PairGain HLU-231 User manual

HIGAIN LINE UNIT
Model List Number Part Number CLEI Code
HLU-231 7B 150-1111-72 T1L2FKHAAA
PAIRGAIN TECHNOLOGIES, INC.
ENGINEERING SERVICES TECHNICAL PRACTICE
SECTION 150-231-172
Revision History of this practice.
Revision 02—January 31, 1997
A) Added CLEI Code

Section 150-231-172 January 31, 1997 Revision 02
Page ii PairGain Engineering - Plant Series HiGain Line Unit HLU-231
TABLE OF CONTENTS
A. GENERAL.......................................................................................................................................1
1. Description and Features....................................................................................................1
2. Applications ......................................................................................................................4
3. Functional Operation.........................................................................................................5
4. Alarms...............................................................................................................................6
5. Options..............................................................................................................................8
6. HDSL Line Voltage Option..............................................................................................14
7. Network Management.......................................................................................................14
8. Installation........................................................................................................................14
9. Specifications...................................................................................................................15
10. Certification.....................................................................................................................16
11. Warranty.........................................................................................................................16
B. APPLICATIONS WITHOUT USING HIGAIN DOUBLERS......................................................17
1. General.............................................................................................................................17
2. Power Consumption..........................................................................................................17
3. Loopback Operation .........................................................................................................18
4. Testing .............................................................................................................................20
5. System Maintenance Menu Screens..................................................................................32
C. APPLICATIONS USING HIGAIN DOUBLERS..........................................................................41
1. General.............................................................................................................................41
2. Power Consumption..........................................................................................................41
3. Loopback Operation .........................................................................................................44
4. Testing .............................................................................................................................46
5. System Maintenance Menu Screens...................................................................................57
USING THIS TECHNICAL PRACTICE
Three types of messages, identified by icons, appear in the text:
A note informs you of special circumstances.
A caution warns you of possible damage to equipment.
A warning indicates the possibility of personal injury.
Copyright 1997 PairGain Technologies, Inc.
PairGain is a registered trademark, and HiGain is a trademark of PairGain Technologies, Inc.

Revision 02 January 31, 1997 Section 150-231-172
HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 1
A. GENERAL
1. DESCRIPTION AND FEATURES
1.1 The PairGain
®
HiGain  Line Unit Model HLU-231 Issue 1, List 7B (Figure 1), is the Central Office
(CO) side of a repeater-less T1 transmission system. When used in conjunction with a HiGain
Remote Unit Model HRU-412, the system provides 1.544 Mbps transmission on two unconditioned
copper pairs over the full Carrier Serving Area (CSA) range. This line unit can be used in
applications with or without the HiGain Doubler Units.
Figure 1. HLU-231, List 7B
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 High-bit-rate Digital Subscriber Line (HDSL) transmission
technology as recommended by Bellcore TA-TSY-001210. The HiGain system complies with TR-
TSY-000063 (Network Equipment Building System (NEBS) Generic Equipment requirements) and
TR-TSY-000499 (Transport System Generic Requirements - TSGR) common requirements.

Section 150-231-172 January 31, 1997 Revision 02
Page 2 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
1.2 HLU-231, List 7B features:
• Selectable DSX-1 Pre-equalizer
• -130 V to -200 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
• Front-panel user option setup
• Front Panel DS1 splitting & bridging access
• Lightning and power cross protection on HDSL interfaces
• 784 kbps full-duplex 2B1Q HDSL Transmission on two pairs
• Front panel status indicating LED
• Automatic front-panel display blanking
• Margin threshold alarm
• HAIS & SAIS options
• Easy default setting of user options
• Circuit ID option
• Single board design
• New 200V PWRF option
• HDSL Unipolar (0, -200V), Bipolar (±100V) switch
• Can line power 3 spans (2 doublers and 1 remote)

