[SR-Users] Question about early media

[Iñaki Baz Castillo]

2010/10/4 Asim Riaz <ariaz78 at gmail.com>:
> Hi List,
> Phone-1 ------->Proxy1 (kamailio)-------------->Proxy-2(3rd party)
> -------------> phone 2
>
> Calls from phone-1 to phone-2, proxy-2 is sending early media without sdp in
> provisional reply, this early media is sourced from different port than
> response (200), what port proxy-1 will use to transmit actual voice, the
> source port in early media or source port in  response(200) which is
> different than early media.

As Daniel said Kamailio doesn't handle media (it's a SIP proxy). You
should mean "Phone-1" instead of "proxy-1".

According to the RFC about SDP (and also RFC 3261): during the same
early dialog (same To-tag) the SDP MUST NOT change. This is, if a UAS
generates a 183 (To-tag=1234) with SDP, it MUST use the same SDP in
other 183's responses and in final 200 OK response.
The client can receives multiple SDP (when there is a proxy doing
parallel forking, but each early dialog (same To-tag) MUST mantain a
fixed SDP.

So, if the client receives a different SDP in the 200 than the SDP it
received in the 183 (I mean in the *same* early-dialog / same To-tag)
then the client MUST ignore others SDP but the first one received. I
insist: I'm speaking about the SDP in the SAME early-dialog.



-- 
Iñaki Baz Castillo
<ibc at aliax.net>