Internet DRAFT - draft-muthu-mmusic-offer-answer-g723-g729
draft-muthu-mmusic-offer-answer-g723-g729
MMUSIC Muthu A M. Perumal
Internet-Draft Cisco Systems
Intended status: BCP Parthasarathi. Ravindran
Expires: October 26, 2012 Sonus Networks
April 24, 2012
Offer/Answer Considerations for G.723 Annex A and G.729 Annex B
draft-muthu-mmusic-offer-answer-g723-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.
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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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."
This Internet-Draft will expire on October 26, 2012.
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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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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 . . . . . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . . . . . . . . . . . 8
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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.
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.
Open item: Should the above be restated as follows?
When the offer has G723 with annexa=no then the answer MUST have
annexa=no for G723.
This is technically correct, but 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
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negotiated with annexb=no.
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.
Open item: Should the above be restated as follows?
When the offer has G729 with annexb=no then the answer MUST have
annexb=no for G729.
This is technically correct, but are there implementations that
omit the annexb parameter in answer and expect the least common
denominator to be used?
When the offer has G.729 with no annexb parameter and the answer has
G.729 with annexb=yes, the offerer and answerer MUST proceed as if
G.729 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.
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4.2. Offer with G279 annexb=yes and answer with G729 and no annexb
parameter
[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
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[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.
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), 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) also provided useful
suggestions in 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.
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[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003.
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
Sonus Networks
Prestige Shantiniketan - Business Precinct
Whitefield Road
Bangalore, Karnataka 560066
India
Email: pravindran@sonusnet.com
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