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HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 3
1.3 The HLU-231, List 7B is identical to the HLU-231, List 7D except for an additional 200V Power
Feed (PWFD) option setting. This 200V setting forces the HLU's simplexed line voltage to its 200
volt output level for all applications.
1.4 In contrast to the List 7B, the List 7D's PWRF option has only two settings, ENABLE (ENA) and
DISABLE (DIS). The DIS prevents the HLU from ever applying its simplex line voltage to the two
HDSL pairs. This setting is used to prevent craft personnel from being exposed to any voltage while
working on the cable pairs. The ENA setting is the normal choice and is the factory default setting.
It causes the HLU to apply 130 volts to the cable pairs for all non-doubler applications and
automatically switches to its 200 volt output level for doubler applications.
1.5 The new List 7B unit has been enhanced with a third choice, identified as 200 VOLT, to the PWRF
option. It forces the HLU to its 200 volt output level for all applications. The 130 volt output is
permanently suppressed. This 200 volt output is needed to provide a 200 volt source to power
remote equipment within the HiGain family (such as PCS remote radio parts) that require more
power than is normally available from the 130 volt HDSL line voltage. The ENA option should be
used for all other doubler and non-doubler applications. Note that the Unipolar/Bipolar switch
option S2, discussed in Section 6, applies to this 200 VOLT setting as it does to the normal ENA
setting.
1.6 As with all HLU option settings, the 200 volt setting can be selected from either the front panel
option setting procedure or from the System Settings screen of the maintenance terminal interface.
The message that identifies this setting on the front panel display is "200". On the System Settings
screen it is called "200 VOLTS". The selection procedure for it is the same as for all HiGain
options.
2. APPLICATIONS
2.1 The HiGain system provides a cost-effective, easy to deploy method for delivering T1 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 T1 repeaters are not required. Cable
pair conditioning, pair separation and bridged tap removal are not required. The performance of the
List 7B is identical to that of the List 7D and is completely independent of whether or not the PWRF
option is set to ENA or 200V.
2.2 The general guidelines require that each loop have less than 35 dB of loss at 196 kHz, with 135 ohms
driving and terminating impedances. Table 1 provides a guide for the loss of various cable gauges
at 196 kHz and 135 ohms. The table applies to the HDSL cable pairs between the HLU, HRU and
HDU modules. Without specific insertion loss measurement data, add 3 dB for each bridged tap and
1 dB for each cable gauge change.
2.3 The HiGain system operates with any number of other T1, 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. The HiGain system also
provides a means of quickly deploying service in advance of fiber-optic transmission systems. With
the HiGain system, service can be provided within hours. Fiber optic systems can be installed at a
leisurely pace and cut-over from the installed HiGain system when convenient to do so. The
installed HiGain system can then be easily removed and utilized elsewhere.

Section 150-231-172 January 31, 1997 Revision 02
Page 4 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
TABLE 1. HDSL LOSS OVER CABLES
Cable Gauge Loss at 196 kHz
(db/kft) Ohms per kft
26/0.4mm 3.88 83
24/0.51mm 2.84 52
22/0.61mm 2.18 32
19/0.91mm 1.54 16
3. FUNCTIONAL OPERATION
3.1 The HiGain system uses PairGain 2-Bit 1-Quartenary (2B1Q) HDSL transceiver systems to establish
two full-duplex 784 kbps data channels between the HLU-231 List 7B and a remotely mounted
HRU-412 HiGain Remote Unit. This provides a total capacity of 1.568 Mbps between the two units.
3.2 A block diagram of the HLU-231 List 7B is shown in Figure 2. The HiGain HLU-231 List 7B
receives a 1.544 Mbps DS1 data stream from the DSX-1 digital cross connect interface. The HLU-
231 List 7B 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 List 7B
recognizes Super Frame (SF) (including D4) or Extended Super Frame (ESF) framing. When the
data is unframed, the HLU-231 List 7B arbitrarily defines a frame bit.
3.3 The HLU-231 List 7B contains a demultiplexer that generates two parallel 784 kbps 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. The HLU-231, List 7B, allocates the DSO time slots
according to the version of HRU-412 to which it is connected. Older version HRUs require the odd
DSO time slots allocated to channel 1 and the even DSO time slots to channel 2. Newer versions
allocated DSO time slots 1 through 12 to channel 1, and time slots 13 through 24 to channel 2. The 8
kbps frame bits of the DS1 stream are included on both HDSL channels. 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 echo canceler and adaptive equalizer receive the signal from the remote end in the
presence of impairments and noise on the copper pairs.
3.4 The received HDSL channels are processed by the transceiver and then passed on to the HLU-231
List 7B 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 List
7B 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 Frame Sync Word (FSW) of each channel, the
multiplexer can reconstruct the original 1.544 Mbps DS1 stream from the payloads of the two HDSL
channels. The CRC fields on the HDSL streams allow the HLU-231 List 7B to determine if errors

