2.10 PSTN Backup and MGCP Fallback

This topic describes how to use the PSTN as a backup path when the IP WAN is not available.

Intersite calls are rerouted over the PSTN in the case of an IP WAN failure.

In the example, calls to the remote site are configured to use the IP WAN first and then use the PSTN as a backup option.

MGCP Fallback: Normal Operation

This topic describes how to provide survivability for remote MGCP gateways.

  • Communication between Cisco Unified Communications Manager and MGCP gateway is broken.
  • MGCP gateway falls back to its default call-control application (H.323 or SIP).

MGCP gateway fallback is a feature that improves the availability of remote MGCP gateways.

A WAN link connects the MGCP gateway at a remote site to the Cisco Unified Communications Manager at a central site, which is the MGCP call agent. If the WAN link fails, the fallback feature keeps the gateway working as an H.323 or SIP gateway and rehomes back to the MGCP call agent when the WAN link becomes active again.

During normal operation of MGCP, while the connectivity to the call agent (Cisco Unified Communications Manager) is acceptable, the following happens:

  • The MGCP gateway is registered with Cisco Unified Communications Manager over the IP WAN.
  • Cisco Unified Communications Manager is the call agent of the MGCP gateway that controls its interfaces. The gateway does not have (or does not use) a local dial plan because all call-routing intelligence is at the call agent.

MGCP Fallback: Fallback Mode

The figure illustrates the operation of MGCP fallback in fallback mode, when the connectivity to the call agent (Cisco Unified Communications Manager) is lost.

When the MGCP gateway loses the connection to its call agent, it falls back to its default call-control application (POTS, H.323, or SIP). The gateway now uses a local dial plan configuration, such as dial peers, voice translation profiles, and so on. Consequently, it can operate independently of its MGCP call agent. Without MGCP fallback, the MGCP gateway would not be able to process calls when the connection to its call agent is lost.