Nortel ICS Install Manual page 567

Line loopback
Norstar ICS
Norstar ICS
The line loopback test loops the full 1.544 Mbps signal
received from the network back to the network. The looped
signal is regenerated without any change in the framing format
and without the removal of any bipolar violations. The line
loopback test can also be invoked and stopped remotely using
the in-band signal or via the facility data link (FDL) in
extended super frame (ESF) format.
The line loopback test must be run in coordination with the T1
or PRI service provider. Some test patterns can cause the DTI
to reset. To avoid this, start the line loopback test from your
system before the T1 or PRI service provider begins their test,
and stop the line loopback test from your system after the T1
or PRI service provider ends their test.
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Tests / 567
T1
T1
network
network
Modular ICS 7.1 Installer Guide