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150-231-175-01, Revision 01
Loopback Operation
HLU-231 List 7E
September 23, 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 5 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-231 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-231 (4-in-7) in-band loopup for 5 seconds. You should be able to see that
an NLOC HLU-231 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-231 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-231 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-231 DS1 input port.
A1LB, A2LB, and A5LB Test Procedures
To perform the HLU A1LB, A2LB, and the A5LB test procedures:
1
Send into the HLU-231 the in-band ARMING and NI LPBK code 11000 for at least 5 seconds.
2
Monitor the output of the HLU-231 for the return of the pattern. Return of the pattern indicates that:
•
either the HRU has looped up (if the SMJK Loopback option is Enabled),
•
or that an external NI has looped up (if the SMJK Loopback option is Disabled) and that the
HLU-231 and HRU units have been ARMED.
3
Verify, if possible, that the HRU Loopback LED is either flashing, indicating that the HRU is armed, or lights
steadily, indicating that it is both armed and in loopback.