Designing a Large H.323 Network
To achieve stability in a large H.323 network, a two-tiered gatekeeper design is
often employed.This is sometimes called a “directory of gatekeepers” approach
since one gatekeeper acts strictly as a gatekeeper for all other gatekeepers.
In this design, two levels of gatekeeper are introduced.The lower level gatekeepers
are traditional gatekeepers: they manage zones, calls, and register endpoints
and gateways. However, rather than being configured with all other
gatekeepers in the network (and all their zones), they are configured to use a
single gatekeeper.This gatekeeper is the upper level gatekeeper. It is a special gatekeeper
in that it does not register any endpoints or manage any zones. Instead, it
is configured with all other gatekeepers and all of the zones (i.e., E.164 prefixes)
that they serve. In this sense this gatekeeper acts as a “directory” of zones. Its primary
function is to assist gatekeepers in locating the correct gatekeeper for any
given endpoint.
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Voice and Video Gatekeeper Design • Chapter 5 145
This design removes the many-to-many gatekeeper configurations required in
a flat or single level design, and creates a hierarchical design where all lower level
gatekeepers lead to a single point of control.This design also makes growing an
H.323 network much easier.When new zones and a new gatekeeper are added,
the only change to the existing network is to add the correct information to the
“directory” gatekeeper. In the flat design, every gatekeeper must be updated with
information about the new gatekeeper.
Note that this hierarchical structure is a logical design of gatekeepers.The
underlying network should provide connectivity between endpoints with the
fewest number of hops possible (while still providing a structured network
design). Adding several additional hops between endpoints can contribute to
slower and lower quality voice and video performance.
NOTE
As of 12.1(5)XM, the upper level, or directory gatekeeper could only service
approximately six lower level gatekeepers. As this limit will likely
change often, you should check with your local Cisco resource or the
Cisco TAC for updated limits.