Section 6, Loopbacks
MX2800 M13 Multiplexer User Manual
brings up the control menu shown in
Data Mode Menu from the Loopback menu
initiating a T1/E1 loopback, select the facility number (1-28). A loopback menu for the facility displays a
menu of nine types of loopbacks. See
to end a loopback test in progress.
Figure 6-2. Loopback Control Menu
Selecting the Data Mode from the Loopback Control menu ends any loopback test in progress.
A Tributary loopback loops the selected T1/E1 back to the network (DS3). The T1/E1 is demultiplexed
through the M23 and M12/G.747 demultiplexers, looped back, and multiplexed back up through the M12/
G.747 and M23 multiplexers. During this loopback, all network receive data is passed to the DSX-1/E1
transmitters, but all data received by the DSX-1/E1 loop side is ignored and substituted with the network
for an illustration of this test.