Revision 02 January 31, 1997 Section 150-231-172
HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 5
are present on the channel due to excessive impairments on the HDSL pairs, or due to excessive
impulse or crosstalk noise.
3.5 The multiplexer removes data link messages from the HDSL channels and passes them to the
microprocessor. This mechanism allows operations messages and status to be exchanged between
the HLU-231 List 7B and the HRU-412 remote unit.
3.6 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 Mbps with up to ±200 bps of offset.
3.7 A DSX-1 interface driver converts the DS1 channel to an Alternate Mark Inversion (AMI) or Binary
Eight Zero Substitution (B8ZS) format. The DSX-1 equalizer is programmable to five different
lengths as determined by the distance between the HLU-231 List 7B and the DSX-1 interface. This
provides CB-119 specification-compliant pulses at the DSX-1 interface over a range of 0-655 feet of
ABAM-specification cable.
3.8 The HLU-231 List 7B contains two separate power converters. The main power supply converts -48
VDC local battery to logic power for the HLU-231 List 7B circuits. The line power supply converts
the -48 VDC battery to an HDSL variable power supply that provides simplex power feed on the two
HDSL cable loops. 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. A user switch option S2 allows the line
voltage to be set to a unipolar (0,-V) or a bipolar (±V/2) mode.
3.9 A female 9-pin (RS-232) DB-9), is provided on the front panel connector (see Figure 3). This
connector provides asynchronous access to the HiGain system maintenance, provisioning and
performance monitoring firmware. The port is configured as DCE with 8 data bits, 1 stop bit and no
parity. Operator interaction with the firmware is via an ASCII terminal or a Personal Computer with
asynchronous communication software. Pressing the keyboard's space bar several times enables the
HLU-231 List 7B to automatically match the terminal line baud rate, from 1200 to 9600 baud.
Figure 7 through Figure 14 show the menu selections available from the terminal for non-Doubler
applications, and Figure 16 through Figure 34 show the menu selections available from the terminal
for Doubler applications. Table 10 defines the various terms used in the non-Doubler System Status
Screen, and Table 21 defines the same terms for the Doubler System Status Screens.

Section 150-231-172 January 31, 1997 Revision 02
Page 6 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
Figure 2. HLU-231, List 7B 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.
Figure 3. DB-9 RS-232 I/O Pin-Outs. A standard RS-232 (DB-9, female) connector on the front panel provides
access to the menu interface feature via a dumb terminal.

Revision 02 January 31, 1997 Section 150-231-172
HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 7
4. ALARMS
4.1 The normally open alarm contacts available across pins 20 & 21 (Figure 4) comprise the HLU-231
List 7B Minor Alarm output. These alarm contacts close for any of the alarm conditions listed
below. Since more than one alarm condition can exist at any given time but only one message can
be displayed, the alarms are listed as follows in their order of priorities. Only the highest priority
alarm is displayed if more than one alarm condition exists. The ALRM message precedes every
specific alarm condition display.
ALARM REASON
ALRM LOSW: Either HDSL loop loses sync.
ALRM LLOS: Loss of the HLU-231 List 7B DS1 input signal.
ALRM RLOS: Loss of HRU-412 DS1 input signal.
ALRM TLOS: The DS1 in
p
ut to a List 6 or 7 HRU-412, whose TLOS switch o
p
tion has been enabled, is not
p
resent
(LOS).
ALRM H1(2)ES: HDSL Loo
p
1 or Loo
p
2 has exceeded the 24 hour user-selected Errored-Seconds C
y
clic Redundanc
y
Check (CRC) threshold.
ALRM DS1: The total number of Bi
p
olar Violations (BPV) at the HLU-231 List 7B or HRU-412 T1 in
p
uts have
exceeded the 24-hour user-selected threshold.
ALRM MAL 1 (2): The mar
g
in on HDSL Loo
p
1 or Loo
p
2 has dro
pp
ed below the minimum threshold value set b
y
the
terminal MARGIN ALARM THRES; as described in Section 5.
4.2 The HLU-231 List 7B STATUS LED flashes RED for the duration of a minor alarm condition. The
ALRM H1(2) ES, and ALRM DS1 alarms can both be inhibited by selecting NONE for the Errored
Seconds Alarm (ESAL) system option. See Section B Paragraph 5.3, and Section C Paragraph 5.5
for System Settings information. The MAL1(2) alarm can be disabled by setting the margin alarm
threshold to 0. A Minor Alarm 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 with 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.
4.3 Note that when both HDSL loops lose sync word (LOSW), a minor alarm condition exists but
because the HLU-231 List 7B 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.
4.4 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.
4.5 Whenever the on-board fuse opens, Pin 32 (FUSEALARM) is driven to -48 V through a 1000 ohm
resistor and the front panel STATUS LED turns red.

