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Versions: 00 draft-ietf-mmusic-sdp-g723-g729

MMUSIC                                                Muthu A M. Perumal
Internet-Draft                                             Cisco Systems
Updates: 4856 (if approved)                     Parthasarathi. Ravindran
Intended status: Standards Track                  Nokia Siemens Networks
Expires: April 18, 2013                                 October 15, 2012


    Offer/Answer Considerations for G.723 Annex A and G.729 Annex B
                   draft-ietf-mmusic-sdp-g273-g729-00

Abstract

   [RFC4856] describes the annexa parameter for G723 and the annexb
   parameter for G729, G729D and G729E. However, the specification does
   not describe the offerer and answerer behavior when the value of the
   annexa or annexb parameter does not match in the SDP offer and
   answer.  This document provides the offer/answer considerations for
   these parameters and updates [RFC4856].

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 18, 2013.

Copyright Notice

   Copyright (c) 2012 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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Offer/Answer Considerations . . . . . . . . . . . . . . . . . . 4
     3.1.  Offer/Answer Considerations for G723 Annex A  . . . . . . . 4
     3.2.  Offer/Answer Considerations for G.729 Annex B, G.729D
           Annex B and G.729E Annex B  . . . . . . . . . . . . . . . . 4
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     4.1.  Offer with G279 annexb=yes and answer with G279
           annexb=no . . . . . . . . . . . . . . . . . . . . . . . . . 5
     4.2.  Offer with G279 annexb=yes and answer with G729 and no
           annexb parameter  . . . . . . . . . . . . . . . . . . . . . 5
     4.3.  Offer with G279 and no annexb parameter and answer
           with G729 annexb=no . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7



























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1.  Introduction

   [RFC4856] describes the annexa parameter for G723 as follows:

      annexa: indicates that Annex A, voice activity detection, is used
      or preferred.  Permissible values are "yes" and "no" (without the
      quotes); "yes" is implied if this parameter is omitted.

   Also, [RFC4856] describes the annexb parameter for G729, G729D and
   G729E as follows:

      annexb: indicates that Annex B, voice activity detection, is used
      or preferred.  Permissible values are "yes" and "no" (without the
      quotes); "yes" is implied if this parameter is omitted.

   However, it does not have any normative statement for the case where
   the value of this parameter does not match in the SDP offer and
   answer.  For example, if the offer has G729 with annexb=yes and the
   answer has G729 with annexb=no, it can be interpreted in two
   different ways:
   o  The offerer and answerer proceed as if G729 is negotiated with
      annexb=yes, or
   o  The offerer and answerer proceed as if G729 is negotiated with
      annexb=no.

   Since [RFC4856] does not state it clearly, various implementations
   have interpreted the offer/answer in their own ways, resulting in a
   different codec being chosen to call failure, when the parameter
   value does not match in the offer and answer.

   [RFC3264] requires SDP extensions that define new fmtp parameters to
   specify their proper interpretation in offer/answer.  But, [RFC4856]
   does not specify it for the Annex A flavor of G.723 and the Annex B
   flavors of G.729, G729D and G729E.

   This document describes the offer/answer considerations for these
   parameters and provides the necessary clarifications.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].







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3.  Offer/Answer Considerations

   [RFC3551] states that

      Receivers MUST accept comfort noise frames if restriction of their
      use has not been signaled.  The MIME registration for G729 in RFC
      3555 specifies a parameter that MAY be used with MIME or SDP to
      restrict the use of comfort noise frames.

   Based on the above, it is best to not use comfort noise frames if the
   SDP offer or answer indicates no support for it.

3.1.  Offer/Answer Considerations for G723 Annex A

   When the offer or answer has G723 and the annexa parameter is absent,
   it MUST be considered as if the offer or answer has G723 with
   annexa=yes.

   When the offer has G723 with annexa=yes and the answer has G723 with
   annexa=no, the offerer and answerer MUST proceed as if G723 is
   negotiated with annexa=no.

   When the offer has G723 with annexa=no then the answer MUST NOT have
   annexa=yes for G723.  Thus the annexa parameter can be turned off by
   the answerer, but cannot be turned on.

      When the offer has G723 with annexa=no, the reason for not
      mandating that the answer MUST have annexa=no for G723 is that
      there are there implementations that omit the annexa parameter in
      answer and expect the least common denominator to be used.

