Cisco Cisco IPCC Web Option Guide De Conception

If the visible network fails between the data center locations, the following conditions apply:

The Unified CM subscribers will detect the failure and continue to function locally, with no impact 
to local call processing and call control. However, any calls that were set up over this WAN link will 
fail with the link.

The Unified ICM Call Routers will detect the failure because the normal flow of TCP keep-alives 
from the remote Peripheral Gateways will stop. Likewise, the Peripheral Gateways will detect this 
failure by the loss of TCP keep-alives from the remote Call Routers. The Peripheral Gateways will 
automatically realign their data communications to the local Call Router, and the local Call Router 
will then use the private network to pass data to the Call Router on the other side to continue call 
processing. This does not cause a failover of the Peripheral Gateway or the Call Router.

Agents might be affected by this failure under the following circumstances:

If the agent desktop (Cisco Agent Desktop or CTI OS) is registered to the Peripheral Gateway 
on side A of the system but the physical phone is registered to side B of the Unified CM cluster.

Under normal circumstances, the phone events would be passed from side B to side A over the 
visible network via the CTI Manager Service to present these events to the side A Peripheral 
Gateway. The visible network failure will not force the IP phone to re-home to side A of the 
cluster, and the phone will remain operational on the isolated side B. The Peripheral Gateway 
will no longer be able to see this phone, and the agent will be logged out of Unified CCE 
automatically because the system can no longer direct calls to the agent's phone.

If the agent desktop (Cisco Agent Desktop or CTI OS) and IP phone are both registered to 
side A of the Peripheral Gateway and Unified CM, but the phone is reset and it re-registers to a 
side B of the Unified CM subscriber.

If the IP phone re-homes or is manually reset and forced to register to side B of a Unified CM 
subscriber, the Unified CM subscriber on side A that is providing the CTI Manager service to 
the local Peripheral Gateway will unregister the phone and remove it from service. Because the 
visible network is down, the remote Unified CM subscriber at side B cannot send the phone 
registration event to the remote Peripheral Gateway. Unified CCE will log out this agent because 
it can no longer control the phone for the agent.

If the agent desktop (CTI toolkit Agent Desktop or Cisco Agent Desktop) is registered to the 
CTI OS Server at the side-B site but the active Peripheral Gateway side is at the side-A site.

Under normal operation, the CTI toolkit Agent Desktop (and Cisco Agent Desktop Server) will 
load-balance their connections to the CTI OS Server pair. At any given time, half the agent 
connections would be on a CTI OS server that has to cross the visible network to connect to the 
active Peripheral Gateway CTI Server (CG). When the visible network fails, the CTI OS Server 
detects the loss of connection with the remote Peripheral Gateway CTI Server (CG) and 
disconnects the active agent desktop clients to force them to re-home to the redundant CTI OS 
Server at the remote site. The CTI toolkit Agent Desktop is aware of the redundant CTI OS 
server and will automatically use this server. During this transition, the CTI toolkit Agent 
Desktop will be disabled and will return to operational state as soon as it is connected to the 
redundant CTI OS server. (The agent may be logged out or put into not-read state, depending 
upon the /LOAD parameter defined for the Unified CM Peripheral Gateway in Unified ICM 
Config Manager).