[Asterisk-Dev] RTP issue with G.729

[Rahul Arvind Jadhav]

Also, there is a way you can specify in SDP that only g729A is supported 
is supported. Try putting attribute line `a=fmtp:18 annexb=no` in the 
SDP. This works with quite good number of devices.

Steve Underwood wrote:

> Daniel Pocock 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 2 byte comfort noise data implies there will be silent timeslots 
> following, with no data. So, loosing a timeslot is no big deal. If you 
> are implementing comfort noise, then handling the 2 byte messages is 
> important. You get much better noise by using them, as per the spec., 
> than by making the noise in other ways. If you are not implementing 
> comfort noise, then I think dropping them is all you can really do.
>
> Regards,
> Steve
>
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-- 
Rahul Arvind Jadhav
Tech Lead, NetYantra (I) Pvt. Ltd.