Selection and Testing of Electronic Components for LM

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Selection and Testing of Electronic Components for LM

ERICSSON

REVIEW

3

1977

SELECTION AND TESTING OF ELECTRONIC COMPONENTS

CROSS STRANDING OF TELEPHONE CABLE

NEW TELEPHONE SET

DIGITAL LINE EQUIPMENTS

OPERATION AND MAINTENANCE CHARACTERISTICS OF AKE

MAGNETO SWITCHBOARD


ERICSSON REVIEW

NUMBERS 1977 -VOLUME 54

Copyright Telefonaktiebolaget LM Ericsson

Printed in Sweden, Stockholm 1977

RESPONSIBLE PUBLISHER DR. TECHN CHRISTIAN JACOB/EUS

EDITOR GUSTAF O. DOUGLAS

EDITORIAL STAFF FOLKE BERG

EDITOR'S OFFICE S-12625 STOCKHOLM

SUBSCRIPTION ONE YEAR $6.00ONE COPY $1.70

Contents

94 • Selection and Testing of Electronic Components for LM Ericsson's

Telephone Exchanges

105 • Cross Stranding of Telephone Cable

112 • New Telephone Set

114 Digital Line Equipments for 8 Mbit/s and 2 Mbit/s

125 • Operation and Maintenance Characteristics of AKE 13

136 • ABJ 101-the Modern Public Magneto Switchboard

COVER

Part of a memory board with electronic components.

In the foreground a capacitor manufactured

by AB Rifa — an Ericsson company.


Selection and Testing of Electronic

Components for LM Ericsson's

Telephone Exchanges

Berndt Agneus and Ivan Borgstrom

Electronic components have formed part of automatic telephone exchanges for

a rather long time. The rapid development that these components, primarily micro

circuits, have experienced during recent years and which can be expected to continue

for a long time is of great importance for the design of new exchange systems.

In fact, the new systems are in the main based on electronic components. In the

design work it is essential to select components that not only have the desired

function but which are also stable during the estimated life of the exchange. The

article deals with various activities, which together are aimed at ensuring the correct

range of components for telephone exchange equipments. The illustrations

with captions provide information regarding various aids that are used in this connection.

The article also gives a summary of electronic components of current

interest and their probable development trends.

UDC 621.3.049.7 Component categories

Electronic components for LM Ericsson's

telephone exchange equipments

are to a certain extent manufactured

within the group. The remainder are

bought externally and usually belong to

the suppliers' standard ranges. In certain

cases, however, components are required

with characteristics that necessitate

either special selection from the

standard range or the introduction of

special "customer adapted" components.

The component quality corresponds

to the category "professional

components", which meet higher reliability

and long-term stability requirements

than so-called entertainment

components.

Electronic components are usually divided

into three main categories as regards

their function, namely passive

components (resistors, capacitors etc.),

discrete semiconductor components

(such as diodes, transistors and

thyristors) and various types of micro

circuits, see fig. 1.

The importance of the

components in the system

design

The design and characteristics of an exchange

system are to a great extent dependent

on the design of the components.

There is in fact mutual effect

since the system design influences the

design of the components.

LM Ericsson's "great" automatic

systems, the 500-line selector system

and the crossbar system, were both

based on electromechanical components.

However, electronic components

were also included in these systems at

an early stage. They were then mainly

used for secondary functions such as

series and parallel resistors, delay

capacitors, CR units for contact protection

etc. These components were often

soldered on to tags on the relays.

The electromechanical systems have

been modernised extensively as and

when the need has arisen. In connection

with this, discrete components (first

discharge valves, later on diodes and

transistors) were brought into use at

quite an early stage. They were then included

in such function units as test

circuits, MFC signalling systems and

charging units.

SPC technique (Stored Program Control)

was first used in LM Ericsson in the

transit exchange system AKE 13, and

was then based on diodes, transistors

and ferrite memories. Fast micro

circuits, including semiconductor

memories, became important for the

further development of the SPC technique.

Micro circuits are now primary elements

in modern exchange systems. They require

very little space in relation to the

large number of logic functions they are

able to perform. They are usually

mounted on printed circuit boards,

which makes for a compact construction

throughout. Reed switches, miniature

relays and certain other components

have also been adapted for

mounting on printed boards.

The development of components and

systems continues in close collaboration.

The need for such development

collaboration will increase as complex

"components" containing very large

numbers of functions are introduced.

An example of such "components" are

microcomputers, which in one or a few

micro circuit packages accommodate

the primary functions of a computer.

