[asterisk-users] G.729 and Voicemail

[Moises Silva]

>
> I would be very surprised if that were true.  Your phones speak many
> codecs, but they negotiate with asterisk on registration which one they
> will be using.  They don't switch codecs based on the remote channel
> (which they don't even know about).  Today, if your phones are negotiating
> 729 on registration, you are definitely transcoding calls to/from the
> PSTN.
>

Assuming we're talking about SIP (and any other voip protocol I know of for
that matter), that is incorrect, codec negotiation is done during the call
setup based on preferences stored in both Asterisk and the phone (that is
what the SDP is for among other things). However at that point Asterisk does
not know that the dial plan is going to call the voicemail application to
play a file in g729 format (how can possibly now that), and therefore when
the file is being played the phone already expects the audio for the call in
the format negotiated during call setup which may or may not be g729. Not
sure if a re-invite could be issued to change the codec type in the middle
of the call, but I suppose it should be possible to implement.

-- 
Moises Silva
Software Developer
Sangoma Technologies Inc. | 50 McIntosh Drive, Suite 120, Markham ON L3R 9T3
Canada
t. 1 905 474 1990 x 128 | e. moy at sangoma.com
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