PairGain HLU-231 User manual

PAIRGAIN TECHNOLOGIES Section 150-231-134
Technical Practice Revision 01
Engineering - PLANT Series February 10, 1995
Copyright © 1995, PairGain Technologies, Inc. PairGain and HiGain are trademarks of PairGain Technologies.
01 Page 1
PairGain Technologies HiGain Line Unit
MODEL HLU-231 Issue 1
List 3D, PairGain # 150-1111-34, CLEI Code: T1LIE044AA
CONTENTS PAGE
A. PRODUCT OVERVIEW 2
1. DESCRIPTION AND FEATURES 2
2. APPLICATIONS 2
3. SPECIFICATIONS 2
4. CERTIFICATION 3
5. WARRANTY 3
B. FUNCTIONAL DESCRIPTION 4
6. OPERATIONAL CAPABILITIES 4
7. POWER CONSUMPTION 6
8. ALARM DESCRIPTION 8
9. SYSTEM OPTION SETTINGS 9
10. LOOPBACK DESIGN DESCRIPTION 13
C. INSTALLATION, TEST AND MAINTENANCE 15
11. INSTALLATION 15
12. TEST PROCEDURES 16
13. DESCRIPTION OF
MAINTENANCE SCREENS 29
CAUTION
This product incorporates static sensitive components.
Proper electrostatic discharge procedures must be
followed. Figure 1. HLU-231 List3D Front Panel. The PairGain
HLU-231 is the local unit used in conjunction with the HRU-
412 remote unit to provide a complete HiGain HDSL
system.

Section 150-231-134
Revision 01
Page 2
A. PRODUCT OVERVIEW
1. DESCRIPTION AND FEATURES
1.01 PairGain’s HiGain Line Unit Model HLU-231
Issue 1, List 3D (Figure 1) is the Central
Office (CO) side of a repeater-less T-1 transmission
system. When used in conjunction with an HRU-412
HiGain Remote Unit, the system provides 1.544
Mb/Sec transmission on two unconditioned copper
pairs over the full Carrier Serving Area (CSA) range.
The “D” designation in the list number indicates that
this line unit can be used in applications with or
without the HiGain Doubler unit (HDU-451).
The CSA includes loops up to 12000 feet of AWG 24
or 9000 feet of AWG 26 wire, including bridged taps.
The HiGain system uses HDSL (High-bit-rate Digital
Subscriber Line) transmission technology as
recommended by Bellcore TA-TSY-001210. HiGain
complies with TR-TSY-000063 (Network Equipment
Building System NEBS) Generic Equipment
requirements) and (TR-TSY-000499 (Transport
System Generic Requirements - TSGR) common
requirements.
1.02 Revision History of this practice.
Revision 01
February 10, 1995
a) Initial release.
b) The initial software release is v. 1.4.
1.03 HLU-231, List 3D features:
• Selectable DSX-1 Pre-equalizer
• V to -210 V self-adjusting line voltage for
HRU-412 and HDU-451 applications
• Front Panel HDSL S/N Margin Display
• Selectable Loopback activation codes
• RS-232 maintenance port
• Non-volatile front-panel operator setup
• Front Panel DS1 splitting & bridging
access
• Lightning and power cross protection on
HDSL interfaces
• Kb/Sec full-duplex 2B1Q HDSL
Transmission on two pairs
• Front panel status indicating LED
• Automatic front-panel display blanking
• DS1 LOS detector (125 consecutive zeros)
• Margin threshold alarm
• HAIS & SAIS options
• Easy return to factory default user settings
• New T-1 transceiver chip
• Circuit ID option
2. APPLICATIONS
2.01 HiGain provides a cost-effective, easy to
deploy method for delivering T-1 High
Capacity Digital Service (HCDS) over metallic pairs.
The fiber-like quality service is deployed over two
unconditioned, non-loaded copper pairs. Conventional
in-line T-1 repeaters are not required. Cable pair
conditioning, pair separation and bridged tap removal,
are not required.
2.02 The general guidelines require that each loop
have less than 35 dB of loss at 196 KHz, with
135 Ohm driving and terminating impedances. The
HiGain system operates with any number of other T-1,
POTS, Digital Data Service (DDS) or other HiGain
Systems sharing the same cable binder group.
HiGain systems can be used with customers requiring
DS1 service on a temporary or permanent basis.
HiGain also provides a means of quickly deploying
service in advance of fiber-optic transmission
systems. With HiGain, service can be provided within
hours. Fiber optic systems can be installed at a
leisurely pace and cut-over from HiGain when
convenient to do so. The HiGain system can then be
easily removed and utilized elsewhere.
3. SPECIFICATIONS
HDSL Line Code
784 Kb/Sec 2B1Q
HDSL Output
+13.5 dBm ± 0.5 dB @ 135 Ohms
HDSL Line Impedance
135 Ohms
Maximum Provisioning Loss
35 dB at 196 KHz, 135 Ohms
Line Clock Rate
Internal Stratum 4 clock
HDSL Startup Time
30 seconds typical, 60 seconds max per span
One-way DS1 Delay
<220 microseconds per span
DSX-1 Line Impedance
100 Ohms

Issue 1, Section 150-231-134
Revision 01
Page 3
DSX-1 Pulse Output
12 Vpk-pk for EXTERNAL equalizer or pre-equalized
for 0-655 feet of ABAM-specification cable
DSX-1 Input Level
+1.5 to -7.5 dB DSX
DS1 Line Rate
1.544 Mbps ± 200 bps
DS1 Line Format
AMI, B8ZS or ZBTSI
DS1 Frame Format
ESF, SF or unframed
Maximum Power Consumption
18 Watts (without doubler), 25 Watts (with List 3,
HDU-451 doubler)
Maximum Heat Dissipation
8 Watts (without doubler), 9 Watts (with List 3,
HDU-451 doubler)
Fusing-Internal
Connected to “FUSE-ALARM” output on pin 32
Span Voltage
-130 to -210 VDC
Margin Indicator
Displays span SNR margin for both spans relative
to 10-7 BER operation
Electrical Protection
Secondary surge protection on DS1 and HDSL
ports. Power cross protection on HDSL ports.
Operating Temperature and Humidity
-40º to 65º Celsius, 5% to 95% relative humidity
(non-condensing)
Mounting
AT&T 220-configuration or equivalent
Dimensions
Height: 5.9 in. (15 cm)
Width: 1.4 in. (3.5 cm)
Depth: 10 in. (25.4 cm)
4. CERTIFICATION
4.01 FCC compliance: The HLU-231 has been
tested and found to comply with the limits for
a Class A. digital devices. pursuant to Part 15 of the
FCC rules. These limits are designed to provide
reasonable protection against harmful interference
when the equipment is operated in a commercial
environment. This equipment generates, uses and
can radiate radio frequency energy and, if not installed
and used in accordance with the instruction manual,
may cause harmful interference to radio
communications. Operation of this equipment in a
residential area is likely to cause harmful interference
in which case the user will be required to correct the
interference at his own expense.
5. WARRANTY
5.01 PairGain Technologies warrants this product
to be free of defects and to be fully functional
for a period of 24 months from the date of original
shipment, given proper installation. PairGain will repair
or replace any unit without cost during this period if
the unit is found to be defective for any reason other
than abuse or improper use or installation.
5.02 This module should not be field repaired. If it
fails, replace it with another unit and return
the faulty unit to PairGain for repair. Any modifications
of the unit by anyone other than an authorized
PairGain representative voids the warranty.
5.03 If a unit needs repair, call PairGain for a
Return Material Authorization (RMA) number
and return the defective unit, freight prepaid, along
with a brief description of the problem, to:
PairGain Technologies, Inc.
14402 Franklin Avenue
Tustin, CA 92680
ATTN.: Repair and Return Dept.
[phone]

