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

[Damien Sandras]

It seems this discussion will lead to nothing, as every side stays on
its position.

However, let me answer a last time, then I will move to something else.

> 
> > Well, let's forget about that and summarize the results of that
> > discussion. There are actually right now 2 problems in OPAL :
> > 
> > 1: Establishing the media streams after having sent or received the ACK
> > takes between 1 or 2 seconds during which the media stream is lost.
> 
> This seems to be only a problem on Linux. I'm not seeing this problem on
> Windows.
> 

I can see that problem on Windows too. Have you tried reproducing the
problem? If so, how?

> What is OPAL during the 1 or 2 seconds? Is this how long it takes to
> open the sound device on Linux? I'll need more information before I can
> work out how to fix the problem
> 

No, it is the time it takes to start the threads, open the device, start
the codecs, and so  on.

You have a debug 4 output, so you can clearly see what happens.

> > 2: If OPAL sends an INVITE with 3 codecs in a given order, and that
> > Asterisk supports the 3 same codecs but with a different priority order,
> > it will send the 200 OK with those 3 codecs in the order it prefers.
> > OPAL will then choose the codec it prefers and send the media with that
> > codec. It could happen that Asterisk uses another codec from the list,
> > ie a codec for which OPAL is not ready to receive a stream.
> > 
> > e.g. :
> > INVITE PCMU, iLBC, PCMA
> > 200 OK iLBC, PCMA, PCMU
> > 
> > OPAL will send the stream using iLBC.
> > Asterisk could decide to send the stream using PCMU.
> > However OPAL expects iLBC...
> 
> Replying to an INVITE with more than one codec has a very specific
> meaning, and OPAL does not support these semantics. Fortunately, very
> few devices seem to do this.

Many devices are doing this, including Asterisk which is very popular,
believe me. Some popular french ITSP's like  Wengo are also working that
way, so it is really not so uncommon...
-- 
 _      Damien Sandras
(o-     
//\   Ekiga Softphone : http://www.ekiga.org/
v_/_ NOVACOM         : http://www.novacom.be/
          FOSDEM          : http://www.fosdem.org/
          SIP Phone       : sip:dsandras at ekiga.net