Subject: RE: [Sip] Question on Service Route Discovery Procedure duringRegistration

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Thu, 20 Apr 2006 07:46:50 +0200

Hi, 

>>Currently the text says that the UA MAY use the Service-Route e.g. to 
>>create a route for future requests.
>> 
>>Now, if we are going to add an option-tag (to be used by the UA in the

>>Require/Supported header) I think we should also say that the UA SHALL

>>use the Service-Route for future request (why would it otherwise ask 
>>for it?), and also HOW the route is created. 24.229 defines how IMS 
>>UEs create the route, so similar text is needed for generic UA
behavior.
>Why must the US a route all requests through this domain? What if it
has multiple registrations?

Ok, in that case the UA could of course choose.

But, I guess the most important thing is the second: IF the UA uses the
Service-Route, it should be specified how the route is created.

>>2. Registrar processing of Path
> 
>>I think we should also take Jonathan's draft,
>>draft-rosenberg-sip-route-construct-00, into consideration, which
allows
>>a registrar to build a Service-Route set based on the received Path
>>headers.
>Lovely idea, and 3608 suggests it as a possibility. Doesn't work for
IMS 
>AFAIk, so it can't be a MUST.

I need to check that. But, is there something special you have in mind
why it wouldn't work with IMS?

Regards,

Christer

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---

From: Paul Kyzivat <[email-masked]>
Date: Thu, 20 Apr 2006 10:11:41 -0400

Christer Holmberg (JO/LMF) wrote:

>> IMS AFAIk, so it can't be a MUST.
> 

The way IMS is organized, it is possible to have two UAs registered to 
the same AOR (Public User Identity), but accessing via different P-CSCFs.

The Path must include the P-CSCF so that requests can reach the intended 
UA via the P-CSCF it uses. That means in the two UA case there must be 
two Paths - one for each registered Contact. This is supported by RFC 3327.

If route-construct were used to construct the Service-Route, then there 
would be two different Service-Routes for the same AOR. But according to 
RFC 3608 there may be only one Service-Route per AOR. So the algorithm 
of route-construct won't work for IMS as currently defined.

I believe Jonathan has advocated a revision to RFC 3608 so that there 
may be a separate Service-Route for each registered contact. But there 
has been no action to make such a change.

	Paul