Session Description Protocol (SDP) Offer/Answer Examples
RFC 4317

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Network Working Group                                        A. Johnston
Request for Comments: 4317                             Tello Corporation
Category: Informational                                        R. Sparks
                                                        Estacado Systems
                                                           December 2005

                   Session Description Protocol (SDP)
                         Offer/Answer Examples

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document gives examples of Session Description Protocol (SDP)
   offer/answer exchanges.  Examples include codec negotiation and
   selection, hold and resume, and addition and deletion of media
   streams.  The examples show multiple media types, bidirectional,
   unidirectional, inactive streams, and dynamic payload types.  Common
   Third Party Call Control (3pcc) examples are also given.

Johnston & Sparks            Informational                      [Page 1]
RFC 4317               SDP Offer/Answer Examples           December 2005

Table of Contents

   1. Overview ........................................................3
   2. Codec Negotiation and Selection .................................3
      2.1. Audio and Video 1 ..........................................3
      2.2. Audio and Video 2 ..........................................4
      2.3. Audio and Video 3 ..........................................5
      2.4. Two Audio Streams ..........................................6
      2.5. Audio and Video 4 ..........................................7
      2.6. Audio Only 1 ...............................................8
      2.7. Audio and Video 5 ..........................................9
      2.8. Audio and Video 6 .........................................10
   3. Hold and Resume Scenarios ......................................12
      3.1. Hold and Unhold 1 .........................................12
      3.2. Hold with Two Streams .....................................13
   4. Addition and Deletion of Media Streams .........................15
      4.1. Second Audio Stream Added .................................15
      4.2. Audio, then Video Added ...................................16
      4.3. Audio and Video, Then Video Deleted .......................17
   5. Third Party Call Control (3pcc) ................................19
      5.1. No Media, Then Audio Added ................................19
      5.2. Hold and Unhold 2 .........................................20
      5.3. Hold and Unhold 3 .........................................21
   6. Security Considerations ........................................22
   7. Informative References .........................................22

Johnston & Sparks            Informational                      [Page 2]
RFC 4317               SDP Offer/Answer Examples           December 2005

1.  Overview

   This document describes offer/answer examples of Session Description
   Protocol (SDP) based on RFC 3264 [1].  The SDP in these examples is
   defined by RFC 2327 [2].  The offers and answers are assumed to be
   transported using a protocol such as Session Initiation Protocol
   (SIP) [3].

   Examples include codec negotiation and selection, hold and resume,
   and addition and deletion of media streams.  The examples show
   multiple media types, bidirectional, unidirectional, inactive
   streams, and dynamic payload types.  Common Third Party Call Control
   (3pcc) [5] examples are also given.

   The following sections contain examples in which two parties, Alice
   and Bob, exchange SDP offers, answers, and, in some cases, additional
   offers and answers.  Note that the subject line (s=) contains a
   single space character.

2.  Codec Negotiation and Selection

2.1.  Audio and Video 1

   This common scenario shows a video and audio session in which
   multiple codecs are offered but only one is accepted.  As a result of
   the exchange shown below, Alice and Bob may send only PCMU audio and
   MPV video.  Note: Dynamic payload type 97 is used for iLBC codec [6].

    [Offer]

      v=0
      o=alice 2890844526 2890844526 IN IP4 host.atlanta.example.com
      s=
      c=IN IP4 host.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0 8 97
      a=rtpmap:0 PCMU/8000
      a=rtpmap:8 PCMA/8000
      a=rtpmap:97 iLBC/8000
      m=video 51372 RTP/AVP 31 32
      a=rtpmap:31 H261/90000
      a=rtpmap:32 MPV/90000

Johnston & Sparks            Informational                      [Page 3]
RFC 4317               SDP Offer/Answer Examples           December 2005

    [Answer]

      v=0
      o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com