Section 150-231-134
Revision 01
Page 4
B. FUNCTIONAL DESCRIPTION
6. OPERATIONAL CAPABILITIES
6.01 HiGain utilizes PairGain’s 2B1Q HDSL
transceiver systems to establish two full-
duplex 784 Kb/Sec data channels between the HLU-
231 and a remotely mounted HRU-412 HiGain
Remote Unit. This provides a total capacity of 1.568
Mb/Sec between the two units.
6.02 A block diagram of the HLU-231 is shown in
Figure 2. The HiGain HLU-231 receives a
1.544 Mb/Sec DS1 data stream from the DSX-1 digital
cross connect interface. The HLU contains a DS1
frame synchronizer controlled by an 8-bit
microprocessor that determines the type of framing on
the DS1 stream and synchronizes to it. The HLU-231
recognizes Superframe (SF) (including D4) or
Extended Superframe (ESF) framing. When the data
is unframed, the HLU-231 arbitrarily defines a frame
bit.
6.03 The HLU-231 contains a demultiplexer that
generates two parallel 784 Kb/Sec data
streams. The data streams contain HDSL frames that
are nominally 4704 bits (6 milliseconds) in length. The
HDSL frames contain a 14 bit Frame Sync Word
(FSW), 6 bit Cyclic Redundancy Check (CRC), 21 bit
operations channel and DS1 payload. The DS1
stream is separated into two parallel streams that
comprise the payloads of the HDSL channels. HDSL
channel 1 contains the DS1 time slots 1 thru 12.
HDSL channel 2 contains the DS1 time slots 13 thru
24 The 8 Kb/Sec frame bits of the DS1 stream are
included on both HDSL channels.
6.04 The two formatted HDSL channels are
passed to the HDSL transceivers which convert them
to 2B1Q format on the HDSL lines. The 2B1Q line
code is designed to operate in a full-duplex mode on
unconditioned pairs. The transceiver’s echo canceler
and adaptive equalizer receive the signal from the
remote end in the presence of impairments and noise
on the copper pairs.
Figure 2. HLU-231 List 3D Block Diagram. PairGain’s HDSL technology provides full-duplex services at standard T-1 rates
over copper wires between an HLU and an HRU, which comprise one HiGain system.

Issue 1, Section 150-231-134
Revision 01
Page 5
6.05 The received HDSL channels are processed
by the transceiver and then passed on to the
HLU-231 multiplexer module. The multiplexer
provides frame synchronization for each of the two
HDSL channels. The multiplexer and HDSL
transceivers work under control of the HLU-231
microprocessor and compensate for data inversions
caused by tip-ring reversals and for channel swaps
caused by pair reversals. The HiGain system allows
for tip-ring or pair reversals, but does not tolerate split
pairs. By synchronizing to the FSW of each channel,
the multiplexer can reconstruct the original 1.544
Mb/Sec DS1 stream from the payloads of the two
HDSL channels. The CRC fields on the HDSL
streams allow the HLU-231 to determine if errors are
present on the channel due to excessive impairments
on the HDSL pairs, or due to excessive impulse or
crosstalk noise.
6.06 The multiplexer removes data link messages
from the HDSL channels and pass them to
the microprocessor. This mechanism allows
operations messages and status to be exchanged
between the HLU-231 and the HRU-412 remote unit.
6.07 The reconstructed HDSL data channel is
buffered in a first-in-first-out buffer (FIFO)
within the multiplexer. A frequency synthesizer in
conjunction with the FIFO regulates the output bit rate
and reconstructs the DS1 clock at the exact rate
received from the remote end. The HiGain system
operates at DS1 rates of 1.544 Mb/Sec with up to
±200 bits/Sec of offset.
6.08 A DSX-1 interface driver converts the DS1
channel to an AMI or B8ZS format. The DSX-
1 equalizer is programmable to five different lengths
as determined by the distance between the HLU and
the DSX-1 interface. This provides CB-119 compliant
pulses at the DSX-1 interface over a range of 0-655
feet of ABAM-specification cable.
6.09 The HLU-231 contains two separate power
converters. The main power supply converts
-48 VDC local battery to logic power for the HLU-231
circuits. The line power supply converts the -48 VDC
battery to a variable -130 VDC to -210 VDC feed that
provides simplex power feed on the two HDSL line
interfaces. The output voltage adjusts itself as a
function of the demands made on it by short loops
without doublers (low voltage) or long loops with
doublers (high voltage). The line power supply can be
turned on or off by the microprocessor and is
automatically shut down in the presence of line short
circuits or microprocessor failure.
6.10 A 9-pin (RS-232) DB-9 connector is provided
on the front panel (see Figure 3). This
connector provides access to HiGain’s maintenance,
provisioning and performance monitoring interface. A
very basic interface is available via a ‘dumb terminal’.
Figures 6 through 30 show the menu selections that
are available from the terminal. Tables 11 and 12
define the various terms used in the screen displays.
The port is configured as DCE with 8 data bits, 1 stop
bit and no parity. Striking the SPACE bar several
times enables the HLU-231 to automatically match the
terminal line baud rate, from 1200 to 9600 baud.
Figure 3. HLU-231 List 3D DB-9 Pin-Outs. A standard
RS-232 (DB-9) connector on the front panel provides
access to the menu interface feature via a dumb terminal.

