Cisco Unified Contact Center Enterprise Solution Reference ...

Chapter 2 Deployment Models
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IPT: Clustering Over the WAN
Latency across the private dedicated link cannot exceed 100 ms one way (200 ms round-trip).
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 Design Considerations for High Availability, page 3-1.
The redundant centralized model is explored in the next section on IPT: Clustering Over the WAN,
page 2-27.
IPT: Clustering Over the WAN
As part of the centralization of call processing, many customers prefer to combine the redundancy of the
distributed Cisco Unified CallManager call processing model with the simplicity of having a single
Cisco Unified CallManager cluster for a single dial plan and voice system to administer. This
combination of models provides for a single Cisco Unified CallManager 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.
Cisco Unified CallManager 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, Cisco Unified
CallManager intra-cluster communications (ICC), 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 separate Unified ICM (PG and Central Controller) private links.
Advantages
No single point of failure, including loss of an entire central site.
Cisco Unified Mobile Agents (Unified MA) 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 Cisco Unified CallManager.
Reduction of servers for distributed deployment.
Best Practices
The highly available (HA) WAN between the central sites must be fully redundant with no single
point of failure. (For information regarding site-to-site redundancy options, refer to the WAN
infrastructure and QoS design guides available at http://cisco.com/go/srnd.) In case of partial failure
of the highly available WAN, the redundant link must be capable of handling the full central-site
load with all QoS parameters. For more information, see the section on Bandwidth Requirements
for Unified CCE Clustering Over the WAN, page 11-17.
A highly available (HA) WAN using point-to-point technology is best implemented across two
separate carriers, but this is not necessary when using a ring technology.
Latency requirements across the highly available (HA) WAN must meet the current Cisco Unified
Communications requirements for clustering over the WAN. Currently a maximum latency of 20 ms
one way (40 ms round-trip) is allowed. This equates to a transmission distance of approximately
Cisco Unified Contact Center Enterprise 7.x SRND
2-27