Multitech MT56DSU-R, MultiDSU56K Owner's Manual

TM

MultiDSU56K

Rack Mount Multi-Rate DSU

Model MT56DSU-R

Owner's Manual

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Owners Manual

P/N 82023101, Rev. B

Model No. MT56DSU-R

This publication may not be reproduced, in whole or in part, without prior
expressed written permission from Multi-Tech Systems, Inc. All rights
reserved.

Copyright © 1995, by Multi-Tech Systems, Inc.

Multi-Tech Systems, Inc. makes no representations or warranties with
respect to the contents hereof and specifically disclaims any implied
warranties of merchantability or fitness for any particular purpose. Fur­thermore, Multi-Tech Systems, Inc. reserves the right to revise this
publication and to make changes from time to time in the content hereof
without obligation of Multi-Tech Systems, Inc. to notify any person or
organization of such revisions or changes.

Record of Revisions

Revision Description

A Manual released. All pages at Revision A.

(06/07/93)

B Manual revised to change cable port numbers and
build
(01/09/95) instructions

Trademarks

Multi-Tech and the Multi-Tech logo are trademarks of Multi-Tech Sys­tems, Inc.
DATAPHONE® is a registered trademark of AT&T.

Multi-Tech Systems, Inc.

2205 Woodale Drive

Mounds View, Minnesota 55112 USA

[phone] or [phone]

Fax [phone]

Tech Support [phone]

BBS [phone] or [phone]

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Contents

Chapter 1 - Introduction and Description

1.1 Introduction ............................................................................... 6

1.2 About This Manual ................................................................... 6

1.3 Description ................................................................................ 7

1.4 CSU/DSU Basics ..................................................................... 8

1.4.1 DSU Functions .............................................................. 8

1.4.2 CSU Functions .............................................................. 8

1.5 Features .................................................................................... 9

1.6 FCC Regulations for Telephone Line Interconnection ..... 10

1.7 Specifications.......................................................................... 12

Chapter 2 -Hardware Installation

2.1 Introduction ............................................................................. 16

2.2 Default DIP Switch and Jumper Settings ........................... 16

2.2.1 12 -Position DIP Switch (# 1-12) .............................. 17

2.2.2 4-Position DIP Switch (# 13-16) ............................... 17

2.2.3 RS232/V.35 Shunt ....................................................... 17

2.3 Changing the Default DIP Switch Settings ........................ 18

2.4 Installation Procedure ........................................................... 20

Chapter 3 - Operation

3.1 Introduction ............................................................................. 24

3.2 Options .................................................................................... 24

3.2.1 Data Rate ..................................................................... 24

3.2.2 Async/Sync .................................................................. 24

3.2.3 Anti-Streaming ............................................................. 25

3.2.4 Elastic Store ................................................................. 25

3.2.5 System Status.............................................................. 26

3.2.6 Circuit Assurance ........................................................ 2 6

3.2.7 Clocking ........................................................................ 27

3.2.8 RTS Forced On ........................................................... 27

3.2.9 DSR Forced On ........................................................... 28

3.2.10 Async Word Length .................................................... 28

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iii

3.2.11 Normal/Diagnostics ..................................................... 28

3.3 LED Indicators ........................................................................ 29

3.4 Functions ................................................................................. 29

3.4.1 Local Area Data Set Applications ............................. 29

3.4.2 Off-Net Extension Applications ................................. 30

Chapter 4 - Troubleshooting

4.1 Introduction ............................................................................. 32

4.2 LED Indicators ........................................................................ 32

4.2.1 RCV Indicator .............................................................. 33

4.2.2 XMT Indicator ............................................................... 3 3

4.2.3 CD Indicator ................................................................. 33

4.2.4 56K Indicator ................................................................ 33

4.2.5 19.2 Indicator ............................................................... 33

4.2.6 CTS Indicator ............................................................... 33

4.2.7 RTS Indicator ............................................................... 34

4.2.8 NS Indicator ................................................................. 34

4.2.9 TM Indicator ................................................................. 34

4.2.10 OOS Indicator .............................................................. 3 4

4.3 Diagnostic Tests ..................................................................... 35

4.3.1 Local Loopback Test ................................................... 35

4.3.2 Digital Loopback Test ................................................. 36

4.3.3 Digital Loopback With Test Pattern Test.................. 37

4.3.4 Test Pattern Test.......................................................... 38

4.3.5 DSU Loopback Test .................................................... 3 9

4.3.6 DSU Back-to-Back Test ............................................. 40

Chapter 5 - Warranty, Service and Tech Support

5.1 Service ..................................................................................... 42

5.2 Limited Warranty .................................................................... 4 2

5.3 Tech Support and BBS.......................................................... 43

5.4 Recording DSU Information ................................................. 4 3

Appendixes

Appendix A - Application Examples ............................................... 46

Appendix B - Interface Signals and Connector Pinouts ............. 50

Glossary

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TM

MultiDSU56K

Chapter 1 - Introduction and Description

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MT56DSU-R Owner's Manual

1.1 Introduction

Congratulations! Your new MT56DSU-R is one of the finest DSU/

CSUs available today. As a combined CSU (Channel Service Unit)

and DSU (Data Service Unit), it provides a direct connection to the

DATAPHONE

®

Digital Service (DDS) network. The MT56DSU-R
connects a computer or Data Terminal Equipment (DTE) to remote
equipment using DDS network lines at 2400, 4800, 9600, 19200 and
56000 bps speeds for point-to-point and multi-point service.

1.2 About This Manual

This manual contains five chapters and two appendixes. In addition,
there is a Glossary and an Index at the end of this manual. The
information in this manual is provided as described below.

Chapter 1 - Introduction and Description contains an introduction
to the MT56DSU-R product and its features and functions.

Chapter 2 - Hardware Installation provides configuration and
installation procedures.

Chapter 3 - Operation describes the functional features and options
of the MT56DSU-R.

Chapter 4 - Troubleshooting explains what to do if your
MT56DSU-R encounters problems in operation.

Chapter 5 - Service, Warranty and Tech Support defines
procedures to follow if the troubleshooting steps in Chapter 4 do not
fix the problem.

Appendix A - Applications Examples illustrates several DSU/CSU
uses that may help in understanding your particular installation site.

Appendix B - Interface Signals lists the various electronic signals
and connector pinouts related to the MT56DSU-R.

6

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Chapter 1 - Introduction and Description

1.3 Description

The MT56DSU-R is a rack-mounted DSU/CSU that is easy to
operate and has the features to allow flexibility in meeting your
transmission requirements. The DDS is a service for transmission of
digital signals via digital transmission facilities exclusively. The
MT56DSU-R is designed to meet AT&T Technical Publication 62310
requirements. As such, the MT56DSU-R provides all of the functions
required on the customer side of the network.