Section 150-231-134
Revision 01
Page 6
7. POWER CONSUMPTION
7.01 The Maximum Current drain is the current
drawn from the shelf power supply when it is
at minimum voltage (42.5 VDC) under a worst case
application.
The doublers mentioned throughout this
practice refer to the HDU-451, List 3, part# 150-1143-
03, low power unit.
The worst case application for the
HLU-231, List 3D occurs on a loop with one doubler,
four 9000 foot, # 26 AWG spans, and an HRU that is
providing 60 mA of CPE current. Under these
conditions the HLU current drain from the 42.5 VDC
battery is 0.58 Amps. This CO current and other
related power parameters for this doubler application
are listed in Table 1. The worst case current drain for
a non-doubler application is 0.43 Amps.
7.02 The maximum shelf current drain allowed is a
function of the shelf’s 48 VDC fuse. Table 2
lists the doubler shelf deployment guidelines, as a
function of the shelf fuse, for the more popular Type
220 mechanical configuration shelves. These
guidelines limit the maximum fuse load to 85% of shelf
rated capacity. Use Table 2 when selecting the
appropriate load fuses for the Building Distribution
Fuse Bus (BDFB) when deploying HiGain equipment
in COs. CAUTION: The HLU-231’s minor ALM
option must be set to DIS (disabled) when using
the Kentrox 23” T-TERM 220 shelf. The alarm
relay contancts on pins 20 & 21 (see Figure 4) are
in conflict with the T-TERMs DSX-1 equalizer
outputs which also appear on pins 20 & 21.
7.03 The maximum HLU-231 power dissipation is
the power that is converted into heat within
the unit. It contributes to the total heat generated and
is used to determine the maximum number of shelves
per bay that do not exceed the maximum power
dissipation density in Watts/sq. ft.
7.04 In CO locations, the maximum power
dissipation for open faced, natural convection
cooled mountings is 120 W/sq. ft. as stated in NEBS
standard TR-NWT-000063 section 4.2.3. The footprint
of a 13 slot 23” SXSS shelf is 7.024 sq. ft. Thus the
maximum allowable dissipation is 840 Watts. For an
SXSS shelf with 10 slots occupied, the maximum
power dissipation is 350 (10 x 35) Watts. This limits
the number of fully loaded shelves to 2.4 per bay.
Note that this is a worst case situation since it
assumes the entire CO is subjected to the maximum
power density. More favorable conditions would permit
increasing the number of shelves per bay without
jeopardizing the CO thermal integrity.
7.05 The thermal loading limitations imposed when
using the HLU-231 in CEVs or other
enclosures are determined by applying the HLU-231
power parameters to the manufacturer’s requirements
for each specific housing.
7.06 The Power Consumption listed in Table 1 is
the total power that the HLU-231 consumes or
draws from its -48 VDC shelf power source. This
parameter is needed when the 231 is located remote
to its serving CO. It determines the battery capacity
required to maintain an 8-hour stand-by battery
reserve for emergency situations. It thus limits the
maximum number of plugs per remote enclosure. Use
this data to perform this analysis on a case by case
basis.

Issue 1, Section 150-231-134
Revision 01
Page 7
TABLE 1. POWER PARAMETERS FOR HLU-231, LIST 3D WITH DOUBLER
60 mA CPE
(Current) CO Voltage (Volts) CO Current (Amps)
Power
Consumption
(Watts)
HLU Power
Dissipation
(Watts)
OFF 42.5 0.50 22 8.25
OFF 48 0.41 22 8.25
OFF 56 0.38 22 8.25
ON 42.5 0.58 25 9.0
ON 48 0.52 25 9.0
ON 56 0.43 25 9.0
TABLE 2. DEPLOYMENT GUIDELINES FOR HLU-231, LIST 3D WITH DOUBLER
Shelf Type Shelf Fuse (Amps) Max # of Doubler Systems per shelf (60 mA CPE I ON) Max # of Doubler Systems per shelf (60 mA CPE I OFF)
-48V New Bays
(J98725P,J98725P,J98725P) 20 13 13
SXSS (CO)
(J98725CA) 10 13 13
Original 220 Bays
(J98725A,B,C,D,E&F) 3.43 5 6
Upgraded 220 Bays
(J98725A,B,C,D,E&F) 20 13 13
SXSS (80 D Cabinet) 57 8
Kentrox T-Term 220 10 13 13
PairGain HCS-417 20 14 14

Section 150-231-134
Revision 01
Page 8
8. ALARM DESCRIPTION
8.01 The normally open alarm contacts available
across pins 20 & 21 comprise the HLU-231’s
Minor Alarm output. These alarm contacts close for
any of the following alarm conditions. Note that the
front panel message which accompanies each alarm
condition is shown in bold letters before each alarm
condition. Since more than one alarm condition can
exist at any given time but only one message can be
displayed, the alarms are listed in their order of
priorities. Only the highest priority alarm is displayed if
more than one alarm condition exists.
1) ALRM LOSW: Either HDSL loop loses sync.
2) ALRM LLOS: Loss of the HLU DS1 input signal.
3) ALRM RLOS: Loss of HRU DS1 input signal.
4) ALRM H1ES: HDSL Loop 1 has exceeded the 24
hour user-selected Errored-Seconds Cyclic
Redundancy Check (CRC) threshold.
5) ALRM H2ES: HDSL Loop 2 has exceeded the 24
hour user-selected Errored-Seconds CRC
threshold.
6) ALRM DS1: The total number of bipolar violations
(BPV) at the HLU and HRU T-1 input have
exceeded the 24-hour user-selected threshold.
7) ALM MAL1(2): The margin on HDSL Loop 1 or
Loop 2 has drooped below the minimum threshold
value set by the dumb terminal MARGIN ALARM
THRES; as described in Section 9.
8.02 The HLU 231’s STATUS LED flashes RED for
the duration of a minor alarm condition.
Alarms 4, 5 & 6 can be inhibited by selecting NONE
for the Errored Seconds Alarm (ESAL) system option.
See Section 9 for System Settings information. The
MAL(X) alarm can be disabled by setting the margin
alarm threshold to 0. The MNALRM can be retired by
executing the Alarm Cut Off (ACO) option. This is
accomplished by pressing the SEL button on the front
panel. This turns the alarm off and replaces the ALRM
message by the ACO message. The second part of
the ALRM message, which defines the cause of the
alarm, remains. Both messages remain until the alarm
condition clears or another alarm occurs.
8.03 Note that when both HDSL loops lose sync
word (LOSW), a minor alarm condition exists
but because the HLU enters a self test cycling mode,
the front panel LED lights yellow instead of red and
the SELF TEST message is displayed instead of the
ALRM message.
8.04 Setting the ALM option to DIS only prevents
the alarm relay from operating on a minor
alarm event. The STATUS LED still flashes red and
the ALRM message is still displayed. See paragraph
7.02.
8.05 Pin 32, FUSEALARM, is driven to -48 V and
the front panel STATUS LED turns red
whenever the on board fuse opens.
8.06 The HLU-231’s front panel tri-color STATUS
LED has the following states:
GREEN - Normal Operation
FLASHING GREEN - HDSL Acquisition
FLASHING RED - Minor Alarm (For conditions see
Paragraph 8.01)
RED - FUSEALRM
YELLOW - Self Test in process or an HLU loopback in
effect (CREM or NLOC).
FLASHING YELLOW - The HLU is in an ARMED
state.

