Subject: [SIP] Provisional responses in other direction

From: Christer Holmberg <[email-masked]>
Date: Mon, 02 Oct 2000 09:54:01 +0300

Hi,

I have a question about a SIP/PSTN issue.

When the caller sends an INVITE, he may include a ISUP MIME message body
in the request, and the callee may send back ISUP MIMEs in the 18x-
and/or 200 responses. But, what happens if the caller wants to send more
ISUP MIMEs before he has received the final response for the INVITE?
re-INVITEs should not be used before the final response to the first
INVITE has been received, and PRACK can not be used since we don't know
when/if there is going to be a ISUP MIME to be sent. 

One solution would be to use the INFO method, but is it allowed to use
INFO before the session has been completely established?

Regards,

Christer Holmberg
Ericsson Finland

---

From: Gonzalo Camarillo <[email-masked]>
Date: Tue, 03 Oct 2000 09:48:10 +0300

Hi,

> INFO before the session has been completely established?

I believe that as soon as you receive the INVITE with a contact header
you can send INFO back to the caller. You do not have to wait until the
session is established (200 OK for the INVITE) for sending INFO. It is
true that it is said in the draft that INFO is used for mid-session
signalling, but I do not see a reason for avoiding sending it in the
middle of the session establishment (before 200 OK has been sent).

Does anybody see any reason that I might be missing?

These INFO messages sent before the 200 OK for the INVITE can be used
for tranfering ISUP messages from the callee to the caller before the
ACM.

Gonzalo

-- 
Gonzalo Camarillo         Phone :  +358  9 299 33 71
Oy L M Ericsson Ab        Mobile:  +358 40 702 35 35
Telecom R&D               Fax   :  +358  9 299 30 52
FIN-02420 Jorvas          Email :  [email-masked]
Finland                   http://www.hut.fi/~gonzalo

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