[Freeswitch-users] Codec Negotiation

[Moises Silva]

On Tue, Jul 10, 2012 at 11:51 AM, Stephen Wilde <wstephen80 at gmail.com>wrote:

> Is this message flow valid?
>
> FS   ----------------  MyProvider
>
> ---> INVITE (w/SDP G729, G711a, G711u)
>
> <--- 100 Trying
>
> <--- 183 Session Progress (w/SDP G729, G711a, G711u)
>
> <--- 200 OK (w/SDP G729, G711a, G711u)
>
>
> What is strange to me is that my provider send back a 183 Session Progress
> with all codec list of Freeswitch INVITE (I expect only the choosen codec).
>
> It's this message flow correct?
>
>
Although strange, I think per spec is correct.

http://www.ietf.org/rfc/rfc3264.txt

Section 7, mentions multiple answers are valid to the offer and it MAY send
media in any of the accepted streams and MUST send media using one of the
accepted formats and it SHOULD use the first one listed in the answer.

Anyone feel free to correct me if my understanding is wrong, as I just
started going thru the SIP related specs myself to troubleshoot and support
this kind of scenarios.

*Moises Silva
**Manager, Software Engineering***

msilva at sangoma.com

Sangoma Technologies

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t.   +1 800 388 2475 (N. America)

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