Automated alternate routing (AAR) provides a mechanism to reroute calls through the PSTN or other network by using an alternate number. Cisco CallManager automatically reroutes calls through the PSTN or other networks when Cisco CallManager blocks a call due to insufficient location bandwidth. With automated alternate routing, the caller does not need to hang up and redial the called party.
When a call is made from the device of one location to the device of another location, location bandwidth gets deducted from the maximum available bandwidth that is available for the call at either location. If not enough location bandwidth for the call exists at either location, instead of blocking the call, Cisco CallManager uses the table of AAR groups and the external number of the terminating directory number to supply the alternate number that is used to reroute the call through the PSTN or other network. The
Cisco IP Phone displays the message "Network congestion, rerouting" by default. Cisco CallManager automatically attempts to reroute the call by using the alternate number. If the reroute is successful, the caller connects to the called party.
AAR supports the following call scenarios for insufficient bandwidth:
• Call originates from a line or directory number (DN) of an IP phone within one location and terminates to a line or DN of another IP phone within another location. This scenario includes calls that terminate at the shared line with terminating IP phone devices that are resident in multiple locations and calls that terminate at the Cisco voice-mail port.
• Incoming call through a gateway device within one location terminates to a line or DN of an IP phone within another location. This scenario includes calls that terminate at the shared line with terminating IP phone devices that are resident in multiple locations and calls that terminate at the Cisco voice-mail port.
Cisco CallManager automatically attempts to reroute calls, due to insufficient bandwidth, through the PSTN or other network only when the AAREnable enterprise parameter (moved to CCM Service Parameters in CCM3.3(4) is set to true. Cisco CallManager uses the device-based AAR calling search space, which is assigned to Cisco IP Phone station devices and gateway devices, when it attempts to route the call to the gateway device that connects to the PSTN or other network. Cisco CallManager uses the external phone number mask and the directory number of the line or DN and the Cisco voice-mail port to derive the alternate number that is used to reroute the call.
The AAR group appears as an entry in the line/DN table, in the Cisco voice-mail port table, and in the gateway device table. AAR group comprises a character string with a default value of the null string. The AAR group represents the dialing area where the line/DN, the Cisco voice-mail port, and the gateway are located.
Cisco CallManager uses the AAR group value to index into the AAR dial prefix matrix table, which contains the prefix digits for transforming the alternate number.
In the following scenario, line/DN 1001 in the HQ site AAR group calls line 2001 in the Branch 1 AAR group. If not enough location bandwidth exists, the call attempts to reroute through the PSTN or other network. To route the call from AAR group HQ to AAR group BR1, Cisco CallManager needs to know the access digit(s) to dial out to the PSTN and the full PSTN digit string since sending the digits "2001" will not be recognized by the PSTN- this is retrieved from AAR Prefix Digit and External Number Mask respectively.
The External Number Mask of the Called Party is prep ended to the dialed digits
The Dial Prefix from AAR Group is added to the Called Number-usually '91'
DN '1001'dials DN '2001
Locations CAC causes CCM to return 'Network Congestion'
CCM checks whether AAR is enabled.
Call is routed out of PSTN
A Route Pattern is matched- the partion must be visible by « the AAR CSS of the Calling Device
Digit String has been transformed from '2001'to 916175212001
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