Pairgain Plant series User manual

PAIRGAIN TECHNOLOGIES Section 150-231-164

Technical Practice Revision 04

Engineering - PLANT Series March 30, 1995

04 Page 1

PAIRGAIN™TECHNOLOGIES HIGAIN™LINE UNIT

MODEL HLU-231 Issue 1

List 6D, PairGain #150-1111-64, CLEI Code: T1LIE144AA

CONTENTS PAGE

A. GENERAL 2

1. INTRODUCTION 2

2. APPLICATIONS 2

3. FUNCTIONAL OPERATION 2

4. ALARMS 4

5. OPTIONS 5

6. INSTALLATION 9

7. SPECIFICATIONS 10

8. CERTIFICATION 10

9. WARRANTY 10

B. APPLICATIONS WITHOUT HIGAIN

DOUBLER HDU-451 11

1. GENERAL 11

2. POWER CONSUMPTION 11

3. LOOPBACK OPERATION 11

4. TESTING 13

5. SYSTEM MAINTENANCE MENU

SCREENS 24

C. APPLICATION WITH HIGAIN DOUBLER

HDU-451 32

1. GENERAL 32

2. POWER CONSUMPTION 32

3. LOOPBACK OPERATION 33

4. TESTING 36

5. SYSTEM MAINTENANCE MENU

SCREENS 46

Figure 1. HLU-231, List 6D 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.

CAUTION

This product incorporates static sensitive components.

Proper electrostatic discharge procedures must be

followed.

Section 150-231-164

Revision 04

Page 2

A. GENERAL

1. INTRODUCTION

1.01 The PairGain HiGain Line Unit Model HLU-231

Issue 1, List 6D (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. 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. 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.

1.02 Revision History of this practice.

Revision 04—March 30, 1995

a) Modified the data in Table 9.

b) Changed the different settings of the DS1

line code to AMI from AUTO.

c) Changes initiated by software Version 1.4.

1.03 HLU-231, List 6D features:

• Selectable DSX-1 Pre-equalizer

• -130 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

• 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

• New T1 transceiver chip

• Circuit ID option

2. APPLICATIONS

2.01 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.

2.02 The general guidelines require that each loop

have less than 35 dB of loss at 196 kHz, with

135 ohms driving and terminating impedances. 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.

3. FUNCTIONAL OPERATION

3.01 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 6D and a remotely mounted

HRU-412 HiGain Remote Unit. This provides a total

capacity of 1.568 Mbps between the two units.

3.02 A block diagram of the HLU-231 List 6D is

shown in Figure 2. The HiGain HLU-231 List 6D

receives a 1.544 Mbps DS1 data stream from the DSX-1

digital cross connect interface. The HLU-231 List 6D

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 6D recognizes Super Frame (SF) (including D4) or

Extended Super Frame (ESF) framing. When the data

is unframed, the HLU-231 List 6D arbitrarily defines a

frame bit.

3.03 The HLU-231 List 6D 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

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payloads of the HDSL channels. The HLU-231, List 6D,

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.

3.04 The received HDSL channels are processed by

the transceiver and then passed on to the HLU-

231 List 6D 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 6D

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 6D 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.

3.05 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 6D and the HRU-412 remote unit.

3.06 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.

3.07 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

6D 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.

Figure 2. HLU-231, List 6D 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.

Section 150-231-164

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3.08 The HLU-231 List 6D contains two separate

power converters. The main power supply

converts -48 VDC local battery to logic power for the

HLU-231 List 6D circuits. The line power supply

converts the -48 VDC battery to a variable -130 VDC to -

210 VDC 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.

3.09 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.

Striking the SPACE bar several times enables the HLU-

231 List 6D to automatically match the terminal line baud

rate, from 1200 to 9600 baud. Figure 6 through Figure

13 show the menu selections available from the terminal

for non-Doubler applications, and Figure 15 through

Figure 33 show the menu selections available from the

terminal for Doubler applications. Table 8 defines the

various terms used in the non-Doubler System Status

Screen, and Table 17 defines the same terms for the

Doubler System Status Screens.

