CUCM - Automated Alternate Routing (AAR)

Automated Alternate Routing (AAR) is a high-availability feature that takes a call which would normally traverse the WAN, but is re-routed through the PSTN because the set bandwidth has been reached between two locations.

To be honest, I haven't deployed AAR at many sites. I guess this has a lot to do with the fact that I'm either really lazy, or that the cost of bandwidth has gone down so much that bandwidth and call admission control (CAC) hasn't been much of a customer requirement, or it's probably a combination of both.

If you would like to deploy AAR, the following steps and options are below, but keep in mind AAR ties directly to Call Admission Control (CAC) which means you'll have to configure and/or pay attention to Location and Region settings.


Configuring Automated Alternate Routing (AAR)

1. Turn the service on!!
1. System > Service Parameters
2. Set “Automated Alternate Routing Enabled” to True. It is False by default.
3. (Optional) Change “AAR Network Congestion Rerouting Text” to alert users that call is being re-routed. By default it is set to “Network Congestion. Rerouting.”
4. If you don't turn this on, callers will experience a re-order tone
2. Call Routing > Automated Alternate Routing Group
3. Create XXX-AAR for each site
1. You can actually create a single AAR group for NANP sites, but it depends on a few things. I would recommend creating an AAR Group for each site to keep everything clean and less confusing for administrators.
4. Set Prefix Digits Within to 9 (Local) or 91 (Long Distance) for AAR calls between phones within this group
5. Set Prefix Digits Between to 9 (Local) or 91 (Long Distance) for AAR calls between phones from AAR Group A to AAR Group B. (this field does not show up if you have ONLY 1 AAR group)
6. AAR Group and CSS
1. The AAR Group and CSS can be set on the Device Pool or the Phone, gateway, or endpoint.
7. Extension AAR Settings
1. Make sure that you have the correct External Phone Number Mask (EPNM) for each phone. This is how AAR figures out what number and how many digits to dial after prepending 91 or 9 within the AAR Group. 
2. If, for some reason, you want AAR triggered calls to go to voicemail or to a different number/group altogether, you can configure these options within "AAR Settings" on the extension
3. The AAR Settings options (voicemail or AAR Destination Mask) take precedence over the External Phone Number Mask
8. Lastly, the AAR triggered number is matched to a route pattern using the AAR Calling Search Space. If an outbound route is matched, the call is pushed out through the PSTN.

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