Loopback Operation
150-231-175-01, Revision 01
42
September 23, 1998
HLU-231 List 7E
4
Once armed, the HLU-231 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.
The HLU is now in Logic Loopback. The Loopback Time-out option is user settable to:
•
NONE (0 minutes)
•
20 minutes
•
60 minutes
•
120 minutes
These selections determine the duration of this loopback unless it is overridden by the Time-out Override
command or a loop-down command is sent. If the Time-out Override code 1101 0101 1101 0110 (D5D6) is
received, the activation sequence described in step 4, above, is repeated and the automatic timed expiration
of the loopback is inhibited. If this Time-out Override is sent, then the only way to loop the HLU-231 down
is to:
•
issue the IR (Intelligent Repeater) LPDN (loop-down) code 1001 0011 1001 0011 (9393) or
•
issue the NI LPDN and Disarm code 11100.
The automatic time-out timer is restored during subsequent loopback sessions.
Some Intelligent Repeater (IR) test sets do not count frame errors as bit errors when the test
pattern is framed and the HLU-231 is set to the AUTO framing mode. To improve compatibility
with those test sets, the HLU-231 generates 201 (NDU2) and 232 (NLOC) ID bit errors. As a result,
the HLU-231 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.
