I had to troubleshoot a point to point T1 circuit that was down.  The circuit is joined between two different carriers.  One side of the circuit was Verizon, and the other side was AT&T.  We weren’t sure who to call originally, so both of the carriers were called to troubleshoot the circuit.

While tests were being done, I was able to go onsite and tell right off the smartjack had no lights on it at all.  AT&T local technician was eventually dispatched to move the connection over to a spare smartjack onsite.  After everything was moved, we rebooted the routers at both ends, but the circuit was still dead. [more]

The technician finally decided to try sending a loopback clear signal down the entire line stating that “It appeared that there was still a software loopback somewhere on the line that wasn’t removed after testing.”  After he sent the signal down the line, we rebooted the routers and the circuit came back up.

This is something handy we can ask the onsite technicians to look for in the case where everything looks like it should be working but isn’t.