Subject: [Simple] MSRP - Ending a Session

From: Paul Kyzivat <[email-masked]>
Date: Mon, 30 Jun 2003 15:43:38 -0400

(We had this discussion a long time ago, but I think it is worth 
revisiting in the context of MSRP as it currently stands.)

I think we can and should specify behavior that results in a graceful 
close of an MSRP session, where messages are not lost. Now that we have 
dedicated tcp connections for each session this is easier than it once 
was. Here is what I have in mind:

- an endpoint SHOULD NOT signal its intent to end the session while it 
has any unconfirmed SEND messages outstanding.

- if an endpoint receives a request to end the session while it has 
unconfirmed SEND messages outstanding, it SHOULD refuse the request to 
end the session.

A request to end a session via reINVITE can be refused by responding 
with an error. (The code 491 is close to the right response, but I don't 
know if it is permitted to use it in this situation.) The advantage of 
this approach is that it doesn't cost any extra in normal cases where 
there is no race condition.

Some requests to end a session (such as BYE) can't meaningfully be 
refused. In those cases the session may not terminate gracefully.

I see conflicts over the ending of a session quite frequently with IM. I 
say something that I think terminates the conversation and shut down the 
window, only to have the other party respond. Typically (at least with 
Sametime) the window is recovered and the session resumes. I think we 
would be ill advised to do something less acceptable.

Of course all the above needs to be SHOULD strength, because UAs must 
have the option of quitting whenenver they feel they must.

	Paul

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