Section 150-231-172 January 31, 1997 Revision 02
Page 8 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
4.6 The HLU-231 List 7B front panel STATUS LED shows the following status:
STATUS MEANING
GREEN Normal Operation.
FLASHING GREEN HDSL Acquisition.
RED FUSEALRM.
FLASHING RED Minor Alarm (For conditions see Paragraph 4.2).
YELLOW Self Test in process or an HLU-231 List 7B loopback in effect (CREM) or (NLOC)
FLASHING YELLOW The HLU-231 List 7B is in an ARMED state.
Figure 4. HLU-231, Card-Edge Connectors. The active pins are highlighted in black.

Revision 02 January 31, 1997 Section 150-231-172
HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 9
5. OPTIONS
5.1 The HLU-231 List 7B contains a non-volatile RAM (NVRAM) which stores the system option
settings. No dip-switches or jumpers are required to configure the HLU-231 List 7B. The options
are set via push-buttons on the front panel, or through the RS-232 interface. They are retained if
shelf power is lost or if the HLU-231 List 7B is unplugged. Table 2 lists the HLU-231 List 7B
option settings. Figure 10 and Figure 22 illustrate the same options on the HLU-231 List 7B non-
Doubler and Doubler System Settings Menu Screens, respectively. In the System Settings menu
(which is identical for both non-Doubler and Doubler applications) the settings shown represent the
factory default settings.
5.2 The SETUP (MODE and SEL) momentary push-buttons are used to set the options from the HLU-
231 List 7B Front Panel. To initiate the OPTION SETTING mode, press the MODE button at least
for one second, but less than three seconds, and release. The message displayed on the front panel
alternates between the first system parameter and its current setting. Pressing theSEL button steps
the display through all possible settings (one at a time) of the parameter being displayed. After the
desired setting has been selected, press the MODE button. This updates the current displayed mode
to the setting selected, then selects the next configurable parameter. After the last parameter has
been selected, the display shows “CONF NO” (Confirm? (Yes/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 selected 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.
5.3 All 14 user options can be set to the factory default values by pressing the SEL button for six seconds
until the message: “DFLT NO” appears. To set the default values press the SEL button while the
“DFLT NO” message is displayed. “DFLT YES” will be displayed indicating the factory default
values are now in effect. To terminate the DFLT mode without setting the factory default values,
press the MODE button or do nothing for 30 seconds. The latter returns the display to its normal
state.
5.4 Pressing the MODE button for three or more seconds causes the display to scroll through the HLU-
231 List 7B software version number, its List #, the type of frame pattern being received from the
DSX-1, and the line code setting of the HLU-231 List 7B, and all 14 option settings. The line code
parameter is the actual DS1 line code being received by the HLU-231 List 7B if the DS1 code
pattern is set to AUTO. Otherwise the line code parameter mimics either of the other two line code
settings, AMI or B8ZS.
5.5 The DS1 line code option should always be set to conform to the type of DS1 service, AMI or B8ZS,
being provided by the HiGain system. The AUTO mode, which can adapt to either AMI or B8ZS,
should only be used in applications that require it (such as when HiGain acts as a standby circuit to
DS1 circuits whose line codes are not known or may be both AMI and B8ZS) since it has the
following two limitations. The AUTO mode will induce one BPV in the DS1 bit stream whenever it
switches from AMI to B8ZS. The AUTO mode allows each HiGain end, HLU and HRU, to set its
DS1 mode to the code it is receiving at its local DS1 input port. This makes each unit’s code
independent of the DS1 code being received at the distant DS1 input port. Thus, if the line codes
being received by HiGain are different in each of the two DS1 directions, the HiGain DS1 output
codes will not match their respective DS1 input codes at the other end. This could cause the

