Subject: Re: [Sip] How to indicate during proxy discovery thataproxysupports"outbound"

From: "Jeroen van Bemmel" <[email-masked]>
Date: Sat, 1 Apr 2006 11:19:53 +0200

Patrick,

> However -- in a general sense, the issue here is that the UA needs to know
> specific features as they pertain to the topology of the network; i.e., 
> that
> the *edge* supports 'outbound'.  My sense is that it's perfectly 
> reasonable
> to think that there will be requirements for UAs to know specific features
> of proxies that sit topologically off of the edge (?-CSCF, for example). 
> In
> this case, the Proxy-Require technique breaks down... and we're left with
> supporting two different methods for achieving (essentially) the same 
> ends.

True, but this also goes for OPTIONS. To send an OPTIONS to the second hop, 
the UAC must not only be aware of the topology, but also of the routing 
logic at the first hop (i.e. second hop for REGISTER might be different than 
INVITE). For IMS it would be impossible (due to e.g. topology hiding, the 
UAC wouldn't be able to learn the hostname / IP address of the S-CSCF for 
example) but also for non-IMS networks this would simply not work. And 
beyond the second hop, things would get "exponentially" more complicated.

For first hop only, both OPTIONS and Proxy-Require seem reasonable to me, 
with a slight preference for the latter. As a more general solution I 
suggest feature tags in the Path / Record-Route headers (as header 
parameters - not URI parameters - to avoid clobbering each mid-dialog 
request with them).

Given the time constraints for outbound (Keith's deadline was yesterday...), 
I propose to agree on a first-hop-only solution for outbound, and leave 
generalization for future work.

Regards,

jeroen 

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---

From: "Hadriel Kaplan" <[email-masked]>
Date: Sun, 2 Apr 2006 15:06:21 -0400

I agree using Proxy-Require (and Require) is the best approach for this
draft. 

Also, RFC 3323 Privacy does it:
   When the privacy service removes the entire Privacy header, if the
   message is a request, the privacy service MUST also remove any
   'privacy' option-tag from the Proxy-Require header field of the
   request.

Do we have consensus?  I can write up some text if you wish.

-hadriel

> -----Original Message-----
> From: Jeroen van Bemmel [mailto:[email-masked]]
> Sent: Saturday, April 01, 2006 4:20 AM
>