Subject: [SIP] Session-timer and REFER

From: Christer Holmberg <[email-masked]>
Date: Thu, 22 Feb 2001 00:30:08 +0200

Hi,

More about the session-timer...

Assume user A establish a call with user B. A session-timer between A
and B is also establish.

Then, B wants to transfer A to user C, using REFER. A will then send
INVITE to C and establish a session. However, the session between A and
B is still open (even if there is no media) so the session-timer will
continue between them.

My first issue is that A (or B) may want to cancel the session-timer
during the session with C, and then maybe use it again if the media is
switched back to B at some stage. One solution would be for either A or
B
to increase the refresh timer during the A-to-C call, and then decrease
it
again if the A-to-B call continues, but is this possible?

The other issue is if B re-boots. Now, if A is sending the refreshes, B
will think it's a new call, so the phone will ring - AND, may start
sending media to B's RTP port specified in the SDP in the re-INVITE. So,
when A is talking to C, he may suddenly start hearing announcements,
ring tones, or even someone talking, from B. A's call control will not
know about this, since it will receive a 200 OK for the re-INVITE in
either case.

Comments?

Regards,

Christer Holmberg
Ericsson Finland