The MT56DSU-R provides user selection of synchronous data
communications at rates of 2400, 4800, 9600, 19200 and 56000
bps, and asynchronous data communications rates up to 19200
bps. It provides three separate interface connections (RS232C, V.35
and DDS).

You will find the MT56DSU-R easy to install, use and maintain. It is
recommended that you read the entire manual early in your
experience with the MT56DSU-R so you can appreciate all of the
MT56DSU-R features and options.

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MT56DSU-R Owner's Manual

1.4 CSU/DSU Basics

A DSU (Data Service Unit) and a CSU (Channel Service Unit) are
typically connected to provide the interface between a DTE (data
terminal equipment) and the DDS (Digital Data Service) or other
four-wire network.

The DSU is used to process serial synchronous or asynchronous
digital data over the DDS network or other four-wire unloaded
twisted-pair wiring network.

The MT56DSU-R can transmit data at 56000, 19200, 9600, 4800
and 2400 bps in multi-point and point-to-point applications.

The MT56DSU-R contains the functions of a Data Service Unit
(DSU) and a Channel Service Unit (CSU) in a single package.

1.4.1 DSU Functions

The DSU encodes data as pulses on the communications line by
converting the customer data stream to bipolar format for
transmission over the digital network.

1.4.2 CSU Functions

The CSU is used to terminate the digital circuit at the customer site.
It performs line conditioning functions, ensures network compliance
with FCC rules, and responds to test commands (either from the
telco central office (CO) or from the CSU).

The figure below shows the MT56DSU-R in a basic DDS network
installation.

Basic DSU/CSU Configuration

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Figure 1-1.

Chapter 1 - Introduction and Description

1.5 Features

The MT56DSU-R provides many useful features. Standard features
include V.35 and RS232 connections and either synchronous and
asynchronous transmission; synchronous at rates up to 56000 bps
and asynchronous up to 19200 bps; selectable digital data rates
that match the services offered by the carriers. Other features
include user-selectable clocking options, elastic store for analog off­net extensions, anti-streaming, and RTS and DSR signal forced-on
selection.

Your Multi-Tech DSU/CSU provides the following features:

 supports direct connection to the DATAPHONE® Digital Data

Service (DDS) or compatible network

 selectable sync speeds of 2400, 4800, 9600, 19200 and 56000

bps
 selectable async speeds of 2400, 4800, 9600, and 19200 bps
 point-to-point and multipoint operation
 Standard RS232C, V.35 and DDS interfaces provided
 anti-streaming (for multi-point operations)
 elastic store (for analog off-net extensions)
 system status
 circuit assurance
 multiple selectable clocking

* External clocking

* Internal clocking

* DDS (slave) clocking
 RTS signal forced on selection
 DSR signal forced on selection
 multiple MT56DSU-R activated diagnostic tests:

* Local loopback test

* Digital loopback test

* Test pattern generator/detector
 multiple telco-activated diagnostic tests:

* DSU loopback test

* CSU loopback test

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MT56DSU-R Owner's Manual

1.6 FCC Regulations for Telephone Line
Interconnection

1. This equipment complies with Part 68 of the FCC rules. On the
outside surface of the rack is a label that contains, among other
information, the FCC registration number and ringer
equivalence number (REN). If requested, this information must
be provided to the telephone company.

2. As indicated in Appendix B, the suitable jack (USOC)
connection arrangement for this equipment is shown. If
applicable, the facility interface codes (FIC) and service order
codes (SOC) are shown.

3. The ringer equivalence number (REN) is used to determine the
quantity of devices which may be connected to the telephone
line. Excessive REN's on the telephone line may result in the
devices not ringing in response to an incoming call. In most, but
not all areas, the sum of the REN's should not exceed five (5.0).
To be certain of the number of devices that may be connected
to the line, as determined by the total REN's, contact the
telephone company to determine the maximum REN for the
calling area.

4. If this equipment causes harm to the telephone network, the
telephone company will notify you in advance. But if advance
notice isn't practical, the telephone company will notify the
customer as soon as possible. Also, you will be advised of your
right to file a complaint with the FCC if you believe it is
necessary.

5. The telephone company may make changes in its facilities,
equipment, operation, or procedures that could affect the
operation of the equipment. If this happens, the telephone
company will provide advance notice in order for you to make
necessary modification in order to maintain uninterrupted
service.

6. If trouble is experienced with this equipment (the model of
which is indicated below) please contact Multi-Tech Systems,
Inc. at the address shown below for details of how to have
repairs made. If the trouble is causing harm to the telephone
network, the telephone company may request you remove the
equipment from the network until the problem is resolved.

10

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Chapter 1 - Introduction and Description

7. No repairs are to be made by you. Repairs are to be made only
by Multi-Tech Systems or its licensees. Unauthorized repairs
void registration and warranty.

8. This equipment cannot be connected to public coin service
provided by the telephone company. (Contact the state public
utility commission, public service commission or corporation
commission for information.)

Manufacture: Multi-Tech Systems, Inc.
Model number: MT56DSU-R
FCC Registration No.: AU7USA-18883-DE-N
Ringer Equivalence: N/A
Modular Jack (USOC) RJ48S
Service Center in U.S.A.: Multi-Tech Systems, Inc.

2205 Woodale Drive
Mounds View, MN 55112
[phone] or
[phone]
U.S. Fax [phone]

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MT56DSU-R Owner's Manual

1.7 Specifications

Model Number MT56DSU-R

Device Operation combined DSU and CSU

Data Rates

Synchronous 2400, 4800, 9600, 19200, 56000 bps
Asynchronous 2400, 4800, 9600, 19200 bps

Interfaces RS232C, V.35, DDS

Temperature 0 to 50o C

Humidity 95% (non-condensing)

Dimensions 0.75" H x 5.5" W x 10.4" D

1.8 cm H x 13.5 cm W x 26 cm D

Weight 0.6 Lbs. (0.3 Kg.)

CertificationFCC Part 15 Class A

FCC Part 68
UL Listed

Compatibility AT&T Pubs 62310 and 41450

FIC Codes 04DU5-24 2.4 Kbps digital interface

04DU5-48 4.8 Kbps digital interface
04DU5-96 9.6 Kbps digital interface
04DU5-19 19.2 Kbps digital interface
04DU5-56 56 Kbps digital interface

USOC Jack RJ48S

Transmitter/Receiver

Modulation bipolar return to zero
Transmit Level 1.4V peak (+6dBm) into 135 Ohm at 2400,

4800,19200, and 56000 bps

0.7V peak (0 dBm) into 135 ohm at 9600

bps

Output Impedance 135 ohms

Receive Levels +6 to -40 dbm at 2400 bps

+6 to -40 dBm at 4800 bps
0 to -40 dBm at 9600 bps
+6 to -40 dBm at 19200 bps
+6 to -45 dBm at 56000 bps

12

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Chapter 1 - Introduction and Description

Input Impedance 135 ohms

Delay Times (in msecs.)

