Cisco Cisco IP Contact Center Release 4.6.1 Wartungshandbuch

system operation. Once the failed process returns, it is immediately updated with the current
state of Unified ICM processes running on its peer.

In order to synchronize one peer with another after a failure, the system performs a state transfer.
The state transfer facility allows a synchronized process (for example, a CallRouter) to copy
the variables in its memory to its peer. The recovering system receives the variables from the
currently executing system and is able to restart with a copy of the current state of Unified ICM
processes. For example, as soon as a failure is detected on the Side A CallRouter, the system
software only uses Side B. When the Side A CallRouter is restarted, the system software invokes
a state transfer to immediately update the Central Controller Side A components with the current
state of their counterparts on Side B.

In order to better understand synchronization and state transfer, it might help to take a closer
look at CallRouter and Logger recovery.

CallRouter Recovery

When a single CallRouter process fails for any reason, the system software continues to operate
without any loss of functions by using the other side of the Central Controller. All attached
devices (PGs, NICs, and Administration & Data Servers or Administration Clients) switch their
active communications paths to the remaining side. This ensures that devices such as PGs
continue to receive CallRouter output through the active CallRouter on the other side of the
system.

As a consequence of the CallRouter failure, the entire side of the Central Controller is removed
from service. The Logger associated with the failed CallRouter sees no further inputs (and will
not until the failed CallRouter is restored to full operation). All components on the failed side
of the Central Controller lose synchronization with the other side. The CallRouter and Logger
must all be resynchronized before normal duplexed operation can resume.

For a single-instance Unified ICM, the recovery process begins when the Node Manager notices
the failure of a CallRouter process and automatically restarts it. Other processes are not impacted.
In a Cisco Unified Intelligent Contact Management Hosted environment, if several Unified ICM
instances are running on the same machine, the Node Manager cannot restart the machine. In
such Cisco Unified Intelligent Contact Management Hosted environments, manual intervention
is required to restart the failed CallRouter process.

The restarted CallRouter immediately initiates a state transfer from its currently executing peer.
Each CallRouter sends a message to its Logger. The Loggers then perform their own state
transfer.

When the state transfer is completed, all processes are now synchronized. The newly on-line
Central Controller sends an in-service status to all local Agents. It then begins processing input
messages. After the state transfer, both sides of the Central Controller see exactly the same
sequence of input messages. At this point the Unified ICM system is returned to full duplexed
operation.

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