< 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 ¶
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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
	skipping to change at page 3, line 9 ¶		skipping to change at page 3, line 9 ¶
	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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