draft-ietf-mmusic-sdp-media-label-01.txt   rfc4574.txt 
MMUSIC O. Levin Network Working Group O. Levin
Internet-Draft Microsoft Corporation Request for Comments: 4574 Microsoft Corporation
Expires: July 1, 2004 G. Camarillo Category: Standards Track G. Camarillo
Ericsson Ericsson
January 2004 August 2006
The SDP (Session Description Protocol) Label Attribute
draft-ietf-mmusic-sdp-media-label-01.txt
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document defines a new Session Description Protocol (SDP) This document defines a new Session Description Protocol (SDP)
media-level attribute: "label". The "label" attribute carries a media-level attribute: "label". The "label" attribute carries a
pointer to a media stream in the context of an arbitrary network pointer to a media stream in the context of an arbitrary network
application that uses SDP. The sender of the SDP document can attach application that uses SDP. The sender of the SDP document can attach
the "label" attribute to a particular media stream or streams. The the "label" attribute to a particular media stream or streams. The
application can then use the provided pointer to refer to each application can then use the provided pointer to refer to each
particular media stream in its context. particular media stream in its context.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology .....................................................2
3. Motivation for the New label Attribute . . . . . . . . . . . . 3 3. Motivation for the New label Attribute ..........................2
4. The Label Attribute . . . . . . . . . . . . . . . . . . . . . 4 4. The Label Attribute .............................................3
5. The Label Attribute in the Offer/Answer Model . . . . . . . . 4 5. The Label Attribute in the Offer/Answer Model ...................4
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Example .........................................................4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. Security Considerations .........................................4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations .............................................5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 9. Acknowledgements ................................................5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 10. References .....................................................6
10.1 Normative References . . . . . . . . . . . . . . . . . . . . 6 10.1. Normative References ......................................6
10.2 Informative References . . . . . . . . . . . . . . . . . . . 6 10.2. Informative References ....................................6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . 7
1. Introduction 1. Introduction
SDP is being used by a variety of distributed over the network SDP is being used by a variety of distributed-over-the-network
applications. These applications deal with multiple sessions being applications. These applications deal with multiple sessions being
described by SDP [4] and serving multiple users or services in the described by SDP [4] and serving multiple users or services in the
context of a single application instance. Applications of this kind context of a single application instance. Applications of this kind
need a means to identify a particular media stream across multiple need a means to identify a particular media stream across multiple
SDP descriptions exchanged with different users. SDP descriptions exchanged with different users.
The XCON framework is an example of a centralized conference The XCON framework is an example of a centralized conference
architecture that uses SDP according to the offer/answer mechanism architecture that uses SDP according to the offer/answer mechanism
defined in [3] to establish media streams with each of the conference defined in [3] to establish media streams with each of the conference
participants. Additionally, XCON identifies the need to uniquely participants. Additionally, XCON identifies the need to uniquely
identify a media stream in terms of its role in a conference identify a media stream in terms of its role in a conference
regardless of its media type, transport protocol, and media format. regardless of its media type, transport protocol, and media format.
This can be acomplished by using an external document that points to This can be accomplished by using an external document that points to
the appropriate media stream and provides information (e.g., the the appropriate media stream and provides information (e.g., the
media stream's role in the conference) about it. media stream's role in the conference) about it. The SIP Event
Package for Conference State [7] defines and uses a concrete format
for such external documents.
This specification defines the SDP [4] "label" media-level attribute, This specification defines the SDP [4] "label" media-level attribute,
which provides a pointer to a media stream which is described by an which provides a pointer to a media stream that is described by an
'm' line in an SDP session description. 'm' line in an SDP session description.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations. compliant implementations.
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the context of external documents that may be created before the the context of external documents that may be created before the
session description itself and need to be handled by automata. session description itself and need to be handled by automata.
The 'i' SDP attribute, defined in RFC 2327 [4], can be used to label The 'i' SDP attribute, defined in RFC 2327 [4], can be used to label
media streams. Nevertheless, values of the 'i' attribute are media streams. Nevertheless, values of the 'i' attribute are
intended for human users and not for automata. intended for human users and not for automata.
The 'mid' SDP attribute, defined in RFC 3388 [6], can be used to The 'mid' SDP attribute, defined in RFC 3388 [6], can be used to
identify media streams as well. Nevertheless, the scope of 'mid' is identify media streams as well. Nevertheless, the scope of 'mid' is
too limited to be used by applications dealing with multiple SDP too limited to be used by applications dealing with multiple SDP
sessions. This is due to the fact that values of the 'mid' attribute sessions. This is because values of the 'mid' attribute are
are meaningful in the context of a single SDP session, not in the meaningful in the context of a single SDP session, not in the context
context of a broader application (e.g., a multiparty application). of a broader application (e.g., a multiparty application).
Another way of referring to a media stream is by using the order of Another way of referring to a media stream is by using the order of
the 'm' line in the SDP session document (e.g., the 5th media stream the 'm' line in the SDP session document (e.g., the 5th media stream
in the session description). This is the mechanism used in the in the session description). This is the mechanism used in the
offer/answer model [3]. offer/answer model [3].
The problem with this mechanism is that it can only be used to refer The problem with this mechanism is that it can only be used to refer
to media streams in session descriptions that exist already. There to media streams in session descriptions that exist already. There
are scenarios where a static document needs to refer, using a are scenarios where a static document needs to refer, using a
pointer, to a media stream that will be negotiated by SDP means and pointer, to a media stream that will be negotiated by SDP means and
created in the future. When the media stream is eventually created, created in the future. When the media stream is eventually created,
the application needs to label the media stream so that the pointer the application needs to label the media stream so that the pointer
in the static document points to the proper media stream in the in the static document points to the proper media stream in the
session description. session description.
