Subject: [Sip] Open Issue #293: Scope of Contact and Record-Route URLS?

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 27 Dec 2001 12:38:47 -0500

Issue:

What is the "scope", temporally speaking, of the URLs inserted into the 
Contact of INVITE and 2xx to INVITE by the UA, and the record-route 
inserted by the proxies? Do these URLs need to be usable outside the 
scope of the dialog created by the INVITE, or are they only within the 
INVITE?

Discussion points:

There is some value in allowing a UA or proxy to insert a URL into 
Record-Route/Contact which contains state specific to the dialog. 
Consider a simple case, where a UA would like the contact in the 2xx to 
INVITE to contain the dialog ID for rapid indexing of re-invite and bye. 
It would like to send a 2xx which looks like:

SIP/2.0 200 OK
Contact: sip:[email-masked]

Now, the drawback is that we have applications which appear to be trying 
to use these contacts outside of the dialog. Speifically, the infamous 
consultation-transfer, which attempts to include this contact in an 
accept-contact header embedded in a Refer-To URL. This would no longer 
work if we specify that Contact URLs are scoped ONLY to within the 
dialog. Now, arguably, consultation transfer doesn't work right now 
anyway....

Proposal:

I think that without a doubt, record-route URLs should be specified to 
only have a scope of the dialog.

Contact is a harder question. I would propose that they be required to 
have broader scope, and that if a UA wants to have state back in a 
message, it can use the various cookie/state mechanisms, else it can act 
as a "virtual proxy" fronting a "virtual UA", and have its virtual proxy 
element insert a record-route with the state. I'm not 100% thrilled with 
this proposal, but I don't want to gratuitously break existing 
spplications which rely on a broader scope.

Comments?

-Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
Chief Scientist                         First Floor
dynamicsoft                             East Hanover, NJ 07936
[email-masked]                 FAX: (973) 952-5050
http://www.jdrosen.net                  PH:  (973) 952-5000
http://www.dynamicsoft.com

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