Victor Kueh wrote:
>
> Dear Vijay,
> >
> > Responses *always* follow the Via list. What you mention above is the
> > From being used to initiate a subsequent request, and only in the
> > absence of (a) the Contact (the bis makes Contact mandatory, so all
> > requests will have a Contact, it was optional in the RFC, if I recall
> > correctly) or, (b) a Route list has not been created.
> >
>
> Since rfc2543bis makes Contact mandatory in INVITE request (if I'm
> not wrong, it is optional in other requests), does it mean that the 'From'
> field is never used anymore for subsequent requests from callee to caller?
You are right; the Contact is mandatory only in an INVITE request.
So, let's take this thing to it's logical conclusion. Given that:
(1) bis makes Contact mandatory in INVITE
(2) INVITE is the only SIP method that establishes a session
Then, here's a simplified (and hopfully accurate) call flow for subsequent
requests after a session has been established; note how the From changes.
First, session establishment:
UAC (A) UAS (B)
INVITE B -------------->
From: A
To: B
Contact: A
<----------- 200 OK
From: A
To: B
Contact: B
Assume the session has been successfully established. B now sends a new
request, say it is a BYE request. As per the bis, B will send the BYE as
follows:
UAC (A) UAS (B)
<--------- BYE A
From: B
To: A
The R-URI for the BYE was obtained from the Contact in the previous request.
The To and From were reversed. More information on this is in the bis,
Section 11.
> Do you , by any chance know, when rfc2543bis is going to be stable,
> i.e becoming a RFC?
Nope. That's a Henning question.
Hope that helps.
- vijay
--
Vijay K. Gurbani vkg@{lucent.com,research.bell-labs.com,acm.org}
Internet Software and eServices Group
Lucent Technologies/Bell Labs Innovations 263 Shuman Blvd., Rm 1A-413
Naperville, Illinois 60566 Voice: +1 630 224 0216 Fax: +1 630 713 0184
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