Section 150-231-164
Revision 04
Page 12
towards the customer. Either loop-up condition is
terminated (looped-down) with the 3 in 5 loop-down
code. Both in-band codes must be present for 5
seconds before the HiGain system responds. Table 2
lists the test procedures that apply when using the
GNLB mode.
3.04
The A1LB loopback selection, Table 3, complies
with that proposed for HDSL systems in the
T1E1.4/92 recommendation with the following additions:
•
Query loopback
•
IOR (Intelligent Office Repeater) power-down
•
Three loopback time-out choices
•
Initiation from either end
•
Repeating bit error signatures
•
Alternate query loopback
These additions make A1LB identical to A2LB described
below. It is given a separate identity to allow future
T1/E1 enhancements to be added without affecting
A2LB.
3.05
A2LB through A5LB are four special address-
able repeater loopback functions which are
supported by the List 6D version of the HiGain system.
These loopbacks provide the HiGain system with
sophisticated maintenance and trouble shooting tools.
Table 4 through Table 7 list the details of these SPLB
functions. A2LB & A5LB are patterned after the Teltrend
addressable T1 repeater loopbacks. A3LB & A4LB are
patterned after the Wescom addressable T1 repeater
loopbacks. All four SPLBs have been enhanced to
handle the specific requirements of the following HiGain
system customers:
•
A2LB (Teltrend) = Southwestern Bell
•
A3LB (Wescom) = New England Telephone
•
A4LB (Wescom Mod 1) = New York Telephone
•
A5LB (Teltrend Mod 1) = Southern New England
Telephone (SNET)
3.06
A5LB differs from A2LB in that A5LB does not
block the arming code from exiting the HLU-231
List 6D into the network. A2LB can be configured to
either block this arming code after two seconds, and
replace it with the AIS code, or to unblock it by executing
the FAR-END ACTIVATE code. Since A5LB never
blocks the arming code from exiting the HLU-231 List
6D, it does not need this FAR-END ACTIVATE code.
A3LB differs from A4LB in that A3LB supports the
additional (1 in 6) Smart-Jack loopback command.
3.07
When T1 loopback tests are performed on the
HiGain system with metallic loopback
connections at either end, the DS1 code that exists at
the metallic loopback interface may be different from the
DS1 code being received at the opposite end when the
DS1 user code is set to AUTO. This is caused by the
fact that in the AUTO DS1 code mode, the HLU-231 List
6D & HRU-412 set their own code independent of each
other. Each end sets its transmit code to match its
receive code. Thus if one end is receiving AMI and the
other B8ZS, their codes are different. For example, if
the HRU-412 has a metallic loopback and the HLU-231
List 6D receive pattern code is changed from AMI to
B8ZS and then the all “0” pattern is sent into the HLU-
231 List 6D, the HLU-231 List 6D changes to its B8ZS
mode while the HRU-412 remains in its AMI mode and
thus loops all “0”. This causes the HRU-412 to indicate
a LOS condition which causes the HLU-231 List 6D to
output the AIS pattern.
3.08
The HiGain system may take longer than normal
to respond to in-band loopback commands when
its framing mode is set to UNFR and the in-band
commands are sent in either an SF or ESF mode. The
frame bits override the command bits and cause errors
in the command sequence. These errors cause the
HiGain system to reject some sequences. This can
extend the detection interval.
3.09
Pressing both the MODE and SEL push-
buttons
on the front panel for at least
three seconds initiates a MANUAL loopback session.
This session allows the user to SEL one of four HiGain
system loopbacks. The message, “MAN LPBK”,
appears on the front panel display followed by the
message “NLO?”. If the SEL push-button is now
pressed, an “NLOC” loopback is executed and the
message changes from “NLO?” to “NLOC”. If the
MODE button is pressed instead of the SEL push-
button, “NLO?” is replaced by “NRE?”. This now allows
an ‘NREM’ loopback to be executed with the SEL push-
button. Pressing the MODE push-button two more times
yields the CRE and CLO loopback options in the
sequence listed. This interactive push-button procedure
permits any of the four HiGain loopbacks to be
executed/activated. The next loopback option can be
presented by pressing the MODE push-button however,
the previously executed loopback will remain active until
the SEL push-button is pressed and a different loopback
is activated. If neither push-button is pressed for a
period of 30 seconds and no loopback is in effect, the
manual loopback session terminates and the normal
margin displays reappear. If any loopback is in effect,
the 30-second time-out is inhibited. The active loopback
and the manual loopback session continue until the
loopback times out in accordance with the user selected