4. ALARMS

4.01 The normally open alarm contacts available

across pins 20 & 21 (Figure 4) comprise the

HLU-231 List 6D 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.

1) ALRM LOSW: Either HDSL loop loses sync.

2) ALRM LLOS: Loss of the HLU-231 List 6D

DS1 input signal.

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.

Figure 4. HLU-231, Card-Edge Connectors. The active

pins are highlighted in black in the above illustration.

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3) ALRM RLOS: Loss of HRU-412 DS1 input

signal.

4) ALRM TLOS: The DS1 input to a List 6 or 7

HRU-412, whose TLOS switch option has

been enabled, is not present (LOS).

5) ALRM H1(2)ES: HDSL Loop 1 or Loop 2 has

exceeded the 24 hour user-selected Errored-

Seconds Cyclic Redundancy Check (CRC)

threshold.

6) ALRM DS1: The total number of Bipolar

Violations (BPV) at the HLU-231 List 6D or

HRU-412 T1 inputs have exceeded the 24-

hour user-selected threshold.

7) ALRM MAL 1 (2): The margin on HDSL Loop

1 or Loop 2 has dropped below the minimum

threshold value set by the terminal MARGIN

ALARM THRES; as described in Section 5.

4.02 The HLU-231 List 6D STATUS LED flashes

RED for the duration of a minor alarm condition.

Alarms 5 & 6 can be inhibited by selecting NONE for the

Errored Seconds Alarm (ESAL) system option. See

Section B Paragraph 5, and Section C Paragraph 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.

4.03 Note that when both HDSL loops lose sync word

(LOSW), a minor alarm condition exists but

because the HLU-231 List 6D 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.

4.04 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.

4.05 Pin 32, FUSEALARM, is driven to -48 V and the

front panel STATUS LED turns red whenever

the on board fuse opens.

4.06 The HLU-231 List 6D 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 4.02).

• RED - FUSEALRM.

• YELLOW - Self Test in process or an HLU-

231 List 6D loopback in effect (CREM) or

(NLOC) (Sections B Paragraph 3, and

Section C Paragraph 3).

• FLASHING YELLOW - The HLU-231 List

6D is in an ARMED state.

5. OPTIONS

5.01 The HLU-231 List 6D 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 6D. 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 6D is unplugged. Table 1 lists the

HLU-231 List 6D option settings. Figure 9 and Figure 21

illustrate the same options on the HLU-231 List 6D 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.

5.02 The SETUP (MODE and SEL) momentary

push-buttons are used to set the options from

the HLU-231 List 6D 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 the SEL 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.

Section 150-231-164

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TABLE 1. HLU-231 LIST 6D 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 Configures the HiGain system to respond to the Teltrend addressable repeater in-

band loopback codes.

A3LB Configures the HiGain system to respond to the Wescom addressable repeater in-

band loopback codes.

A4LB Configures the HiGain system to respond to the Wescom Mod 1 addressable repeater

in-band loopback codes.

A5LB Configures the HiGain system to respond to the Teltrend Mod 1 addressable repeater

in-band loopback codes.

PWRF DIS Disables powering to the HRU-412.

ENA* Enables powering to the HRU-412.

ZBTS ON Tells the HiGain system that the ESF frame is operating in its Zero Byte Time Slot

Interface (ZBTSI) mode.

OFF* Tells the HiGain system that the ESF frame is operating in its normal non-ZBTSI

mode.

ESAL 17 Activates (closes) the minor alarm relay contacts on pins 20 & 21 and flashes the red

STATUS LED when 17 Errored Seconds (ES) (17 HDSL cyclic redundancy 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 relay contacts on pins 20 & 21 and flashes the red

STATUS LED when 170 ES (170 HDSL CRC errors on either HDSL loop 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.

