Loopback Operation
150-431-115-01, Revision 01
42
September 22, 1998
HLU-431 List 1E
A1LB, A2LB, and A5LB Test Procedures
To perform the HLU A1LB, A2LB, and the A5LB test procedures:
1
Send into the HLU-431 the in-band ARMING and NI LPBK code 11000 for at least 5 seconds.
2
Monitor the output of the HLU-431 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-431 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.
4
Once armed, the HLU-431 can be looped back by sending Intelligent Office Repeater (IOR) LPBK activation
code 1101 0011 1101 0011 (D3D3) for at least 5 seconds. The tester observes, the following activation
response, in the order presented:
a
2 seconds of AIS (all ones pattern)
b
2 seconds of returning data pattern
c
231 logic errors (including the frame bit) occurring in the returned pattern comprising:
•
10 errors, if ILR-1 (Doubler 1) was sent
•
200 errors, if ILR-20 (Doubler 2) was sent
•
20 errors, if ILR-2 (HRU) was sent
d
normal looped data
This error pattern repeats every 20 seconds as long as the IOR loopback pattern is being sent. This also applies
to ILR, Time-out Override, and Query commands.
Some Intelligent Repeater (IR) test sets do not count frame errors as bit errors when the test
pattern is framed and the HLU-431 is set to the AUTO framing mode. To improve compatibility
with those test sets, the HLU-431 generates 201 (NDU2) and 232 (NLOC) ID bit errors. As a result,
the HLU-431 may indicate one more or one less bit error, depending on the test set type and the
number of frame bits contained in the block of errored bits. To avoid this uncertainty, PairGain
recommends sending the IR commands unframed.