Cisco Cisco IP Contact Center Release 4.6.1 Maintenance Manual

run again as a synchronized process. The following figure shows how synchronized execution
and hot standby are applied in the system software.

Figure 1: Duplexed Unified ICME Fault Tolerance

PGs and NICs use the hot standby approach to fault tolerance. Note that the duplexed NIC in
the figure above is implemented on two separate computers. Each computer has active and idle
connections to the sides of the Central Controller. NIC fault tolerance is described in more detail
later in this chapter.

Duplicated Communication Paths

Each NIC, Peripheral Gateway, and Administration & Data Server or Administration Client
has two communication paths to the Central Controller (see above figure). The two paths connect
the device (for example, a PG) to a Central Controller Agent process on each side of the Central
Controller. The Central Controller Agent is a software process that manages communications
between the Central Controller and nodes in the Unified ICM system.

At any one time, one of the two communications paths is active and the other is idle. All
communication traffic between the Central Controller and the device is sent on the active path.
If the active path fails for any reason, the second path is activated and all traffic is switched to
the newly active path. The previously active path becomes the idle path.

The communication protocols use buffering and acknowledgments to ensure that no messages
are lost during the path failure and switch-over. After a communication path failure, the device
periodically attempts to re-establish communication along the failed path.

Administration Guide for Cisco Unified ICM/Contact Center Enterprise & Hosted Release 8.x