Subject: RE: [SIP] Re: Codecs G729 and their various flavors

From: Shawn Pouliotte <[email-masked]>
Date: Fri, 6 Jul 2001 14:35:06 -0700

Hi There, 

You don't need a different payload type for 729b/729ab as you can determine
that you are receiving silence from the payload length. Voice is nx10 bytes
and silence is 4 bytes. Silence and Voice can be sent together giving
(nx10)+4 as payload length hence payload type 18 along with payload length
is enough to determine what is being sent. 

As 729a and 729 codecs can also interoperate with one-another, you don't
need to distinguish between the 2 payloads. 

Hope that helps
Shawn

-----Original Message-----
From: Colin Perkins [mailto:[email-masked]]
Sent: Friday, July 06, 2001 2:13 PM
To: Manoj Bhatia
Cc: Shawn Pouliotte; 'Gregory Paterno'; Henning G. Schulzrinne;
[email-masked]; [email-masked]
Subject: Re: [SIP] Re: Codecs G729 and their various flavors 

The rules for use and signalling of G.729 in RTP are defined in:
	draft-ietf-avt-profile-new-10.txt
and 	draft-ietf-avt-rtp-mime-04.txt

According to those drafts, it is legal to use payload type 18 for Annex B
frames (indeed, that is the default). They also define a parameter for use
in SDP a=fmtp: lines to explicitly signal the presence/absence of annex B 
frames if that is necessary.

If there are problems with these definitions, they should be brought to the
attention of the AVT working group, since the revised profile is about to
be submitted for publication as a draft standard RFC.

Colin

--> Manoj Bhatia writes:
>Hi
>
>The fact is that g.729 /g.729a  pair shall not interoperate with
>g.729b/g.729ab.
>The static payload '18' defined so far is being used for g.729/g.729a by
>
>SIP folks  .
>Some are now interested in using g.729b/g.729ab pair for obvious
>advantages in
>VAD,DTX etc.
>
>So, my question is that why don't we have a static payload defined for
>g.729b/g729ab
>pair just like we had '18' for the other pair.
>
>Or is it legal to use '18' for this pair too ?
>
>To avoid interop issues, can we lay down rules to state that when to use
>'18' and when
>not to use '18' especially if a SIP-UA agent has the ability to support
>'all' the four flavors of
>g729 and is interested in advertising that in its SDP ?
>
>thanks
>-manoj
>
>
>Shawn Pouliotte wrote:
>
>>
>>
>> Hi
>>
>> -G.729 is CS-ACELP, an 8kbps speech Codec (G.729r8)
>> -G.729a (G.729 Annex A) is a reduced complexity version of G.729 and
>> is still an 8k voice Codec
>> -G.729b (G.729 Annex B) is a spec for Voice Activity Detection (VAD),
>> Discontinuity Transmission (DTX), and Comfort Noise Generation (CNG).
>> More simply stated, Annex B is silence suppression for use with G.729
>> or G.729a voice codecs and is not a codec in itself.
>>
>> G.729 and G.729a operate on a 10 mSec speech frame corresponding to 80
>> samples at a rate of 8kbps. This yields an 80bit speech fame every 10
>> mSec. If silence suppression etc. are used (such as Annex B), the
>> frame length will vary. In the case of annex B, SID frames are 15 bits
>> rather than 80 bits for a speech frame.
>>
>> Hope that helps
>> Shawn
>>
>> -----Original Message-----
>> From: Gregory Paterno [mailto:[email-masked]]
>> Sent: Thursday, July 05, 2001 12:08 PM
>> To: Henning G. Schulzrinne
>> Cc: [email-masked]; [email-masked]
>> Subject: RE: [SIP] Re: Codecs G729 and their various flavors
>>
>> "G.729 is silence suppression and distinguishable by payload
>> length."
>>
>> Where could I find information on the payload length supporting
>> silence suppression for G.711 and G.729b?
>>
>> Thanks.
>>
>> -----Original Message-----
>> From: [email-masked]
>> [mailto:[email-masked]]On Behalf Of Henning G.
>> Schulzrinne
>> Sent: Thursday, July 05, 2001 11:36 AM
>> To: [email-masked]
>> Cc: [email-masked]; [email-masked];
>> [email-masked];
>> [email-masked]; [email-masked]
>> Subject: [SIP] Re: Codecs G729 and their various flavors
>>
>> Ameet Kher wrote:
>> >
>> > Hi
>> >
>> > I am trying to follow up on some previous discussions on this
>> list
>> > about whether to use dynamic
>> > payload types for various flavors of the G729 codec. Presently
>> the
>> > IANA list has defined a static payload type
>> > and encoding name only for the G729r8 codec. Should we be using
>> > dynamic payloads for G729b, G729ab, G729a ?
>>
>> All new codecs only use dynamic payload types.
>>
>> > And use X-* as encoding names ? I am sure we cannot use the
>> same
>>
>> Using X-* is a certifiably bad idea. The argument has been made
>> numerous
>> times on this list, but let me know if you'd like another
>> rendition of
>> it.
>>
>> > static payload value (18) for all these flavors.
>>
>> You can use the same payload type (doesn't matter if static or
>> dynamic)
>> if the codecs are distinguishable by looking at the payload.
>> G.729a is
>> just a reduced-complexity implementation, that has the same bit
>> pattern,
>> so there doesn't seem to be a need for a new payload type.
>>
>> G.729 is silence suppression and distinguishable by payload
>> length.
>>
>> I have no idea what G.729ab would be; it is not mentioned at
>> http://www.itu.int/itudoc/itu-t/rec/g/g700-799/index.html
>>
>>
>> >
>> > - Ameet
>> >
>> >
>> >
>> > --
>> > ******************************
>> > AMEET KHER, Software Engineer
>> > Cisco Systems
>> > Tel : (919) 392-8431
>> >
>> >
>>
>> --
>> Henning Schulzrinne   http://www.cs.columbia.edu/~hgs
>>
>> _______________________________________________
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>>
>> _______________________________________________
>> This list is for continuing development of the SIP protocol.
>> The sip-implementor's list is the place to discuss implementation,
>> and to receive advice on understanding existing sip.
>> To subscribe to it, send mail to
>> [email-masked] with "subscribe" in the body.
>
>--
>Manoj Bhatia                           |        |         |
>[email-masked]                       |       :|:       :|:
>7025 Kit Creek Road, RTP, NC - 27709   |     :|||||:   :|||||:
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