Re: [Ekiga-list] Receiving SIP RTP before media description [was ekiga answers with delay ...?]

[Julien Puydt <jpuydt free fr>]

Damien Sandras a écrit :
> Le dimanche 26 novembre 2006 à 12:33 +1100, Craig Southeren a écrit :
>
> [...]
>
> > If anything, it would be a bug in OPAL, and so I have copied this email
> > to the correct OPAL mailing list so that other people who are
> > knowledgeable in SIP may see it.
>
> Most of the OPAL bugs are inside the Ekiga bug tracker. I have moved
> those I don't plan to fix to the openh323 bug tracker.
>
> However, I think the paragraph in the SIP RFC is clear, when you send an
> offer, you must be ready to receive media for all codecs in that offer
> before the offer has been acknowledged. I understand it sounds weird,
> but that is one of the limitations of OPAL.
>
> Another limitation is that the codec to use is determined from the 200
> OK answer in a way that is not necessarily correct.
>
> For example, if you send an INVITE with iLBC, PCMU and PCMA as available
> codecs, and the answer comes with PCMU, PCMA and iLBC (in that order)
> back, how do you determine if you have to send iLBC or PCMU? OPAL will
> send PCMU because it is the preferred codec in the answer.
>
> However, the codec to use should be determined by the RTP payload. So
> OPAL should be able to send and receive PCMU/PCMA/iLBC, and choose the
> correct one as soon as it receives RTP from the remote peer.
>
> However, that is a non trivial change to OPAL.
>
> What do you think?

Here is how gstreamer does, as far as I know : they get the data and 
feed it to their codecs, which return something which measures their 
confidente it is "correct data" for them.

So by elimination, they get the right codec, which can then be confirmed 
and better tuned afterwards.

Snark