System Configuration Guide for Cisco Unified Communications Manager, Release 12.5(1)

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Updated:
February 2, 2024

Chapter: Call Admission Control Overview

Call Admission Control Overview

About Call Admission Control

Use call admission control (CAC) to regulate voice quality over a WAN link.

Voice quality can degrade when too many active calls exist 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 at the same time on a particular link. 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 that active calls on the link consume.

Call admission control operates by rejecting a call for bandwidth and policy reasons. When a call is rejected due to call admission control, the phone of the called party does not ring, and the caller receives a busy tone. The caller also receives a message on their phone, such as “Not enough bandwidth.” If you have enabled automated alternate routing (AAR), call admission control automatically diverts calls to alternate public switched telephone network (PSTN) routes when WAN bandwidth is not available.

Call Admission Control Configuration

Choose from one of the following task flows to implement call admission control (CAC).

Task Flow

Description

Enhanced Locations Call Adminssion Control Task Flow

Use enhanced locations CAC in distributed deployments, where multiple clusters manage devices in the same physical sites using the same WAN uplinks. Enhanced locations CAC lets you regulate voice quality by limiting the amount of bandwidth that is available for calls over links between the locations. It also allows you to control call admissions for immersive video calls, such as TelePresence, separately from other video calls.

RSVP Configuration Task Flow

Use RSVP to implement call admission control in complex, multi-tiered topologies that include IP telephony and videoconferencing applications. RSVP is also able to handle dynamic changes to bandwidth.

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