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Chapter 1 IP Telephony Deployment Models

Multi-Site WAN with Centralized Call Processing

Use Media Gateway Control Protocol (MGCP) gateways for the PSTN if you do not require H.323
functionality. This practice simplifies the dial plan configuration. H.323 might be required to
support specific functionality not offered with MGCP, such as support for Signaling System 7 (SS7)
or Non-Facility Associated Signaling (NFAS).

Implement the recommended network infrastructure for high availability, connectivity options for
phones (in-line power), Quality of Service (QoS) mechanisms, and security. (See

Network

Infrastructure, page 2-1

Follow the provisioning recommendations listed in the section on

Call Processing, page 6-1

Multi-Site WAN with Centralized Call Processing

The multi-site WAN model with centralized call processing consists of a single call processing agent that
provides services for many sites and uses the IP WAN to transport IP telephony traffic between the sites.
The IP WAN also carries call control signaling between the central site and the remote sites.

Figure 1-2

illustrates a typical centralized call processing deployment, with a Cisco CallManager cluster as the call
processing agent at the central site and an IP WAN with QoS enabled to connect all the sites. The remote
sites rely on the centralized Cisco CallManager cluster to handle their call processing. Applications such
as voice mail and Interactive Voice Response (IVR) systems are typically centralized as well to reduce
the overall costs of administration and maintenance.

Note

In each solution for the centralized call processing model presented in this document, the various sites
connect to an IP WAN with QoS enabled.