T1 LOOPBACK JACK WIRING

How to make a T1 Loopback plug for testing both Line and
4. Once service is verified through the Smart Jack, you should see if you can plug the loopback plug at the end of your Internal (or Inside) wiring. If you have a buscuit jack at the end of an extension from the smart jack, you can plug the loopback plug into it and the ISP can tell you if you are "clean" through the Inside Wiring.
How do I make an T1/E1 loopback connector? - Digium
Dec 15, 2010In order to perform a loopback test of the E1/T1 port, a loopback plug (also known as loopback connector or loopback cable) is needed. An T1/E1 loopback connector can easily be made using a single RJ45 connector and two 4-in (10-cm) wires. Materials Needed: Unused RJ-45 plug; Two strands of Category 5 (Cat-5) wire, each 4-in (10-cm) long