__net loops__
L) line
P) payload
U) inband up
D) inband down
The Line loop and the Payload loop both occur in the local CSU and both face the network only.
The line loop is very near the network port, passing through a minimum of the CSU circuitry.
This is the well known CSU loop that is often invoked by a telephone company. The
Payload loop goes through more of the CSU circuitry before looping the signal back towards the T1.
Inband Up is used to establish a loop on a far end CSU. It will only work on a point to point full T1 circuit. When the Inband Up command is used the local CSU sends the standard CSU loop up code to the far end CSU. Hopefully this will establish a looped condition, it should put the far end CSU in a Line Loop. With this loop established, the user may wish to select a Net Test signal from the __net signals__ menu.
A Line Loop or a Payload Loop can be terminated by using N) end tests, but this will not end any loops that may exist in a far end CSU. If "U) inband up" has been used to put a far end CSU into a loop, "D) inband down" must be used to terminate that loop.