sdp_offer_answer_examples.txt

This gives examples of Session Description Protocol (SDP) offer/answer exchanges. Examples include

    [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
      a=rtpmap:0 PCMU/8000
      m=audio 51372 RTP/AVP 97 101
      a=rtpmap:97 iLBC/8000
      a=rtpmap:101 telephone-event/8000

    [Answer]

      v=0
      o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 0 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      m=audio 49170 RTP/AVP 97 101
      a=rtpmap:97 iLBC/8000
      a=rtpmap:101 telephone-event/8000

2.7.  Audio and Video 5

   Alice and Bob establish an audio and video session in the first
   exchange with a single audio and video codec.  In the second
   exchange, Alice adds a second video codec, which Bob accepts.  This
   allows Alice and Bob to switch between the two video codecs without
   another offer/answer exchange.

    [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 99
      a=rtpmap:99 iLBC/8000
      m=video 51372 RTP/AVP 31
      a=rtpmap:31 H261/90000






Johnston & Sparks            Informational                      [Page 9]

RFC 4317               SDP Offer/Answer Examples           December 2005



    [Answer]

      v=0
      o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 49172 RTP/AVP 99
      a=rtpmap:99 iLBC/8000
      m=video 51374 RTP/AVP 31
      a=rtpmap:31 H261/90000

    [Second-Offer]

      v=0
      o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
      s=
      c=IN IP4 host.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 99
      a=rtpmap:99 iLBC/8000
      m=video 51372 RTP/AVP 31 32
      a=rtpmap:31 H261/90000
      a=rtpmap:32 MPV/90000

    [Second-Answer]

      v=0
      o=bob 2808844564 2808844565 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 49172 RTP/AVP 99
      a=rtpmap:99 iLBC/8000
      m=video 51374 RTP/AVP 31 32
      a=rtpmap:31 H261/90000
      a=rtpmap:32 MPV/90000

2.8.  Audio and Video 6

   This example shows an audio and video offer that is accepted, but the
   answerer wants the video sent to a different address than that of the
   audio.  This is a common scenario in conferencing where the video and
   audio mixing utilizes different servers.  In this example, Alice
   offers audio and video, and Bob accepts.





Johnston & Sparks            Informational                     [Page 10]

RFC 4317               SDP Offer/Answer Examples           December 2005


    [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

    [Answer]

      v=0
      o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 49174 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      m=video 49172 RTP/AVP 32
      c=IN IP4 otherhost.biloxi.example.com
      a=rtpmap:32 MPV/90000
























Johnston & Sparks            Informational                     [Page 11]

RFC 4317               SDP Offer/Answer Examples           December 2005


3.  Hold and Resume Scenarios

3.1.  Hold and Unhold 1

   Alice calls Bob, but when Bob answers he places Alice on hold.  Bob
   then takes Alice off hold in the second offer.  Alice changes port
   number in the second exchange.  The media session between Alice and
   Bob is now active after Alice's second answer.  Note that a=sendrecv
   could be present in both second offer and answer exchange.  This is a
   common flow in 3pcc [5] scenarios.

    [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 97
      a=rtpmap:0 PCMU/8000
      a=rtpmap:97 iLBC/8000

    [Answer]

      v=0
      o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 placeholder.biloxi.example.com
      t=0 0
      m=audio 49172 RTP/AVP 97
      a=rtpmap:97 iLBC/8000
      a=sendonly

    [Second-Offer]

      v=0
      o=bob 2808844564 2808844565 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 49170 RTP/AVP 97
      a=rtpmap:97 iLBC/8000









Johnston & Sparks            Informational                     [Page 12]

RFC 4317               SDP Offer/Answer Examples           December 2005



    [Second-Answer]

      v=0
      o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
      s=
      c=IN IP4 host.atlanta.example.com
      t=0 0
      m=audio 49178 RTP/AVP 97
      a=rtpmap:97 iLBC/8000

3.2.  Hold with Two Streams

   In this example, two audio streams have been established in the first
   offer/answer exchange.  In this second offer/answer exchange, one of
   the audio streams is placed on hold.  Alice offers two media streams,
   a bidirectional audio stream and a send-only telephone event stream.
   Bob accepts both streams.  Bob then puts Alice's audio stream on hold
   but not the tone stream.  Alice responds with identical SDP to the
   initial offer.

    [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 97
      a=rtpmap:0 PCMU/8000
      a=rtpmap:97 iLBC/8000
      m=audio 49172 RTP/AVP 98
      a=rtpmap:98 telephone-event/8000
      a=sendonly

    [Answer]

      v=0
      o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 49172 RTP/AVP 97
      a=rtpmap:97 iLBC/8000
      m=audio 49174 RTP/AVP 98
      a=rtpmap:98 telephone-event/8000
      a=recvonly




Johnston & Sparks            Informational                     [Page 13]

RFC 4317               SDP Offer/Answer Examples           December 2005


    [Second-Offer]

      v=0
      o=bob 2808844564 2808844565 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 49172 RTP/AVP 97
      a=rtpmap:97 iLBC/8000
      a=sendonly
      m=audio 49174 RTP/AVP 98
      a=rtpmap:98 telephone-event/8000
      a=recvonly

    [Second-Answer]

      v=0
      o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
      s=
      c=IN IP4 host.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0 97
      a=rtpmap:0 PCMU/8000
      a=rtpmap:97 iLBC/8000
      m=audio 49172 RTP/AVP 98
      a=rtpmap:98 telephone-event/8000
      a=sendonly
























Johnston & Sparks            Informational                     [Page 14]

RFC 4317               SDP Offer/Answer Examples           December 2005


4.  Addition and Deletion of Media Streams

   This section shows addition and deletion of media streams.

4.1.  Second Audio Stream Added

   In this example, the first offer/answer exchange establishes a single
   audio stream with a single codec.  The second offer/answer exchange
   adds a second audio stream for telephone events.  The second stream
   is added by Bob's media server (different connection address) to
   receive RFC 2833 telephone-events (DTMF digits, typically) from
   Alice.  Alice accepts.  Even though the second stream is
   unidirectional, Alice receives RTCP packets on port 49173 from the
   media server.

    [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 97
      a=rtpmap:0 PCMU/8000
      a=rtpmap:97 iLBC/8000

   [Answer]

      v=0
      o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 49170 RTP/AVP 97
      a=rtpmap:97 iLBC/8000
















Johnston & Sparks            Informational                     [Page 15]

RFC 4317               SDP Offer/Answer Examples           December 2005



    [Second-Offer]

      v=0
      o=bob 2808844564 2808844565 IN IP4 host.biloxi.example.com
      s=
      c=IN IP4 host.biloxi.example.com
      t=0 0
      m=audio 49170 RTP/AVP 97
      a=rtpmap:97 iLBC/8000
      m=audio 48282 RTP/AVP 98
      c=IN IP4 mediaserver.biloxi.example.com
      a=rtpmap:98 telephone-event/8000
      a=recvonly

    [Second-Answer]

      v=0
      o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
      s=
      c=IN IP4 host.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 97
      a=rtpmap:97 iLBC/8000
      m=audio 49172 RTP/AVP 98
      c=IN IP4 host.atlanta.example.com
      a=rtpmap:98 telephone-event/8000
      a=sendonly

4.2.  Audio, then Video Added

   An audio-only session is established in the initial exchange between
   Alice and Bob using PCMU codec.  Alice adds a video stream that is
   accepted by Bob.

    [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
      a=rtpmap:0 PCMU/8000







Johnston & Sparks            Informational                     [Page 16]

RFC 4317               SDP Offer/Answer Examples           December 2005