I've installed two cisco 1841 routers with csu/dsu cards in them to support a closed circuit t1. The configuration for the serial port is as follows:
Router A: interface serial 0/0/0 ip address 192.168.1.1 255.255.255.0 ip access-group 101 in ip access-group 102 out encapsulation ppp service-module t1 clock source internal service-module t1 timeslots 1-24 crypto map myMap
Router B: interface serial 0/0/0 ip address 192.168.1.2 255.255.255.0 ip access-group 101 in ip access-group 102 out encapsulation ppp service-module t1 cablelength short 220ft service-module t1 timeslots 1-24 cypto map myMap
Everything seems to work fine, except the serial connection goes down for30secs about every 30min. We had the ISP out there to test the line and they tried to sync up the oscillators with some magical machine, and that helped the timing a little bit, but we still see the problem.
Our guess at this point is that there is a hardware problem, and we are considering swapping out both routers. Does anybody have any other ideas at this point that I can try? Or even commands I can use to test the line and narrow down the problem? I tried following the Cisco troubleshooting guide for t1 lines, but maybe I missed something.
Also, Router B is connected from the terminal to the serial port with a cable that is roughly 140ft. Perhaps the cable is messing things up?