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Incoming Calls Redundancy

Hello Experts,


How can we create redundancy for incoming to my PRI.


Scenerio - I have one 4331 VGW with one PRI (PRIMARY) (573-XXXX and 588-XXXX) ranges. Now I want to add another 3945 VGW and add one new PRI (Secondary) ( with same DID ranges) with same service provider.


1. How will service provider route the to these 2 PRI as DID ranges are same (which gateway wll be hit for incoming).

1. How can i make redundancy in case my primary pri is down or 4331 VGW is down.





Dennis Mink

SIP can do this fairly easy inbound, you would need to talk to your provider to see if they can load balance or active/standby 2 PRI's inbound.


outbound is easy. your cucm can do this. both with MGCP and SIP trunks on your gatways this is easy using Route groups

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Cisco Employee

Hi Ani

1. For incoming redundancy you can contact PSTN provider and it depends on his routing algorithm whether circular of Top Down approach. You need to keep your call routing same for calls coming from either of the PRI.
2. For making redundancy of outgoing calls you can either do preferences on dial-peers (if H323/Sip gw) or you can add following ports to same Route group in circular/Top down fashion (if mgcp gw).

Hello Saurabh / Dennis ,


Both are H.323 VGWs.


For Outbound - I will add second gateway (VGW2) and one more gateway from another site in Route Group for redundancy (I believe the caller ID will get changed).


For Incoming - What is the difference between Circlular and Top/Down Algo and which one is preferred. How will it failover in case of PRI or VGW1 down.





Hi Anirudh


For incoming calls , only PSTN provider can decide whether he wants to send call in round robin fashion on 2 VGW's or send call to other gateway once all channels of first one are finished.


Whenever a call is sent from provider and gateway is down, the SETUP message won't be acknowledged and then provider routes the call to second gateway.


You need to have this discussion with the provider.

For inbound, you are not supposed to worry about the hunting. You cannot control it. Only your Telco does.

For outbound, ensure that you also have "Stop Routing on Busy/Unallocated" service parameters set to False.

Nipun Singh Raghav
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