The Cisco CallManager Model
This dial plan model requires that all Cisco CallManagers located within a cluster
be connected through an intercluster trunk with a route pattern for each of the
other clusters within the domain.This creates quite a bit of overhead as you add
new Cisco CallManager clusters since you will have to reconfigure the Cisco
CallManager every time a new cluster is added or a dial plan changes.With this
deployment, the gatekeeper handles call admission control but not dial plan resolution.
This setup is pretty close to what you might think of as a normal PBX.
The Cisco CallManager will need two routes configured for each destination,
one for the WAN and one for the PSTN. Calls are then automatically routed
over the PSTN if there are insufficient resources on the WAN.