Zone Designs
To create an optimum H.323 zone design, it is important to understand what
zones are, what functions they perform and how calls are routed between zones.
Think of designing an IP network: it is critical to understand what subnets are
and how packets are routed between subnets. Although H.323 zones are typically
much larger than one IP subnet, the same type of understanding is required.
Zones are simply collections of endpoints, gateways and Multipoint Control
Units (MCUs—provide H.323 conferencing of three or more devices).They can
be grouped in any manner that makes administration and organization easier.You
can use one large zone or many small zones, though an eye should be kept on
future scalability. One gatekeeper services each zone, though a gatekeeper can
service multiple zones.You create zones by:
Configuring each gatekeeper to place subnets into specific zones
Configuring endpoints and gateways to register with specific gatekeepers
(based on the subnets they are in)
www.syngress.com
146 Chapter 5 • Voice and Video Gatekeeper Design
To accomplish the former task, you should use the zone subnet command
to define what subnets the gatekeeper will service.A gatekeeper can service many
subnets, and any requests from subnets not configured on a gatekeeper will be
rejected. Using this command allows you to control the gatekeeper that endpoints
and CallManagers use for registration.This should be done in all cases,
though this is critical if you are using multicast since with multicast an endpoint
will find all available gatekeepers and register with the first one to respond. If
more than one gatekeeper is configured to service the same subnet, the endpoint
may register with a gatekeeper to which you did not intend it to register.