The isdn backup config is working for one branch office whereas the same config is not working for the other..

we have a channelized E1 leased line connectivity and four branch offices.. we have set up isdn as backup for it and the config is working fine in one branch office but not in the others.. the line and the NT box is working fine.. any solution for it???

Could be many issues. First check with your ISDN provider and have them test the ISDN numbers. What kind of ISDN equipment are you using? You need to make sure you have the correct parameters configured. They might not be the same in each branch office, because the branch offices might be served by different local ISDN switches from different vendors. That can mean that you have to select a different type of framing format or ISDN switch type and the SPID format might be different. It could also be a long distance carrier issue, which might affect some branch offices but not others. For example it may have been provisioned for vioce over ISDN instead of data.

Don't worry about getting the routers to talke to each other yet, you at least need to be able to complete an end-to-end ISDN call first, then you can move on to getting the LAN-to-LAN connectivity. Many ISDN problems like this are usually a provisioning issue and need to be resolved by the carrier. If you can make end to end ISDN calls, then it's obviously an NT1 or router issue and it's something configurational. Don't know what routers you're using, but you'll need to do some debug commands.