Re: [MMUSIC] I-D Action: draft-ietf-mmusic-sdp-g723-g729-01.txt

"Parthasarathi R" <partha@parthasarathi.co.in> Thu, 23 May 2013 18:37 UTC

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From: "Parthasarathi R" <partha@parthasarathi.co.in>
To: "'Dale R. Worley'" <worley@ariadne.com>
References: <20130520161935.17435.91264.idtracker@ietfa.amsl.com> <C5E08FE080ACFD4DAE31E4BDBF944EB113508A6A@xmb-aln-x02.cisco.com> <002801ce564b$51e52230$f5af6690$@co.in> <201305230204.r4N247r25245471@shell01.TheWorld.com>
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Date: Thu, 23 May 2013 23:46:41 +0530
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Cc: fluffy@cisco.com, mmusic@ietf.org
Subject: Re: [MMUSIC] I-D Action: draft-ietf-mmusic-sdp-g723-g729-01.txt
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Dale,

The current scope of this draft is to add the offer/answer (O/A)
consideration to RFC 4856 as it is missing in RFC 4856. The draft provides
clarification like "annexb=no" is in the offer whether annexb=yes is allowed
by the answerer or not.

Your proposal breaks RFC 4856 default value for annexb as the missing annexb
parameter in SDP implies that Annexb is supported as per 4856. The reason
for the default annexb value as "Yes" instead of "no" is as follows:

RFC3551 snippet related to G729 AnnexB:
      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.

If the answerer supports RFC3551, then the answerer has to support RFC3555
for annexb parameter. Annexb value default value is "Yes" in RFC 3555 as per
RFC 3551. RFC 4856 obsoletes RFC 3555 without changing "annexb" related
requirement. Please let me know any reason that you wish to change AnnexB
parameter default value now.

Thanks
Partha

> -----Original Message-----
> From: Dale R. Worley [mailto:worley@ariadne.com]
> Sent: Thursday, May 23, 2013 7:34 AM
> To: Parthasarathi R
> Cc: fluffy@cisco.com; mmusic@ietf.org
> Subject: Re: [MMUSIC] I-D Action: draft-ietf-mmusic-sdp-g723-g729-
> 01.txt
> 
> > > From: Cullen Jennings (fluffy)
> > >
> > > What happens when an endpoint that understands the [annexb]
> attribute
> > > sends [an] offer to an endpoint that does not understand or
> implement
> > > the [annexb] attribute ?
> 
> > From: "Parthasarathi R" <partha@parthasarathi.co.in>
> >
> > As per Sec 2.1.9 RFC 4856, "annexb=no" has to be sent by Answerer in
> case
> > the answerer does not support G729 AnnexB. The exact RFC snippet is
> 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."
> >
> > Please let me know whether you wish to explicitly mention in the
> draft that
> > Answerer *MUST* send "annexb=no".
> 
> No, if the offerer sends "annexb=yes" and the answerer *does not
> understand it*, that is, does not support this I-D, the answer will
> not contain an annexb parameter.  You should make sure the draft
> describes how the *offerer* detects this situation and ensures that
> the operation of the codec is done as well as possible.
> 
> Dale