Issue 1, Section 150-231-134
Revision 01
Page 9
9. SYSTEM OPTION SETTINGS
9.01 The HLU-231 contains a non-volatile RAM
which stores the system option settings. No
dip-switches or jumpers are required to set the HLU-
231 configuration. The options are set via
pushbuttons on the front panel or through the RS-232
interface. The options are retained if shelf power is
lost or if the HLU-231 is unplugged. Table 3 lists the
HLU-231 option settings. Note that only those options
enclosed by quotes can be set by the front panel
buttons. All 14 options can be set via the RS-232
port. Figure 13 illustrates the set-up menu used to set
these options from the RS-232 port. The settings
shown in the second column of Figure 13 represent
the factory default settings. The third column values
(in parenthesis) indicate the other parameter options.
9.02 The SETUP (MODE and SEL) momentary
pushbuttons are used to set the four options
shown in quotes in Table 3 from the front panel. To
initiate an OPTION SETTING mode, press the MODE
button for one second and release. The message
displayed on the front panel alternates between the
system parameter and its current setting. Pressing the
SEL button steps the display through all possible
settings (one at a time) of the MODE (parameter)
being displayed. After the desired setting has been
chosen, press MODE. This does two things. First it
updates the current displayed mode to the setting
chosen. It then selects the next configurable
parameter. After the last parameter has been
selected, the displays shows CONF/NO. If the MODE
button is now pressed, none of the changed
parameters are installed. If the SEL button is pressed,
a YES message is displayed and the chosen changes
are installed. In either case the display returns to its
normal mode. The display also returns to its normal
mode, without installing any new changes, if neither
button is pressed for 30 seconds.
9.03 All 14 user options can be set to their default
values by pressing the SEL button for six
seconds. When released, the message: ”DFLT NO”
appears. To install the default values press the SEL
button again. The “YES” will follow indicating that the
default values are now in effect. To terminate this
DFLT mode without reverting the options to their
default values, press the MODE button or do nothing
for 30 seconds. The latter returns the display to its
normal state.
9.04 Pressing the MODE button for three or more
seconds causes the display to scroll through
the HLU software version number, its List # and the
type of frame pattern being received from the DSX-1,
if the FRMG option is set to AUTO. If FRMG is set to
UNFR, it displays UNFR. See Table 10 for these
additional messages. The line code parameter mimics
the line code setting LNCD: AMI or B8ZS.
9.05 The CIRCUIT ID option is set by choosing the
“H” option from the dumb terminal main menu
shown in Figure 6. The message “enter circuit ID #:
24 characters max” follows the “H” selection. Press
the RETURN key after entering the chosen set of
alpha-numeric ID characters; choose “C” to confirm.
Note if more than 24 characters are entered, a “Beep”
is emitted and only the first 24 characters are
accepted. The ID appears in all HLU screens as
shown in Figures 6 through 30. The ID does not
appear on the HRU screens when the maintenance
port is accessed at the remote unit. Note that the
Circuit ID is not set to its default (all blanks) setting
when the DFLT setting option is utilized.
9.06 To set the DS0 BLOCKING option first select
the SYSTEMS SETTINGS (“C” choice) from
the main menu. The menu shown in Figure 13
appears. Enter the letter “B” shown in parenthesis of
the DS0 blocking selection. The DS0 channels are
blocked or unblocked by entering each channel’s
number. Multiple channels can be selected by
inserting a space between each entry. After all the
new settings have been made, enter “E” for exit and
then “C” for confirm. The new choices are now
installed. If DS0 blocking is invoked in a HiGain
system that has an earlier version HRU that does not
support the blocking option, blocking will only occur at
the DS1 output of the HLU. The HRU DS1 output will
not be blocked. Also, all blocked channels are opened
for all HiGain loopback tests. This allows the standard
full bandwidth T-1 loopback tests to be performed.
9.07 To set the MARGIN ALARM THRESHOLD
select “G” from the system settings menu.
Enter the desired minimum acceptable alarm
threshold from the 0 to 15 dB range. This causes a
minor alarm to occur if either the margin on HDSL
loop 1 (MAL1) or loop 2 (MAL2) drops below the
selected threshold value. Since the margin can never
drop below 0, choosing “0” for the margin threshold
turns the margin alarm off.
9.08 The other dumb terminal system settings are
set in a similar manner. Enter the letter in
parenthesis of the parameter to be changed. Each
entry of this letter scrolls the parameter to its next
value. Press the ENTER key after each selection is
made. After all selections have been made, enter “E”
and then “C” to the resulting Confirm message. This
activates the new choices and returns control to the
main menu.

Section 150-231-134
Revision 01
Page 10
9.09 The new T-1 transceiver chip in both List 6
units allows each unit to process both B8ZS
and AMI code inputs, regardless of the DS1 code
setting (AMI or B8ZS). Earlier units caused input
BPVs if B8ZS patterns were processed while in AMI
mode. When the newer units are in AMI mode, they
can receive B8ZS but can only transmit AMI. For this
reason, mixed systems (those consisting of both List 6
and older List 1, 2, 3, 3A & 4) units will respond
differently in each direction for B8ZS inputs when in
their AMI mode.
9.10 The SELF-TEST mode that occurs when both
HDSL loops are not in sync has been
enhanced to include the input DS1 transceiver chip in
the self test procedure. This process can cause the
AIS pattern, that is normally transmitted from the HLU
during these out of sync intervals, to exhibit
occasional BPVs.
9.11 The HAIS option provides two choices for the
T-1 transmit outputs at both the HLU & HRU
for HDSL loss of sync conditions. The “1LP” choice
causes the AIS pattern to be transmitted at both T-1
outputs when either of the two HDSL loops
experience an out of sync (LOSW) condition or when
a margin alarm occurs. This choice causes the 12
channels on the surviving loop to be lost as they are
replaced by the AIS pattern. However it does allow
both down & upstream equipment to be made aware
of the loss of one HDSL loop or a loop with low
margin. This is the preferred setting to be able to
initiate an AIS state with just one conductor open in
either of the HDSL pairs. Short loops, below about 16
dB of loss at 200 KHz, can remain in sync with one
conductor open. Since the loop is still in sync, no
LOSW condition occurs. However, the margin on a
one conductor loop drops about 5 to 10 dB. Thus if
the Margin alarm is set to 5 dB below the normal
margin at turn-up, then when one conductor does
open, a minor alarm occurs and causes the AIS
condition. This alerts the maintenance personnel of
the problem. The “2LP” choice requires both HDSL
loops to be out of sync (LOSW) before the AIS signal
is transmitted. This choice preserves the integrity of
the 12 surviving channels when just one loop is lost.
9.12 All user options that affect the operation in
both the HLU & HRU, such as HAIS, SAIS &
DS0 blocking, will not be available in older versions of
the HRU that do not support these newer options.
9.13 Note that the PairGain HCS-417 & 418
shelves and some 220-configuration shelves
deployed in remote cabinets do not have external
equalizers. The EXT EQL option may not be used in
these applications.

