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Resource-Based CAC 595

Any additional calls that try to exceed the bandwidth limit are rejected and the call is either rerouted or a reorder tone returns to the caller.

CallManager continues to admit new calls onto a WAN link until the available bandwidth for that link (bandwidth allocated to the location minus all active voice conversations) drops below zero.

Automatic Alternate Routing

Prior to CallManager version 3.3, if a call was blocked due to insufficient location bandwidth, the caller would receive a reorder tone and manually have to redial the called party through the PSTN. Automated alternate routing (AAR), introduced in CallManager version 3.3, provides a mechanism to reroute calls through the PSTN or another network WAN link by using an alternate number when Cisco CallManager blocks a call because of insufficient location bandwidth. With automated alternate routing, the caller does not need to hang up and redial the called party.

The fully qualified E.164 address, also known as the PSTN number, is obtained from the external phone number mask configured on the called device. The calling device is associated with an AAR group, which is configured with the digits that will be prepended to the phone number mask to access the PSTN gateway and reroute the call over the PSTN.

Location-Based CAC Summary

Table 8-15 evaluates location-based CAC against the CAC evaluation criteria described earlier in this chapter.

Table 8-15 Location-Based CAC Evaluation Criteria

Evaluation Criteria




VoX supported

VoIP only



Toll bypass or IP telephony

IP Telephony only



Platforms and releases

CallManager 3.0


(AAR was added in CallManager release 3.3.)



PBX trunk types supported




End to end, local, or IP cloud

End-to-end between originating and terminating location,


although locations have no knowledge of the network topology


in between



Per call, interface, or endpoint

Per call



Topology awareness




Guarantees QoS for duration of call




Postdial delay




Messaging network overhead