RTS/CTS DCD on DCD off

2400 8.1 7.5 7.0
4800 4.3 2.6 3.5
9600 2.2 1.6 1.5
19200 1 0.8 0.7
56000 0.4 0.3 0.2

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MT56DSU-R Owner's Manual

14

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TM

MultiDSU56K

Chapter 2 -Hardware Installation

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MT56DSU-R Owner's Manual

2.1 Introduction

This chapter provides the information needed to configure and
install the MT56DSU-R in a Multi-Tech Systems CC216G modem
rack. This manual assumes the reader is familiar with the function
and operation of data communications equipment and is technically
qualified to provide installation service.

2. 2 Default DIP Switch and Jumper Settings

The MT56DSU-R printed circuit board contains a 12-position DIP
switch block which is labeled 1 through 12 and a 4-position DIP
switch block which is labled 13 through 16 as shown in Figure 2-1.
They are located behind the LEDs on the front of the board. Each
individual switch is numbered and can be in either the up (OPEN) or
down (CLOSED) position.

The MT56DSU-R is shipped from the factory with the configuration
DIP switches set to the most common settings.

The factory-set (default) settings are: 56K Data Rate, DDS Clocking,
RTS Forced On, DSR Forced On, Sync Mode, Loopback Test
Disabled, Test Pattern Disabled, Circuit Assurance Disabled, System
Status Disabled, 10-Bit Async Word Length, Elastic Store Disabled,
and Anti-Streaming Disabled. If you need to change any of these
settings, refer to the Changing Defaults sections below.

The MT56DSU-R switches are shown below.

MT56DSU-R Board Layout

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Figure 2-1.

Chapter 2 - Hardware Installation

2.2.1 12 -Position DIP Switch (# 1-12)

The 12-position DIP switch is used to set data rate, clocking, RTS
control, DSR control, and Async/Sync operation, diagnostic modes
(Loopback Test, Test Pattern ), Circuit Assurance, and System
Status. The default settings are shown in Table 2-1. If you want to
make changes to one of these settings, refer to section 2.3.

2.2.2 4-Position DIP Switch (# 13-16)

The 4-position DIP switch is used to select Async Word Length,
Elastic Store, and Anti-Streaming options. The defaults are 10-Bit
Async Word Length, Elastic Store disabled, and Anti-Streaming
disabled. If changes to these settings are required, refer to section

2.3.

2.2.3 RS232/V.35 Shunt

Data terminal equipment with either a RS232 or V.35 interface can
be connected to the DB25 connector on the backplane of the rack.
The 16-pin shunt on the back of the MT56DSU-R board must be
placed in either the "V.35 position or the "RS232" position. The
interface is determined by the position of this 16-pin shunt. The
MT56DSU-R is shipped from the factory with the 16-pin shunt in the
RS232 position.

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17

MT56DSU-R Owner's Manual

2.3 Changing the Default DIP Switch Settings

Use Table 2-1 to determine the DIP switch setting changes required
for your MT56DSU-R to operate in your particular environment.
You may want to record your switch setting changes for future
reference (e.g., troubleshooting, equipment moves/changes, calling
Tech Support). The DIP switches are illustrated in Figure 2-1.

The factory default settings are indicated by an * in the Table 2-1.

Table 2-1. MT56DSU-R Switch Settings

Switch Description

Data Rate (in bps)

2400 4800 9600 19.2K 56K (*)

-1 Down Down Down Down Up *

-2 Down Up Down Up Up *

-3 Down Down Up Up Up *

Clocking

Internal External DDS (*)

-4 Up Down Down *

-5 Up Down Up *

-6 Up - RTS controlled by DTE

Down - RTS forced On *

-7 Up - DSR depends on the status of the link

Down - DSR forced on *

-8 Up - Synchronous operation *

Down - Asynchronous operation

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RTS Control

DSR Control

Async/Sync Operation

Chapter 2 - Hardware Installation

Table 2-1. MT56DSU-R Switch Settings (Cont'd)

Switch Description

Normal/Diagnostics Mode

-9 Up - normal operating mode *

Down - Loopback Test enabled

-10 Up - normal operating mode *

Down - Test Pattern enabled

Link Status Options

-11 Up - Circuit Assurance disabled *

Down - Circuit Assurance enabled

-12 Up - System Status disabled *

Down - System Status enabled

Async Word Length

9-Bit 10-Bit* 11-Bit

-13 Up Down * Up

-14 Down Up * Up

Elastic Store

-15 Up - Elastic Store disabled *

Down - Elastic Store enabled

-16 Up - Anti-Streaming enabled

Down - Anti-Streaming disabled *

* Factory default selection

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Anti-Streaming

19

MT56DSU-R Owner's Manual

2.4 Installation Procedure

After your CC216G modem rack has been installed in your computer
cabinet or in a stand-alone cabinet of your choosing, the MT56DSU­R can be inserted into the rack. Refer to the Rack Mounted Modems
Owner's Manual for rack installation procedures. Then, perform the
following procedure in Table 2-2 to install the MT56DSU-R.

Table 2-2. Installation

1. Verify that the DIP switches on the MT56DSU-R are set for your
particular configuration; refer to Table 2-1.

2. Before the MT56DSU-R is inserted into the modem rack, the
16-pin shunt on the back of the board needs to be in correct
position. If the MT56DSU-R is being connected to a RS232
interface, the 16-pin shunt needs to be placed in the "RS-232"
position. If the MT56DSU-R is being connected to a V.35
interface, place the 16-pin shunt in the "V.35" position.

3. Determine which slot the MT56DSU-R board is going to be
placed in the rack. Apply the DSU LED sticker to the door, refer
to the Rack Mounted Modems Owner's Manual for the notes
about the CC216G.

4. Open the door of the modem rack.

5. Ensure that the MT56DSU-R board is positioned so that the
LEDs are toward the top of the board, insert the board in the
slot you have choosen to add the DSU LED sticker. The board's
gold edge connector will mate with the rack's backplane. The
edge connector is offset so that the board cannot be inserted
incorrectly.

6. To connect the DTE to the MT56DSU-R using an RS232 cable,
connect the cable to the RS232 port on the DTE and the other
end to the DB25 connector on the back of the rack. Refer to the
Rack Mounted Modems Owner's manual for cable connections.

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Chapter 2 - Hardware Installation

Table 2-2. Installation (cont'd)

7. To connect the DTE to the MT56DSU-R using a V.35 interface,
connect the V.35 Interface Adapter cable (CADSUR35) supplied
by Multi-Tech to the V.35 interface on the DTE and the other
end to the DB25 connector on the back of the rack. Refer to
Appendix A in this manual for V.35 Interface Adapter cable
information. Refer to the Rack Mounted Modems Owner's
manual for cable connections on the rack.

