Dear Mr. Purvis:

It is little difficult to explain all the details why we like to define communications within a given zone. We had many discussions on this subject.

If one has to build a large H.323 network (a H.323 network may consist of IP, ATM, FR, LAN, and/or other transport networks - in any possible combinations), it will require many gatekeepers consisting of many zones. The present H.323v2 signaling scheme is inadequate (even non-existence) to provide inter-gatekeeper communications between the zones (I am not even raising the issues whether any solutions are scalable or not).

Considering this very fundamental problem, AT&T is bringing contribution in the ITU-T SG16 September'98 Geneva meeting (the contribution is under internal review of AT&T) to solve that problem. This contribution is supposed to provide solution that is known as "non-hierarchical" inter-gatekeeper communications model. The proposed solution is expected to provide inter-gatekeeper communications protocol (IGCP) that will try to reuse of the existing H.323v2 signaling with extensions (that is, not to create a complete new sets of signaling schemes).

As I mentioned earlier that there can be other solutions as well. For example, "hierarchical" and "hybrid (non-hierarchical + hierarchical)".

Once the inter-gatekeeper communications between the zones are addressed, then next question comes what happens if the domain is created that includes multiple zones. A communication protocol is needed for inter-domain communications as well. It is expected that a little extension of the IGCP that is used for the inter-zone communications can also be applicable for inter-domain communications.

To customize the above schemes in an "administrative domain" environment does not require too much work once the fundamental problems are solved.

With respect to my comments on Section 1.5, I need to clarify. I mention that AT&T conurbation that is expected to be submitted will use the zone message sets. This message set is only one of them. However, there are many other message sets that need to be used for IGCP. AT&T's contributions will address each one of them, and it will be seen how powerful the solution is irrespective of the fact there can "many zones" across a large H.323 network.

You are absolutely right (at least from our experience) it is the same message set that can be used. The important point is to create the right message sets that solve the problems for all situations. AT&T's expected contribution will provide all those message sets (hopefully to reuse the exiting H.323v2 message sets with extensions) considering "NON-HIERARCHICAL" inter-gatekeeper communications model.

I also hope that this response will address many of the questions raised by Mr. J. Toga.

The entire H.323 team of ITU-T SG16 is working very hard to provide right solutions of this very complex problem. Hopefully, we are near to solve this problem (at least I am personally very hopeful to have solutions for all models as I described - the upcoming AT&T's contribution will be a step in that direction).

Thank you for providing an opportunity to clarify many of the points.

Sincerely,

Radhika R. Roy AT&T, USA Tel: 732 949 8657

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From: Chris Purvis WVdevmt-WS[SMTP:cpurvis@MADGE.COM] Reply To: Mailing list for parties associated with ITU-T Study Group 16 Sent: Thursday, August 06, 1998 5:23 AM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Zones and administrative domains

No doubt this will be discussed in the next call, but...

With respect to the emails from Messrs Roy and Toga, can someone please explain to me why inter-administrative-domain communication and inter-zonal communication within an administrative domain require separate consideration? Mr Roy's email appears to accept that when things come down to actual messages (section 1.5), the same information requires communication. Given that everybody appears to be agreed that the smallest possible administrative domain is a single zone, and that nobody appears to want to exclude the possibility of having some sort of hierachy, I fail to see why we need to do any more than define communication between administrative domains and remember that zones are degenerate administrative domains. If I've missed something fundamental, please tell me!

Regards, Chris

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Dr Chris Purvis - Senior Development Engineer, WAVE CC Software Madge Networks Ltd, Wexham Springs, Framewood Road, Wexham, Berks. Phone:+44 1753 661359 email: cpurvis@madge.com