In example one (see Figure 1: S8300E, R640 Server with survivable core servers in normal operation), the duplicated server is acting as the main server in a survivable core server environment. Two survivable core servers have been positioned in the network. Through administration on the main server, another duplicated server is selected as the primary backup or 1st alternative to the main server. A third duplicated server pair is acting as a secondary backup or 2nd alternative in case the 1st alternative fails or there is WAN fragmentation. For example one, the intent of the survivable core server configuration is to keep all Media Gateways under the control of a single server.

A catastrophic failure occurs on the main servers (see Figure 2: Catastrophic main server failure). The Media Gateway can no longer communicate with the main server. The primary search timer activates.

The administered values of the survivable core servers are assigned to the Media Gateways in the 'mgc list' configuration, the order in the list defines the search order. Based on the values in the mgc list of the survivable core servers, the Media Gateway placed the 1st alternative survivable core server higher on its priority list then the 2nd alternative survivable core server.

When the primary search timer expires (see Figure 3: main servers fail- survivable core server recovery of failure), the Media Gateways request service from the highest survivable core server on its list (1st alternative). The 1st alternative survivable core server acknowledges the request and takes control of the Media Gateway.

The primary search timer is configured on the G4xx gateways CLI using the set reset-times primary-search. The default value is 1 minute and the configurable range is 1-59 minutes.