Gatekeeper Zones:
A zone is the collection of H.323 nodes such as gateways, terminals, and MCUs registered with the gatekeeper. There can only be one active gatekeeper per zone. These zones can overlay subnets and one gatekeeper can manage gateways in one or more of these subnets.
Gatekeeper Clusters:
A gatekeeper cluster is a group of up to five gatekeepers within a gatekeeper zone. The cluster shares the following information within the zone:
Bandwidth
Current calls
CPU utilization
Alternative available gatekeepers
Gateways within the zone
Remote gatekeepers
In the event of high call volume or gatekeeper failure, gateways can be redirected to other gatekeepers in the cluster. This ability to cluster gatekeepers together and reroute calls increases gatekeeper reliability and scalability.
Gatekeeper cluster members share information via Gatekeeper Update Protocol (GUP), a Cisco proprietary protocol. Because gatekeepers share information, a gateway only needs to register with one gatekeeper in the cluster. Similarly, LRQ message exchanges from remote gatekeepers are only sent to one gatekeeper in the cluster. These factors make gatekeeper clusters more scalable than other redundant solutions such as Hot Stand-by Routing Protocol (HSRF).
Each gatekeeper must have the following characteristics:
Compatible gatekeeper configuration. Each gatekeeper must have a configuration compatible with all other gatekeepers in the cluster. For example, each gatekeeper's zone definitions should declare the same set of alternate zones on all other gatekeepers in the cluster.
Representing the entire gatekeeper cluster. Each gatekeeper can stand for the whole cluster because each gatekeeper has the registration and availability information for every endpoint in the cluster. For example, LRQs from remote gatekeepers are only sent to one gatekeeper in the cluster. This local gatekeeper uses the remote clustured gatekeepers in a round robin fashion to balance the LRQ load between different elements of the cluster.
Using Gatekeeper Update Protocol (GUP) for communication.
Registering the same enpoints. Each zone should be capable of registering the same endpoints, such as a gateway. For example, each zone gatekeeper supports the same set of zone prefixes, so that endpoints can register with any gatekeeper the cluster.
Using a maximum of five gatekeepers. For local clusters, this means that there can be no more than four alternate gatekeepers included with the maximum of five gatekeepers, including the local zone.
Redirecting gateways. Although each gateway registers with a single gatekeeper, any gateway can be redirected to a different gatekeeper in if its original gatekeeper is at capacity or fails.
Using alternate gatekeepers. Each gateway is informed of alternate gatekeepers at registration (RCF) in priority order and registered with the highest priority alternate gatekeeper in event of failure. A gateway can also move to another gatekeeper if its primary gatekeeper fails.
