I have a CUCM 7 cluster.
We have 4 isdn lines (UK based)
each using 30 channels.
2 voice gateways are deployed and each has 2 isdn lines and H323 is being used.
I have setup the voice gateways in a route list and route group etc. on the CUCM.
My question is, if in the event that the first 30 channels go down. Cucm wont be able to dial out as it will just be handing off the number to the gateway.
Should I bundle each pair into 60 channels using a trunk group?
Well if you have the dial-peer succession correct on the gateway with preference orders, it will failover to the 2nd PRI. However with H323 there will be a timeout element to this, although I'm not sure how that behaves if the 1st PRI is actually down, it may not delay and go straight to the 2nd PRI.
You could use MGCP which will remove any element of delay and CM will be well aware of the channel states.