Section 150-431-114
Release 01
Page 38
19.05
A2LB through A5LB are four special addressable
repeater loopback functions, which are supported
by the HLU-431, List 1D HiGain system. These
loopbacks provide the HiGain system with sophisticated
maintenance and troubleshooting tools. Table 14 through
Table 17 list the details of these SPLB functions. A2LB
and A5LB are patterned after the Teltrend addressable T1
repeater loopbacks. A3LB and 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
)
19.06
A5LB differs from A2LB in that A5LB does not
block the arming code from exiting the HLU-431,
List 1D into the network. A2LB can be configured to
either block this arming code after two seconds and
replace it with the AIS code, or, unblock it by executing
the Far-End Activate code. Since A5LB never blocks the
arming code from exiting the HLU-431, List 1D, 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.
19.07
Two additional loopback points are added for
each HDU-451 doubler that is used, as shown in
Figure 15. NDU1 and NDU2 are executed toward the
network. CDU1 and CDU2 are toward the customer. All
four loopbacks can be initiated by the 16-bit in-band
commands in SPLB states A1LB, A2LB and A3LB as
described in Tables 13, 14, and 15 respectively. NDU1
and NDU2, along with the rest of the loopbacks toward the
network, can be issued from the Loopback Menu shown in
Figure 23. (See Section C Paragraph 19.10 below for front
panel-initiated loopbacks.) The simplest HiGain system
includes two loopback locations: the HLU-431, List 1D
and the HRU-412. The most complex HiGain system
application includes the HLU-431, List 1D, HRU-412 and
two in-line HDU-451 doublers. Refer to the PairGain
HiGain Intelligent Repeater Application Note #910, Part
#325-910-100, for more SPLB details.
19.08
When T1 loopback tests are performed on the
HiGain system with metallic loopback
connections at either end, the T1 code which exists at the
metallic loopback interface may be different from the T1
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-431, List 1D and HRU-
412 set their own codes independently 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-431, List 1D receive
pattern code is first changed from AMI to B8ZS, and next,
the all “0” pattern is sent into the HLU-431, List 1D, then
the HLU-431, List 1D changes to its B8ZS mode while the
HRU-412 remains in its AMI mode, and thus loops back
the all “0” pattern. This causes the HRU-412 to indicate
an LOS condition, which then causes the HLU-431, List
1D to output the AIS pattern.
19.09
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.
19.10
Depressing 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 select one of eight HiGain system loopbacks.
The message, “MAN LPBK,” appears on the front panel
display followed by the message “NLO?” If the SEL push
button is pressed at this time, an NLOC loopback is
executed, changing the message from “NLO?” to
“NLOC.” If the Mode button is pressed instead of the
SEL push button, “NLO?” is replaced by “ND1?” This
now allows an NDU1 loopback to be executed (if it is a
doubler application) with the SEL push button. If this
same routine is followed, all eight loopbacks (NLOC,
NDU1, NDU2, NREM, CLOC, CDU2, CDU1, and
CREM) are presented and can be initiated in the sequence
listed. 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.
