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.
Voice and Video Gatekeeper Design • Chapter 5 153
Even with video calls, users are accustomed to dialing phone numbers to
complete calls. It is the gatekeeper’s responsibility to resolve the dialed phone
number to the correct IP address. In video networks, admission control and call
control are critical functions.
Admission control is important because sensitive data is often kept in video
presentations, such as new product plans or financial announcements. It is vital
that a gatekeeper monitor the endpoints that have access to this content.
Call control is important because video usually requires more bandwidth than
voice calls. For this reason, the gatekeeper must closely monitor call admission to
assure both that the network has adequate bandwidth to provide a quality call
and that the call does not consume so much bandwidth that other applications
are ineffective.