Information Technology Reference
In-Depth Information
A single cluster of CUCM servers is deployed for redundancy in the server farm. IP
phones are deployed on PoE- and QoS-enabled LAN switches. The CUCM cluster sup-
ports up to 30,000 IP devices in a cluster. Gateway routers are configured with PRI cards
to legacy PBXs and the PSTN. A single cluster of Unity or Unity Connection servers sup-
port voice-mail and unified messaging requirements. IP phones are deployed on PoE inline
power LAN switches.
Multisite WAN with Centralized Call Processing Model
The centralized WAN call processing model is a solution for medium enterprises with one
large location and many remote sites. Figure 14-11 shows the centralized call processing
model. A CUCM cluster with multiple servers is deployed for redundancy at the large site.
Call processing and voice-mail servers are located only at the main site. Remote-site IP
phones register to the CUCM cluster located in the main site. PoE switches are used to
power all IP phones. Remote sites use voice-enabled gateway routers with SRST for call
processing redundancy in the event of a WAN failure.
CUCM Cluster
Unity: Voice Mail
SRST
Router
Site B
V
WAN
V
WAN Router and
PSTN Gateway
PSTN
V
SRST
Router
Site C
Figure 14-11
Multisite WAN with Centralized CM Deployment Model
On the WAN, QoS features are configured to prioritize the VoIP packets over other
packet types. In the event of WAN failure, SRST-configured routers forward calls through
the PSTN. The PSTN circuit can be used for local inbound and outbound calls at the re-
mote site. In this model, call admission control (CAC) is configured to impose a limit on
the number of on-net calls permitted between sites.
Multisite WAN with Distributed Call Processing Model
The multisite WAN with distributed call processing is a solution for large enterprises with
several large locations. Figure 14-12 shows the distributed WAN model. Up to 30,000