Section 150-231-172 January 31, 1997 Revision 02
Page 10 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
customer’s received data to be AMI instead of B8ZS and thus violate the one’s density rules by
having excessive zeroes.
TABLE 2. HLU-231 LIST 7B SYSTEM OPTIONS
Mode Selection Description
EQL EXT* Replaces the internal equalizer with a 12 Vpk-pk drive source for an external equalizer.
0 Sets the Equalizer to DSX-1 for 0-133 feet.
133 Sets the Equalizer to DSX-1 for 133-266 feet.
266 Sets the Equalizer to DSX-1 for 266-399 feet.
399 Sets the Equalizer to DSX-1 for 399-533 feet.
533 Sets the Equalizer to DSX-1 for 533-655 feet.
LBPK DIS Configures the HiGain system to ignore all in-band Smart-Jack loopback commands.
ENA* Enables the HiGain system to recognize all in-band Smart-Jack loopback commands.
SPLB GNLB* Configures the HiGain system to respond to the generic (3/4 in 7) in-band loopback codes.
A1LB &
A2LB Confi
g
ures the HiGain s
y
stem to res
p
ond to the Teltrend addressable re
p
eater in-band
loopback codes.
A3LB Confi
g
ures the HiGain s
y
stem to res
p
ond to the Wescom addressable re
p
eater in-band
loopback codes.
A4LB Confi
g
ures the HiGain s
y
stem to res
p
ond to the Wescom Mod 1 addressable re
p
eater in-
band loopback codes.
A5LB Confi
g
ures the HiGain s
y
stem to res
p
ond to the Teltrend Mod 1 addressable re
p
eater in-
band loopback codes.
PWRF DIS Disables powering to the HRU-412.
ENA* Enables
p
owerin
g
to the HRU-412. The out
p
ut volta
g
e automaticall
y
ad
j
usts to -130V for
non-doubler applications and -200V for doubler applications.
200V Forces the HDSL sim
p
lexed line volta
g
e to its hi
g
her -200V out
p
ut level for all o
p
eratin
g
conditions.
ZBTS ON Tells the HiGain s
y
stem that the ESF frame is o
p
eratin
g
in its Zero B
y
te Time Slot Interface
(ZBTSI) mode.
OFF* Tells the HiGain system that the ESF frame is operating in its normal non-ZBTSI mode.
Table continued on next page

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HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 11
TABLE 2. HLU-231 LIST 7B SYSTEM OPTIONS (CONTINUED)
Mode Selection Description
ESAL 17 Activates (closes) the minor alarm rela
y
contacts on
p
ins 20 & 21 and flashes the red STATUS
LED when 17 Errored Seconds (ES) (17 HDSL c
y
clic redundanc
y
check (CRC) errors on either
HDSL loop or a total of 17 BPVs) occur within a 24-hour period.
170 Activates (closes) the minor alarm rela
y
contacts on
p
ins 20 & 21 and flashes the red STATUS
LED when 170 ES (170 HDSL CRC errors on either HDSL loo
p
or a total of 170 BPVs) 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 loopbacks to 60 minutes after initiation.
120 Sets automatic cancellation of all loopbacks to 120 minutes after initiation.
ALM DIS* O
p
ens the minor alarm rela
y
contacts if closed, and disables activation of the minor alarm rela
y
when a minor alarm condition occurs.
ENA Enables activation of the minor alarm relay when a minor alarm condition occurs.
DS1 AUTO The HLU-231 List 7B & HRU-412 inde
p
endentl
y
monitor their incomin
g
DS1 bit streams for
the Binar
y
Ei
g
ht Zero Substitution (B8ZS)
p
attern. If either unit detects this
p
attern, it enters
its B8ZS mode. It reverts back to its Alternate Mark Inversion (AMI) mode if no B8ZS
patterns are received for five seconds.
B8ZS Places both the HLU-231 List 7B & HRU-412 into their B8ZS modes.
AMI* Places both the HLU-231 List 7B & HRU-412 into their AMI modes.
FRMG AUTO* Confi
g
ures the HiGain s
y
stem to o
p
erate in an auto-framin
g
(AUTO) mode in which it
continuousl
y
searches the in
p
ut T1 bit stream for a valid SF or ESF frame
p
attern. This feature
is re
q
uired for fractional T1 a
pp
lications (DS0 blockin
g
) where it insures
p
ro
p
er channel time
slot ali
g
nment. While the HiGain s
y
stem can also
p
rocess unframed data in this AUTO mode,
it is recommended that the unframed (UNFR) mode be used for all unframed a
pp
lications.
Usin
g
the AUTO mode for unframed a
pp
lications runs the risk of detectin
g
“
p
seudo-valid”
frame sequences, which can affect the data integrity.
UNFR Confi
g
ures the HiGain s
y
stem to o
p
erate in an unframed mode. This mode disables the auto
framing process and forces the HiGain system to function as a transparent bit pipe.
Table continued on next page

