On TD26 - Fast TCS and M/S negotiation in H.323v4

[Paul E. Jones]

Bob,

That text in section 8.2.1 has been removed via the Implementers Guide.
There were a few issues with the text as it was, with a "race condition"
being the most notable.

If an aggressive endpoint sends a SETUP w/ fastStart and the other end
returns Alerting without fastStart, the calling endpoint may assume that FC
was rejected, so it sends a Facility with H.245 messages.  Then (perhaps at
the same time), the called endpoint returns CONNECT with fastStart... now,
what state are things in?  The caller thought that it terminated FC and the
called party thinks that FC was accepted.

One could say "the caller should then recognize that FC was indeed
accepted", but it defeats the purpose of "terminating FC".  The reason for
that text was so that the calling EP could do its best to try to get the
H.245 tunnel up and channels open before CONNECT-- we could get into a
terrible mess.

Now, there could be work-arounds to this issue, but I believe that the
procedural explanation to work-around the race condition may be far worse.
However, I am not opposed to a work-around.  Apparently, the removal of that
text has caused some confusion, so it may be worth reinstating that text and
defining some general guidelines.

However, we need to think through this carefully.  Contributions are
definitely solicited :-)  We could leave the text as it is in the IG (which
I believe fixes the issues) or we could reinstate the text and provide some
guiding text (which may reduce incompatibilities with V2 equipment).

Paul

----- Original Message -----
From: "Bob Gilman" <rrg at LUCENT.COM>
To: <ITU-SG16 at mailbag.cps.intel.com>
Sent: Tuesday, June 06, 2000 7:17 PM
Subject: Re: On TD26 - Fast TCS and M/S negotiation in H.323v4


> Paul-
> The problem is that inclusion of an H.245 message in the tunnel terminates
> FastStart according to section 8.2.1 of H.323.  This could be "satisfied"
> by using the early H.245 element for the replys so that FastStart could
proceed.
> At least this mechanism would make it easy to know that the responder (the
> called endpoint) was able to overlap FastStart and H.245.
> -Bob
> ----------------------------------------------------
> Bob Gilman       rrg at lucent.com      +1 303 538 3868
>
>
> Paul Long wrote:
> >
> > Bob,
> >
> > H.323 only says that fastStart and h245Control cannot both be included
in
> > _Setup_, so it could indeed be included in the Setup-UUIE type.
> >
> > Paul Long
> > Smith Micro Software, Inc.
> >
> > -----Original Message-----
> > From: Callaghan, Robert [mailto:Robert.Callaghan at ICN.SIEMENS.COM]
> > Sent: Tuesday, June 06, 2000 10:27 AM
> > To: ITU-SG16 at MAILBAG.INTEL.COM
> > Subject: Re: On TD26 - Fast TCS and M/S negotiation in H.323v4
> >
> > Paul,
> >
> > It would be required in the SETUP, CALL PROCeeding, ALERT, FACILITY, and
> > CONNECT message in that all of these messages can be sent before Fast
> > Start
> > is completed or may not be present with Fast Start elements based on v2.
> >
> > Bob
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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