150-431-115-01, Revision 01
Loopback Operation
HLU-431 List 1E
September 22, 1998
41
The more common generic, SPLB in-band loopback commands for doubler loopbacks are listed in
. The
commands are very specific combinations of either 6 or 7 bits that continuously repeat. All NXXX loopbacks are
towards the network. All CXXX loopbacks are towards the customer.
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-431 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-431 (4-in-7) in-band loopup for 5 seconds. You should be able to see that
an NLOC HLU-431 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-431 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-431 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-431 DS1 input port.
Table 13.
SPLB Loopback Command Set
Loopback
Command
NDU1
1 1 0 0 0 0 (2-in-6)
NDU2
1 1 1 0 0 0 (3-in-6)
CDU1
1 1 1 1 0 0 (4-in-6)
CDU2
1 1 1 1 1 0 (5-in-6)
