Subject: [Sip] Forking, early media and RTCP

From: Christer Holmberg <[email-masked]>
Date: Mon, 01 Oct 2001 17:15:46 +0300

Hi,

A couple of weeks ago, during the media-line-matching discussion, it was
mentioned that the m= lines in the request and the response MUST match.
It was also said that it is not possible, if two codecs are used, to use
a single port for both codecs on one client, and two separate ports for
the codecs on the other nodes, since that will mess up the RTCP
signalling.

However, I think that this will happen also when an INVITE forks, and
more than one UAS wants to send and/or receive early media. In this case
the UAC is going to use a single port for multiple streams, but
communicate with multiple (the only difference from the m= line issue is
that the remote ports now probably will be on separate IP addresses).
What will happen to the RTCP signalling now?

Using the manyfolks extension I think this is not a problem, because
whenever we receive a 18x for a new leg we may reserve a new media port
for that leg and send it in the "final SDP" in the PRACK. In basic SIP,
however, that is not possible.

Regards,

Christer Holmberg
Ericsson Finland

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