150-388-151-01, Revision 01
Troubleshooting
HLU-388 List 5A
September 15, 1999
49
You can terminate loopbacks manually and exit the MAN LPBK mode by simultaneously pressing the MODE
and SEL buttons for 3 or more seconds. If no loopback is active, the MAN LPBK mode automatically terminates
after 30 seconds.
All loopbacks can be initiated by inband commands in the T1 payload or by a command from the HiGain system
(front-panel buttons or maintenance screen selections). When a loopback is active, the method by which it was
activated is indicated in the Loopback and Status screens by the annotation HG (HiGain) or PL (Payload) adjacent
to the identified loopback. For example, NREM (HG) indicates that the loopback was initiated by the HiGain
system.
L
OOPBACK
T
EST
P
ROCEDURES
The following sections provide step-by-step test procedures for verifying the integrity of the HDSL channels at
every module location as well as the DS1 channels to the customer and the local DSX-1 interface.
General Troubleshooting Tips
If trouble is encountered on the DSX-1 interface of the HLU-388, verify that the:
•
HLU is making a positive connection with its mounting assembly (shelf) connector.
•
HLU internal equalizer is set to the correct distance range (see
). All equalizers should be
set to the distance from the DSX-1 to the shelf.
GNLB Test Procedures
is a graphical representation of the various generic loopback configurations with the
associated GNLB commands shown. See
for a description of these commands.
To perform the GNLB loopback test procedure:
1
Have the CO tester send the NREM (3-in-7) inband loopup code for 5 seconds. You should be able to observe
the NREM message on the front-panel display. (The Status LED on the front panel should be green, and the
loopback mode should also be identified on the Span Status screen.)
2
Have the CO tester transmit a T1 test signal towards the HLU-388 and verify that the returned (looped) signal
to the test set is error-free.
3
If step 2 fails, have the CO tester transmit the (3-in-5) inband loopdown code.
4
Have the CO tester send the NLOC (4-in-7) inband loopup for 5 seconds. You should be able to observe the
NLOC message on the front-panel display. (The Status LED on the front panel should be yellow, and the
loopback mode should also be identified on 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.
•
SMJK loopback commands are only activated by inband commands.
•
SMJK can exist with other network loopbacks.
