[Asterisk-Users] G729 Codec

[Andres]

steve at daviesfam.org wrote:

>On Tue, 3 Aug 2004, Steve Underwood wrote:
>
>  
>
>>Eh? G.729 has no particular features to allow more effective packet loss 
>>concealment. iLBC has, but at the cost of a substantially higher bit 
>>rate. In fact G.711 is a little ahead of G.729 in the regard, since 
>>packets are completely independant. The smoothing in G.729 means you 
>>need the previous packet to decode the current one properly.
>>    
>>
>
>For IAX2, at least, Asterisk oes not use the lost-packet-concealment of 
>any codec.  This is because the incoming frames "clock" Asterisk.  For 
>iLBC's lost packet concealment to work, Asterisk would have to start 
>calling the decoder with a NULL at the point when the missing packet shold 
>have arrived.
>  
>
This certainly explains why we get terrible audio at 10% packet loss 
between Asterisk servers between 2 end points using iLBC, but if we use 
2 SPA2000s using G.729 to commincate directly with each other (and 
having the same 10% packet loss), they sound pretty good.  We had been 
trying to figure why iLBCs loss concealment wasn't helping much.  I was 
never able to explain this until now:)

Thanks.

-- 
Andres
Network Admin
http://www.telesip.net