2 Jun
2004
2 Jun
'04
11:26 p.m.
Nils / Klaus,
--On 02 June 2004 20:08 +0200 Nils Ohlmeier <nils(a)iptel.org> wrote:
On Wednesday 02 June 2004 20:03, Alex Bligh wrote:
> --On 02 June 2004 18:38 +0100 Alex Bligh <alex(a)alex.org.uk> wrote:
> > Consider the situation whereby after an INVITE occurs which ser
> > initially routes to A (which is, say, busy) and subsequently routes to
> > B. Perhaps it has gone through t_on_failure or some other mechanism of
> > sequential forking. Assume the INVITE has been OK'd and ACK'd.
> >
> > What mechanism does ser use to ensure subsequent transactions on the
> > call-leg (such as BYE, re-INVITE etc.) are sent to B and not A? IE
> > where is
> > the state being stored and how?
>
> I am obviously assuming (transaction) stateful forwarding and that
> record_route is on (else the proxy wouldn't even get to see BYE etc.)
Nils said:
In this case the Route header resulting out of the
Record-Route header
includes all informations required to route any subsequent in-dialog
request to it's destination. So any re-INVITE or BYE can be routed
stateless to its destination.
Klaus said:
This is done in outside the proxy - for in-dialog
requests, the request
URI contains the "contact" of the other party (or the Route header for
strict routers (old SIP RFC))
This implies ser is looking either at the parameters in the Record-Route:
header added by ser on the INVITE (which is what Nils seems to suggest) OR
relies on the initiating UA using as a Request-URI for subsequent in-dialog
messages the Contact: header added by the UA providing the OK response to
INVITE.
I think it's probably the latter that's happening. But can I rely on this?
IE Is it mandatory for the subsequent in-dialog transactions to use the
Contact: address supplied by the UAS, and is it mandatory for the UAS to
add a Contact: header at all? I'm reading the call flow example on p167 of
"SIP: Understanding the Session Initiation Protocol" and it doesn't seem to
be there. What's concerning me is that I can see it works, but I can't tell
why or if it will always work. I am probably being very dumb.
Alex