Issue 1, Section 150-231-134
Revision 01
Page 11
TABLE 3. SYSTEM OPTION SETTINGS
Mode Selection Description
“EQL” EXT* Replaces the internal equalizer with a 12 Vp/p driver for external
equalizers.
0 Sets Equalizer to DSX-1 for 0-133 feet.
133 Sets Equalizer to DSX-1 for 133-266 feet.
266 Sets Equalizer to DSX-1 for 266-399 feet.
399 Sets Equalizer to DSX-1 for 399-533 feet.
533 Sets Equalizer to DSX-1 for 533-655 feet.
LPBK DIS Configures HiGain to ignore all in-band “smart-jack” loopback commands.
ENA* Enables HiGain to recognize all in-band “smart-jack” loopback commands.
SPLB GNLB Configures HiGain to respond to the generic 3/4 in 7 and 5/6 in 7 in-band
loopback codes.
A1LB&A2LB* Configures HiGain to respond to the Teltrend addressable repeater in-
band loopback codes.
A3LB Configures HiGain to respond to the Wescom addressable repeater in-
band loopback codes.
A4LB Configures HiGain to respond to the Wescom Mod 1 addressable
repeater in-band loopback codes.
A5LB Configures HiGain to respond to the Teltrend Mod 1 addressable
repeater in-band loopback codes.
PWRF DIS Disables powering to the HRU over the HDSL pairs.
ENA* Enables powering to the HRU over the HDSL pairs.
ZBTS ON Tells HiGain that the ESF frame is operating in its ZBTSI mode.
OFF* Tells HiGain the ESF frame is operating in its normal non-ZBTSI mode.
ESAL 17 Activates (grounds) the Minor Alarm (MNRALM) relay output contacts on
pins 20 & 21 and turns the STATUS LED to flashing red when 17 Errored
Seconds (ES) (17 HDSL CRC errors on either HDSL loop or a total of 17
BPV”s and FERR) occur within a 24-hour period.
170 Activates (grounds) the Minor Alarm (MNRALM) relay output contacts on
pins 20 & 21 and turns the STATUS LED to flashing red when 170
Errored Seconds (ES) (170 HDSL CRC errors on either HDSL loop or a
total of 170 BPVís and FERR) occur within a 24-hour period.
NONE* Prevents generation of a minor alarm due to excessive Errored Seconds.
“LBTO” NONE Disables automatic time-out cancellation of all loopbacks.
20 Sets automatic cancellation of all loopbacks to 20 minutes after initiation.
60 Sets automatic cancellation of all loopback to 60 minutes after initiation.
120* Sets automatic cancellation of all loopback to 120 minutes after initiation.
ALM DIS* Opens the alarm relay contacts, if closed, and prevents another relay
alarm closure from occurring.
ENA Enables activation of the minor alarm relay when a minor alarm condition
occurs.
Table continued on next page

Section 150-231-134
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TABLE 3. SYSTEM OPTION SETTINGS (CONTINUED)
Mode Selection Description
“LNCD” B8ZS Places both the HLU & HRU into their B8ZS modes.
AMI* Places both the HLU & HRU into their AMI modes.
“FRMG” AUTO Configures HiGain to operate in an auto-framing (AUTO) mode in which it
continuously searches the input T1 bit stream for a valid SF or ESF frame
pattern. This feature is required for fractional T1 applications (DS0
blocking) where it insures proper channel time slot alignment. While
HiGain can also process unframed data in this AUTO mode, it is
recommended that the UNFR mode be used for all unframed applications.
Using the AUTO mode for unframed applications runs the risk of
detecting “pseudo valid” frame sequences, which can affect the data
integrity.
UNFR* Configures HiGain to operate in an unframed mode. This mode disables
the auto framing process and forces HiGain to function as a transparent
bit pipe.
HAIS 2LP* Causes HiGain to transmit the AIS signal at both the HLU & HRU T1
output ports when both of the HDSL loops are not in sync (LOSW).
1LP Causes HiGain to transmit the AIS signal at both the HLU & HRU T1
output ports when either of the two HDSL loops is not in sync (LOSW) or
if a margin alarm occurs.
SAIS ENA* Causes the List 6 and 7 HRU to transmit the AIS signal towards the NI
when in NREM or SMJK loopback.
DIS Causes the List 6 HRU to transmit the signal from the network towards the
NI and the List 7 to open and terminate its NI when in its NREM or SMJK
loopback states. The AIS signal is turned off.
CONF YES Confirms that all nine operating modes are to be updated to their current
choices.
NO* Prevents the most recently selected operating mode choices form being
updated. They remain as they were before the system option settings
procedure was entered.
MARgin Alrm
Trsh 0 to 15 dB
(4*) The Margin Alarm Threshold can only be set via the RS-232 maintenance
port. It determines the minimum allowable margin below which a minor
alarm will occur.
DS0 BLK/NONE* The DS0 blocking option can only be set via the RS-232 maintenance port
with a dumb terminal. See Figure 13. The 4-character HLU front panel
only displays the status of the blocking option. NONE indicates no
channels are blocked. BLK indicates at least one channel is blocked
“xxxx” Panel Set Only these options can be set from the front panel buttons. All of the
options can only be set from the RS-232 maintenance port.
* Indicates HLU-231 factory settings. HiGain can be set to these default settings by pressing the SEL button for
6 seconds and then selecting the YES response to the resulting DFLT message.