8. To connect the phone line to the MT56DSU-R using the phone
cable supplied by Multi-Tech, connect the DB9 connector of the
cable to the DB9 connector on the rack and the RJ-48
connector to the wall jack. Refer to Appendix A in this manual
for the phone cable information. Refer to the Rack Mounted
Modems Owner's manual for the DB9 connection on the rack.

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MT56DSU-R Owner's Manual

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MultiDSU56K

Chapter 3 - Operation

TM

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MT56DSU-R Owner's Manual

3.1 Introduction

This chapter provides information on the operating functions of the
MT56DSU-R. During normal operation the MT56DSU-R requires no
operator intervention.

Many of the optional features of the MT56DSU-R are selected by
setting a switch. Please refer to changing the default DIP switch
settings in Installation (Chapter 2) to change your particular
environment.

3.2 Options

The switchable features of the MT56DSU-R are:

 Data Rate  Clocking
 Async/Sync  RTS Forced On
 Anti-Streaming  DSR Forced On
 Elastic Store  Async Word Length
 System Status  Normal/Diagnostics
 Circuit Assurance

The MT56DSU-R has a pre-configured (default) setting for each of
these options when shipped from the factory. Chapter 2 of this
manual covers the changing of these option DIP switches. Chapter 4
covers the Normal/Diagnostic switch function. The following sections
describe the option in terms of the operation of the MT56DSU-R in a
DDS or other 4-wire network.

3.2.1 Data Rate

This option allows selection of the MT56DSU-Rs data transmission
rate. The data rate selected here must match the DDS or other 4­wire network line rate that you subscribed for with your telco.

The default for this function is a data rate of 56K bps. (Refer to
Chapter 2 for option switch selection.)

3.2.2 Async/Sync

This option allows selection of the MT56DSU-Rs type of data
transmission used. The transmission type selected here must match
the DTE. The default is sync (synchronous data transmission).

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Chapter 3 - Operation

3.2.3 Anti-Streaming

This option is typically enabled on remote DSUs using multi-point
lines. When enabled, the anti-streaming feature prevents a
streaming (jammed) DTE from affecting the communications from
remote sites(in a multi-point circuit) that are operating properly.

When Anti-Streaming is enabled, the MT56DSU-R will detect when
the DTE device holds RTS (Request To Send) on for longer than 20
seconds. The MT56DSU-R then forces RTS and CTS off internally
and sends the DDS Idle Channel signal to the network. The DTEs
interface is ignored until the streaming DTE is repaired. The RTS
LED is continuously lit and the CTS LED is off when a streaming
DTE has been detected.

The default for this function is Anti-Streaming disabled. (Refer to
Chapter 2 for changing the default DIP switch settings.)

3.2.4 Elastic Store

This function allows the MT56DSU-R to compensate for small timing
phase drifts that occur in applications using analog modems for
off-net (non-DDS) extensions. An analog off-net extension
application is described in Appendix A. This option should be
enabled on all MT56DSU-Rs that are connected to analog modems.

Notes for off-net (elastic store enabled) sites:

 a special DCE-DCE cross-over cable is required (not supplied

by Multi-Tech).

 the modem located with the MT56DSU-R must be set for

external timing. The modem located at the far end of the off-net
extension must be set for slave timing.

 with applications using controlled carrier, the CTS delay of the

far-end modem of the off-net extension must be set for a longer
period than the MT56DSU-Rs CTS delay time.

The default for this function is Elastic Store disabled. (Refer to
Chapter 2 for changing the default DIP switch settings.)

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MT56DSU-R Owner's Manual

3.2.5 System Status

With this option enabled, the MT56DSU-R conditions the DSR
signal with additional parameters to provide added information to
the connected DTE concerning the Ready status of the
communications channel. Normally when this option is enabled, this
signal is on when the MT56DSU-R is powered on and not in test
mode.

On most modems, the Data Set Ready (DSR) signal at the DTE
interface is used to provide a basic indication of the modem actually
being ready to transfer data. The System Status option simply
provides a better means of informing the DTE of a ready condition.

The default for this function is System Status disabled, preventing
the DTE from interpreting momentary line interruptions as a
communications channel failure. (Refer to Chapter 2 for changing
the default DIP switch settings.)

3.2.6 Circuit Assurance

This option, when enabled, causes the MT56DSU-R to condition the
CTS signal to inform the DTE of the transmit ready status of the
entire communications channel.

In most installations, the CTS signal at the DTE interface is the
basic RTS signal delayed in time. Even though this could imply that
the communications channel is ready for data to be sent, it is not
typically conditioned by channel status to indicate an actual ready
status.

With the Circuit Assurance function enabled, the MT56DSU-R does
not turn the CTS signal on unless both the CD is on and the RTS/
CTS delay has timed out.

The default for this function is Circuit Assurance disabled. (Refer to
Chapter 2 forchanging the default DIP switch settings.)

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Chapter 3 - Operation

3.2.7 Clocking

This option allows selection of the MT56DSU-Rs clocking (timing for
synchronization) from one of three sources. These clocking sources
are discussed below.

Internal clocking enables the MT56DSU-R to accept timing from its
internal timing oscillator.

External clocking allows the MT56DSU-R to derive timing from any
external device that can supply timing to the External Transmit Clock
line on the MT56DSU-Rs DTE interface connector. This external
clock must be within 0.008% of the nominal data rate.

DDS timing allows the MT56DSU-R to accept timing signals from
the DDS networks receive bipolar signal. Use this selection
whenever the MT56DSU-R is connected to the DDS network lines.

The default for this function is DDS Clocking enabled. (Refer to
Chapter 2 for changing the default DIP switch settings.)

3.2.8 RTS Forced On

With this option enabled, the MT56DSU-R provides a continuous
CTS signal, disregarding the state of the RTS signal at the DTE
interface connector. This will provide a continuous outbound
indication to the network and remote (far-end) device that there is a
Carrier on condition.

For many (e.g., point-to-point) networks, it is best to maintain a
carrier on status on the communications channel to help minimize
line turnaround delays. This option is usually enabled for central site
DSU installations with multi-point lines (i.e., when continuous
outbound carrier on is desired). This option must be disabled on
the remote station of a multi-point installation.

When this option is disabled, the MT56DSU-R receives and uses
the RTS signal from the DTE.

The default for this function is RTS Forced On. (Refer to Chapter 2
for changing the default DIP switch settings.)

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MT56DSU-R Owner's Manual

3.2.9 DSR Forced On

When this option is enabled, the MT56DSU-R forces the DSR signal
on continuously regardless of the condition of the received DDS
signal (OOS or Test). The permanent DSR signal is used to
eliminate momentary link interruptions that may be interpreted by
the DTE as a communications channel failure.

With this option disabled, the DSR is handled as described in the
System Status section earlier in this chapter.

The default for this function is DSR Forced On. (Refer to Chapter 2
for changing the default DIP switch settings.)

