Implementing Multiple Gatekeepers
When determining how many gatekeepers to implement in a network,
you should examine whether your current network is mostly centralized
or more distributed. If your company has one large campus for its headquarters
and only small remote offices, this is a mostly centralized network.
If your company has a headquarters location, but several large
remote facilities, this is a distributed network.
A centralized network can probably be implemented with a single
gatekeeper, given the gatekeeper is placed in a central location. A distributed
network is probably best served by several gatekeepers. Often
each large location will be its own zone, maintained with its own gatekeeper.
Whether a site is large enough to warrant its own gatekeeper is
partially a function of how many users are there and how many H.323
endpoints and gateways there are. The number of H.323 endpoints and
gateways is important since this directly affects the amount of activity on
the H.323 network. The number of users at a site is indirectly important
since this can affect how large the H.323 network may eventually grow.
A simple yet effective design is to place one gatekeeper at each of
your company’s major sites (again, this is a subjective decision). Each of
Configuring & Implementing…
Continued
152 Chapter 5 • Voice and Video Gatekeeper Design
A Gatekeeper’s Role in
Voice and Video Networking
A gatekeeper plays a key role in a voice network. It translates addresses so that
when a user dials a telephone number, the gatekeeper determines the IP address
associated with it.The gatekeeper will admit endpoints and calls into the network
based on configured parameters.The gatekeeper can also provide authentication
and accounting of all calls placed in the network.
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the gatekeepers will maintain that zone and any zones that connect via
a WAN connection to that site. Gateways and endpoints (CallManagers
and so on) will join the correct zone via the configuration on the endpoint
and the configuration on the gatekeeper.
For example, CallManager allows you to configure the IP address of
the gatekeeper in the Gatekeeper Name field. This controls the gatekeeper
with which the CallManager will register. The gatekeeper is configured
to place certain IP ranges into specific zones. For example, the
commands that follow place 10.10.10.10 (a CallManager, perhaps) into
the zone engineering.
zone local engineering company.com
zone subnet engineering 10.10.10.10/32 enable
Alternatively you could configure the gatekeeper to allow the entire
subnet to join the zone engineering.
zone local engineering company.com
zone subnet engineering 10.10.10.0/24 enable
Each gatekeeper will be aware of all other gatekeepers. A structured
dial plan will be established so that each gatekeeper knows how
to route calls based on the E.164 or technology prefix.
If your company is just starting to deploy an H.323 network, you
can probably deploy the gatekeeper(s) on an existing router. In this case,
add a new subnet to the gatekeeper and configure the router’s new IP
address as a secondary IP address or as a new loopback. Use this as the
address used by endpoints and CallManagers to register with the gatekeeper.
If the H.323 network grows large enough to warrant a separate
router as the gatekeeper, simply move this IP address to the new gatekeeper
router. That way all your endpoints can still register with the
same IP address.