Subject: [SIP] Registration, Routing, and Record-Route

From: David Shrader <[email-masked]>
Date: Mon, 13 Nov 2000 11:24:38 -0500

I have a scenario that I am trying to solve using SIP. The pieces don't
quite seem to come together for me. Do you have any thoughts?

Given the following constraints (lets assume for this scenario):

1. A sip user agent must access a service provider network via a specific
proxy that is to be used for the life of the particular registration. (After
re-boot or network condition, a different proxy may be used to register.)

2. The service provider will route all calls to that user agent via the
specific proxy also for the life of the particular registration.

3. The SIP UA registers its current location with the network domain server
via the proxy.

4. The network domain server receiving an INVITE for the user, determines
the users current location and needs to now route all calls to the current
location via the proxy. Is there a SIP mechanism associated with the
registration that can indicate this?

I think that the REGISTER message in step 3 has a Request-URI of the network
domain server and is routed to the IP address of the proxy. The proxy would
then look at the Request-URI and forward the request on to the network
domain server. 

One thought I had was that a Record-Route added by the proxy would establish
a route that would be taken for all of subsequent registration requests on
that registration "call leg". This, however, would not necessarily apply to
subsequent INVITEs for new calls.

Anybody have any thoughts on this problem?

David

----------------------------
David Shrader
Master Consultant, Inc.
[email-masked]
http://www.EyeForTheFuture.com

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