Subject: Re: [dispatch] [sipcore] Requests sent within early dialog -- CSeq mgmt

From: "Dale Worley" <[email-masked]>
Date: Wed, 30 Sep 2009 17:31:56 -0400

On Wed, 2009-08-26 at 17:10 -0400, Szilagyi, Mike wrote:
> I’ve not been able to find definitive text regarding this issue so I’m
> hoping someone can provide clarification.  If a request (INFO or
> UPDATE) is sent on a dialog in the early state, how are the CSeq
> numbers managed by the UAS.  Here’s an example to demonstrate my
> confusion:

The model is that a CANCEL is not an independent transaction from the
INVITE, in the way that the UPDATE is an independent transaction from
the INVITE.  Indeed, CANCEL isn't even routed the same way that the
UPDATE is.  A CANCEL transaction is sort of a "second half" of the
INVITE transaction that it is canceling.  That is why the CANCEL has the
same CSeq as the INVITE.

(Also, your example shows the UPDATE being sent by the UAC before it
receives a non-100 response.  That can't be done, since the UAC doesn't
know the to-tag to use; there isn't an early dialog established at that
point.)

Dale