Subject: [Sip] Tying up a loose end on GRUU

From: [email-masked]
Date: Sun, 8 Apr 2007 20:15:27 -0400

I don't know if others are concerned, but I want to take one last look
at the problem Michael Procter raised.  (See, I spelled it right that
time, Michael!)

Conceptually, the problem is that a GRUU isn't just a URI that gets a
request to the proper UA, but using it as a request-URI allows the
response to return to the UAC, and the route-set constructed thereby
to work for maintaining a dialog.  That's what we *really* mean by
"routes to the proper UA".

But given that we now have a more rigorous statement of the problem, I
think that we can be assured that the solution we've identified works
reliably.  Viz., that whenever there is an addressability or
reachability or name interpretation discontinuity between the incoming
hop that a request takes to a SIP proxy, and the outgoing hop to which
it is forwarded, the proxy must record-route itself (and perhaps
double record-route itself).  It is clear that this is necessary
because the proxy cannot know what the UAS contact URI (or the next
record-route) will be, as it is processing the request, not the
response.

The exception to this rule is if the proxy is able to reliably predict
what the UAS contact or next record-route will be, and to determine
that it will have no reachability problems.  But except in closed
systems where all behaviors are centrally controlled, this is never
possible.

Dale

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From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 09 Apr 2007 08:41:44 -0400

I think we are covered along these lines in the GRUU spec.

I'm going to submit an update now, so we can move things along.

Thanks,
Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
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