3.2.10 Async Word Length

This option allows you to select the word length to be used by the
MT56DSU-R for asynchronous data transmissions. The Async Word
Length selections are 9-, 10- and 11-bits. The async word length
selected here must match the async word length set at the DTE.

The default for this function is a 10-bit async word(1 start, 8 data, no
parity, 1 stop bit) length. (Refer to Chapter 2 for changing the default
DIP switch settings.)

3.2.11 Normal/Diagnostics

The default for this option is Normal (standard CSU/DSU
operation). For information on the Diagnostics selection, refer to
Chapter 4.

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Chapter 3 - Operation

3. 3 LED Indicators

The front panel of the MT56DSU-R contains ten LED indicators that
can help in troubleshooting network or device problems. Chapter 4
of this manual contains detailed information on the LED indicators.

3.4 Functions

This section describes the two optional MT56DSU-R modes of
operation. The MT56DSU-R can be used as either a point-to-point
Local Area Data Set (at speeds up to 56K bps), or in an off-net
extension application using conventional analog lines and modems
(to complete DDS communications in areas without DDS
availability).

3.4.1 Local Area Data Set Applications

Your MT56DSU-R can be used as a point-to-point LADS (Local Area
Data Set) at transmission speeds of 2400, 4800, 9600, 19200 or
56000 bps over 4-wire, non-loaded metallic wire pairs.

The MT56DSU-R conforms to the signal power requirements of
Bellcore Pub. 41028 (data sets used on LADC), when used at
subrate speeds (less than or equal to 19200 bps). The MT56DSU-R
does not meet this requirement at the 56K bps rate. The 56K bps
rate may be used in applications with customer-supplied lines, or
lines not covered by Pub 41028, or other tariff requirements.

The installation of the MT56DSU-R in a LADS application is the
same as for DDS applications, except for the timing (Clocking)
setting. LADS applications require one MT56DSU-R to be set for
Internal timing and the other MT56DSU-R to be set for DDS timing
(refer to Chapter 2 of this manual). The network cable connection
requires cross-over wiring; the transmit pair of each MT56DSU­R must be connected to the receive pair of the far-end MT56DSU-R.

The MT56DSU-R uses 4-wire non-loaded metallic circuits for LADS
applications. The table below outlines approximations for the
maximum cable length for limited distance applications.

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MT56DSU-R Owner's Manual

Wire Gage

Data Rate 19 AWG 22 AWG 24 AWG 26 AWG

2400 bps 22.0 15.0 12.0 9.5 miles
4800 bps 19.0 13.0 10.0 8.0 miles
9600 bps 15.0 10.0 7.0 5.5 miles
19200 bps 11.9 7.0 5.0 4.0 miles
56000 bps 10.0 6.0 4.2 3.0 miles

Note that line characteristics will vary depending on cable type/
manufacturer, splices, bridge taps, etc.

An example of a typical LADS application is shown in Appendix A of
this manual.

3.4.2 Off-Net Extension Applications

The MT56DSU-R can be used as an off-net extension with standard
analog modems and lines to complete DDS circuits in areas where
the DDS is not available or where a customer requirement is for an
extension of the circuit for a special application.

In applications using the MT56DSU-R for an off-net extension, one
MT56DSU-R may be set for External Timing and the other set for
DDS Timing; however, in this application, the clock (timing) being
supplied must be accurate to +/-0.008% of the enabled data
transmission rate.

The Elastic Store option is used in off-net extension applications
with analog modems to compensate for small timing phase drifts
that typically occur in such applications. A cross-over cable is
required to connect the MT56DSU-R DTE connector to the analog
modem in this application.

The analog modem at the same end as the MT56DSU-R must have
External Timing enabled; the modem at the end of the off-net
extension must have Slave Timing enabled.

In MT56DSU-R applications that use controlled carrier, the CTS
delay for the analog modem at the end of the off-net extension must
be longer than the CTS delay of the MT56DSU-R.

An example of a typical off-net extension application is shown in
Appendix A of this manual.

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MultiDSU56K

Chapter 4 - Troubleshooting

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MT56DSU-R Owner's Manual

4.1 Introduction

All of the indicators used in normal operation of the MT56DSU-R are
labeled on the LED overlay on the rack door. Each LED is labeled,
as explained below. The LEDs provide status and maintenance
information on the MT56DSU-R, as well as the attached network
and line. There are no door switches on the MT56DSU-R.

4. 2 LED Indicators

The door contains ten LEDs each with a two- or three-letter overlay
describing its meaning. During normal operation, the LEDs light
(flash or continuously lit) to indicate the operating status. During
test mode, the LEDs light during Test Pattern test execution (refer to
the Test Pattern section later in this chapter).

The LED overlay is shown in Figure 4-1. The top three letters (DSU)
on the overlay describe the type of board in the slot behind the
overlay. There is no LED behind the top three letters. The LEDs
are described in the following paragraphs.

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Figure 4-1. LED Overlay

Chapter 4 - Troubleshooting

4.2.1 RCV Indicator

The RCV (Receive) LED lights when the MT56DSU-R receives data
( 0 or a space) from the network.

This LED should appear to flash during normal data reception.

4.2.2 XMT Indicator

The XMT (Transmit) LED lights to indicate the DTE is sending data
(0 or a space) across the DTE connector.

This LED should appear to flash during normal data transmission.

4.2.3 CD Indicator

The CD (Carrier Detect) LED lights when the MT56DSU-R has
received the data carrier from the network. This indicator will go off
when the MT56DSU-R is receiving the idle code or no signal at all. If
RTS is off on the remote DSU, the remote sends an idle code to the
local DSU.

4.2.4 56K Indicator

The 56K LED lights when the Data Rate selection is set at 56000
bps. This indicator will be off for all other data rates. Refer to
Chapter 2 for switch settings.

4.2.5 19.2 Indicator

The 19.2 LED lights when the Data Rate selection is set at 19200
bps. This indicator will be off for all other data rates. Refer to
Chapter 2 for switch settings.

4.2.6 CTS Indicator

The CTS (Clear to Send) LED lights when the MT56DSU-R
generates a CTS in response to either an RTS signal received at the
DTE connector, or RTS forced on by the corresponding DIP switch.

CTS is always off during a No Signal condition. If the Circuit
Assurance option is enabled, the CTS will be off whenever Carrier
Detect is off.

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4.2.7 RTS Indicator

The RTS LED lights when the RTS signal is received from the DTE.
The DIP switch for RTS Forced On does not affect this indicator.
Refer to Chapter 2 for switch settings.

4.2.8 NS Indicator

The NS (No Signal) LED lights when no signal at all is received from
the network, or when the signal is too weak for normal MT56DSU-R
operation. This indicator will also flash to indicate that errors have
been detected when using the Test Pattern diagnostic feature.

4.2.9 TM Indicator

The TM (Test Mode) LED lights when one of the Test switches is set
to the down (Test enabled) position. When the TM LED is lit, normal
operation (network transmit/receive) cannot occur. Refer to the
Diagnostic Tests section for more information.

