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

Paul Long Plong at SMITHMICRO.COM
Wed May 31 10:17:32 EDT 2000


Like I said before, H.323 clearly states that a Setup cannot contain both a
fastStart and h245Control component. Period. 8.2.1/H.323v3: "The calling
endpoint >>>shall not<<< include both a fastStart element and encapsulated
H.245 messages in h245Control in the same Setup message..." What part are
people having trouble understanding?

That covers it for the calling EP. Q.931 is equally clear about what the
called EP is required to do. "When a SETUP or RELEASE message
is received which has one or more mandatory information elements with
invalid content [e.g., fastStart and h245Control both present], a RELEASE
COMPLETE message with cause No. 100, 'invalid information element contents'
shall be returned."

If a calling EP had some way to determine which version the called EP was
before it sent Setup, we could make this version-specific behavior (which
has its own problems, remember), but since Setup is the first message, we
cannot do this.

Paul Long
Smith Micro Software, Inc.

-----Original Message-----
From: Paul E. Jones [mailto:paulej at PACKETIZER.COM]
Sent: Wednesday, May 31, 2000 12:29 AM
Subject: Re: On TD26 - Fast TCS and M/S negotiation in H.323v4


If we could follow such logic, I would agree that this procedure would
worth perusing.  Unfortunately, the inclusion of fastStart and tunneled
H.245 messages in the SETUP message is not defined.  There is no way to
predict how a V2 device will behave when receiving these messages.  I
the idea, but I'm afraid we will compromise backward compatibility by
including it.

Let's assume a V2 device does *not* recognize the tunneled H.245 in
(ignores it), but accepts the Fast Connect proposal.  Assume, also, that
the CONNECT message, the endpoint includes the fastStart element *and* a
tunneled TCS message.  What could the calling endpoint *safely* assume?

Assume that CONNECT was the first message received following the SETUP
that helps complicate matters further for you. :-)

I just need further convincing.


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