Inter-Cluster Communication
Inter-cluster communication is often required in very large, or widely distributed
installations, where more than one CallManager cluster is required to handle the
load. H.323 inter-cluster trunks are established to communicate between the different
clusters.
The latest release of Cisco CallManager can support up to eight servers
within a cluster, and all members of the cluster must reside on the same LAN.
However, even though an individual CallManager server can support up to 2,500
IP phones, there is a fixed limit of 10,000 IP phones per cluster. From these limitations,
it is obvious that several clusters would be required in very large local
networks, or any geographically dispersed network.
There are three types of implementations that might require multiple clusters
as well as inter-cluster communication:
Large MANs These are expected to have ample bandwidth to carry
the CallManager traffic, and therefore require no call admission control.
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Figure 4.2 Intra-Cluster Real-Time Communication
106 Chapter 4 • AVVID Clustering
Multisite WANs with distributed call processing (At least one
CallManager at remote sites) Gatekeepers are used to provide call
admission control.
Multisite WANs with centralized call processing (No CallManager
at remote sites) The Cisco CallManager locations feature is used to
implement call admission control.
Unfortunately, most Cisco CallManager features do not function between
CallManager clusters.You must therefore consider that only the following features
will exist between clusters:
Basic call setup
G.711 and G.729 calls
Call transfer
Call park
Call hold
Calling line ID
Multiparty conference
For this reason, you must take care when designing your IP Telephony network,
in order to reduce unnecessary CallManager clusters.