4.2.10 OOS Indicator

The OOS (Out of Service) LED lights when an outage condition
exists. This occurs when there is a failure in the digital service
detected by the network, and the telco sends a repetitive OOS
sequence.

If this indicator is on , check the remote DSU for proper installation
and operation. If the remote DSU is installed and operating correctly,
then report the Out-Of-Service condition to the telephone company.

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Chapter 4 - Troubleshooting

4.3 Diagnostic Tests

The MT565SU-R is set to a default of Normal (non-diagnostic) mode
at the factory. When diagnostics are to be run, change the DIP
switches as described in Chapter 2 of this manual.

When a failure occurs in the digital facility (telco equipment), the
network will detect the failure and send a repetitive OOS signal
sequence to your equipment. Your equipment can detect local loop
failure by the absence or distortion of the digital signal. If an OOS is
received when data is expected, check the remote (far-end)
transmitting equipment. If the remote equipment is transmitting
properly, contact your telephone company. If the telco is required to
perform remote tests, the channel will be temporarily interrupted and
loss of data may occur.

The following sections describe the tests that are available for the
MT56DSU-R.

4.3.1 Local Loopback Test

This test allows you to test the local DTE and local MT56DSU-R.
Use the following steps to perform the Local Loopback Test.

1. Set DIP switch #9 to the down position.

2. The Test (TM) LED lights, and if you send data from your DTE,
it should be looped back to your DTE. If you have access to a
Bit Error Rate Tester, this can be used in place of the DTE.

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MT56DSU-R Owner's Manual

4.3.2 Digital Loopback Test

This test allows you to test the local DTE, the local MT56DSU-R, the
communications link, and the remote MT56DSU-R. Use the
following steps to perform the Digital Loopback Test.

1. Set DIP switch #9 on the remote MT56DSU-R to the down
position.

2.The Test (TM) LED lights, and if you send data from the local DTE,
it should be looped back to the local DTE. If you have access to
a Bit Error Rate Tester, this can be used in place of the local
DTE.

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Chapter 4 - Troubleshooting

4.3.3 Digital Loopback With Test Pattern Test

This test allows you to test the local MT56DSU-R, the
communications link, and the remote MT56DSU-R. Use the
following steps to perform the Digital Loopback Test with the Pattern
Test.

With this test enabled, the MT56DSU-R sends and detects a pre­defined 15-bit pseudo-random test pattern. When an error is
detected by the MT56DSU-R, the NS (No Signal) LED flashs.

1. Set DIP switch #9 on the remote MT56DSU-R to the down
position

2. Set DIP switch #10 on the local MT56DSU-R to the down
position.

3. The test pattern is generated and either detected as a good test
pattern (test patterns match) or as a failed test (test pattern
received does not match the pattern sent).

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MT56DSU-R Owner's Manual

4.3.4 Test Pattern Test

This test allows you to test the local MT56DSU-R, the
communications link, and the remote MT56DSU-R.

With this test enabled, the MT56DSU-R sends and detects a pre­defined 15-bit pseudo-random test pattern. When an error is
detected by the MT56DSU-R, the NS (No Signal) LED flashs.

To enable the Test Pattern Test, perform the following.

1. Set the DIP switch # 10 on both the local and remote
MT56DSU-R boards to the down position.

2. The test pattern is generated and either detected as a good test
pattern (test patterns match) or as a failed test (test pattern
received does not match the pattern sent).

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Chapter 4 - Troubleshooting

4.3.5 DSU Loopback Test

This test lets you verify proper MT56DSU-R operation by matching
a transmitted signal to the "looped-back" receive signal. Refer to
Appendix B for cable description.

1. Obtain a DSU Loopback cable (CADSURLB) from Multi-Tech, or
assemble one. Refer to Appendix B for instructions on building
the Loopback cable .

2. Plug the Loopback cable into the DB9 connector on the DSU
being tested.

3. If you send data from your DTE, it should be "looped back" to
your DTE. If you have access to a Bit Error Rate Tester, this
can be used in place of the DTE.

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MT56DSU-R Owner's Manual

4.3.6 DSU Back-to-Back Test

This test lets you connect two MT56DSU-Rs with a back-to-back
cable to verify proper DSU operation. Using a DSU that is known to
be operational, you can test a second DSU that is suspect.

1. Obtain a DSU Back-to-Back cable (CADSURBB) from Multi­Tech, or assemble one. Refer to Appendix B for instructions on
building the Back-to-Back cable .

2. On the good DSU board, set DIP switch #9 to the down
position.

3. Set one DSU to internal clocking and the other DSU to DDS
clocking.

4. Plug the Back-to-Back Cable into the line backplane connector
on each DSU.

5. If you send data from your DTE, it should be "looped back" to
your DTE. If you have access to a Bit Error Rate Tester, this
can be used in place of the DTE.

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TM

MultiDSU56K

Chapter 5 - Warranty, Service and

Tech Support

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MT56DSU-R Owner's Manual

5.1 Service

In the event service is required, equipment may be sent, freight
prepaid, to our factory. Return shipping charges will be paid by
Multi-Tech Systems. Include a description of the problem, a return
shipping address, and a check or purchase order for out-of-warranty
repairs. The standard repair charge for an MT56DSU-R is $125.
Multi-Tech pays the return freight. Send equipment to this address:

MULTI-TECH SYSTEMS, INC.

2205 Woodale Drive

Mounds View, Minnesota 55112

Attn: Service

You should also check with the people that supplied you with your
equipment on the availability of local service and/or loaner units, in
your part of the country. You may call us at 1-800-972-2439, or if in
Minnesota, at 612-785-3500.

5.2 Limited Warranty

Multi-Tech Systems, Inc. (MTS) warrants that its products will be
free from defects in material or workmanship for a period of two
years from the date of purchase, or if proof of purchase is not
provided, two years from date of shipment. MTS MAKES NO

OTHER WARRANTY, EXPRESSED OR IMPLIED, AND ALL
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE HEREBY DISCLAIMED.

This warranty does not apply to any products which have been
damaged by lightning storms, water, or power surges or which have
been neglected, altered, abused, used for a purpose other than the
one for which they were manufactured, repaired by the customer or
any party without MTSs written authorization, or used in any
manner inconsistent with MTSs instructions.

MTSs entire obligation under this warranty shall be limited (at
MTSs option) to repair or replacement of any products which prove
to be defective within the warranty period, or, at MTSs option,
issuance of a refund of the purchase price. Defective products must
be returned by Customer to MTSs factory transportation prepaid.

MTS WILL NOT BE LIABLE FOR CONSEQUENTIAL DAMAGES
AND UNDER NO CIRCUMSTANCES WILL ITS LIABILITY
EXCEED THE PURCHASE PRICE FOR DEFECTIVE PRODUCTS.