Table continued on next page

Issue 1, Section 150-231-164

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TABLE 1. HLU-231 LIST 6D SYSTEM OPTIONS (CONTINUED)

Mode Selection Description

ALM DIS* Opens the minor alarm relay contacts if closed, and disables activation of the minor

alarm relay 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 6D & HRU-412 independently monitor their incoming DS1 bit

streams for the Binary Eight Zero Substitution (B8ZS) pattern. If either unit detects

this pattern, 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 6D & HRU-412 into their B8ZS modes.

AMI* Places both the HLU-231 List 6D & HRU-412 into their AMI modes.

FRMG AUTO* Configures the HiGain system 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 the HiGain system can also process

unframed data in this AUTO mode, it is recommended that the unframed (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 the HiGain system to operate in an unframed mode. This mode disables

the auto framing process and forces the HiGain system to function as a transparent bit

pipe.

HAIS 2LP* Causes the HiGain system to transmit the AIS signal at both the HLU-231 List 6D &

HRU-412 T1 output ports when both of the HDSL loops are not in sync (LOSW).

1LP Causes the HiGain system to transmit the AIS signal at both the HLU-231 List 6D &

HRU-412 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 & 7 HRU-412 to transmit the AIS signal towards the Customer

Interface (CI) when in NREM or Smart-Jack loopback (see Figure 5).

DIS Causes the List 6 HRU-412 to transmit the signal from the network towards the CI &

the List 7 HRU-412 to open & terminate its RCV CI port when an HRU NREM or

Smart-Jack loopback is executed. The AIS signal is disabled (towards the NI) and the

network signal is transmitted back to the network.

CONF YES Confirms that all twelve operating modes (listed above) are to be updated to their

current selections.

NO* Prevents the most recently selected operating mode selections form being updated.

They remain as they were before the system option settings mode was entered.

MARG 0 to 15 dB The Margin Alarm Threshold can only be set via the RS-232 maintenance port with a

terminal (Figure 9 (non-Doubler) and Figure 21 (Doubler)). It determines the minimum

allowable margin below which a minor alarm can occur.

4 dB* (Default value)

Table continued on next page

Section 150-231-164

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TABLE 1. HLU-231 LIST 6D SYSTEM OPTIONS (CONTINUED)

Mode Selection Description

DS0 BLK The DS0 blocking option can only be set via the RS-232 maintenance port with a

terminal (Figure 9 (non-Doubler) and Figure 21 (Doubler)). The 4-Character HLU-231

List 6D front panel LED readout only displays the status of the blocking option. BLK

indicates at least one channel is blocked.

NONE* NONE indicates no channels are blocked.

*Indicates HLU-231 List 6D factory (default) settings.

5.03 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.

5.04 Pressing the MODE button for three or more

seconds causes the display to scroll through the

HLU-231 List 6D 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 6D, and all

14 option settings. The line code parameter is the actual

DS1 line code being received by the HLU-231 List 6D 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.

5.05 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

customer’s received data to be AMI instead of B8ZS and

thus violate the one’s density rules by having excessive

zeroes.

5.06 The following three user options cannot only be

set using a terminal: CIRCUIT ID, DS0

BLOCKING and MARGIN ALARM THRESHOLD.

5.07 The CIRCUIT ID option is set by choosing the

“H” option from the terminal MAIN MENU

Screen shown in Figure 6 for non-Doubler applications

and Figure 15 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 6D screens as

shown in Figures 7 - 13 for non-Doubler applications,

and Figures 15 - 33 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).

5.08 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 9 (for non-Doubler applications) and

Figure 21 (for Doubler applications) appears. Press B

as 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 6D. 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.

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5.09 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 6D

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 6D 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 6D during

these out of sync intervals, to exhibit occasional BPVs.

5.13 The HAIS option provides two selections for the

T1 transmit outputs at both the HLU-231 List 6D

& 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 6D & 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.

6. INSTALLATION

6.01 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

Technologies.

6.02 The HLU-231 List 6D is designed to mount 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 6D

slot pin-outs are shown in Figure 4.

6.03 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.

