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The Session Description Protocol (SDP) Label Attribute
RFC 4574

Document type: RFC - Proposed Standard (August 2006; No errata)
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: WG Document
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 4574 (Proposed Standard)
Responsible AD: Allison Mankin
Send notices to: jo@acm.org, csp@csperkins.org, rohan@ekabal.com, jon.peterson@neustar.biz

Network Working Group                                           O. Levin
Request for Comments: 4574                         Microsoft Corporation
Category: Standards Track                                   G. Camarillo
                                                                Ericsson
                                                             August 2006

         The Session Description Protocol (SDP) Label Attribute

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 (2006).

Abstract

   This document defines a new Session Description Protocol (SDP)
   media-level attribute: "label".  The "label" attribute carries a
   pointer to a media stream in the context of an arbitrary network
   application that uses SDP.  The sender of the SDP document can attach
   the "label" attribute to a particular media stream or streams.  The
   application can then use the provided pointer to refer to each
   particular media stream in its context.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................2
   3. Motivation for the New label Attribute ..........................2
   4. The Label Attribute .............................................3
   5. The Label Attribute in the Offer/Answer Model ...................4
   6. Example .........................................................4
   7. Security Considerations .........................................4
   8. IANA Considerations .............................................5
   9. Acknowledgements ................................................5
   10. References .....................................................6
      10.1. Normative References ......................................6
      10.2. Informative References ....................................6

Levin & Camarillo           Standards Track                     [Page 1]
RFC 4574                  SDP Label Attribute                August 2006

1.  Introduction

   SDP is being used by a variety of distributed-over-the-network
   applications.  These applications deal with multiple sessions being
   described by SDP [4] and serving multiple users or services in the
   context of a single application instance.  Applications of this kind
   need a means to identify a particular media stream across multiple
   SDP descriptions exchanged with different users.

   The XCON framework is an example of a centralized conference
   architecture that uses SDP according to the offer/answer mechanism
   defined in [3] to establish media streams with each of the conference
   participants.  Additionally, XCON identifies the need to uniquely
   identify a media stream in terms of its role in a conference
   regardless of its media type, transport protocol, and media format.
   This can be accomplished by using an external document that points to
   the appropriate media stream and provides information (e.g., the
   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,
   which provides a pointer to a media stream that is described by an
   'm' line in an SDP session description.

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 [1] and indicate requirement levels for
   compliant implementations.

3.  Motivation for the New label Attribute

   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
   the context of external documents that may be created before the
   session description itself and need to be handled by automata.

   The 'i' SDP attribute, defined in RFC 2327 [4], can be used to label
   media streams.  Nevertheless, values of the 'i' attribute are
   intended for human users and not for automata.

Levin & Camarillo           Standards Track                     [Page 2]

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