rtpmap:0 PCMU/8000
--boundary1
Content-Type: application/resource-lists+xml
Content-Disposition: recipient-list
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list>
<entry uri="sip:B@example.org" />
</list>
</resource-lists>
--boundary1--
On receiving the INVITE, the transcoder generates a new INVITE
towards the callee. The transcoder acts as a B2BUA, not as a proxy.
Therefore, this new INVITE (3) belongs to a different transaction
Camarillo Expires December 3, 2005 [Page 5]
Internet-Draft Conference Transcoding Model June 2005
than the INVITE (1) received by the transcoder.
When the transcoder receives a final response (4) from the callee, it
generates a new final response (6) for INVITE (1). This new final
response (6) SHOULD have the same status code as the one received in
the response from the callee (4).
3.1 Unsuccessful Session Establishment
Figure 3 shows a similar message flow as the one in Figure 3.
Nevertheless, this time the callee generates a non-2xx final response
(4). Consequently, the transcoder generates a non-2xx final response
(6) towards the caller as well.
A T B
| | |
|-----(1) INVITE SDP A----->| |
| | |
|<-(2) 183 Session Progress-| |
| |-----(3) INVITE SDP TB---->|
| | |
| |<----(4) 404 Not Found-----|
| | |
| |---------(5) ACK---------->|
|<----(6) 404 Not Found-----| |
| | |
|---------(7) ACK---------->| |
| | |
Figure 3: Unsuccessful session establishment
The ambiguity in this flow is that, if the provisional response (2)
gets lost, the caller does not know whether the 404 (Not Found)
response means that the initial INVITE (1) did not reach the
transcoder or that the INVITE generated by the transcoder (4) did not
reach the callee. To resolve this ambiguity, the callee can either
require the use of the reliable provisional responses [5] SIP
extension or send an OPTIONS request to the transcoder to check
whether it is reachable.
4. Callee's Invocation
If a UA receives an INVITE with an offer that is not acceptable, it
can redirect it to the transcoder by using a 302 (Moved Temporarily)
response. The Contact header field of the 302 (Moved Temporarily)
response contains the URI of the transcoder plus a "?body="
parameter. This parameter contains a recipient-list body with B's
Camarillo Expires December 3, 2005 [Page 6]
Internet-Draft Conference Transcoding Model June 2005
URI. Note that some escaping (e.g., for Carriage Returns and Line
Feeds) is needed to encode a recipient-list body in such a parameter.
Figure 4 shows the message flow for this scenario.
<t>
Please view in a fixed-width font such as Courier.
A T B
| | |
|-------------------(1) INVITE SDP A------------------->|
| | |
|<--------------(2) 302 Moved Temporarily---------------|
| | |
|-----------------------(3) ACK------------------------>|
| | |
|-----(4) INVITE SDP A----->| |
| | |
|<-(5) 183 Session Progress-| |
| |-----(6) INVITE SDP TB---->|
| | |
| |<-----(7) 200 OK SDP B-----|
| | |
| |---------(8) ACK---------->|
|<----(9) 200 OK SDP TA-----| |
| | |
|--------(10) ACK---------->| |
| | |
| ************************* | ************************* |
|** Media **|** Media **|
| ************************* | ************************* |
Figure 4: \{Callee's invocation of a transcoder
Note that A does not necessarily need to be the one performing the
recursion on the 302 (Moved Temporarily) response. Any proxy in the
path between A and B may perform such a recursion.
5. Security Considerations
TBD.
Need to mention how consent applies to this work when consent is more
mature.
Need to mention TLS [1] and S/MIME [2].
Camarillo Expires December 3, 2005 [Page 7]
Internet-Draft Conference Transcoding Model June 2005
6. IANA Considerations
This document does not contain any IANA actions.
7. Contributors
This document is the result of discussions amongst the conferencing
design team. The members of this team include Eric Burger, Henning
Schulzrinne and Arnoud van Wijk.
8. References
8.1 Normative References
[1] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[2] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Certificate Handling", RFC 3850, July 2004.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] 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.
[5] Rosenberg, J. and H. Schulzrinne, "Reliability of Provisional
Responses in Session Initiation Protocol (SIP)", RFC 3262,
June 2002.
[6] Camarillo, G., "Framework for Transcoding with the Session
Initiation Protocol",
draft-camarillo-sipping-transc-framework-00 (work in progress),
August 2003.
[7] Camarillo, G., "Transcoding Services Invocation in the Session
Initiation Protocol (SIP) Using Third Party Call Control
(3pcc)", draft-ietf-sipping-transc-3pcc-02 (work in progress),
September 2004.
[8] Camarillo, G. and A. Roach, "Requirements and Framework for
Session Initiation Protocol (SIP)Uniform Resource Identifier
(URI)-List Services", draft-ietf-sipping-uri-services-02 (work
in progress), December 2004.
[9] Camarillo, G. and A. Johnston, "Conference Establishment Using
Request-Contained Lists in the Session Initiation Protocol
Camarillo Expires December 3, 2005 [Page 8]
Internet-Draft Conference Transcoding Model June 2005
(SIP)", draft-ietf-sipping-uri-list-conferencing-02 (work in
progress), December 2004.
8.2 Informational References
[10] Handley, M., "SDP: Session Description Protocol",
draft-ietf-mmusic-sdp-new-24 (work in progress), February 2005.
Author's Address
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
Camarillo Expires December 3, 2005 [Page 9]
Internet-Draft Conference Transcoding Model June 2005
Intellectual Property Statement
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 procedures with respect to rights in RFC 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.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 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.
Copyright Statement
Copyright (C) The Internet Society (2005). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Camarillo Expires December 3, 2005 [Page 10]
| PAFTECH AB 2003-2026 | 2026-04-23 03:52:43 |