6.04. The HLU-231, LCD and all other HiGain HLU-

231 line units built to date are incompatible with

the newer Kentrox 224 shelves when these shelves are

optioned to connect their -V line (which is normally -48 V

to -130 V). The -V line connects to pin 40, while the

HLU-231 connects both pins 39 and 40 to the -48 V line.

Section 150-231-164

Revision 04

Page 10

7. 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 & Humidity

-40°to +65°Celsius, 5 to 95% (non-condensing)

Mounting

AT&T 220-configuration or equivalent.

Dimensions

Height: 5.9” (15 cm)

Width: 1.4” (3.5 cm)

Depth: 10” (25.4 cm)

8. CERTIFICATION

8.01 FCC compliance: The HLU-231 List 6D 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.

9. WARRANTY

9.01 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,

improper use, or installation.

9.02 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.

9.03 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.

(714) 832-9922

(800) 638-0031

Issue 1, Section 150-231-164

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B. APPLICATIONS WITHOUT USING HIGAIN

DOUBLER HDU-451

1. GENERAL

1.04 This section addresses HLU-231 List 6D

operation when used without doublers. For

applications without Doublers, the HLU-23 1List 6D is

directly connected to the HRU-412 by the two cable

pairs.

2. POWER CONSUMPTION

2.01 The three most important power demands of an

HLU-231 List 6D 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 6D, on a per slot and

per shelf basis, are as follows:

Maximum Power Dissipation:

• Per Slot = 8.0 Watts

• Per Shelf = 104 Watts

Maximum Power Consumption:

• Per Slot = 18 Watts

• Per Shelf = 234 Watts

Maximum Current Drain:

• Per Slot = 0.423 Amps

• Per Shelf = 5.5 Amps

Note that 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”.

2.02 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.

2.03 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 6D

shelf is 7.024 sq. ft. Thus the maximum bay dissipation

is limited to 840 Watts. At 104 Watts per shelf, this

limits the number of fully loaded HLU-231 List 6D

shelves to 8 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.

2.04 The thermal loading limitations imposed when

using the HLU-231 List 6D in Controlled

Environmental Vault (CEV) or other enclosures are

determined by applying the HLU-231 List 6D's power

parameters to the manufacturer's requirements for each

specific housing.

2.05 The Maximum Power Consumption is the total

power that the HLU-231 List 6D consumes or

draws from its -48 V 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 line units remote enclosure. Use

the above data to perform this analysis on a case by

case basis.

2.06 The Maximum Current Drain is the maximum

current drawn from the shelf power supply when

it is at its minimum voltage (-42.5 V). This determines

the shelf fusing requirements. HLU-231 List 6D shelves

are fused at 10 A. A fully loaded shelf of 13 HLU-231s

draws 5.5 A in the worst case. This is well within the 10

A fuse limit.

3. LOOPBACK OPERATION

3.01 The HiGain system has a family of loopback

options. The most important of these is the

“Smart-Jack” loopback which enables the HRU-412 to

respond to the standard (2/3 in 5) Smart-Jack in-band

loopback codes and thus emulate the functions of a

standard Network Interface Device (NID). This option

can be enabled or disabled from either the front panel

buttons or the terminal SYSTEM SETTINGS MENU.

3.02 In addition to the Smart-Jack loopback, the

HiGain system can be configured for one of five

special in-band loopback (“SPLB”) command

sequences. These are selected from the SPLB user

option shown in Table 1 and Figure 10 (non-Doubler

applications). The non-Doubler loopback locations are

shown in Figure 5.

3.03 “GNLB” is the HiGain system Generic loopback

code. The GNLB allows in-band codes 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

to loop-up the HLU/CREM (6 in 7) or HRU/CLOC (5 in 7)

Section 150-231-164

Revision 04

Page 12

towards the customer. Either loop-up condition is

terminated (looped-down) with the 3 in 5 loop-down

code. Both in-band codes must be present for 5

seconds before the HiGain system responds. Table 2

lists the test procedures that apply when using the

GNLB mode.

