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H323 Overflow Call Routing

For fault tolerance we have 2 RightFax servers, one at each of our main sites. The servers each use a single PRI connected to an H323 gateway. Only 8 channels are in use, with the server set to use the 1st 5 inbound, and the last 3 outbound. The PRI group is set for 8 channels.

The carrier is distributing inbound calls evenly between PRIs at each site. All calls route through the 4.1(3)sr1 Call Manager. All inbound from PSTN site A calls should route to site A server, and overflow to site B server (100mb TLS between sites). Site B calls to site B server, and overflow to site A. Initial setup was a site A route list with a 1st choice site A route group and 2nd choice site B route group. Site B route list flips the route groups. Unique site A and site B CSSs on the gateways route calls via the appropriate route list.

All works fine until the server refuses a call, or if the server PRI is unplugged. The caller gets fast busy, with the 2nd route group gateway never attempted. If I reverse the route group order the call goes to the other gateway, but still will not overflow.

I have tried using dial peer max-conn instead of relying on the channel not available from the server. I have also tried putting both gateways in a single route group. If I set the route group to circular it does alternate gateways, but if the gateway refuses the call it still goes fast busy.

I also tried VOIP peers with a lower preference pointing to the other gateway, but suspect VOIP peer to VOIP peer may not be allowed (allow-connections h323 to h323 is configured).

Any ideas?

Cisco Employee

Re: H323 Overflow Call Routing

What version IOS is on the GWs?

Once it fails, do all fax calls fail?

Make sure your GW IOS matches the ccm version as shown in the callmanager compatibility matrix:

Try a couple GW debugs:

debug h225 events

debug h245 events

deb voip ccapi err

deb voip vtsp err

deb isdn q931

Hope this helps


Re: H323 Overflow Call Routing


Thanks for the reply. Strangely enough, this started working for no apparent reason.

Regards, Dave

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