Subject: [SIP] Session-timer issue with ISUP

From: Christer Holmberg <[email-masked]>
Date: Mon, 12 Feb 2001 15:01:17 +0200

Hi,

I would like to clarify an issue with the session-timer - again related
to SIP/PSTN interworking.

The session-timer draft says:

"If the refreshing re-INVITE is used solely for refreshing, it MUST
still contain a session description, unchanged from the previous
INVITE. The session description MUST somehow indicate that it has not
changed. In the case of SDP, this is accomplished by including the
same value for the origin field as previous messages to its peer."

First, I assume that it is NOT allowed to send a new ISUP body in the
re-INVITE (INFO MUST be used for that, since it doesn't affect the SIP
part of the call). If it is allowed, I would not only have to compare
the SDP body to the original INVITE, but also the ISUP body - and any
other possible body...

Second, if the first assumption is correct, I wonder if it is possible
not to send the ISUP bodies in the re-INVITEs at all? The minus is that
parts of the keep-alive mechanism provided by the session-timer
dissapears, but the plus is that the refresh re-INVITE messages will be
smaller (the initial INVITE message may be pretty big, if it contains
both SDP and ISUP, and possible also other message body types...). I
guess one has to compare the number of smaller messages compared to how
many times the UAS will crash.

Comments?

Regards,

Christer Holmberg
Ericsson Finland