3.04 The A1LB loopback selection, Table 3, complies

with that proposed for HDSL systems in the

T1E1.4/92 recommendation with the following additions:

• Query loopback

• IOR (Intelligent Office Repeater) power-down

• Three loopback time-out choices

• Initiation from either end

• Repeating bit error signatures

• Alternate query loopback

These additions make A1LB identical to A2LB described

below. It is given a separate identity to allow future

T1/E1 enhancements to be added without affecting

A2LB.

3.05 A2LB through A5LB are four special address-

able repeater loopback functions which are

supported by the List 6D version of the HiGain system.

These loopbacks provide the HiGain system with

sophisticated maintenance and trouble shooting tools.

Table 4 through Table 7 list the details of these SPLB

functions. A2LB & A5LB are patterned after the Teltrend

addressable T1 repeater loopbacks. A3LB & A4LB are

patterned after the Wescom addressable T1 repeater

loopbacks. All four SPLBs have been enhanced to

handle the specific requirements of the following HiGain

system customers:

• A2LB (Teltrend) = Southwestern Bell

• A3LB (Wescom) = New England Telephone

• A4LB (Wescom Mod 1) = New York Telephone

• A5LB (Teltrend Mod 1) = Southern New England

Telephone (SNET)

3.06 A5LB differs from A2LB in that A5LB does not

block the arming code from exiting the HLU-231

List 6D into the network. A2LB can be configured to

either block this arming code after two seconds, and

replace it with the AIS code, or to unblock it by executing

the FAR-END ACTIVATE code. Since A5LB never

blocks the arming code from exiting the HLU-231 List

6D, it does not need this FAR-END ACTIVATE code.

A3LB differs from A4LB in that A3LB supports the

additional (1 in 6) Smart-Jack loopback command.

3.07 When T1 loopback tests are performed on the

HiGain system with metallic loopback

connections at either end, the DS1 code that exists at

the metallic loopback interface may be different from the

DS1 code being received at the opposite end when the

DS1 user code is set to AUTO. This is caused by the

fact that in the AUTO DS1 code mode, the HLU-231 List

6D & HRU-412 set their own code independent of each

other. Each end sets its transmit code to match its

receive code. Thus if one end is receiving AMI and the

other B8ZS, their codes are different. For example, if

the HRU-412 has a metallic loopback and the HLU-231

List 6D receive pattern code is changed from AMI to

B8ZS and then the all “0” pattern is sent into the HLU-

231 List 6D, the HLU-231 List 6D changes to its B8ZS

mode while the HRU-412 remains in its AMI mode and

thus loops all “0”. This causes the HRU-412 to indicate

a LOS condition which causes the HLU-231 List 6D to

output the AIS pattern.

3.08 The HiGain system may take longer than normal

to respond to in-band loopback commands when

its framing mode is set to UNFR and the in-band

commands are sent in either an SF or ESF mode. The

frame bits override the command bits and cause errors

in the command sequence. These errors cause the

HiGain system to reject some sequences. This can

extend the detection interval.

3.09 Pressing both the MODE and SEL push-

buttons on the front panel for at least

three seconds initiates a MANUAL loopback session.

This session allows the user to SEL one of four HiGain

system loopbacks. The message, “MAN LPBK”,

appears on the front panel display followed by the

message “NLO?”. If the SEL push-button is now

pressed, an “NLOC” loopback is executed and the

message changes from “NLO?” to “NLOC”. If the

MODE button is pressed instead of the SEL push-

button, “NLO?” is replaced by “NRE?”. This now allows

an ‘NREM’ loopback to be executed with the SEL push-

button. Pressing the MODE push-button two more times

yields the CRE and CLO loopback options in the

sequence listed. This interactive push-button procedure

permits any of the four HiGain loopbacks to be

executed/activated. The next loopback option can be

presented by pressing the MODE push-button however,

the previously executed loopback will remain active until

the SEL push-button is pressed and a different loopback

is activated. If neither push-button is pressed for a

period of 30 seconds and no loopback is in effect, the

manual loopback session terminates and the normal

margin displays reappear. If any loopback is in effect,

the 30-second time-out is inhibited. The active loopback

and the manual loopback session continue until the

loopback times out in accordance with the user selected

Issue 1, Section 150-231-164

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LBTO setting. Only one loopback can exist at any given

time. Pressing both push-buttons, again for three

seconds, terminates any active loopback, ends the

MANUAL loopback session and returns the display to

normal mode. Note that these same loopbacks can be

initiated from the RS-232 maintenance port by choosing

the LOOPBACK MODE, option D, from the MAIN

MENU. This displays the Loopback Menu (Figure 10),

from which any of the loopbacks can be

initiated/terminated.

