Cisco Cisco IP Contact Center Release 4.6.1 Design Guide

The Unified CCE design model for clustering over the WAN assumes the Unified CCE agents are 
remotely located at multiple sites connected by the visible WAN. Each agent location requires WAN 
connectivity to both of the data center locations across the visible WAN where the Unified CM and 
Unified ICM components are located. These connections should be isolated and provide for redundancy 
as well as making use of basic SRST functionality in the event of a complete network failure, so that the 
remote site would still have basic dial tone service to make emergency (911) calls.

If side A of the WAN at the Unified MA location fails, the following conditions apply:

Any IP phones that are homed to the side-A Unified CM subscribers will automatically re-home to 
the side-B subscribers (provide the redundancy group is configured).

Agent desktops that are connected to the CTI OS or Cisco Agent Desktop server at that site will 
automatically realign to the redundant CTI OS server at the remote site. (Agent desktops will be 
disabled during the realignment process.)

If both sides of the WAN at the Unified MA location fail, the following conditions apply:

The local voice gateway will detect the failure of the communications path to the Unified CM cluster 
and will go into SRST mode to provide local dial-tone functionality.

The agent desktop will detect the loss of connectivity to the CTI OS Server (or Cisco Agent Desktop 
Server) and automatically log the agent out of the system. While the IP phones are in SRST mode, 
they will not be able to function as Unified CCE agents.

This section analyzes the failover recovery of each individual part (products and subcomponents inside 
each product) of the Unified CCE solution.

In larger deployments, it is possible that the Unified CM to which the agent phones are registered will 
not be running the CTI Manager service that communicates with the Unified CM Peripheral Gateway for 
Unified CCE. When an active Unified CM (call processing) service fails, all the devices registered to it 
are reported “out of service” by the CTI Manager service locally and to any external client, such as the 
Peripheral Gateway on a different subscriber CTI Manager service.

Unified CM call detail reporting (CDR) shows the call as terminated when the Unified CM failure 
occurred, although the call may have continued for several minutes after the failure because calls in 
progress stay in progress. IP phones of agents not on calls at the time of failure will quickly register with 
the backup Unified CM subscriber. The IP phone of an agent on a call at the time of failure will not 
register with the backup Unified CM subscriber until after the agent completes the current call. If MGCP, 
H.323, or SIP gateways are used, then the calls in progress survive, but further call control functions 
(hold, retrieve, transfer, conference, and so on) are not possible.

When the active Unified CM subscriber fails, the PG receives out-of-service events from Unified CM 
and logs out the agents. To continue receiving calls, the agents must wait for their phones to re-register 
with a backup Unified CM subscriber, then log back into their Unified CCE desktop application to have 
its functionality restored. Upon recovery of the primary Unified CM subscriber, the agent phones 
re-register to their original subscriber to return the cluster to the normal state, with phones and devices 
properly balanced across multiple active subscribers.