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Chapter 5 - Warranty, Service and Tech Support

5.3 Tech Support and BBS

Multi-Tech has an excellent staff of tech-support personnel available
to help you get the most out of your Multi-Tech product. If you have
any questions about the operation of this unit, please call Tech­Support at 1-800-972-2439 in the U.S. and Canada.

Multi-Tech Systems also maintains a Bulletin Board Service (BBS)
for its customers. The information available via the BBS includes:
new product information, product upgrade data, problem solving tips
and a message service for you to leave questions for which you
would like additional information. The phone number for the Multi­Tech BBS is 1-800-392-2432 in the U.S. and Canada and for
Worldwide calls [phone].

The BBS can be accessed by any asynchronous modem operating
at transmission speeds of 14.4K, 9600, 4800, 2400 or 1200 bps.
Configurer your modem for no parity, one stop bit and a word length
of 8 data bits.

5.4 Recording DSU Information

Please fill in the following information on your MT56DSU-R. This
will help Tech-Support in answering your question. The same
information is requested on the Warranty Registration Card.

DSU Model No: _________________

DSU Serial No: _________________

The model number and revision level are on the board.

Please note any LED indicator conditions or test results. Use the
space below to note the status:

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MultiDSU56K

Appendixes

TM

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MT56DSU-R Owner's Manual

Appendix A - Application Examples

Introduction

This section illustrates several types of applications in which the
MT56DSU-R is typically used. These types include:

 DDS point-to-point application,
 DDS multi-point (polled) application,
 Local Area Data Set,
 External Clocking application, and
 Analog Off-Net Extension application

DDS Point-To-Point Application

In this application, the MT56DSU-R provides the interface between
the DDS line and the DTE at your site. Your network provider will
provide (at your request) a DDS line connecting the desired
locations. The figure below depicts a sample DDS Point-to-point
application.

Figure A-1. DDS Point-To-Point Application

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Appendix A - Application Examples

DDS Multi-Point (Polled) Application

Since your Central Office (CO) equipment must include Multi-point
Junction Units (MJUs) and other special arrangements for this type
of service, you may need to coordinate efforts with your network
service provider.

The MT56DSU-R at the host end is the Master Station (also called
the Control Station), which typically has RTS forced on. The
attached MT56DSU-Rs are called "Remote stations and have RTS
controlled by the DTE.

Multi-point DDS provides communication between a control station
and two or more remote stations. All data transmitted by the control
station is sent to each remote station. For data transmitted from the
remote stations, the MJUs combine bit streams from the remote
stations into a single, serial bit stream sent to the control station. All
stations on the same multi-point circuit must run at the same bit rate
(any of the DDS customer service rates).

The figure below shows a typical Multi-point (Polled) application.

Figure A-2. DDS Multi-Point Polled Application

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MT56DSU-R Owner's Manual

Local Area Data Set Application

In this application, two pairs of wires provide the connection
between two MT56DSU-R devices. The two pairs can be up to the
equivalent of 3 miles of 26 AWG wire at 56000 bps, or longer for
subrate applications (see distances chart in section 3.4.1 of this
manual).

The figure below depicts a typical Local Area Data Set application.

Figure A-3. Local Area Data Set Application

External Clocking Application

This application is similar to theLocal Area Data Set application
except for the timing option setting. In the example below, the DTE
connector of the T1 mux is connected to the DTE connector of the
MT56DSU-R. Here, the MT56DSU-R must receive timing
information from the T1 mux. The MT56DSU-R is set for external
timing in this type of application. At the DTE end, DDS timing is
selected, providing normal clocking to the DTE.

The figure below shows a typical External Clocking application.

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Figure A-4. External Clocking Application

Appendix A - Application Examples

Analog Off-Net Extension Application

In this application, the MT56DSU-R is used with conventional
analog modems and lines to complete DDS circuits in an area where
DDS is not available (Site #3 in the example below) , or where the
customer requires an extension of the DDS circuit for a special
application.

Figure A-5. Analog Off-Net Extension Application

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MT56DSU-R Owner's Manual

Appendix B - Interface Signals and Connector Pinouts

RS232C DB9 CONNECTOR

DESCRIPTION

This connector ties the MT56DSU-R to the DDS Network. The DB9S
connector has the following pinout configuration

PIN IDENTIFICATION

Pin Description Destination

1 Transmit Pair To Line
2 N/C
3 Transmit Pair To Line
4 Receive Pair From Line
5 N/C
6 N/C
7 N/C
8 Receive Pair From Line
9 N/C

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Appendix B - Interface Signals and Connector Pinouts

RS232C DB25S CONNECTOR

13
12
11
10
9 — Test Voltage (+V)
8 — Carrier Detect (CD)
7 — Signal Ground (SG)
6 — Data Set Ready (DSR)
5 — Clear To Send (CTS)
4 — Request To Send (RTS)
3 — Received Data (RD)
2 — Transmit Data (SD)
1

Transmitter Signal —
Element Timing

Receive Clock (RC) —

Transmit Clock (TC) —

As viewed from the rear

25
24
23
22
21
20
19
18
17
16
15
14

DESCRIPTION

This connector ties the MT56DSU-R to the DTE. The DB25S
connector has the following pinout configuration.

PIN IDENTIFICATION

Pin Description Signal

2 Transmit Data SD
3 Received Data RD
4 Request To Send RT S
5 Clear To Send CTS
6 Data Set Ready DSR
7 Signal Ground S G
8 Carrier Detect CD
9 Test Voltage +V
15 Transmit Clock TC
17 Receive Clock R C
24 DTE Transmitter Signal Element Timing

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MT56DSU-R Owner's Manual

V.35 INTERFACE ADAPTER CABLE

DESCRIPTION

This adapter cable should be used when the MTDSU56-R is
configured for V.35 DTE interface. You can order the V.35 Interface
Adapter cable (CADSUR35) from Multi-Tech. This cable uses a 25­pin male connector at one end and a 34-pin Winchester female
connector at the other end.

SCHEMATIC

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Appendix B - Interface Signals and Connector Pinouts

LINE CABLE

DESCRIPTION

This cable lets you connect the MT56DSU-R to your DDS Network.
You can order the Line cable (CA248) from Multi-Tech, or build one
using the instructions below.

SCHEMATIC

BUILD INSTRUCTIONS

1. Strip cable insulation 3/4" .

2. Strip wires 1,3,4 and 8 on one end of cable and 1,2,7 and 8 on
other end a 1/4"

3. Cut unstriped wires off.

4. Solder wire 1 on one connector to 1 on the other.

5. Solder wire 3 on one connector to 2 on he other..

6. Solder wire 4 on one connector to 7 on the other..

7. Solder wire 8 on one connector to 8 on the other..

8. Cover solder connections with 1"of shrink tube.

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LOOPBACK CABLE

DESCRIPTION

This cable lets you test the MT56DSU-R when a second DSU is not
available. It tests the DSU by having the DSU generate a signal,
then the cable loops the signal back to the DSU for comparison to
the original signal sent. You can order this cable (CADSURLB) from
Multi-Tech, or build one using the instructions below. Refer to
Chapter 4 for test procedures.