4. TESTING

4.01 Table 2 through Table 7 provide step-by-step

test procedures for the HLU-231 List 6D 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.

4.02 The HLU-231 List 6D 4-character front panel

display has many useful system diagnostic

messages. They are listed in Table 8. This display

turns on when power is initially applied to the HLU-231

List 6D. To conserve power, the display only remains on

for five minutes if neither the MODE or SEL buttons are

pressed. The use of either button activates the 4-

character display and restarts the 5-minute power-

control timer.

4.03 If trouble is encountered on the HLU-231 List

6D DSX-1 interface, verify that the HLU-231 List

6D is making a positive connection with its mounting

assembly (shelf) connector. Also, verify that the HLU-

231 List 6D internal equalizer is set to TEXT for driving

the external equalizer or to the correct distance range

per Table 1 for external equalization. All installations

should be set to the largest distance range value that

does not exceed the distance from the DSX-1 to the

shelf.

4.04 The transmit and receive T1 DSX-1 ports have

splitting access and bridging miniature 210-

series jacks as shown in Figure 2. Connecting one

cable between the two bridging 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-231 List 6D. If plugs are inserted into both

SPAN jacks, the BRG jacks can be used to send and

receive test patterns towards the DSX-1.

Figure 5. HLU-231 non-Doubler 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 150-231-164

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TABLE 2. HLU-231 GNLB TEST PROCEDURES

Step Action

1 Have the CO tester send the HRU-412 (3 in 7) in-band loop-up code for five seconds. Observe that

the HLU-231 List 6D displays the “NREM” message indicating an HRU loopback is in effect (Figure

5).

2 Have the CO tester transmit a T1 test signal into the HLU-231 List 6D and verify that the returned

(looped) signal is error free.

3 If the above test fails, have the CO tester transmit the (3 in 5) in-band loop-down code. Verify that

the HLU-231 List 6D display returns to normal.

4 Have the CO tester send the HLU-231 List 6D (4 in 7) in-band loop-up for five seconds. Observe

that the HLU-231 List 6D displays the “NLOC” message indicating an HLU-231 List 6D loopback is

in effect.

5 Repeat Step 2. If the test passes, the problem is in the cable pair or the HRU-412. If it fails, the

problem is in the CO equipment.

6 The NREM and NLOC loopbacks can also be initiated from the front panel of the HLU-231 List 6D

with the MODE and SEL push-buttons (Section B Paragraph 3.09).

7 The HLU-231 List 6D can be looped-up from the remote location (CREM) by issuing the (6 in 7)

command at the HRU-412 DS1 input port.

8 The HRU-412 can be looped-up from the remote location (CLOC) by issuing the (5 in 7) command

at the HRU-412 DS1 input port.

Note 1

When T1 loopback tests are performed on the HiGain system with metallic loopback connections at either end,

the DS1 code that occurs at the metallic loopback interface may be different from the DS1 code being received

at the opposite end when the DS1 user code is set to AUTO. For example, if the HRU-412 has a metallic

loopback and the HLU-231 List 6D receive pattern code is changed from AMI to B8ZS and then the all “0”

pattern is sent into the HLU-231 List 6D, the HRU-412 remains in its AMI mode and thus loops all “0”. This

causes the HRU-412 to indicate a LOS condition which then causes the HLU-231 List 6D to output the AIS

pattern.

