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Collaboration, Voice & AV · Intermediate

Call Admission Control (CAC)

Mechanisms that limit the number of voice or video calls on a network path so admitted calls keep acceptable quality.

Definition

QoS prioritizes voice packets, but if too many calls are placed onto a link the priority queue overflows and all calls suffer. CAC prevents this by counting calls or bandwidth and rejecting or rerouting new calls once the limit is reached. Options include CUCM locations and ELCAC, RSVP-based CAC, gatekeeper bandwidth limits and CUBE max-conn on dial peers.

Example

max-conn 10 on a CUBE dial peer limits that trunk to ten simultaneous calls.

Exam tip

Remember that CAC complements QoS: QoS protects voice from data, CAC protects voice from other voice.

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