[Asterisk-Dev] SIP/IAX repacking cpu cost?

[Steve Kann]

Andrew Kohlsmith wrote:

>On February 18, 2005 10:09 am, Kevin P. Fleming wrote:
>  
>
>>SIP-IAX on the other hand requires queuing and dequeueing frames between
>>two different channel drivers. There is no way this can be as efficient
>>as the frames staying inside a single channel driver (or protocol
>>driver, in this case), no matter how much "tuning" may be done.
>>    
>>
>
>When converting the RTP stream to IAX2 audio frames, does Asterisk have to 
>take the audio frame apart or transcode it?  i.e. if I have a gsm stream from 
>a SIP phone to Asterisk and it's headed to an IAX2 destination on another 
>Asterisk host, does Asterisk have to transcode from gsm to ulaw or slinear 
>and then back to gsm, or is the SIP RTP gsm stream "compatible" with the gsm 
>stream format in the IAX2 audio frames?
>  
>

It shouldn't and won't transcode if the codecs on both ends are the 
same.  Not only would that waste CPU, it would degrade audio quality, 
since you lose information each time you encode/decode.

-SteveK