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Session Description Protocol (SDP) Capability Negotiation
RFC 5939

Internet Engineering Task Force (IETF)                      F. Andreasen
Request for Comments: 5939                                 Cisco Systems
Category: Standards Track                                 September 2010
ISSN: 2070-1721

       Session Description Protocol (SDP) Capability Negotiation

Abstract

   The Session Description Protocol (SDP) was intended to describe
   multimedia sessions for the purposes of session announcement, session
   invitation, and other forms of multimedia session initiation.  SDP
   was not intended to provide capability indication or capability
   negotiation; however, over the years, SDP has seen widespread
   adoption and as a result it has been gradually extended to provide
   limited support for these, notably in the form of the offer/answer
   model defined in RFC 3264.  SDP does not define how to negotiate one
   or more alternative transport protocols (e.g., RTP profiles) or
   attributes.  This makes it difficult to deploy new RTP profiles such
   as Secure RTP or RTP with RTCP-based feedback, negotiate use of
   different security keying mechanisms, etc.  It also presents problems
   for some forms of media negotiation.

   The purpose of this document is to address these shortcomings by
   extending SDP with capability negotiation parameters and associated
   offer/answer procedures to use those parameters in a backwards
   compatible manner.

   The document defines a general SDP Capability Negotiation framework.
   It also specifies how to provide attributes and transport protocols
   as capabilities and negotiate them using the framework.  Extensions
   for other types of capabilities (e.g., media types and media formats)
   may be provided in other documents.

Andreasen                    Standards Track                    [Page 1]
RFC 5939               SDP Capability Negotiation         September 2010

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5939.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Andreasen                    Standards Track                    [Page 2]
RFC 5939               SDP Capability Negotiation         September 2010

Table of Contents

   1. Introduction ....................................................4
   2. Conventions Used in This Document ...............................7
   3. SDP Capability Negotiation Solution .............................7
      3.1. SDP Capability Negotiation Model ...........................7
      3.2. Solution Overview .........................................10
      3.3. Version and Extension Indication Attributes ...............14
      3.4. Capability Attributes .....................................17
      3.5. Configuration Attributes ..................................22
      3.6. Offer/Answer Model Extensions .............................32
      3.7. Interactions with ICE .....................................45
      3.8. Interactions with SIP Option Tags .........................47

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