I have two Cisco 2509's attached to a AT&T T1 using Paradyne 3610 CSU/DSUs at both ends. My routers are conncted to the CSU/DSUs via DB-60 to V.35 DTE cables. The serial 0 interface will come up and then within a minute the protocol will go down.
I tied the local loop back at the CSU/DSU and the serial 0 line when down when running the test. I set debug on for the serial port and it looks like it getting not reply and the serial line shows down during the debug.
I had AT&T check the line between their two CSU/DSU units and they say there is no problem. I had configured my routers and tested them before sending them using my own CSU/DSU's. I have noticed that I have no DTR light on the AT&T CSu/DSU unit. The other T1's I have working show a DTR light on the CSU. I also noticed that clocking on my CSU/DSU is set for external. Where is the clocking suppose to come from?
Any suggestion would be appricated. Thanks