Section 150-231-172 January 31, 1997 Revision 02
Page 12 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
TABLE 2. HLU-231 LIST 7B SYSTEM OPTIONS (CONTINUED)
Mode Selection Description
HAIS 2LP* Causes the HiGain s
y
stem to transmit the AIS si
g
nal at both the HLU-231 List 7B & HRU-412
T1 output ports when both of the HDSL loops are not in sync (LOSW).
1LP Causes the HiGain s
y
stem to transmit the AIS si
g
nal at both the HLU-231 List 7B & HRU-412
T1 out
p
ut
p
orts when either of the two HDSL loo
p
s is not in s
y
nc (LOSW) or if a MARGin
alarm occurs.
SAIS ENA* Causes the List 6 & 7 HRU-412 to transmit the AIS si
g
nal towards the Customer Interface (CI)
when in NREM or Smart-Jack loopback (see Figure 6).
DIS Causes the List 6 HRU-412 to transmit the si
g
nal from the network towards the CI & the List 7
HRU-412 to o
p
en & terminate its RCV CI
p
ort when an HRU NREM or Smart-Jack loo
p
back
is executed. The AIS si
g
nal is disabled (towards the NI) and the network si
g
nal is transmitted
back to the network.
CONF YES Confirms that all twelve o
p
eratin
g
modes (listed above) are to be u
p
dated to their current
selections.
NO* Prevents the most recentl
y
selected o
p
eratin
g
mode selections form bein
g
u
p
dated. The
y
remain as they were before the system option settings mode was entered.
MAR
G0 to 15 dB The Mar
g
in Alarm Threshold can onl
y
be set via the RS-232 maintenance
p
ort with a terminal
(Fi
g
ure 10 for non-Doubler and Fi
g
ure 22 for Doubler). It determines the minimum allowable
margin below which a minor alarm can occur.
4 dB* Default value
Mode Selection Description
DS0 BLK The DS0 blockin
g
o
p
tion can onl
y
be set via the RS-232 maintenance
p
ort with a terminal
(Fi
g
ure 10 for non-Doubler and Fi
g
ure 22 for Doubler). The 4-Character HLU-231 List 7B
front
p
anel LED readout onl
y
dis
p
la
y
s the status of the blockin
g
o
p
tion. BLK indicates at least
one channel is blocked.
NONE* NONE indicates no channels are blocked.
*Indicates HLU-231 List 7B factory default settings.

Revision 02 January 31, 1997 Section 150-231-172
HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 13
5.6 The following three user options cannot only be set using a terminal: CIRCUIT ID, DS0
BLOCKING and MARGIN ALARM THRESHOLD.
5.7 The CIRCUIT ID option is set by choosing the “H” option from the terminal MAIN MENU Screen
shown in Figure 7 for non-Doubler applications and Figure 16 for Doubler applications. The
message “enter circuit ID # (24 characters max):” follows the “H” selection. Press Enter after
entering the chosen set of alpha-numeric ID characters; choose Cto 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-231 List 7B screens as shown in Figures 8 - 14 for non-Doubler applications, and
Figures 16 - 34 for Doubler applications. The ID does not appear on the HRU-412 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 (see paragraph 5.03).
5.8 From the MAIN MENU Screen, to set the DS0 BLOCKING option, first press Cto select the
SYSTEMS SETTINGS MAIN MENU Screen. The menu shown in Figure 10 (for non-Doubler
applications) and Figure 22 (for Doubler applications) appears. Press Bas shown in parenthesis of
the DS0 blocking selection. The DS0 channels are blocked or unblocked by entering each channel
number. Multiple channels can be selected by inserting a space between each entry. After all the
new settings have been made, press Efor (“Exit”) and C(“Confirm”). The new choices are now
installed. If DS0 blocking is invoked in a HiGain system that has an earlier version HRU-412 that
does not support the blocking option, blocking will only occur at the DS1 output of the HLU-231
List 7B. The HRU-412 DS1 output will not be blocked. Also, all blocked channels are temporarily
“unblocked” for all HiGain system loopback tests. This allows the standard full bandwidth T1
loopback tests to be performed.
5.9 To set the MARGIN ALARM THRESHOLD select “G” from the SYSTEM SETTINGS MAIN
MENU Screen. Enter the desired minimum acceptable alarm threshold from the 0 to 15 dB range.
This causes a minor alarm to occur (Section 4) 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.
5.10 Other system settings are set using a terminal in a similar manner. Enter the key represented by the
letter in parenthesis of the parameter to be changed. Each entry of this letter scrolls the parameter to
its next value. After all selections have been made, press Eto “Exit” and Cto “Confirm” the
changes. This activates the new choices and returns control to the MAIN MENU Screen.
5.11 The new T1 transceiver chip in the List 7B allows the unit to process both B8ZS and AMI code
inputs, regardless of the DS1 code setting (AMI or B8ZS). Earlier units caused input BPV, if B8ZS
patterns were processed while in the AMI mode. When the newer units are in the AMI mode, they
can receive B8ZS but can only transmit AMI. For this reason, mixed systems (those consisting of
both List 7B and older List 1, 2, 3, 3A & 4) units will respond differently in each direction for B8ZS
inputs when in their AMI modes.
5.12 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-231 List 7B during these out of sync intervals, to
exhibit occasional BPVs.

