Verilink TAC 2130 S/T (880-503296-001) Product Manual - Manual (Page 57)

Diagnostics
Verilink TAC 2130 User Manual 5-13
A T1 loopback plug can be made by taking a male RJ-45 connector
and placing two short jumper wires where a cable would normally
go. One jumper is placed from pin 1 to pin 5, the other jumper
connects pin 2 to pin 4. See
Figure 5-5 for a drawing of a T1
loopback plug.
NOTE: When using a T1 loopback plug it might be necessary to
temporarily change the timing selection in the IDCSU. If the
IDCSU is set to recover network clock, it will be trying to
recover a clock it is trying to recover. The clock frequency
will drift. For this test, set the IDCSU clock source to Internal.
Remember to change it back after the test.
Figure 5-5 T1 Loopback Plug
RJ -45
8
Cable Side
Connector
2 4 5 1
RJ-45 plug held with plastic latching tab unseen at bottom