Specifications

Chapter 7 Multisite WAN with Centralized Call Processing
Centralized Call Processing Model
7-2
Cisco IP Telephony Network Design Guide
78-11103-03
Figure 7-1 Multisite WAN with Centralized Call Processing
In Figure 7-1 the Cisco CallManager cluster is located at the central site. Because
all IP phones within this cluster must register with a single Cisco CallManager,
this solution can scale to 2500 users per cluster. Multiple clusters can be installed
at the aggregation site to further scale the solution, and these clusters can be
interconnected using H.323.
The primary advantage of this model is the ability to centralize call processing.
This reduces the equipment required at the remote branch, while eliminating the
administration of multiple PBXs or key systems, which would have traditionally
been used. Figure 7-1 shows that the IP WAN is backed up by an Integrated
Services Digital Network (ISDN) connection, which can provide a redundant IP
WAN path for call processing. This scheme is particularly attractive for small
branch offices of less than 20 people and for telecommuters. Life-line services can
be provided by dedicated POTS lines or cellular phones.
IP WAN
PSTN
ISDN backup
V
V
IP
IP
IP
IP
IP
IP
V
IP
IP
IP
40811
Aggregation
Branch offices
Cluster