Subject: [Simple] sip proxy/registrar as presence agent

From: Kundan Singh <[email-masked]>
Date: Tue, 15 Oct 2002 18:17:41 -0400 (EDT)

Hi

I have a question on implementation of PA co-located with proxy/registrar
server.

If the server wants to support both the following kinds of scenarios:
- acts as a presence agent that sends NOTIFY to subscriber (if approved)
when user phone REGISTERs. This subscription can be managed (approved,
rejected) from the web interface, for example.
- allow end-points (colocated with presence agents) to REGISTER. This
end-point acts as a presence agent and manages its own buddy list for IM
and call.

Suppose subscriber S, SUBSCRIBEs to the server P for target user,
but the target user phone/endpoint is not yet REGISTERed.
and the subscriber is not yet approved by the target user.
P sends back "202 Pending".

Now target user's phone/endpoint R (colocated with PA) REGISTERs with P.
How can the server P inform the target endpoint R that the user S was/is
interested in subscribing to R.
(1) If the server P sends new SUBSCRIBE to R (like a UAC) then it can not
do digest authentication because P may not know the password for user S.
And R may not know how to authenticate P (not in buddy list).
(2) S will refresh SUBSCRIBE after sometime, that will get proxied to R
also, and it can work. But this will happen only once every one hour
("Expires:" header).
(3) The target user will have different identifiers: bob@server for
PA colocated with proxy, and bob@endpoint_address for PA colocated with
endpoint. And S will have to SUBSCRIBE to both independently.

What is the right approach so that R can know that S had sent SUBSCRIBE
and then R can start sending NOTIFY to S.

Thanks.

---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 16 Oct 2002 00:45:17 -0400

The right solution is for the server to terminate the subscription, with 
a specific reason that informs the client that it should re-subscribe. 
In particular, the Subscription-State header in the NOTIFY would look like:

NOTIFY sip:[email-masked] SIP/2.0
Subscription-State: terminated;reason=deactivated

the client would genreate a brand new SUBSCRIBE (not on the same 
dialog), which the server can then proxy.

-Jonathan R.

Kundan Singh wrote:
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