Issue 1, Section 150-231-134
Revision 01
Page 13
10. LOOPBACK DESIGN DESCRIPTION
10.01 The HiGain family of loopbacks is shown in
Figure 4. The most important of these is the
Smart Jack loopback. It is enabled by the LPBK user
option. It configures the HRU-412 to respond to the
standard NIU 2/3 in 5 in-band loopback codes. It
should be enabled when the HRU is used to replace
an external NIU.
10.02 In addition to the SmartJack loopback, HiGain
can be configured for one of five special in-
band loopback command sequences. These are
selected from the SPLB user option shown in Figure
14.
10.03 GNLB is the HiGain Generic loopback code.
The GNLB allows in-band codes from the
network to loop-up either the HLU/NLOC (4 in 7) or
HRU/ NREM (3 in 7) towards the network. In addition,
it allows in-band codes from the Network Interface
(NI) to loop-up the HLU/ CREM (6 in 7) or
HRU/CLOC (5 in 7) towards the customer. For
doubler applications it permits looping doubler 1
towards the network NDU1 (2 in 6) or towards the
customer CDU1 (4 in 6). Doubler 2 is looped towards
the network with NDU2 (3 in 6) or towards the
customer CDU2 (5 in 6). Either loop-up condition is
terminated (looped-down) with the 3 in 5 loop-down
code. All messages must be present for five seconds
before HiGain responds. Table 4 lists the test
procedures that apply when using the GNLB mode.
10.04 The A1LB loopback selection (Table 5)
complies with that proposed for HDSL
systems in the T-1/E-1.4/92 recommendation with the
following additions:
1) Query loopback
2) IOR powerdown
3) Three loopback time-out choices
4) Initiation from either end
5) Repeating bit error signatures
6) Alternate Query loopback
These additions make A1LB identical to A2LB
described below. It is given a separate identity to
allow future T-1/E-1 enhancements to be added
without affecting A2LB.
Figure 4. HLU-231, List 3D Loopback Configurations. The most important of the HiGain family of loopback options is the
Smart-Jack loopback, which emulates the functions of a standard NID.

Section 150-231-134
Revision 01
Page 14
10.05 A2LB through A5LB are four special
addressable repeater loopback functions
which are supported by the List 6 version of HiGain.
These loopbacks provide HiGain with sophisticated
maintenance and trouble shooting tools. Tables 6 thru
9 list the details of these Special Loopback (SPLB)
functions. A2LB & A5LB are patterned after the
Teltrend addressable T-1 repeater loopbacks. A3LB &
A4LB are patterned after the Wescom addressable T-
1 repeater loopbacks. All four SPLBs have been
enhanced to handle the specific requirements of the
following HiGain customers:
A2LB (Teltrend) = Southwestern Bell (default setting)
A3LB (Wescom)=New England Tel.
A4LB (Wescom Mod 1) =New York Tel.
A5LB (Teltrend Mod 1) =Southern New England Tel.
(SNET)
10.06 A5LB differs from A2LB in that A5LB does not
block the arming code from exiting the HLU
into the network. A2LB can be configured to either
block this arming code after 2 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, it does
not need this FAR-END ACTIVATE code. A3LB
differs from A4LB in that A3LB supports the
additional 1 in 6 SmartJack loopback command.
10.07 Two additional loopback points are added for
each HDU-451 doubler that is used as shown
in Figure 6. NDU1 and NDU2 are executed towards
the network. CDU1 and CDU2 are towards the
customer. All four loopbacks can be initiated by the 16
bit in-band commands in SPLB states A1LB, A2LB &
A3LB as described in Tables 3, 4 & 7 respectively.
NDU1 and NDU2, along with the rest of the
loopbacks towards the network, can be issued form
the Loopback Menu shown in Figure 15. See
paragraph 10.09 for front panel- initiated loopbacks.
The simplest HiGain system includes two loopback
locations: The HLU and the HRU. The most complex
HiGain application includes the HLU, HRU & two in-
line HDU-451 doublers. Refer to the PairGain HiGain
Intelligent Repeater Application Note # 910 Part #
325-910-100 for more SPLB details.
10.08 HiGain may take longer than normal to
respond to inband loopback commands when
its framing mode is set to UNFR and the inband
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
HiGain to reject some sequences. This can extend the
detection interval.
10.09 Depressing both the MODE and SEL
pushbuttons on the front panel for at least
three seconds initiates a MANUAL loopback session.
This session allows the user to SEL one of eight
HiGain loopbacks. The message, MAN LPBK,
appears on the front panel display followed by the
message NLO?. If the SEL 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 button, NLO? is replaced
by ND1?. This now allows an NDU1 loopback to be
executed (if it is a doubler application) with the SEL
button. If it is not a doubler application, NRE? follows
NLO?. If this same routine is followed, all eight
loopbacks (NLOC, NDU1, NDU2, NREM, CLOC,
CDU2, CDU1 & CREM) are presented and can be
initiated in the sequence listed. Note that NDU1,
NDU2, CDU1 & CDU2 only can appear in doubler
applications. Once a loopback is executed, it can be
terminated and the next loopback option presented by
pressing the MODE button. If neither button is
pressed for a period of 30 seconds and no loopback is
in effect, this manual loopback session terminates and
the normal margin displays reappear. If any loopback
is in effect, this 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 LBTO setting. Only one loopback can
exist at any given time. Depressing both buttons,
again for 3 seconds, terminates any active loopback,
ends the MANUAL loopback session and returns the
display to normal. Note that these same loopbacks
can be initiated from RS-232 maintenance port by
choosing the LOOPBACK MODE, option D, from the
main menu. This displays the Loopback Menu, shown
in Figure 15, from which any of the eight loopbacks
can be initiated.

Issue 1, Section 150-231-134
Revision 01
Page 15
C. INSTALLATION, TEST AND MAINTENANCE
11. INSTALLATION
11.01 Upon receipt of the equipment, visually
inspect it for signs of damage. If the
equipment has been damaged in transit, immediately
report the extent of damage to the transportation
company and to PairGain.
11.02 The HLU-231 is designed to mount in a 220-
configuration ORB shelf or equivalent SXSS,
Kentrox T-Term and Wescom 342-30 shelves. The
HLU-231 slot pin-outs are shown in Figure 5.
Figure 5. HLU-231 List 3D Pin-Outs. The active pins are highlighted in black in the above illustration.

