Subject: RE: [Sipping] Immediate NOTIFIES change in sip-events-01

From: "Brian Stucker" <[email-masked]>
Date: Thu, 8 Nov 2001 10:59:14 -0600

ACKing the response to the SUBSCRIBE seems like a bad idea. If for no other
reason than it then precludes the ability for a user to fork a SUBSCRIBE out
to create subscriptions with all of another user's contacts, without
explicit knowledge of what all those contacts are. The ACK model basically
is going to limit us to essentially no useful forking mechanism for
SUBSCRIBE/NOTIFY because we do not receive all of the provisional responses
like an INVITE does.

Using the INVITE as a model for how to process the 3-way handshake for
SUBSCRIBE/NOTIFY is really like trying to build an apple by taking apart an
orange.

We can detect forking with the mechanism Adam has proposed. We can either
accept or get rid of forked subscriptions that we didn't get the 2xx
response for with his mechanism as well. It's not broken, and it's
efficient.

If I recall, this all started around the 200/202 problem of trying to denote
if a subscription is pending. Here's a solution for that, and other
problems:

Replace the new Subscription-Expires header with a Subscription-Status
header. The contents of the header is simply a status code, and optional
reason string. We can use this new header to denote the status of the
subscription dialog itself, instead of using the message body. This is
exactly what Subscription-Expires was designed to do, but has just been
extended a bit. Make the immediate NOTIFY, and make the Subscription-Status
header mandatory in the NOTIFY for event packages in which the subscription
can have more than one state (the only package I know of that fits this bill
is for REFER, packages such as presence would require the header to be
present).

Subscription-Status: 182 Queued		=> Subscription is Pending
Subscription-Status: 200 OK			=> Subscription is Active
Subscription-Status: 4xx, 5xx, 6xx		=> Subscription is
Terminated

All other status-codes are not allowed as a starting point for the
discussion.

Thoughts?

Regards,

Brian Stucker
Nortel Networks

-----Original Message-----
From: Sean Olson (EUS) [mailto:[email-masked]]
Sent: Thursday, November 08, 2001 9:50 AM
To: 'Brazier Lachlan'; 'Jonathan Rosenberg '; ''James Undery' '; Stucker,
Brian [NGB:B635:EXCH]; ''Fairlie-Cuninghame, Robert' '; [email-masked] '
Subject: RE: [Sipping] Immediate NOTIFIES change in sip-events-01

> Hello, 
> 
>as SUBSCRIBE is compared to INVITE, can't we send an ACK request to the 
>response of the SUBSCRIBE? I'm not sure if a ACK would pass a 
>proxy when no 
>INVITE did before???? 
I understand what you are going for, but I have two immediate 
gut reactions. 1) I hope no proxies out there try to block 
an ACK because they don't remember the ACK. 2) ACK is so closely 
tied to INVITE in the current spec. that it would be difficult 
to extend it to other methods in most implementations. 
BR, 
sean

---

From: "James Undery" <[email-masked]>
Date: Thu, 8 Nov 2001 17:12:40 -0000

Hi,

Close to what I suggested although, with your header Subscription-Status it
should not replace Subscription-Expires, and 182 has a totally different
meaning to pending, I'd use 202.

James

-----Original Message-----
From: Brian Stucker [mailto:[email-masked]]
Sent: 08 November 2001 16:59
To: Sean Olson (EUS); 'Brazier Lachlan'; 'Jonathan Rosenberg '; ''James
Undery' '; ''Fairlie-Cuninghame, Robert' '; [email-masked] '
Subject: RE: [Sipping] Immediate NOTIFIES change in sip-events-01

-----Original Message-----
From: Sean Olson (EUS) [mailto:[email-masked]]
Sent: Thursday, November 08, 2001 9:50 AM
To: 'Brazier Lachlan'; 'Jonathan Rosenberg '; ''James Undery' '; Stucker,

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