Subject: [Sip] Bug #113 Overlapping transactions

From: "Peterson, Jon" <[email-masked]>
Date: Thu, 10 Jan 2002 19:07:04 -0600

Please note that I'm speaking below to the issue of overlapping concurrent
transactions in SIP, NOT to the issue of handling partial dialed numbers in
the PSTN, which is commonly referred to as overlap signaling.

There didn't seem to be very much controversy in the recent bug #113 thread
about allowing overlapping non-INVITE transactions. The general feeling is
that we want to leave the door open for non-INVITE methods to overlap
provided that they define their own ordering mechanisms as necessary.

There was a bit more discussion on the subject of whether or not overlapping
INVITE transactions should be allowed. It has been pointed out that allowing
overlapping INVITEs would introduce some backwards compatibility problems.
In past discussion, probably the single most important motivation for
overlapping INVITEs has been the proposed early media mechanism. Some
support was raised for a proposed UPDATE or OFFER method that would present
an alternative to sending an overlapping INVITE during an early dialog. No
strenuous objections were raised to this line of inquiry. I understand that
there are now some people looking at putting out a proposal along these
lines that should be available shortly.

Since we need to wrap this up if at all possible for bis-06, I'd like to
suggest that we do the following:

Disallow overlapping INVITE transactions in the baseline spec with the
understanding that an extension (along the lines of UPDATE or OFFER) could
provide the necessary functionality for early media or other services that
need to modify a session during the early dialog stage.

Allow overlapping non-INVITE.

Is this okay with everyone? Please do speak up if this isn't okay with you.

Jon Peterson
NeuStar, Inc.

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From: Sean Olson <[email-masked]>
Date: Fri, 11 Jan 2002 06:58:00 -0800 (PST)

I would like to know the objections to overlapping
INVITEs that wouldn't also apply to overlapping
non-INVITEs. I personally favor an overlapping
INVITE for solving early media over any new UPDATE
or OFFER methods. It just seems much more 
straightforward in my mind. Are there large
technical hurdles to overlapping INVITE transactions
that I am not seeing?

BR,
sean

> this isn't okay with you.

=====
--
Sean Olson <[email-masked]>

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From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 11 Jan 2002 10:56:07 -0500

> technical hurdles to overlapping INVITE transactions

Good question.

INVITE has the unfortunate problem that it does TWO things -
it manipulates session state, and it manipulates dialog
state.

Now, this new UPDATE mechanism would have the important
property that it only updates the session state, not
dialog state. SO, you can't have overlapping UPDATEs either,
but an UPDATE can overlap with INVITE, since the protracted
INVITE transaction exists primarily because of the duration
involved in querying the user to manipulate dialog state.

Note also that services in the network are driven off of
dialog state, not session state, so UPDATE processing would not
confuse proxies and other things, as an overlapping INVITE would.

Thanks,
Jonathan R.

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