Section 150-231-134
Revision 01
Page 16
12. TEST PROCEDURES
12.01 Tables 4 through 9 provide step by step test
procedures for the HLU-231 unit as a function
of the loopback option selected. These procedures
allow verification of the integrity of the HDSL channels
at every module location as well as the DS1 channels
to the customer and the local DSX-1 interface.
12.02 The HLU 4 character front panel display has
many useful system diagnostic messages.
They are listed in Table 10. This display turns on
when power is initially applied to the 231. In order to
conserve power, it only remains on for five minutes if
neither the MODE nor SEL buttons are pressed. The
use of either button restarts the 5 minute power-
control timer.
12.03 If trouble is encountered on the DSX-1
interface, verify that the unit is making a
positive connection with the mounting assembly’s
connector. Also, verify that the pre-equalizer is
properly set. All installations should be set to the
largest value that does not exceed the distance from
the DSX-1 to the shelf
12.04 The transmit and receive T-1 DSX-1 ports
have splitting access and bridging miniature
210-series jacks as shown in Figure 5. Connecting
one cable between the two BRG jacks and another
between the two SPAN jacks splits the XMT and RCV
and creates metallic loopbacks towards both the
DSX-1 and the HLU. If plugs are inserted in both
SPAN jacks. The BRG jacks can be used to send &
receive test patterns towards the DSX-1.
TABLE 4. TEST PROCEDURES FOR GNLB OPTION
Step Action
1 Have the C.O. tester send the HRU (3 in 7) in-band loop-up for 5 seconds. Observe that the HLU
displays the “NREM” message indicating an HRU loopback is in effect (see Figure 4).
2 Have the C.O. tester transmit a T1 test signal into the HLU and verify that the returned (looped-
back) signal is error free.
3 If the above test fails, have the C.O. tester transmit the (3 in 5) in-band loop-down code. Verify
that the HLU display returns to normal.
4 Have the C.O. tester send the HLU (4 in 7) in-band loop-up for 5 seconds. Observe that the HLU
displays the “NLOC” message indicating an HLU loopback is in effect.
5 Repeat step “2”. If the test passes, the problem is in the cable pair or the HRU. If it fails, the
problem is in the C.O. equipment
6 The NREM and NLOC loopbacks can also be initiated from the front panel of the HLU with the
MODE and SEL pushbuttons. See Paragraph 10.9 for details.
7 The HLU can be looped-up from the remote location (CREM) by issuing the 6 in 7 command at
the HRU’s DS1 input port.
8 The HRU can be looped-up from the remote location (CLOC) by issuing the 5 in 7 command at
the HRU’s DS1 input port.
9 Doubler 1 can be looped-up from the remote location (CDU1) by issuing the 4 in 6 command at
the HRU’s DS1 input port.
10 Doubler 1 can be looped-up from the network location (NDU1) by issuing the 2 in 6 command at
the HLU’s DS1 input port.
11 Doubler 2 can be looped-up from the remote location (CDU2) by issuing the 5 in 6 command at
the HRU’s DS1 input port.
12 Doubler 2 can be looped-up from the network location (NDU2) by issuing the 3 in 6 command at
the HLU’s DS1 input port.

Issue 1, Section 150-231-134
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Page 17
TABLE 5. TEST PROCEDURES FOR A1LB OPTION
Step Action
1 Send into the HLU the inband ARMING and NIU (Network Interface Unit) LPBK code 11000
for at least 5 seconds, or at least 4 repetitions of the 16-bit ESF Data Link ARMING code 0001
0010 11111111.
2 Monitor the output of the HLU-231 for the return of the pattern. Return of pattern indicates that
either the HRU has looped-up (If the SMART-JACK LOOPBACK option is ENABLED) or that
an external NIU has looped up (If the SMART-JACK LOOPBACK option is DISABLED) and
that the HLU and HRU units have been ARMED. Verify that the HLU display intermittently
indicates ‘ARM and also “SMJK” if the HRU is in loopback. Also verify, if possible, that the
LOOPBACK LED of the HRU-412 is flashing, indicating that the HRU is armed or that it is on
solid, indicating that it is both armed and in loopback.
3 Once armed the HLU can be looped back (NLOC in Figure 4) by sending IOR (Intelligent
Office Repeater) LPBK activation code 1101 0011 1101 0011 for at least 5 seconds. The
tester observes the following activation response:
• 2 seconds of AIS (all ones), followed by:
• 5 seconds of returning data pattern, followed by:
• 231 logic errors (including the frame bits) occur in the returned pattern(10 errors if ILR-1
were sent), followed by:
• normal looped data. (Note that this error pattern will repeat every 20 seconds as long as
the IOR loopback pattern is being sent. This same 20 second repeat scenario also applies
to ILR, Time-Out Override and Query commands.)
The HiGain Line Unit is now in Logic Loopback (NLOC of Figure 4). The display on the HLU-
231 periodically shows NLOC (network local loop) and ARM (the HLU is still armed) in
addition to the margin displays. The Loopback Time-out option, which is user settable to
NONE, 20, 60 or 120 minutes, determines 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 is received, the “activation sequence” described in “3”
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 down is to issue the IR (Intelligent
Repeater) LPDN (loopdown) code 1001 0011 1001 0011 or to issue the NIU (Network
Interface Unit) LPDN and Disarm code 11100. The automatic time-out timer is restored during
subsequent loopback sessions.
4 Upon completion, the tester sends IOR LPDN code 1001 0011 1001 0011 to loop-down the
HiGain Line Unit. The unit remains ARMED however, as indicated by the ARM message on
the HLU-231 and the flashing of the HRU-412’s LOOPBACK LED.
Table continued on next page

Section 150-231-134
Revision 01
Page 18
TABLE 5. TEST PROCEDURES FOR A1LB OPTION (CONTINUED)
Step Action
5 Using the following codes, a NETWORK tester can activate loopbacks NLOC or NREM or
SMJK (if enabled) shown in Figure 4. A CUSTOMER tester can activate loopbacks CLOC or
CREM.
ADDRESSABLE 1 (A1LB) REPEATER LOOPBACK COMMANDS
ARMING or NIU LPBK (inband) Arming code 11000 11000..
ARMING or NIU LPBK (ESF Data
Link) Arming code 1111(F)*1111(F)0100(4)1000(8)
IR LPDN or DISARM (inband) Disarming code 11100 11100..
DISARM (ESF Data Link) Disarming code 1111(F)1111(F)0010(2)0100(4)
IOR LPBK (NLOC & CREM 231
errors) HLU Loop up 1101(D)0011(3)1101(D)0011(3)
ILR-1 LPBK (NDU1 & CDU1 10 bit
errors) Doubler-1 Loop up 1100(C)0111(7)0100(4)0001(1)
ILR-20 LPBK (NDU2 & CDU2 200
bit errors) Doubler-2 Loop up 1100(C)0111(7)0101(5)0100(4)
ILR-2 LPBK (NREM & CLOC 20 bit
errors) HRU Loop up 1100(C)0111(7)0100(4)0010(2)
IR LPDN Loop down
(HLU or HRU) 1001(9)0011(3)1001(9)0011(3)
IR QUERY LPBK Query loopback 1101(D)0101(5)1101(D)0101(5)
IR ALTERNATE QUERY LPBK Alternate Query
loopback 1101(D)0101(5)1110(E)1010(A)
TIME-OUT OVERRIDE Loopback Time-
out Override 1101(D)0101(5)1101(D)0110(6)
FAR END NIU ACTIVATE Unblock AIS &
pass 2 in 5 1100(C)0101(5)0101(5)0100(4)
IOR POWER DOWN (HLU) Removes HDSL
line power 0110(6)0111(7)0110(6)0111(7)
Note: the left most bit arrives first in all 8 sequences. The detection algorithm functions reliably
with a random 10E-3 bit error ratio (BER) on the facility. The IOR POWER DOWN code must
remain present for the duration of the power down mode. When this code is removed, HiGain
returns to its normal unlooped and unarmed state. *This is the HEX number for the 4 bit group.
6 After testing is complete, send the universal loopdown [IR (Intelligent Repeater) LPDN] code if
the system is to loopdown but remain ARMED. Send the disarm code 11100 if all the
equipment is to be looped down, disarmed and returned to normal operation. Note that the
ARMED mode has an automatic time-out of 120 minutes.
7 All of the above loopbacks can also be initiated from the front panel of the HLU with the MODE
and SEL pushbuttons. See Paragraph 10.9 for details.

