Use call admission control to maintain a desired level of voice quality over a WAN link. For example, you can use call admission control to regulate the voice quality on a T1 line connecting your main campus and a remote site.
Voice quality can begin to degrade when there are too many active calls on a link and the amount of bandwidth is oversubscribed. Call admission control regulates voice quality by limiting the number of calls that can be active on a particular link at the same time. Call admission control does not guarantee a particular level of audio quality on the link, but it does allow you to regulate the amount of bandwidth consumed by active calls on the link.
There are two types of call admission control that you can use with Cisco CallManager:
The Locations feature, available in Cisco CallManager, provides call admission control for centralized call processing systems. A centralized system uses a single Cisco CallManager to control all the locations. Figure 5-1 illustrates call admission control using locations. For more information, refer to the "Configuring Locations" section and to the Cisco IP Telephony Network Design Guide.
Figure 5-1 Call Admission Control Using Locations in a Centralized System
An H.323 gatekeeper, also known as a Multimedia Conference Manager (MCM), provides call admission control in a distributed system with a separate Cisco CallManager or Cisco CallManager cluster at each site. Figure 5-2 illustrates call admission control using gatekeeper technology. Only one gatekeeper can be registered per Cisco CallManager cluster. Refer to the Cisco IP Telephony Network Design Guide for more information about deployment of gatekeeper-based call admission control.
Figure 5-2 Call Admission Control Using H.323 Gatekeeper Technology in a Distributed System