4. The Label Attribute 4. The Label Attribute
This specification defines a new media-level value attribute: This specification defines a new media-level value attribute:
'label'. Its formatting in SDP is described by the following BNF 'label'. Its formatting in SDP is described by the following ABNF
[2]: [2]:
label-attribute = "a=label:" pointer label-attribute = "a=label:" pointer
pointer = token pointer = token
The 'label' attribute contains a token which is defined by an token = 1*(token-char)
token-char = %x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39
/ %x41-5A / %x5E-7E
The token-char and token elements are defined in [4] but included
here to provide support for the implementor of this SDP feature.
The 'label' attribute contains a token that is defined by an
application and is used in its context. The new attribute can be application and is used in its context. The new attribute can be
attached to 'm' lines in multiple SDP documents allowing the attached to 'm' lines in multiple SDP documents allowing the
application to logically group the media streams across SDP sessions application to logically group the media streams across SDP sessions
when necessary. when necessary.
5. The Label Attribute in the Offer/Answer Model 5. The Label Attribute in the Offer/Answer Model
This specification does not define a means to discover whether or not This specification does not define a means to discover whether or not
the peer endpoint understands the 'label' attribute because 'label' the peer endpoint understands the 'label' attribute because 'label'
values are informative only at the offer/answer model level. values are informative only at the offer/answer model level.
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specification. specification.
6. Example 6. Example
The following is an example of an SDP session description that uses The following is an example of an SDP session description that uses
the 'label' attribute: the 'label' attribute:
v=0 v=0
o=bob 280744730 28977631 IN IP4 host.example.com o=bob 280744730 28977631 IN IP4 host.example.com
s= s=
i=A Seminar on the session description protocol
c=IN IP4 192.0.2.2 c=IN IP4 192.0.2.2
t=0 0 t=0 0
m=audio 6886 RTP/AVP 0 m=audio 6886 RTP/AVP 0
a=label:1 a=label:1
m=audio 22334 RTP/AVP 0 m=audio 22334 RTP/AVP 0
a=label:2 a=label:2
7. Security Considerations 7. Security Considerations
An attacker may attempt to add, modify, or remove 'label' attributes An attacker may attempt to add, modify, or remove 'label' attributes
from a session description. This could result in an application from a session description. This could result in an application
behaving in a non-desirable way. So, it is strongly RECOMMENDED that behaving in a non-desirable way. So, it is strongly RECOMMENDED that
integrity protection be applied to the SDP session descriptions. For integrity protection be applied to the SDP session descriptions. For
session descriptions carried in SIP [5], S/MIME is the natural choice session descriptions carried in SIP [5], S/MIME is the natural choice
to provide such end-to-end integrity protection, as described in RFC to provide such end-to-end integrity protection, as described in RFC
3261 [5]. Other applications MAY use a different form of integrity 3261 [5]. Other applications MAY use a different form of integrity
protection. protection.
8. IANA Considerations 8. IANA Considerations
The IANA has registered the following new SDP attribute:
Contact name: Orit Levin oritl@microsoft.com. Contact name: Orit Levin oritl@microsoft.com.
Attribute name: "label". Attribute name: "label".
Type of attribute Media level. Type of attribute: Media level.
Subject to charset: Not. Subject to charset: Not.
Purpose of attribute: The 'label' attribute associates a media Purpose of attribute: The 'label' attribute associates a media
stream with a label. This label allows the media stream to be stream with a label. This label allows the media stream to be
referenced by external documents. referenced by external documents.
Allowed attribute values: A token. Allowed attribute values: A token.
9. Acknowledgements 9. Acknowledgements
Robert Sparks, Adam Roach, and Rohan Mahy provided useful comments on Robert Sparks, Adam Roach, and Rohan Mahy provided useful comments on
this document. this document.
10. References 10. References
10.1 Normative References 10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Crocker, D. and P. Overell, "Augmented BNF for Syntax [2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997. Specifications: ABNF", RFC 4234, October 2005.
[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with [3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002. Session Description Protocol (SDP)", RFC 3264, June 2002.
[4] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session [4] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session
Description Protocol", draft-ietf-mmusic-sdp-new-21 (work in Description Protocol", RFC 4566, July 2006.
progress), October 2004.
10.2 Informative References 10.2. Informative References
[5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[6] Camarillo, G., Eriksson, G., Holler, J. and H. Schulzrinne, [6] Camarillo, G., Eriksson, G., Holler, J., and H. Schulzrinne,
"Grouping of Media Lines in the Session Description Protocol "Grouping of Media Lines in the Session Description Protocol
(SDP)", RFC 3388, December 2002. (SDP)", RFC 3388, December 2002.
[7] Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
Initiation Protocol (SIP) Event Package for Conference State",
RFC 4575, August 2006.
Authors' Addresses Authors' Addresses
Orit Levin Orit Levin
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
USA USA
EMail: oritl@microsoft.com EMail: oritl@microsoft.com
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
EMail: Gonzalo.Camarillo@ericsson.com EMail: Gonzalo.Camarillo@ericsson.com
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
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/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.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
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on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
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such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
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The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Disclaimer of Validity Acknowledgement
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 (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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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