MMUSIC Working Group A. Johnston Internet-Draft MCI Expires: February 16, 2005 R. Sparks dynamicsoft August 18, 2004 Session Description Protocol Offer Answer Examples draft-ietf-mmusic-offer-answer-examples-05 Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each 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 become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on February 16, 2005. Copyright Notice Copyright (C) The Internet Society (2004). 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 Expires February 16, 2005 [Page 1] Internet-Draft SDP Offer Answer Examples August 2004 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 . . . . . . . . . . . . . . . . . . . . 6 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 . . . . . . . . . . . . . . . . . . . . 11 3. Hold and Resume Scenarios . . . . . . . . . . . . . . . . . . 11 3.1 Hold and Unhold 1 . . . . . . . . . . . . . . . . . . . . 11 3.2 Hold with Two Streams . . . . . . . . . . . . . . . . . . 13 4. Addition and Deletion of Media Streams . . . . . . . . . . . . 14 4.1 Second Audio Stream Added . . . . . . . . . . . . . . . . 14 4.2 Audio then Video Added . . . . . . . . . . . . . . . . . . 15 4.3 Audio and Video, then Video Deleted . . . . . . . . . . . 16 5. Third Party Call Control (3pcc) . . . . . . . . . . . . . . . 18 5.1 No Media, then Audio Added . . . . . . . . . . . . . . . . 18 5.2 Hold and Unhold 2 . . . . . . . . . . . . . . . . . . . . 19 5.3 Hold and Unhold 3 . . . . . . . . . . . . . . . . . . . . 20 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 8. Informative References . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 22 Intellectual Property and Copyright Statements . . . . . . . . 23 Johnston & Sparks Expires February 16, 2005 [Page 2] Internet-Draft SDP Offer Answer Examples August 2004 1. Overview This document describes offer answer examples of Session Description Protocol (SDP) based on RFC 3264 [1]. The SDP in these examples are 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]. Johnston & Sparks Expires February 16, 2005 [Page 3] Internet-Draft SDP Offer Answer Examples August 2004 [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 49170 RTP/AVP 32 a=rtpmap:32 MPV/90000 2.2 Audio and Video 2 Alice can support PCMU, PCMA, and iLBC codecs, but not more than one at the same time. Alice offers all three to maximize chances of a successful exchange and Bob accepts two of them. Audio only session is established in initial exchange between Alice and Bob using either PCMU or PCMA codecs (payload type in RTP packet tells which is being used). Since Alice only supports one audio codec at a time, a second offer is made with just that one codec to limit the codec choice to just one. Note: the version number is incremented in both SDP messages in the second exchange. Now only the PCMU codec may be used for media session between Alice and Bob. Note: The declined video stream still present in the second exchange of SDP with ports set to zero. Johnston & Sparks Expires February 16, 2005 [Page 4] Internet-Draft SDP Offer Answer Examples August 2004 [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 49172 RTP/AVP 0 8 a=rtpmap:0 PCMU/8000 a=rtpmap:8 PCMA/8000 m=video 0 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 51372 RTP/AVP 0 a=rtpmap:0 PCMU/8000 m=video 0 RTP/AVP 31 a=rtpmap:31 H261/90000 [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 0 Johnston & Sparks Expires February 16, 2005 [Page 5] Internet-Draft SDP Offer Answer Examples August 2004 a=rtpmap:0 PCMU/8000 m=video 0 RTP/AVP 31 a=rtpmap:31 H261/90000 2.3 Audio and Video 3 Alice offers three audio and two video codecs, while Bob accepts with a single audio and video codec. As a result of this exchange, Bob and Alice use iLBC for audio and H261 for video. Note: change of dynamic payload type from 97 to 99 between the offer and the answer is OK since it references same codec. [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 49172 RTP/AVP 99 a=rtpmap:99 iLBC/8000 m=video 51374 RTP/AVP 31 a=rtpmap:31 H261/90000 2.4 Two Audio Streams Alice offers two separate streams, one audio with two codecs and the Johnston & Sparks Expires February 16, 2005 [Page 6] Internet-Draft SDP Offer Answer Examples August 2004 other with RFC 2833 [4] tones (for DTMF). Bob accepts both audio streams choosing the iLBC codec and telephone-events. [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 2.5 Audio and Video 4 Alice and Bob establish an audio and video session with a single