[Asterisk-Dev] (Re)Invite for codec change

[Karl Brose]

Andrew Lindh wrote:

>I don't always need asterisk in the media path. I need to make sure it stays
>in there somewhere for billing/accounting, music on hold, "extension" status,
>and other cool or required features. The only things it needs to be in the
>media path for is pound (#) transfers, which I don't use, or
>wiretaping/recording....not every call.
>
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>An issue is asterisk as an IVR/voice mail and mismatched calls. If I am
>connected to the IVR/voicemail as G.711 and then transfer to a device/user
>that uses G.729 it would be nice to have asterisk not have to transcode.
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>
Well, if you are connected to voice mail, it will have to transcode for 
anything other than the format the
vm files are encoded as.

>I don't care if it stays in the middle, but I don't want to burn CPU time
>doing simething the device DSP can do.
>
>Here is an example from a call from x301 to x389. The call is setup as
>G.711 but the other phone only supports G729A. I don't want asterisk to
>completely get out of the way, I just want it to make sure they both use
>g.729 (x301 supports both, but defaults to g.711). There is no need for
>asterisk to transcode as x301 supports g729 too. But I don't want to force
>every call to the lowest codec....
>
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>

Yes, sure.
If  x301  and asterisk are offering g711 and g729 on the intial 
offer/answer exchange for their leg
they must be able accept format changes anytime between those codecs, I 
believe, if they comply
with the RFCs. The question is, can Asterisk's bridge handle such 
switches on the fly and how to make it so.
The SIP code currently doesn't allow for specific codec preference 
orders at the peer level, only
at the channel level, so that could be a root of problems, since these 
options are most useful at
the specific peer level. I do have complete code for this actually 
running in production.  But there
needs to be more powerful media stream logic and configurability.


>204.213.176.229  389         323d84c72f0  00102/00000   G729A 
>204.213.176.201  301         d02cda15-f9  00101/00002   ULAW  
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