   When the offer has G723 with no annexa parameter and the answer has
   G723 with annexa=yes, the offerer and answerer MUST proceed as if
   G723 is negotiated with annexa=yes.

3.2.  Offer/Answer Considerations for G.729 Annex B, G.729D Annex B and
      G.729E Annex B

   In this section G729 represents any of G729 or G729D or G729E.

   When the offer or answer has G729 and the annexb parameter is absent,
   it MUST be considered as if the offer or answer has G729 with
   annexb=yes.

   When the offer has G729 with annexb=yes and the answer has G729 with
   annexb=no, the offerer and answerer MUST proceed as if G729 is
   negotiated with annexb=no.




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   When the offer has G729 with annexb=no then the answer MUST NOT have
   annexb=yes for G729.  Thus the annexb parameter can be turned off by
   the answerer, but cannot be turned on.

      When the offer has G729 with annexa=no, the reason for not
      mandating that the answer MUST have annexa=no for G729 is that
      there are there implementations that omit the annexa parameter in
      answer and expect the least common denominator to be used.

   When the offer has G729 with no annexb parameter and the answer has
   G729 with annexb=yes, the offerer and answerer MUST proceed as if
   G729 is negotiated with annexb=yes.


4.  Examples

4.1.  Offer with G279 annexb=yes and answer with G279 annexb=no

           [Offer with G279 annexb=yes]

           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 18
           a=rtpmap:18 G729/8000
           a=fmtp:18 annexb=yes

           [Answer with G729 annexb=no]

           v=0
           o=bob 1890844326 1890844326 IN IP4 host.bangalore.example.com
           s=
           c=IN IP4 host.bangalore.example.com
           t=0 0
           m=audio 19140 RTP/AVP 18
           a=rtpmap:18 G729/8000
           a=fmtp:18 annexb=no

   In the above example the offerer and answerer proceed as if G729 is
   negotiated with annexb=no.

4.2.  Offer with G279 annexb=yes and answer with G729 and no annexb
      parameter






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           [Offer with G279 annexb=yes]

           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 18
           a=rtpmap:18 G729/8000
           a=fmtp:18 annexb=yes

           [Answer with G729 and no annexb parameter]

           v=0
           o=bob 1890844326 1890844326 IN IP4 host.bangalore.example.com
           s=
           c=IN IP4 host.bangalore.example.com
           t=0 0
           m=audio 19140 RTP/AVP 18
           a=rtpmap:18 G729/8000

   In the above example the offerer and answerer proceed as if G729 is
   negotiated with annexb=yes.

4.3.  Offer with G279 and no annexb parameter and answer with G729
      annexb=no

           [Offer with G279 and no annexb parameter]

           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 18
           a=rtpmap:18 G729/8000

           [Answer with G729 annexb=no]

           v=0
           o=bob 1890844326 1890844326 IN IP4 host.bangalore.example.com
           s=
           c=IN IP4 host.bangalore.example.com
           t=0 0
           m=audio 19140 RTP/AVP 18
           a=rtpmap:18 G729/8000
           a=fmtp:18 annexb=no




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   In the above example the offerer and answerer proceed as if G729 is
   negotiated with annexb=no.


5.  Security Considerations

   There is no extra security consideration apart from what is described
   in [RFC4856].


6.  IANA Considerations

   There is no IANA consideration for this draft.


7.  Acknowledgement

   Thanks to Flemming Andreasen (Cisco), Miguel A. Garcia (Ericsson),
   Ali C. Begen (Cisco), Paul Kyzivat, Roni Even (Huawei), Kevin Riley
   (Sonus), Ashish Sharma (Sonus), Kevin P. Fleming (Digium) and Harprit
   S. Chhatwal (InnoMedia) for their valuable inputs and comments.
   Martin Dolly (ATT) and Hadriel Kaplan (Acme Packet) provided useful
   suggestions at the mic at IETF-83.


8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC4856]  Casner, S., "Media Type Registration of Payload Formats in
              the RTP Profile for Audio and Video Conferences",
              RFC 4856, February 2007.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              July 2003.










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Authors' Addresses

   Muthu Arul Mozhi Perumal
   Cisco Systems
   Cessna Business Park
   Sarjapur-Marathahalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: mperumal@cisco.com


   Parthasarathi Ravindran
   Nokia Siemens Networks
   Bangalore, Karnataka
   India

   Email: partha@parthasarathi.co.in

































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