Implementing multisite Cisco Unified Communications Manager deployments over an IP WAN requires additional planning to ensure the quality and availability of voice and video calls.
When an IP WAN connects multiple sites in a Cisco Unified Communications deployment, QoS must be implemented to prioritize voice and video packets over data packets. However, to avoid an oversubscription that is caused by too many voice and video calls, a mechanism is necessary to limit the number of calls that are allowed at the same time between certain locations. CAC is the mechanism that ensures that voice calls do not oversubscribe the IP WAN bandwidth and thus impact voice quality.
In this section, we describe the CAC mechanisms that are provided by Cisco Unified Communications Manager, and explain how to implement enhanced location CAC within a cluster and between clusters. We also describe how AAR can be used in some scenarios to reroute calls that are denied by CAC over the PSTN.