Section 150-231-172 January 31, 1997 Revision 02
Page 14 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
5.13 The HAIS option provides two selections for the T1 transmit outputs at both the HLU-231 List 7B &
HRU-412 for HDSL loss of sync conditions. The “1LP” selection causes the AIS pattern to be
transmitted at both T1 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 from 5 to 10 dB. Thus if the Margin alarm is set to 5 dB below the
normal margin at turn-up, 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.
5.14 All user options that affect the operation in both the HLU-231 List 7B & HRU-412, such as HAIS,
SAIS & DS0 blocking, are not available in older versions of the HRU-412, List 1, 2, 3, 3A and 4,
that do not support these newer options.
5.15 The PairGain HCS-417 & 418 shelves and some 220-configuration shelves deployed in remote
cabinets do not have external equalizers. Therefore, the EXT EQL option may not be used in these
applications.
Figure 5. HDSL Line Voltage Switch S2.

Revision 02 January 31, 1997 Section 150-231-172
HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 15
6. HDSL LINE VOLTAGE OPTION
6.1 The symmetry of the HDSL line powering voltage can be set by the S2 switch, located on the printed
circuit board, as shown in Figure 5.
6.2 The factory default setting is Unipolar (-). It sets the HDSL line voltage to 0 V on loop 2 and to
either -130 V (for non-doubler applications) or -200 V (for doubler applications) on loop 1. This
setting keeps the HDSL cable pair voltage at or below ground potential, thereby avoiding corrosion
problems caused by cable voltages more positive than ground.
6.3 The bipolar selection sets the HDSL line voltage to +65 V on loop 2 and -65 V on loop 1, for non-
doubler applications. Doubler applications will have +100 V on loop 2 and -100 V on loop 1. This
setting reduces the maximum ground referenced voltage to 100 V, but applies positive voltage to the
cable pairs, which could accelerate corrosion on the cable pairs.
6.4 Setting the PWRF option to 200V forces the HDSL line voltage to the higher -200V (Unipolar) or
±100V (Bipolar) for all operating conditions.
6.5 The line voltage power supply, used for both options, is ground referenced, but also ground isolated
by 200 kohms. This ground isolation reduces problems due to induced noise currents and large surge
voltages, which are ground referenced. It also reduces ground fault currents, which improves the
product’s safety. The safety issue thus depends solely on the differential voltage across loop 1 and
loop 2, and is independent of S2’s setting.
7. NETWORK MANAGEMENT
7.1 The HLU-231, List 7B has a Network Management Control Bus available on pin 46. This allows the
7B to be managed by various PairGain Management System protocols through the HMU-319
common control card.
8. INSTALLATION
8.1 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 Technologies.
8.2 The HLU-231 List 7B mounts in a 220-configuration Office Repeater Bay (ORB) shelf or equivalent
Small Cross Section Shelf (SXSS), Kentrox T-Term, Wescom 342-30 shelves, or PairGain HLS-410
(19”) or HLS-419 (23”). The HLU-231 List 7B slot pin-outs are shown in Figure 4.
8.3 The ALM option must be disabled (DIS) when using the Kentrox 220 T-Term shelf. This is required
to resolve a conflict between the HLU alarm relay output and the Kentrox external equalizer output.
Both use the same pins, 20 and 21.
8.4 If the burn-in pin 23 is used in the user's shelf, R39, shown in Figure 5, must be removed to
disconnect the HLU's burn-in circuit from this backplane pin to avoid performance disruption.

