Cisco Cisco IPCC Web Option Leaflet

Latency across the private separate link cannot exceed 100 ms one way (200 ms round-trip), but 
50 ms (100 ms round-trip) is recommended.

Latency between Unified ICM Central Controllers and remote PGs cannot exceed 200 ms one way 
(400 ms round-trip).

The private link cannot traverse the same path as public traffic. The private link must have path 
diversity and must reside on a link that is completely path-independent from Unified ICM public 
traffic. This link is used as part of the system fault tolerant design. For more information, see the 
chapter on 

.

The redundant centralized model is explored in the next section on 

.

As part of the centralization of call processing, many customers prefer to combine the redundancy of the 
distributed Unified CM call processing model with the simplicity of having a single Unified CM cluster 
for a single dial plan and voice system to administer. This combination of models provides for a single 
Unified CM cluster with its subscriber servers split across data center locations to provide a single 
cluster with multiple distributed call processing servers for a highly available and redundant design, 
known as clustering over the WAN.

Unified CM clustering over the WAN may also be used with Unified CCE for contact centers to allow 
full agent redundancy in the case of a data center (central site) outage. Implementation of clustering over 
the WAN for Unified CCE does have several strict requirements that differ from other models. 
Bandwidth between central sites for Unified ICM public and private traffic, Unified CM intra-cluster 
communication signaling (ICCS), and all other voice-related media and signaling must be properly 
provisioned with QoS enabled. The WAN between central sites must be highly available (HA) with 
redundant links and redundant routers.

No single point of failure, including loss of an entire central site.

Cisco Unified Mobile Agents (Remote Agent) require no reconfiguration to remain fully operational 
in case of site or link outage. When outages occur, agents and agent devices dynamically switch to 
the redundant site.

Central administration for both Unified ICM and Unified CM.

Reduction of servers for distributed deployment.

Cisco highly recommends deploying a minimum of three WAN links for systems that employ 
clustered over the WAN. At least two links should be deployed for the highly available network that 
carries the Unified ICM public traffic (see 

). A separate WAN link should be used for 

the Unified ICM private traffic (see 

). If QoS and bandwidth are configured correctly 

(see the guidelines in the chapter on 

, 

for more details), these WAN links can be converged with other corporate traffic as long as the 
private and public traffic are not carried over the same link. The Unified CM ICCS traffic should 
preferably be carried over the highly available network used by the Unified ICM public 
communications.