Subject: [Sip] RE: Event ID (was RE: Events Last Call.)

From: "Fairlie-Cuninghame, Robert" <[email-masked]>
Date: Mon, 18 Feb 2002 15:55:18 -0800

Hi Adam, 

We did propose something in the key-events draft
(draft-culpepper-key-events-00.txt) whereby a proxy extracts the Route set
from the INVITE-initiated dialog for all hops between itself and the
intended UA [Section 7.10]. It would need to be adapted to work with your
sub-dialog approach (rather than as Pre-loaded Routes). It is a bit messy
but I would rather have a slightly messy mechanism for proxies to create
subscription sub-dialogs than for all application proxies to become
B2BUA's!!!

The goal of the mechanism is simply for proxies to ensure that the message
gets to the right UA and that the UA can correlate the subscription as being
delivered as a sub-dialog of the other dialog. Now handling the UA is easy -
this can be done explicitly with headers at worst. The Route-snatching
should take care of the proxies described in Section 7.10. 

Regards,

Robert.

PS. We are currently heavily reworking the draft to bring it into line with
the new SIP Events draft (for instance the Applies-To header will be
removed).

> -----Original Message-----
> From: Adam Roach [mailto:[email-masked]]
> Sent: 18 February 2002 23:31
> To: 'Fairlie-Cuninghame, Robert'; Adam Roach
> Cc: [email-masked]'
> Subject: RE: Event ID (was RE: Events Last Call.)
> 
> 
> > -----Original Message-----
> > From: Fairlie-Cuninghame, Robert [mailto:[email-masked]]
> > 
> > Now I don't think this is necessarily contrary to the Id 
> > parameter but the
> > way you justify the complexity added by the Id parameter scares me.
> > Basically, if you are solving the problem for an UA endpoint 
> > delivering a
> > subscription through an existing INVITE dialog then IMO you 
> must also
> > address how a proxy can also accomplish this in an equally 
> guaranteed
> > manner. 
> 
> I hat B2BUAs at least as much as you do, and fully understand your
> objection. As soon as you propose something that works, I'll
> incorporate it.
> 
> /a
> 

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 20 Feb 2002 01:22:21 -0500

> subscription sub-dialogs than for all application proxies to become

There are a lot of issues that need to be resolved before this works. 

First and foremost, bis states that the URI inserted into record-routes
are scoped just for that dialog. In other words, you can only use those
URI within that specific dialog. An entity along the path which tries to
use those URI as pre-loaded routes into a new dialog, that may not work
with bis as specified. I think the scoping of RR in this way is really
important, since the user part, or other params, can be populated with
dialog specific state that the proxy wants to get back.

So, if the UAS wants to subscribe to the caller along the same path, it
pretty much has to embed the SUBSCRIBE in the dialog, and thus the
problem..

Another interesting problem is this - how does a UA authenticate and
then authorize a subscription from an application along the call path?
This is a really hard problem, and certainly one solution is that if the
element was a b2bua, it can use our normal (?) e2e authentication
mechanisms.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
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