Note 2

The HiGain system may take longer than normal to respond to in-band commands when its framing mode is set

to UNFR and the in-band commands are sent in either an SF or ESF mode. The frame bits override the

command bits and cause errors in the command sequence. These errors cause the HiGain system to reject

some sequences. This can extend the detection interval.

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TABLE 3. HLU-231 A1LB TEST PROCEDURES

Step Action

1 Send into the HLU-231 List 6D the in-band ARMING and NI LPBK code 11000 for at least

five seconds, or at least four repetitions of the 16-bit ESF Data Link ARMING code 1111

1111 0100 1000 (FF48). (Left bit arrives first)

2 Monitor the output of the HLU-231 List 6D for the return of the pattern. Return of pattern

indicates that either the HRU-412 has looped-up (if the SMART-JACK LOOPBACK option is

ENABLED) or that an external NI has looped up (if the SMART-JACK LOOPBACK option is

DISABLED) and that the HLU-231 List 6D and HRU-412 units have been ARMED. Verify

that the HLU-231 List 6D display intermittently indicates “ARM” and also “SMJK” if the HRU-

412 is in loopback. Also verify, if possible, that the LOOPBACK LED of the HRU-412 is

flashing, indicating that the HRU-412 is armed or that it lights steadily, indicating that it is

both armed and in loopback.

3 Once armed the HLU-231 List 6D can be looped back (NLOC in Figure 5) by sending

Intelligent Office Repeater (IOR) LPBK activation code 1101 0011 1101 0011 (D3D3) for at

least five seconds. The tester observes the following activation response:

• Two seconds of AIS (all ones), followed by:

• Five seconds of returning data pattern, followed by:

• 231 logic errors (including the frame bit) 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 5). The display on the HLU-

231 List 6D periodically shows NLOC (network local loop) and ARM (the HLU-231 List 6D 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 (D5D6) 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-

231 List 6D down is to issue the IR (Intelligent Repeater) LPDN (loop-down) code 1001 0011

1001 0011 (9393) or to issue the NI 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 (9393) to loop-

down the HLU-231 List 6D. The unit remains armed however, as indicated by the ARM

message on the HLU-231 List 6D and the flashing of the HRU-412 LOOPBACK LED.

Table continued on next page

Section 150-231-164

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TABLE 3. 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 5. A customer tester can activate loopbacks CLOC or CREM.

ADDRESSABLE 1 (A1LB) REPEATER LOOPBACK COMMANDS

ARMING or NI LPBK (in-band) Arming code 11000 11000 ...

ARMING or NI LPBK (ESF Data

Link) Arming code 1111(F)*1111(F)0100(4)1000(8)

IR LPDN or DISARM (in-band) 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-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 NI 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 sequences. The detection algorithm functions reliably

with a random 10-3 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, the

HiGain system 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-231 List 6D

with the MODE and SEL push-buttons (Section B Paragraph 3.09).

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TABLE 4. HLU-231 A2LB TEST PROCEDURES

Step Action

1 Send into the HLU-231 List 6D the in-band ARMING and NI LPBK code 11000 for at least

five seconds, or at least four repetitions of the 16-bit ESF Data Link ARMING code 1111

1111 0100 1000 (FF48). (Left bit arrive first)

2 Monitor the output of the HLU-231 List 6D for the return of the pattern. Return of pattern

indicates that either the HRU-412 has looped-up (if the SMART-JACK LOOPBACK option is

ENABLED) or that an external NI has looped up (if the SMART-JACK LOOPBACK option is

DISABLED) and that the HLU-231 List 6D and HRU-412 units have been ARMED. Verify

that the HLU-231 List 6D display intermittently indicates “ARM” and also “SMJK” if the HRU-

412 is in loopback. Also verify, if possible, that the LOOPBACK LED of the HRU-412 is

flashing, indicating that the HRU-412 is armed or that it lights steadily, indicating that it is

both armed and in loopback.

3 Once armed the HLU-231 List 6D can be looped back (NLOC in Figure 5) by sending IOR

LPBK activation code 1101 0011 1101 0011(D3D3) for at least five seconds. The tester

observes the following activation response: