RE: [Sip] NOTIFY establishes a dialog

[Adam Roach <adam@dynamicsoft.com>]

> From: hisham.khartabil@nokia.com [mailto:hisham.khartabil@nokia.com]
> 
> In RFC3265, it is mentioned that NOTIFY can certainly 
> establish a dialog if it arrives before the 200 of a 
> SUBSCRIBE. What happens when the 200 for the SUBSCRIBE now 
> arrives with record-route headers? Does the route-set get 
> updated? (keeping in mind that the dialog is now in the 
> established state).

Not if it's part of the same dialog as the aforementioned NOTIFY.

In the case that the SUBSCRIBE 200 doesn't match any dialog that's
already been established (e.g. by a NOTIFY), then it *does* establish
a dialog. If the event package doesn't allow forking, such a dialog
conceptually terminates after the the subscriber 481s the corresponding
NOTIFY.

> the NOTIFY establishes the dialog, but does not carry record-route
> headers. If the same assumption is made as above, the record-route
> headers appearing in the 200 response to the SUBSCRIBE are ignored
> since the dialog is in established state. Isn't this a problem? the
> route-set is lost.

Section 3.1.5 of 3265 clearly states:

   If a proxy wishes to see all of the SUBSCRIBE
   and NOTIFY requests for a given dialog, it MUST record-route the
   initial SUBSCRIBE and any dialog-establishing NOTIFY requests. Such
   proxies SHOULD also record-route all other SUBSCRIBE and NOTIFY
   requests.

A consequence of this clause is that a proxy which Record-Routes the
200 response will also Record-Route the NOTIFY in the same dialog.
A further consequence is that the route set in a SUBSCRIBE 200 and
that of a NOTIFY in the same dialog will always be identical.

/a
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