Principles for the selection

of electronic components

Components in telephone exchange

eauiartiants musLhe_abJe to perform the


BERNDTAGNEUS

Älvsjö Electronics Factory

IVAN BORGSTRÖM

Telephone Exchange Division

Telefonaktiebolaget LM Ericsson

Fig. 1

Column 1 (lett)

Some types of resistors and capacitors (passive

components)

(From top to bottom)

Plastic foil capacitor with epoxy cover

Tantalum capacitor, dry type

Attenuator In the form of thick-film resistors on a ceramic

substrate

Varnished film resistor

Column 2

Discrete semiconductor components

Display of the 7-segment type

Light-emitting diode for visible light

Transistor In TO 18 metal case

Rectifier diode in a glass envelope for 1 A

Fast logic diode In a D 35 envelope

Column 3

Micro circuits

Programmable memory in a 24-pin DIL ceramic and metal

package

Digital micro circuit In a 16-pln ceramic Dual-in-Llne (DIL)

package

Linear micro circuit in an 8-lead metal envelope

intended task with high reliability during

the whole life of the equipment. In

addition to this basic requirement a

number of other important factors must

be taken into consideration when

selecting electronic components, in order

to obtain a suitable range of components.

Among these may be mentioned:

Technical status and trend. Is the component

based on a new technique or

new materials? If so, how well is the new

technique developed and how well are

the characteristics defined? Is the development

likely to proceed towards the

type represented by the component, or

in other words has it got a future?

Supply. Since electronic components

are to a great extent purchased from different

manufacturers it is important to

know which manufacturers are able or

will be able to supply a particular component.

For reasons such as supply reliability

it is essential that there will be

several approved suppliers for each

type of component.

95

Need. The current and future need for

the component is investigated in collaboration

with circuit and system designers.

The quantities used affect supply

and price.

Price situation and tendency. A comparison

with alternative components or

circuit designs is made in order to assess

the financial side of the component

selection.

Standardization and coordination. It is

in the interests of both LM Ericsson and

the customers that the range of components

used in equipments is limited, so

that the number of different items is not

greater than is absolutely necessary

with regard to the function and reliability

requirements. Consequently the introduction

of new components requires

that the proposals by component

specialists are submitted to special

standardization committees for decision.

Component selection and policy

questions of particular importance are

referred to a component council.


Fig. 2

Curve tracer

The special type of oscilloscope, which is called a

curve tracer, Is a universal Instrument tor testing

semiconductor components. A family of curves are displayed

on the screen. These give an overall picture of the

electrical characteristics of the component. The curves

can provide Important data, such as amplification factor,

breakdown voltage and reverse current

Fig. 3

Light microscope

Microscopes are valuable aids in construction and fault

analyses of electric components. By means of direct

observation or photography using light or electronic

microscopes It Is possible to study and assess the design

of component details or determine the causes of faults.

Mlcroscoplng is indispensable when studying intricate

conductive patterns or wire bondings on semiconductor

crystals

Coordination between different divisions

and companies in the Ericsson

Group in questions relating to choice of

electronic components takes place, for

example, through a special component

and circuit committee, within specialist

groups and through centrally distributed

component information.

Rules for use. The conditions that are to

apply for the use of the new component

in circuit designs are considered in

connection with the component selection.

In order to attain the desired reliability

and life it is often necessary to reduce,

to a greater or lesser extent, the

values given in the manufacturer's

component data for permissible electrical

loads and operating temperatures.

Permissible design data are given in

special documents which also contain

additional information for the designers.

Production engineering aspects. When

manufacturing equipments it must be

possible to check, assemble and connect

the components using rational

methods and production aids. This

means, for example, that questions

concerning automatic assembly, soldering

and cleaning of components

must be considered.

Current component range

Equipments belonging to different exchange

systems, which have been designed

at different times, are manufactured

continuously and often in parallel.

The components have been selected

during different development epochs.

In order to prevent this from having any

negative effects the component range is

continously standardized and modernized.

The most important types of passive

components, discrete semiconductor

components and micro circuits used in

the LM Ericsson exchange equipments

are described below.

PASSIVE COMPONENTS

Passive components comprise various

types of resistors, capacitors and transformers.

Resistors

Carbon film resistors constitute the

most common type. The resistive element

consists of a carbon film on a

ceramic rod. Operational experience

has shown that the carbon film resistor

is the most reliable type of component

in telecommunication equipment.

In addition to carbon film resistors,

metal film resistors are used where low

temperature dependence is required.

This type of resistor is being used to an

increasing extent in electronic equipment.

A third type of film resistor that has recently

been introduced is the metallic

oxide resistor, where the resistive element

consists of tin oxide with antimony

oxide added.

Thick-film resistors, manufactured by

means of screen printing and firing a resistive

paste on to a ceramic substrate,

are used as attenuators and fuse resistors.

Capacitors

This category of component includes

many different types, whose characteristics

and thus fields of use are mainly

determined by their dielectric.

