Cables Unlimited TST-LOOP-003 Smartronix Superlooper T1/E1 Loopback Tester (Yellow)
A simple and compact product, The T1 Loopback Jack and Plug quickly and easily checks the RX/TX pairs of T1 circuit cables helping to determine if a signal exists. It can be plugged directly into a T1 CSU/DSU or can be attached to the end of a network patch cable. If a signal is present T1 Loopback Plug sends the signal back to the source illuminating the port light.