Cisco Cisco Unified Contact Center Enterprise 9.0(2) Installation Guide

Stopping the side B Central Controller puts side A (from a Central Controller 
prospective) into a simplex condition. 

Once all Central Controller services are stopped on side B, the Central Controller 
is started on side A.

For the period of time when the side B Central Controller is stopping the logger 
and router services until the time that the side A Central Controller (Logger and 
Router) services come on line, the Service Provider’s default network routing 
plan is invoked.

The side A CallRouter requires successful connectivity with 50% of the 
configured PGs for that instance.

Before proceeding with the upgrade of the B side central controller, testing should 
be completed with side A in a simplex condition. Only upon successful 
completion of testing should a “Go” decision be made to continue with upgrading 
the B side central controller.

To stop the upgrade at this point, stop the ICM software on the upgraded machines 
and start ICM on the non-upgraded machines. Once the non-upgraded machines 
are back on line the upgraded machines can be brought back to their original state 
using the stored image. If no issues are identified, or if a problem is assessed as 
“non-critical” to the business, the upgrade continues.

Only upon successful completion of side A simplex testing should a “Go” 
decision be made to continue with upgrade of the side B Central Controller. 

Once the Central Controller has successfully synchronized, testing should be 
completed in duplex mode.