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Collaboration, Voice & AV · Intermediate

Automated Alternate Routing (AAR)

A CUCM feature that reroutes internal calls over the PSTN when locations-based CAC blocks them for lack of WAN bandwidth.

Definition

When CAC denies an on-net call, AAR builds a PSTN number from the called party's external phone number mask plus the AAR group prefix and routes it using the AAR CSS. AAR groups on directory numbers define the prefixes between groups. AAR is triggered only by insufficient bandwidth, not by WAN failure or an unregistered destination, which is handled by CFUR.

Example

A Branch user calls HQ extension 2001; CAC fails, so AAR dials 9-1-408-555-2001 via the PSTN.

Exam tip

AAR fires on CAC rejection only; for unregistered phones during WAN outages use Call Forward Unregistered.

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