[Asterisk-Dev] RTP issue with G.729

[Kevin Walsh]

Daniel Pocock [daniel at readytechnology.co.uk] wrote:
> I've had some interoperability reports from people testing various phones
> with the G.729A codec. 
> 
> Some phones send a 12 byte RTP frame.  I am guessing that these phones
> are appending 2 bytes of VAD data (as per the G.729B specification),
> even though my codec example is only adhering to the G.729A
> specification (it expects RTP frames to be 10 bytes).
> 
> Should I just discard any bytes that are not a multiple of 10?  Eg, if a
> 12 byte RTP frame is received, should I discard the last 2 bytes?
> 
> Sometimes a 2 byte frame is received - should I simply drop these
> frames, or would doing so mean a timeslot is lost?
> 
> Furthermore, does Asterisk's RTP implementation tell the phone that only
> G.729A is supported?  If so, is the phone at fault for not respecting
> the version of the protocol supported by Asterisk?
> 
> Or is it a fault with Asterisk for somehow giving the phone the
> impression that G.729B is supported?
> 
> The codec is at http://www.readytechnology.co.uk/open/g729
>
The frame.c source offers some clues in this area.  Look at the various
"smoother" functions.

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