audio and video codec. In a second exchange, Bob changes his address for media and Alice accepts with the same SDP as the initial exchange (and as a result does not increment the version number). [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 97 Johnston & Sparks Expires February 16, 2005 [Page 7] Internet-Draft SDP Offer Answer Examples August 2004 a=rtpmap:97 iLBC/8000 m=video 51372 RTP/AVP 31 a=rtpmap:31 H261/90000 [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 97 a=rtpmap:97 iLBC/8000 m=video 49170 RTP/AVP 31 a=rtpmap:31 H261/90000 [Second-Offer] v=0 o=bob 2808844564 2808844565 IN IP4 host.biloxi.example.com s= c=IN IP4 newhost.biloxi.example.com t=0 0 m=audio 49178 RTP/AVP 97 a=rtpmap:97 iLBC/8000 m=video 49188 RTP/AVP 31 a=rtpmap:31 H261/90000 [Second-Answer] 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 97 a=rtpmap:97 iLBC/8000 m=video 51372 RTP/AVP 31 a=rtpmap:31 H261/90000 2.6 Audio Only 1 Alice wishes to establish an audio session with Bob using either PCMU codec or iLBC codec with RFC2833 tones, but not both at the same time. The offer contains these two media streams. Bob declines the first one and accepts the second one. If both media streams had been Johnston & Sparks Expires February 16, 2005 [Page 8] Internet-Draft SDP Offer Answer Examples August 2004 accepted, Alice would have sent a second declining one of the streams, as shown in Section 4.3. [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 which allows Alice and Bob to switch between the two video codecs without another offer/answer exchange. [Offer] v=0 Johnston & Sparks Expires February 16, 2005 [Page 9] Internet-Draft SDP Offer Answer Examples August 2004 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 [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 Johnston & Sparks Expires February 16, 2005 [Page 10] Internet-Draft SDP Offer Answer Examples August 2004 2.8 Audio and Video 6 This scenario shows an audio and video offer that is accepted, but the answerer wants the video sent to a different address than 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. [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 3. Hold and Resume Scenarios 3.1 Hold and Unhold 1 Alice calls Bob, but Bob answers placing 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 Johnston & Sparks Expires February 16, 2005 [Page 11] Internet-Draft SDP Offer Answer Examples August 2004 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 [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 Johnston & Sparks Expires February 16, 2005 [Page 12] Internet-Draft SDP Offer Answer Examples August 2004 3.2 Hold with Two Streams 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 [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 Johnston & Sparks Expires February 16, 2005 [Page 13] Internet-Draft SDP Offer Answer Examples August 2004 [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 4. Addition and Deletion of Media Streams This section shows addition and deletion of media streams. 4.1 Second Audio Stream Added 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 2nd 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 Johnston & Sparks Expires February 16, 2005 [Page 14] Internet-Draft SDP Offer Answer Examples August 2004 a=rtpmap:97 iLBC/8000 [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 Audio only session is established in initial exchange between Alice and Bob using PCMU codec. Alice adds a video stream which 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 Johnston & Sparks Expires February 16, 2005 [Page 15] Internet-Draft SDP Offer Answer Examples August 2004 a=rtpmap:0 PCMU/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 49172 RTP/AVP 0 a=rtpmap:0 PCMU/8000 [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 0 a=rtpmap:0 PCMU/8000 m=video 49172 RTP/AVP 31 a=rtpmap:31 H261/90000 [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 0 a=rtpmap:0 PCMU/8000 m=video 49168 RTP/AVP 31 a=rtpmap:31 H261/90000 4.3 Audio and Video, then Video Deleted Alice and Bob establish an audio and video session. In a second exchange, Bob deletes the video session resulting in an audio only session. [Offer] v=0 o=alice 2890844526 2890844526 IN IP4 host.atlanta.example.com Johnston & Sparks Expires February 16, 2005 [Page 16] Internet-Draft SDP Offer Answer Examples August 2004 s= c=IN IP4 host.atlanta.example.com t=0 0 m=audio 49170 RTP/AVP 97 a=rtpmap:97 iLBC/8000 m=video 51372 RTP/AVP 31 a=rtpmap:31 H261/90000 [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 