[asterisk-users] Codec G.129 A vs A/B

[Steve Underwood]

On 06/04/2010 02:27 AM, Kyle Kienapfel wrote:
> http://en.wikipedia.org/wiki/G.729
> Looks like theres A and B and no "A/B" so theres nothing to worry about
>    
What's the point of quoting a page, if you are not actually going to 
read it?
> On Thu, Jun 3, 2010 at 9:09 AM, Alejandro Cabrera Obed
> <aco1967 at gmail.com>  wrote:
>    
>> Dear all, I've read that Asterisk supports only the G.729 A audio
>> codec. I have several Grandstream IP phones with G.729 A/B codec
>> implementation.
>>
>> Does G.729 A/B mean both version A and version B, or A/B is a new
>> version different from A and B and it's not supported by Asterisk ???
>>      
G.729 is the base codec, which hardly anyone uses

G.729 Annex A is a stripped down version which doesn't sound as good, 
but takes only half the compute power. This is the one almost everyone 
uses - who cares about voice quality, anyway? The bit stream is 
identical to G.729, so they are fully interworkable. For thos reason SDP 
does not distinguish between G.729 and G.729A.

G.729 Annex B is a CNG/VAD add on for either of the above codecs. This 
feature may be turned on and off in the SDP, using the annexb parameter. 
A codec which cannot support Annex B is, therefore, always able to 
interwork with a codec that does support it.

G.729AB or G.729A/B are the usual ways people described a codec which 
uses the Annex A version of the encoding and decoding, and which 
supports CNG/VAD.

Steve