SCHEMATIC

BUILD INSTRUCTIONS

1. Strip cable insulation 3/4" .

2. Cut wires 2, 5, 6, 7,9 off.

3. Strip wires 1, 3, 4 and 8 a 1/4"

4. Solder wires 1 and 8 together.

5. Solder wires 3 and 4 together.

6. Cover solder connections with 1"of shrink tube.

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Appendix B - Interface Signals and Connector Pinouts

BACK-TO-BACK CABLE

DESCRIPTION

This cable lets you test a suspect DSU by connecting it to a known
good DSU. It tests the suspect DSU by connecting its Transmit
signal to the good DSUs Receive circuits. You can order it from
Multi-Tech (CADSURBB), or build one using the instructions below.
Refer to Chapter 4 for test procedures.

SCHEMATIC

BUILD INSTRUCTIONS

1. Strip cable insulation 3/4" .

3. Strip wires 1and 3 on one end of cable and 4 and 8 on other
end a 1/4"

2. Cut unstriped wires off.

4. Solder wire 1on one connector to 8 on the other.

5. Solder wire 3 on one connector to 4 on the other..

6. Cover solder connections with 1"of shrink tube.

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MultiDSU56K

Glossary

TM

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MT56DSU-R Owner's Manual

This section defines several of the terms used in this manual. For an
overview of DSU basics, refer to section 1.8 of this manual.

A

ALBO (Automatic Line Build Out) - part of equalizer circuitry

used to compensate for various gauges and alterations of local
loops.

Anti-Streaming - an option that prevents a streaming (jammed)
DTE from affecting other devices on a multi-point network.

Asynchronous communications - communications between
computer devices at irregular intervals. To do so, the device adds
start and stop bits to each character it sends.

B

BERT (bit error rate tester) - the type of testing used to verify the

operating parameters of a data communications line.

bps (bits per second) - unit of measure for data transmission.

C

Central Office (CO) - the telephone company site where switching

equipment is located (as opposed to customer premises).

Channel - the digital path on a cable on which data is transmitted. A
logical way to look at the path data travels when sent between
locations.

Circuit assurance - an optional conditioning of the CTS signal.

Clear To Send (CTS) - an interface signal that indicates whether the

modem or DSU is ready to accept a data transmission from the
DTE.

CO (Central Office) - facility where communications common
carriers terminate customer lines and locate line interconnection
equipment.

Clocking - a synchronous device circuit that sends signals at a
precise frequency corresponding to the bit rate of that device.

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Glossary

Control station - the station on a DDS multipoint circuit that is

nearest the host system and transmits data to each remote station
and receives a single serial bit stream from the remote stations via
the MJU.

Crossover cable - a cable with a conductor that runs the length of
the cable, but connects to a different pin number at each end
(connects pins 2 to 3 and 3 to 2 from DTE to DSU/CSU).

CSU (Channel Service Unit) - a device used to terminate a digital
circuit (such as DDS or T1) at the customer site. Used in
combination with a DSU.

D

Data Communications Equipment (DCE) - equipment that

provides the function to establish, maintain and terminate a
connection. Additionally, provides the signal conversion required for
communications between DTE and data circuit or telephone line.
See also DTE.

DDS (Dataphone Digital Service) - AT&Ts private-line end-to-end
digital service, with data rates (typically) at 2400, 4800, 9600,
19200, and 56000 bps. Now an AT&T Accunet family offering. The
DDS is a synchronous network that uses the ABATS test system,
which requires little manual intervention.

Default - the factory set position or value that a device assumes at
startup. An alterable parameter.

Digital loopback - a type of diagnostic test where the transmitted
signal is returned to the sending device after passing through a data
communications link; the returned signal is then compared to the
transmitted signal.

DSR (data set ready) - an RS232 signal that indicates the DCE and
line are ready to receive data.

DSU (Data Service Unit) - a device used to interface a users DSU
to a digital circuit (such as DDS or T1). Used in combination with a
CSU.

Data Terminal Equipment (DTE) - a device that provides output
data in the form of digital signals. See also DCE.

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E

Elastic store - an option that causes the DSU to allow for timing

phase drifts in non-DDS applications.

F

Four-wire circuit - two twisted-pair circuits with each pair

transmitting signals in the opposite direction.

J

Jumper - a wire that connects two or more pins; a configurable

component on a printed circuit board.

L

LBO (Line Build Out) - process of inserting a loss in a short

transmission line to make it act like a longer line.

Leased line - a permanent communication line between a computer
and a terminal providing private, continuous access to the
connection by a subscriber for a fixed fee.

LED (Light Emitting Diode) - a light source that emits visible light.

Local loopback - a type of diagnostic test where the transmitted

signal is returned to the sending device after passing through a local
communications loop; the returned signal is then compared to the
transmitted signal.

M

Master station - see control station.

MJU (Multipoint Junction Unit) - a digital data bridge, located at

telco office, for the DDS network. Used to combine remote stations
bit streams into one serial bit stream for transmission to the control
station.

Multi-drop - see multipoint.

Multipoint - a single line or circuit that connects several stations

supporting terminals located in different areas. Usually requires
some type of pooling method. Contrast point-to-point.

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Glossary

Multipoint circuit - a type of DDS network that includes one control

station, attached remote stations, and all channel, MJU and digital
access lines for station interconnection.

O

OCU (Office Channel unit) - a DSU/CSU located in the telco

central office.

OOS (Out Of Service) - a condition that occurs when a digital
service failure is detected by the network.

P

Point-to-point - a circuit with two point directly connected, with no

intermediate nodes, computers or branched circuits (but possibly
switching facilities). A type of connection that links two (and only
two) logical entities (e.g., a phone line circuit). Contrast multipoint.

R

Remote station - a device on a multipoint DDS network that

communicates with the master station via the OCU. All remote
stations on the DDS must operate at the same bit rate. (AKA,
outlying station.)

RJ (Registered Jack) - a connector for use at customer site (e.g.,
RJ11, RJ45, RJ48).

RTS (Request To Send) - a lead on the terminal interface. Also a
communications device handshaking signal; generated by the
receiving device in order to condition a remote transmitter to begin
data transmission.

S

Serial - a type of communications between two devices in which

data is transmitted one bit at a time.

Subrate - a data transmission rate of less than or equal to 19.2K
bps.

Synchronous transmission - data communications where the
transmitting and receiving devices are synchronized and characters
or bits are sent at a fixed rate.

System status - optional conditioning of the DSR signal.

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T

Test pattern - a diagnostic test for sending , detecting and checking

a pre-defined pattern of bits.

Two-wire circuit - A circuit in which one channel (line) is used for
communications in both directions. Contrast four-wire circuit.

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