WAN Network congestion and AAR

Unanswered Question
Jun 24th, 2009


I know the concept of AAR is used when the bandwidth has been reached as set by the location CAC. But is there a similar way either on the WAN router using IP SLA commands etc and the callmanager to reroute the call over PSTN when the network becomes congested and latency becomes excessive



I have this problem too.
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Dennis Mink Wed, 06/24/2009 - 22:41

AAR simply looks at the bandwidth you allocate between your regions, it will not look at Qos or latency, it will keep adding calls via WAN as long as the bandwidth you allocate is not exceeded, disregarding Qos oand or latency.

bigcappa1 Wed, 06/24/2009 - 23:21


Thats what I am saying in my question. I know AAR only works this way, so what I am asking is what is out there to perform a similar function of intelligently routing the call out the PSTN in the situation where the WAN is congested and there is some unknown reason for an increase in latency even with QoS applied. Could we bring the IOS SLA information into play and if so how would this work with callmanager



Jonathan Schulenberg Mon, 07/06/2009 - 16:58

You can use RSVP-enabled CAC which can actively deny the call and AAR can engage from there.

I'm not sure how you could configure the router to know that it should deny the RSVP RESV request upon poor interface performance though. Hopefully this helps you in the right direction at least.

MARK BAKER Mon, 07/13/2009 - 06:44

I'm not sure if you are using H323 or SIP for your gateways, but here is a feature that works with H323 and SIP gateways that might be what you are looking for.

call fallback active

To enable a call request to fall back to alternate dial peers in case of network congestion, use the call fallback active command in global configuration mode. To disable PSTN fallback, use the no form of this command.

I believe this works with the IP SLA monitor feature. I think you also have to enable it on the dial-peer after global configuration as well.

Hope this helps,


bigcappa1 Mon, 07/13/2009 - 23:42


I was in our local Cisco offices and ran this passed some of the SEs and basically as the SRND (get out clause here)states that the QoS be enabled over the WAN to support voice then congestion should not occur through latency etc, the only method of rerouting calls is through CAC but this is bandwidth limit control. I will run this command passed them as I am in a meeting again this afternoon as in reality network congestion will affect the whole link no matter what type of QoS is applied

Thanks for the information



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