Subject: RE: [Sip] How to indicate during proxy discoverythataproxysupports"outbound"

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Mon, 3 Apr 2006 00:46:48 +0200

Hi,

I agree on the fact that the issue with OPTIONS is that it adds an extra
round trip.

However, if the OPTIONS request is addressed for the outbound proxy, why
would we use the Proxy-Require? For this particular request the outbound
proxy would be an UAS - not a proxy. So, we would use the Require
header. And, in that case it wouldn't matter if there are other proxies
between the UAC and the outbound proxy, because they don't care about
the Require header.

...and, there is no need to set Max-Forwards to zero.

Regards,

Christer

-----Original Message-----
From: Jeroen van Bemmel [mailto:[email-masked]] 
Sent: 1. huhtikuuta 2006 12:20
To: Patrick Timmons; 'Hadriel Kaplan'; 'Cullen Jennings'; 'Dean Willis';
[email-masked]
Cc: 'Juha Heinanen'
Subject: Re: [Sip] How to indicate during proxy
discoverythataproxysupports"outbound"

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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_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip

---

From: "Hadriel Kaplan" <[email-masked]>
Date: Sun, 2 Apr 2006 20:59:26 -0400

The proxy-require idea is to put it in the Register.  So an outbound proxy
would remove the option-tag and forward the register on, resulting in no
round trips on success.

The Require: piece would be in case the UA is directly attached to the
Registrar.  

-hadriel

> From: Christer Holmberg (JO/LMF) [mailto:[email-masked]]
> Sent: Sunday, April 02, 2006 6:47 PM
> To: Jeroen van Bemmel; Patrick Timmons; Hadriel Kaplan; Cullen Jennings;
> Dean Willis; [email-masked]
> Cc: Juha Heinanen
> Subject: RE: [Sip] How to indicate during proxy