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Robert Craig

AAR with centralized gateway

Hey folks. I understand CAC when used for calls between remote sites. However, we are migrating all sites to a centralized pair of SIP Cubes at the head office. Now, how can I implement CAC with AAR for that route? I've already tried implementing it, however when the bandwidth is exceeded for a remote site to make a call through the CUBE and on to ATT PSTN, it just says "Not enough bandwidth". The call does not reroute the call over the remote site GW. Is this possible or is it only limited to calls within CUCM? Below is call flow.


Remote IP Phone - MPLS - Corporate Office - PSTN SIP Router (at coporate office) 

I'd like a call to reroute over the local GW at the remote office if the bandwidth is utilized instead of through the corporate office SIP router. Any help is appreciated.



Marcelo Morais


 the AAR feature enables CUCM to establish an alternate path for the voice media when the preferred path between two intra-cluster endpoints runs out of available bandwidth, as determined by the locations mechanism for CAC.

 Check the link: AAR Configuration.


 In other words, AAR is only supported between phones registered to the same CUCM. If CUCM is not aware, it can not invoke AAR.


Hope this helps.


OK, so how would location bandwidth be used from headend to remote end? If that path is out of bandwidth and I can't use AAR, what would be an alternative routing method I could use from the PSTN - in?





I think you are already halfway there. Your calls through the centralised CUBE obviously have CAC active as you get the "out of bandwidth" notification. so at that stage your AAR calling search space will decide on how to route the call next.  So if you have your remote site GW all have separate partitions that the CUBE is NOT in, then populate your AAR CSS with those partitions, forcing it to make the call to these out the remote site GW. Alternatively, in your AAR group configuration, prefix for instance 999 then add a Route Patters say 999.! and point that to your remote GW.   


so more ways than one to skin a cat.   good luck

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 QoS protects one thing from another ... for example: Voice from Data.
 Location Bandwidth protects Voice from Voice ... it guarantees that your Voice packet will not be dropped.
 In CUCM Administration > Service Parameter > Cisco CallManager, there is an option called 'Stop Routing on Out of Bandwidth Flag Required Field' (False by defaut), if you configured a Route List with 2x Route Groups then in the case of a 'Out of Bandwidth' the call will route to the second Route Group.

 Hope this helps

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