draft-ietf-mmusic-sdp-media-label-00.txt   draft-ietf-mmusic-sdp-media-label-01.txt 
MMUSIC O. Levin MMUSIC O. Levin
Internet-Draft Microsoft Corporation Internet-Draft Microsoft Corporation
Expires: March 29, 2005 G. Camarillo Expires: July 1, 2004 G. Camarillo
Ericsson Ericsson
September 28, 2004 January 2004
The SDP (Session Description Protocol) Label Attribute The SDP (Session Description Protocol) Label Attribute
draft-ietf-mmusic-sdp-media-label-00.txt draft-ietf-mmusic-sdp-media-label-01.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is subject to all provisions This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of 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 is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with which he or she become aware will be disclosed, in accordance with
RFC 3668. RFC 3668.
skipping to change at page 1, line 37 skipping to change at page 1, line 37
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on March 29, 2005. This Internet-Draft will expire on July 1, 2004.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). Copyright (C) The Internet Society (2004).
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
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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 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . 7 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 [2] 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 [6] 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 acomplished 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.
This specification defines the SDP [2] "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 which 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.
3. Motivation for the New label Attribute 3. Motivation for the New label Attribute
Even though SDP and its extensions already provide a few ways to Even though SDP and its extensions already provide a few ways to
refer to a media stream, none of them is appropriate to be used in refer to a media stream, none of them is appropriate to be used in
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 [2], 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 [4], 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 due to the fact that values of the 'mid' attribute
are meaningful in the context of a single SDP session, not in the are meaningful in the context of a single SDP session, not in the
context of a broader application (e.g., a multiparty application). context 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 in the 'm' line in the SDP session document (e.g., the 5th media stream
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 BNF
[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 The 'label' attribute contains a token which 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.
At the offer/answer level, it means that the fact that an offer does At the offer/answer level, it means that the fact that an offer does
not contain label attributes does not imply that the answer should not contain label attributes does not imply that the answer should
not have them. It also means that the fact that an offer contains not have them. It also means that the fact that an offer contains
label attributes does not imply that the answer should have them too. label attributes does not imply that the answer should have them too.
In addition to the basic offer/answer rule above, applications that In addition to the basic offer/answer rule above, applications that
use "label" as a pointer to media streams MUST specify its usage use 'label' as a pointer to media streams MUST specify its usage
constraints. For example, such applications MAY mandate support for constraints. For example, such applications MAY mandate support for
"label". In this case, the application will define means for 'label'. In this case, the application will define means for
negotiation of the "label" attribute support as a part of its negotiation of the 'label' attribute support as a part of its
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=
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
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: Any octet string. 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] Handley, M. and V. Jacobson, "SDP: Session Description [2] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Protocol", RFC 2327, April 1998. Specifications: ABNF", RFC 2234, November 1997.
[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] Camarillo, G., Eriksson, G., Holler, J. and H. Schulzrinne, [4] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session
"Grouping of Media Lines in the Session Description Protocol Description Protocol", draft-ietf-mmusic-sdp-new-21 (work in
(SDP)", RFC 3388, December 2002. 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] Koskelainen, P. and H. Khartabil, "Requirements for Conference [6] Camarillo, G., Eriksson, G., Holler, J. and H. Schulzrinne,
Policy Control Protocol", draft-ietf-xcon-cpcp-reqs-04 (work in "Grouping of Media Lines in the Session Description Protocol
progress), August 2004. (SDP)", RFC 3388, December 2002.
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
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