Information Technology Reference
In-Depth Information
Gatekeepers: Provide dial plan unification, CAC, device registration, and call rout-
ing services to the VoIP network and are often used to unify multiple different VoIP
networks as a single call routing hub. Gatekeepers are recommended when intercon-
necting more than two CUCM networks, to reduce dial plan and call routing configu-
ration and provide centralized CAC.
CUCM Gatekeeper
MPLS
LAN
V
Gateway
PSTN
IP Phones
(Terminals)
MCU
Figure 14-20
H.323 Components
Gatekeeper Use for Scalability By definition, H.323 networks are peer-to-peer,
autonomous systems. This means that configuration is required on each device about all
other devices in the network with which it needs to communicate (a mesh configuration),
including network addressing, call routing, CAC, and other configuration parameters (a
logical connection). As a network grows, the number of logical connections required
grows exponentially. For example, if a gatekeeper is not used, logical connections need to
be configured on each gateway to connect to every single other gateway on the network.
The number of logical connections is represented by the following formula:
L = ( N * ( N - 1)) / 2
where N is the number of devices in the network.
For example, in a net work w ith 7 dev ices, 21 log ic al connections must be config ured to
ensure that each device can communicate with every other device.
Alternatively, this configuration can be consolidated into a centralized system called a
gatekeeper. In a gatekeeper-controlled system, each device needs to be configured with
only a logical connection to the gatekeeper. In this fashion, the number of configurations
required is exponentially reduced, and administration can be done from a central point.
Going back to the earlier configuration example, only 7 logical connections need to be
configured in a gatekeeper-controlled environment as opposed to the 21 that have to be
configured without it. In a larger network of 100 devices, it is 100 versus 4950 connections!
 
 
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