Subject: [AVT] Regarding G.729

From: Sharma Kanchinadham <[email-masked]>
Date: Mon, 14 Jan 2002 10:11:51 -0600

simao wrote :

>Maybe the least confusing way to view G.729 is to think of it as having 4
operating modes:
>6.4, 8, and 11.8 kbit/s; and the silence removal (aka VAD/CNI) mode.
(please note,
>>again, that eventhough the treatment of the signal to arrive at the 8
kbit/s bitstream is
 >different inside the G.729 and G.729A, the bits seen on the wire are
indistinguishable). So
>RTP needs to be concerned with 4 payload types for the whole G.729
standard: G729-6.4,
> G729, G729-12.2, and G729-SID (the VAD/CNI mode one).

I believe there is no seperate payload type for G.729-SID. Please see the
following draft

http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-mime-06.txt

The VAD/Silence suppression is negotiated using the "annexb" parameter.
Absence of this parameter or ommission of the a line means "YES".

Please let me know if i am missing anything.

Thanks ,
Sharma Kanchinadham
Worldcom

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From: Simão Campos-Neto <[email-masked]>
Date: Mon, 14 Jan 2002 12:20:53 -0500

Thanks, Sharma,

Sorry, I was a bit loose on my terminology. What I had in mind were
Figures 4,5,6,7 and 8 in
 http://www.ietf.org/internet-drafts/draft-ietf-avt-profile-new-12.txt

Annex B bit packing in Fig 5 is effectively a different payload from
Fig.4, although accomodated within the same general G729 payload type.
G.729D and E are different ones, which should also have an Annex B-type
of parameter (Specifics in G.729 Annex F and G, actually, but defined as
'annexb' in the MIME registration draft since the VAD/DTX bit packing is
the same for 6.4, 8, and 11.8 kbit/s). I am not sure how the receiver is
supposed to know when the bits in the G729 packet (for a "G729B"- or
"G729AB"-type communication) are according to Figure 4 or Figure 5,
since this will dynamically change over the course of the communication.
I guess that the receiver will infer the payload type from the packet
size and signal that to the speech decoder.

Simão.
--
Sharma Kanchinadham wrote:
> 
> simao wrote :
> 
>> Maybe the least confusing way to view G.729 is to think of it as having 4 operating modes:
>> 6.4, 8, and 11.8 kbit/s; and the silence removal (aka VAD/CNI) mode. (please note,
>> again, that eventhough the treatment of the signal to arrive at the 8 kbit/s bitstream is
>> different inside the G.729 and G.729A, the bits seen on the wire are indistinguishable). So
>> RTP needs to be concerned with 4 payload types for the whole G.729 standard: G729-6.4,

-- 
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Simão Ferraz de Campos Neto, Scientist *All comments strictly my own*
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