97 a=rtpmap:97 iLBC/8000 m=video 49170 RTP/AVP 31 a=rtpmap:31 H261/90000 [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 49174 RTP/AVP 97 a=rtpmap:97 iLBC/8000 m=video 0 RTP/AVP 31 a=rtpmap:31 H261/90000 [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=video 0 RTP/AVP 31 a=rtpmap:31 H261/90000 Johnston & Sparks Expires February 16, 2005 [Page 17] Internet-Draft SDP Offer Answer Examples August 2004 5. Third Party Call Control (3pcc) This section shows examples common in Third Party Call Control (3pcc) flows [5]. Call hold and resume flows are also common in 3pcc. 5.1 No Media, then Audio Added The first offer from Alice contains no media lines, so Bob accepts with no media lines. In the second exchange, Alice adds an audio stream which Bob accepts. [Offer] v=0 o=alice 2890844526 2890844526 IN IP4 host.atlanta.example.com s= c=IN IP4 host.atlanta.example.com t=0 0 [Answer] v=0 o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com s= c=IN IP4 host.biloxi.example.com t=0 0 [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 97 a=rtpmap:97 iLBC/8000 [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 97 a=rtpmap:97 iLBC/8000 Johnston & Sparks Expires February 16, 2005 [Page 18] Internet-Draft SDP Offer Answer Examples August 2004 5.2 Hold and Unhold 2 The first offer from Alice contains the connection address 0.0.0.0 and a random port number, which means that Bob can not send media to Alice (the media stream is "black holed" or "bh"). Bob accepts with normal SDP. In the second exchange, Alice changes the connection address, Bob accepts, and a media session is established. [Offer] v=0 o=alice 2890844526 2890844526 IN IP4 host.atlanta.example.com s= c=IN IP4 0.0.0.0 t=0 0 m=audio 23442 RTP/AVP 97 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 [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 97 a=rtpmap:97 iLBC/8000 [Second-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 Expires February 16, 2005 [Page 19] Internet-Draft SDP Offer Answer Examples August 2004 5.3 Hold and Unhold 3 The first offer from Alice contains an audio stream, but the answer from Bob contains the connection address 0.0.0.0 and a random port number, which means that Alice can not send media to Bob (the media stream is "black holed" or "bh"). In the second exchange, Bob changes the connection address, Alice accepts, and a media session is established. [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 97 a=rtpmap:97 iLBC/8000 [Answer] v=0 o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com s= c=IN IP4 0.0.0.0 t=0 0 m=audio 9322 RTP/AVP 97 a=rtpmap:97 iLBC/8000 [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 [Second-Answer] v=0 o=alice 2890844526 2890844526 IN IP4 host.atlanta.example.com s= c=IN IP4 host.atlanta.example.com t=0 0 Johnston & Sparks Expires February 16, 2005 [Page 20] Internet-Draft SDP Offer Answer Examples August 2004 m=audio 49170 RTP/AVP 97 a=rtpmap:97 iLBC/8000 6. Security Considerations SDP offer and answer messages can contain private information about addresses and sessions to be established between parties. If this information needs to be kept private, some security mechanism in the protocol used to carry the offers and answers must be used. For SIP, this means using TLS transport and/or S/MIME encryption of the SDP message body. 7. IANA Considerations This document introduces no IANA considerations. 8 Informative References [1] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [2] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. [3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [4] Schulzrinne, H. and S. Petrack, "RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals", RFC 2833, May 2000. [5] Rosenberg, J., Peterson, J., Schulzrinne, H. and G. Camarillo, "Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April 2004. [6] Duric, A. and S. Andersen, "RTP Payload Format for iLBC Speech", draft-ietf-avt-rtp-ilbc-05 (work in progress), June 2004. Johnston & Sparks Expires February 16, 2005 [Page 21] Internet-Draft SDP Offer Answer Examples August 2004 Authors' Addresses Alan Johnston MCI 100 South 4th Street St. Louis, MO 63102 EMail: alan.johnston@mci.com Robert J. Sparks dynamicsoft 5100 Tennyson Parkway Suite 1200 Plano, TX 75024 EMail: rsparks@dynamicsoft.com Johnston & Sparks Expires February 16, 2005 [Page 22] Internet-Draft SDP Offer Answer Examples August 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Johnston & Sparks Expires February 16, 2005 [Page 23]