Review the Deployment Model 
chapter in the Cisco Unified Communications System Description for a guide to site models that have been tested and verified for Cisco Unified Communications Release 5.0.
The following deployment models were designed and tested as part of testing for the contact center environment:
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Single-site—In this model, all the voice gateways, agents, desktops, IP Phones, and call processing servers such as Unified CallManager, Unified ICM, and Customer Response Solutions (CRS) and/or Unified CVP are located at the same site and have no WAN connectivity between any contact center software modules.
•Multi-site centralized—In the multi-site WAN model with centralized call processing, the Unified CallManager cluster resides at a central (or hub) campus and communication with remote offices occurs over the IP WAN. The central site or data center provides the call processing services and acts as the hub for the remote sites. This model also contains distributed voice gateways for locally dialed calls.
•Multi-site WAN distributed—In the multi-site WAN model with distributed call processing, typically some sites have their own Unified CallManager cluster and are interconnected with inter-cluster trunks (ICT Trunking). Similar to the multi-site centralized model, sites in the multi-site WAN distributed model are deployed with distributed voice gateways. Communication between sites occurs over the IP WAN.
See also the When your upgrade plan is in place and you are ready to upgrade, go to Performing a System Upgrade on the Optimize tab. topic.