Issue 1, Section 150-231-134
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Page 19
TABLE 6. TEST PROCEDURES FOR A2LB OPTION
Step Action
1 Send into the HLU the inband ARMING and NIU (Network Interface Unit) LPBK code 11000
for at least 5 seconds, or at least 4 repetitions of the 16-bit ESF Data Link ARMING code 0001
0010 11111111.
2 Monitor the output of the HLU-231 for the return of the pattern. Return of pattern indicates that
either the HRU has looped-up (If the SMART-JACK LOOPBACK option is ENABLED) or that
an external NIU has looped up (If the SMART-JACK LOOPBACK option is DISABLED) and
that the HLU and HRU units have been ARMED. Verify that the HLU display intermittently
indicates ‘ARM and also “SMJK” if the HRU is in loopback. Also verify, if possible, that the
LOOPBACK LED of the HRU-412 is flashing, indicating that the HRU is armed or that it is on
solid, indicating that it is both armed and in loopback.
3 Once armed the HLU can be looped back (NLOC in Figure 4) by sending IOR (Intelligent
Office Repeater) LPBK activation code 1101 0011 1101 0011 for at least 5 seconds. The
tester observes the following activation response:
• 2 seconds of AIS (all ones), followed by:
• 5 seconds of returning data pattern, followed by:
• 231 logic errors (including the frame bits) occur in the returned pattern(10 errors if ILR-1
were sent), followed by:
• normal looped data. (Note that this error pattern will repeat every 20 seconds as long as
the IOR loopback pattern is being sent. This same 20 second repeat scenario also applies
to ILR, Time-Out Override and Query commands.)
The HiGain Line Unit is now in Logic Loopback (NLOC of Figure 4). The display on the HLU-
231 periodically shows NLOC (network local loop) and ARM (the HLU is still armed) in
addition to the margin displays. The Loopback Time-out option, which is user settable to
NONE, 20, 60 or 120 minutes, determines 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 is received, the “activation sequence” described 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 down is to issue the IR (Intelligent
Repeater) LPDN (loopdown) code 1001 0011 1001 0011 or to issue the NIU (Network
Interface Unit) LPDN and Disarm code 11100. The automatic time-out timer is restored during
subsequent loopback sessions.
4 Upon completion, the tester sends IOR LPDN code 1001 0011 1001 0011 to loop-down the
HiGain Line Unit. The unit remains ARMED however, as indicated by the ARM message on
the HLU-231 and the flashing of the HRU-412’s LOOPBACK LED.
Table continued on next page

Section 150-231-134
Revision 01
Page 20
TABLE 6. TEST PROCEDURES FOR A2LB OPTION (CONTINUED)
Step Action
5 Using the following codes, a NETWORK tester can activate loopbacks NLOC or NREM or
SMJK (if enabled) shown in Figure 4. A CUSTOMER tester can activate loopbacks CLOC or
CREM.
ADDRESSABLE 2 (A2LB) REPEATER LOOPBACK COMMANDS
ARMING or NIU LPBK (inband) Arming code 11000 11000..
ARMING or NIU LPBK (ESF Data
Link) Arming code 1111(F)*1111(F)0100(4)1000(8)
IR LPDN or DISARM (inband) Disarming code 11100 11100..
DISARM (ESF Data Link) Disarming code 1111(F)1111(F)0010(2)0100(4)
IOR LPBK (NLOC & CREM 231
errors) HLU Loop up 1101(D)0011(3)1101(D)0011(3)
ILR-1 LPBK (NDU1 & CDU1 10 bit
errors) Doubler-1 Loop up 1100(C)0111(7)0100(4)0001(1)
ILR-20 LPBK (NDU2 & CDU2 200
errors) Doubler-2 Loop up 1100(C)0111(7)0101(5)0100(4)
ILR-2 LPBK (NREM & CLOC 20
bit errors) HRU Loop up 1100(C)0111(7)0100(4)0010(2)
IR LPDN Loop down
(HLU or HRU) 1001(9)0011(3)1001(9)0011(3)
IR QUERY LPBK Query loopback 1101(D)0101(5)1101(D)0101(5)
IR ALTERNATE QUERY LPBK Alternate Query
loopback 1101(D)0101(5)1110(E)1010(A)
TIME-OUT OVERRIDE Loopback Time-
out Override 1101(D)0101(5)1101(D)0110(6)
FAR END NIU ACTIVATE Unblock AIS &
pass 2 in 5 1100(C)0101(5)0101(5)0100(4)
IOR POWER DOWN (HLU) Removes HDSL
line power 0110(6)0111(7)0110(6)0111(7)
Note: the left most bit arrives first in all 8 sequences. The detection algorithm functions reliably
with a random 10E-3 bit error ratio (BER) on the facility. The IOR POWER DOWN code must
remain present for the duration of the power down mode. When this code is removed, HiGain
returns to its normal unlooped and unarmed state. *This is the HEX number for the 4 bit group.
6 After testing is complete, send the universal loopdown [IR (Intelligent Repeater) LPDN] code if
the system is to loopdown but remain ARMED. Send the disarm code 11100 if all the
equipment is to be looped down, disarmed and returned to normal operation. Note that the
ARMED mode has an automatic time-out of 120 minutes.
7 All of the above loopbacks can also be initiated from the front panel of the HLU with the MODE
and SEL pushbuttons. See Paragraph 10.9 for details.