Section 150-231-172 January 31, 1997 Revision 02
Page 16 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
9. SPECIFICATIONS
HDSL Line Code 784 kbps 2B1Q.
HDSL Output +13.5 dBm ±0.5 dB at 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 Start-up Time 30 seconds (typical), 60 seconds (maximum) per span.
One-way DS1 Delay <220 microseconds per span.
DSX-1 Line Impedance 100 ohms.
DSX-1 Pulse Output 12 V
pk
-
pk
for EXTERNAL equalizer or pre-equalized for 0-655 feet of ABAM-
specification cable.
DSX-1 Input Level +1.5 to -7.5 dBDSX.
DS1 Line Rate 1.544 Mbps ±200 bps.
DS1 Line Format AMI, B8ZS or ZBTSI.
DS1 Frame Format ESF, SF or UNFR.
Maximum Power Consumption 18 Watts (without Doubler); 35 Watts (with Doubler).
Maximum Heat Dissipation 8 Watts (without Doubler); 12.5 Watts (with Doubler).
Fusing Internal; connected to “FUSE-ALARM” output on pin 32.
HDSL Span Voltage -130 to -210 VDC.
Margin Indicator Displays HDSL span SNR margin for both HDSL spans relative to 10-7 BER
operation.
Electrical Protection Secondary surge protection on DS1 & HDSL ports. Power cross protection on
HDSL ports.
Operating Temperature -40°to +149°F (-40°to +65°C)
Operating Humidity 5 to 95% (non-condensing)
Mounting AT&T 220-configuration or equivalent.
Dimensions
Height: 5.9 inch (15 cm)
Width: 1.4 inch (3.5 cm)
Depth: 10 inch (25.4 cm)
Weight 1 lb. 14 oz.

Revision 02 January 31, 1997 Section 150-231-172
HiGain Line Unit HLU-231 PairGain Engineering - Plant Series Page 17
10. CERTIFICATION
10.1 FCC compliance: The HLU-231 List 7B was tested and found to comply with the limits for 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 electrical
interference in which case the user will be required to correct the interference at his own expense.
11. WARRANTY
11.1 PairGain Technologies warrants this product to be free of defects and to be fully functional for a
period of sixty (60) 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, improper use, or installation.
11.2 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.
11.3 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.
2120 Ritchey St.
Santa Ana, CA 92705-5101
ATTN.: Customer Repair Facility
[phone]
[phone]

Section 150-231-172 January 31, 1997 Revision 02
Page 18 PairGain Engineering - Plant Series HiGain Line Unit HLU-231
B. APPLICATIONS WITHOUT USING HIGAIN DOUBLERS
1. GENERAL
1.4 This section addresses HLU-231 List 7B operation when used without doublers. For applications
without Doublers, the HLU-231 List 7B is directly connected to the HRU-412 by the two cable pairs.
2. POWER CONSUMPTION
2.1 The three most important power demands of an HLU-231 List 7B on the shelf power supply are its
maximum power consumption, its maximum power dissipation and its maximum current drain.
These three parameters for the HLU-231 List 7B, on a per slot and per shelf basis, are as follows:
POWER DISTRIBUTION PER SLOT PER SHELF
Maximum Power Dissipation: 7.0 Watts 91 Watts
Maximum Power Consumption: 16 Watts 208 Watts
Maximum Current Drain: 0.4 Amps 5.2 Amps
The worst case conditions under which these parameters were measured
include a 9,000 ft., AWG 26 loop, 60 mA of Customer Premier Equipment (CPE)
current, a fully loaded 13 slot shelf, and a -42.5 V shelf battery voltage with
HLU-231, 4-character display “OFF”.
2.2 The Maximum Power Dissipation measures the power that is converted into heat build up within the
unit. It contributes to the total heat generated in the space around the unit. It is used to determine
the maximum number of fully loaded shelves per bay that does not exceed the maximum allowable
power dissipation density in Watts/sq. ft.
2.3 In Central Office locations, the maximum power dissipation for open faced, natural convection
cooled mountings is limited to 120 Watts/sq. ft. per Section 4.2.3 of the NEBS standard TR-NWT-
000063. The footprint of a standard 13 slot 23” HLU-231 List 7B shelf is 7.024 sq. ft. Thus the
maximum bay dissipation is limited to 8 40 Watts. At 91 Watts per shelf, this limits the number of
fully loaded HLU-231 List 7B shelves to 9 per bay. Note that this is a worst case situation in that it
assumes the entire Central Office is subjected to the maximum power density. Conditions other than
these worst case ones would permit increasing the number of shelves per bay without jeopardizing
the CO thermal integrity.
2.4 The thermal loading limitations imposed when using the HLU-231 List 7B in Controlled
Environmental Vault (CEV) or other enclosures are determined by applying the HLU-231 List 7B's
power parameters to the manufacturer's requirements for each specific housing.