[Asterisk-Dev] RTP issue with G.729

[Daniel Pocock]

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