Troubleshooting
150-231-185-05, Revision 05
46
September 13, 1999
HLU-231 List 8E
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). Therefore, whenever 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-231, 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 per
. All equalizers should be
set to the distance from the DSX-1 to the shelf.
The transmit and receive T1 DSX-1 ports have splitting access jacks and miniature, 210-series, bridging jacks as
shown in
. Connecting one cable between the two bridging jacks and another between the two
SPAN jacks splits the XMT and RCV and creates metallic loopbacks towards both the DSX-1 and the HLU-231.
If separate plugs are inserted into both SPAN jacks with the other end disconnected, the BRG jacks can be used
to send and receive test patterns towards the DSX-1.
GNLB Test Procedures
is a graphical representation of the various generic loopback configurations with the
associated GNLB commands shown. Also, refer to
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-231 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.
