Core Issue
During the Cisco CallManager fallback, some phones may become unavailable. You can reroute the call to a voice mail box.
Resolution
The alias command provides a mechanism for rerouting calls to telephone numbers that are unavailable during fallback. Up to 50 sets of rerouting alias rules can be created for calls to telephone numbers that are unavailable during Cisco CallManager fallback. Sets of alias rules are created using the alias command.
An alias is activated when a telephone registers that has a phone number matching a configured alternate-number alias. Under that condition, an incoming call is rerouted to the alternate number. The alternate-number argument can be used in multiple alias commands, allowing you to reroute multiple different numbers to the same target number.
Issue the alias tag number-pattern to alternate-number command to translate incoming Direct Inward Dial (DID) on a PRI to a IP phone in Cisco CallManager Express. You can also issue this for call forwarding if one of the Cisco Survivable Remote Site Telephony (SRST) phones is busy, with a fixed timeout period.
For more information, refer to alias (call-manager-fallback).
