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150-388-125-01, Revision 01
Loopback Operation
HLU-388 List 2E
September 15, 1998
41
GNLB L
OOPBACK
T
EST
P
ROCEDURES
To perform the GNLB loopback test procedure:
1
Have the CO tester send the HRU (3-in-7) in-band loopup code for five seconds. You should be able to see
that an HRU NREM loopback is in effect by observing the NREM message on the front panel display.
(Loopback states are indicated by the green LOOP LED on the front panel and also display in the Span Status
screen.)
2
Have the CO tester transmit a T1 test signal into the HLU-388 and verify that the returned (looped) signal is
error-free.
3
If step 2 fails, have the CO tester transmit the (3-in-5) in-band loopdown code.
4
Have the CO tester send the HLU-388 (4-in-7) in-band loopup for 5 seconds. You should be able to see that
an NLOC HLU-388 loopback is in effect. (Loopback states are indicated by the green LOOP LED on the front
panel and also display in the Span Status screen.)
5
Repeat Step 2. If the test passes, the problem is in the downstream direction. If it fails, the problem is in the
upstream direction.
Notes on Non-doubler GNLB Loopback Test Procedures:
•
The HLU-388 can be looped up from the remote location (CREM) by issuing the (6-in-7) command at the
HRU DS1 input port.
•
The HRU can be looped up from the remote location (CLOC) by issuing the (5-in-7) command at the HRU
DS1 input port.
Notes on Doubler GNLB Loopback Test Procedures:
•
Doubler #1 can engage loopback from the remote location (CDU1) by issuing the (4-in-6) loopback command
at the HRU DS1 input port.
•
Doubler #1 can engage loopback from the local location (NDU1) by issuing the (2-in-6) loopback command
at the HLU-388 DS1 input port.
•
Doubler #2 can engage loopback from the remote location (CDU2) by issuing the (5-in-6) loopback command
at the HRU DS1 input port.
•
Doubler #2 can engage loopback from the local location (NDU2) by issuing the (3-in-6) loopback command
at the HLU-388 DS1 input port.