GATEKEEPERS:
A Gatekeeper is the most important component of an H.323 enabled network. It acts as the
central point for all calls within its zone and provides call control services to registered
endpoints. In many ways, an H.323 gatekeeper acts as a virtual switch. One important function
of the Gatekeeper concerns the function of bandwidth management. A network manager can use
the Gatekeeper component of the H.323 network to control in advance the number of
simultaneous users conferencing over the network. This control allows the manager to keep the
network from becoming clogged or delayed due to the transmission of excessive audio and video
conferencing data. Finally, Gatekeepers may also
MULTIPOINT CONTROL UNITS (MCU)
The Multipoint Control Unit (MCU) supports conferences between three or more endpoints.
Under H.323, an MCU consists of a Multipoint Controller (MC), which is required, and zero or
more Multipoint Processors (MP). The MC handles H.245 negotiations between all terminals to
determine common capabilities for audio and video processing. The MC also controls conference
resources by determining which, if any, of the audio and video streams will be multicast. Thus
"MCU s provide a more powerful and flexible architecture for hosting multipoint conferences."
With a brief overview of the H.323 network, a look at the different software and hardware
technologies utilizing the H.323 standard will now be addressed.
A special note from Intel (http://www.andygrove.com/technology/itj/q21998/articles/art_4.htm)
dealing with deployment difficulties of H.323 network should close out the discussion on this
section:
H.323 Deployment Obstacles
In order to achieve H.323 deployment in real networks, limitations at both the network
level and the client platform level must be resolved at the H.323 client. The client should
scale performance based on the available bandwidth. Given the inconsistencies of
networks with best effort traffic, (i.e., no guaranteed Quality of Sevice (QoS), the
Internet), it is extremely important to provide mechanisms for fault tolerance and error
resiliency at the client platform, if it is to be used on an unmanaged network such as the
Internet. At the network level, broad connectivity, policy management, and security are
considered the major issues in the deployment of a new technology such as H.323.
Switched Circuit Network connectivity is achieved in the H.323 context by using
gateways for H.320, H.324, H.323, POTS, and other endpoints on other networks. Policy
management is achieved using gatekeepers to provide call admission, authentication, and
zone management. Deployment of QoS protocols such as RSVP can also help with policy
management. The security of media streams is another important factor in the success of
H.323 deployment, especially in unsecured environments such as the Internet.
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