H.245 and MGs

Tom-PT Taylor taylor at NORTELNETWORKS.COM
Tue Mar 9 17:14:27 EST 1999

Sorry about the blank response!  Let's try again!

This isn't QUITE as simple a question as it looks.
I'd recommend looking at it from the two separate points of view:
>From the endpoint's point of view, I would say the answer is "yes" (as Ritu
says).  A gatekeeper is allowed to send you a DRQ to clear the call.
Depending on how the endpoint is written, though, this may not be trivial to
achieve, since without pregranted ARQs it is reasonable for an endpoint to
want to match up DRQs with individual ARQs.

As a gatekeeper, though, I wonder why one would want to implement that.  For
the gatekeeper to be aware of a call when using pregranted ARQs, it must be
routing call signalling, so it can quite happily terminate the call by means
of ReleaseComplete - which will NOT break poorly written endpoints.

The related question is whether an endpoint sends a DRQ on "normal" call
termination in these cases.  If the gatekeeper is routing call-signalling it
is arguably unnecessary (ReleaseComplete clears the call); if not, then
potentially the first the gatekeeper knows about the call is the DRQ at its
end (not useful!)!  Note that H.323v2 section 8.5.2 assumes that ARQ has
happened at the beginning of the call, so behaviour where this is absent
(due to pregranted ARQ) is arguable.

This leaves a question mark over the use of the other call-specific RAS
message, BRQ.  Bandwidth issues with pregranted ARQs are discussed in both a
contribution and a TD from the recent Monterey meeting (I forget the

Dr Chris Purvis - Senior Development Engineer, WAVE CC Software
Madge Networks Ltd, Wexham Springs, Framewood Road, Wexham, Berks.  ENGLAND
Phone: +44 1753 661 359  email: cpurvis at madge.com 

> -----Original Message-----
> From: rtgupta at hss.hns.com [mailto:rtgupta at hss.hns.com]
> Sent: 09 March 1999 5:19
> To: srini at trillium.com
> Cc: h323implementors at imtc.org; ITU-SG16 at mailbag.cps.intel.com
> Subject: Re: call clearing by GK
> Hi srini,
>        Gatekeeper can clear an ongoing call by sending DRQ to 
> an endpoint.
> Refer to section 8.5.3, ITU-T H.323 recommendation.
> Thanks,
> Ritu.
> _____________________________________________________________________
> Ritu Gupta                                     |       email:
> rtgupta at hss.hns.com
> Senior Software Engineer,           |                   
> rtgupta at hotmail.com
> Hughes Software Systems,                  |       phone:
> 91-80-2286390/91/92(W)
> Banglore, Karnataka                       |
> 91-80-3374075(H)
> INDIA.                                         |       Fax     :
> 91-80-2286393
> _____________________________________________________________________
> Restlessness and discontent are the first necessities of progress.
> srini at trillium.com (Srinivasa Beereddy) on 03/09/99 05:29:43 AM
> Please respond to srini at trillium.com (Srinivasa Beereddy)
> To:   h323implementors at imtc.org, ITU-SG16 at mailbag.cps.intel.com
> cc:
> Subject:  call clearing by GK
> I have a question on call clearing by Gatekeeper. Can a 
> GateKeeper send DRQ
> to clear the call in a preGrantedArq case?
> thanks in advance.
> Srini
> Trillium Digital Systems, Inc.
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