Aluminium electrolytic capacitors of the

long-life type are used for regulating the

operating times of relays. In this case a

large capacitance per unit of volume is

an essential characteristic.

Tantalum electrolytic capacitors are

usually chosen for electronic circuits

when the requirements are small size

and moderate capacitance values at low

voltages.

Polyester film capacitors are being used

to a great extent nowadays in transmission,

time and contact protection

circuits instead of the traditional paper

capacitors

Polystyrene capacitors are used when

close tolerances and good stability are

required, for example in tuned circuits.

Both polystyrene and polyester film

capacitors are manufactured with a

moulded epoxy cover and are constructed

for mounting on printed

hoarriffc nnfi lion irt ralnw QjatQ


Fig. 4

X-ray camera

The Inner construction and manufacture of components

can be of great importance to function characteristics and

life. One way of Investigating the Inside of the component

Is to open the case and cut through the component. However,

this method Is usually destructive, so that the component

properties are changed entirely.

It Is often possible to obtain valuable Information regarding

the structure of the component by means of an X-ray

photograph. Inner mechanical faults can also be detected

on such pictures. In addition the possibility remains of carrying

out supplementary electrical measurements on the

unaffected component after the X-ray Investigation

Fig. 5

Desk calculator

Agreatnumber of measurements.provldlng large amounts

of measured values, are often carried out In connection

with component Investigations. These values must be processed

In order to obtain essential data in a clear form. A

desk calculator is used for this purpose which can be programmed

to process the test material In a suitable way and

give the result as a printout or on a diagram. The desk

calculator Is also used for certain component data calculations,

for example when dimensioning transformer wind-

Transformers and inductors

Transformers with a core of plate

frames or tape are used in transmission

circuits that transmit alternating current

superposed on a direct current.

Ferrite transformers with different types

of cores, in certain cases adjustable, are

used as current transformers and for

filtering in power equipment, in tuned

circuits and oscillators, for impedance

matching and pulse transmission.

DISCRETE SEMICONDUCTOR

COMPONENTS

These components contain individual

semiconductor components, each of

which performs just one single function.

They are still used in modern exchange

systems along with micro

circuits, and consist mainly of transistors

and diodes, but thyristors and

optical semiconductor components are

also included in this category.

Transistors

All modern transistors are made of silicon

and usually manufactured by

means of so-called planar technology.

For quality reasons a metal can with

glass lead-throughs for the conductors

is used.

Diodes

The diodes used in exchange systems

97

can be divided into three main

categories: rectifier diodes, switch

diodes and voltage regulation diodes.

The switch diodes are used in logic

circuits and must therefore have a short

recovery time in the reverse direction.

The voltage regulation diodes give a defined

voltage level in circuits where a

stable reference voltage is required.

Special semiconductor components

Among semiconductor components

that are used to a limited extent for special

functions may be mentioned the

thyristor, which closes a circuit when a

pulse is applied to its gate electrode,

and the unijunction transistor, which is

used for starting time circuits and

thyristors.

Opto-electronic components have recently

been introduced that use visible

or infra-red light for their operation.

Among them are light-emitting diodes,

displays and opfo couplers.

Red, yellow and green light-emitting

diodes are used for indicating different

states in equipments, and displays

show a figure or a letter depending on

the applied electrical signals.

The opto coupler, on the other hand,


Fig. 6

Humidity test

High air humidity Is one of the most serious adverse environmental

conditions to which electrical components

can be exposed. The dampness can affect the outside of

the components by corroding metal surfaces and reduce

the Insulation between the leads. It can also seep Into the

components and In so doing impair their caracterlstlcs or

cause total breakdown.

Humidity testing Is carried out in an climatic chamber,

where the air humidity and temperature are either

held constant or varied cyclically with time. The components

can either just be stored In the chamber or they

can also be connected to an electrical voltage source

during the humidity tests

Fig. 7

Programming equipment

In a certain type of semiconductor memories, designated

PROM (Programmable Read Only Memories), the contents

of the memory cells are fed In with the aid of special programming

equipment A metallic connection is thereby

burnt off electrically in the cells that are to be programmed.

The memory program can be fed in in different ways:

manually via a push-button set, from a punched tape or

with the aid of a previously programmed memory (master).

The equipment also checks that the programming Is correct

uses infra-red lights as the transfer

medium between a light-emitting diode

and, for example, a photo transistor.

MICRO CIRCUITS

Micro circuits are built up of a number

of interworking semiconductor elements

and can integrate a number of

analogue functions, digital functions or

memory functions.

Analogue micro circuits

In analogue circuits the voltages on the

inputs and outputs can vary continuously

over certain ranges and are thus

not limited to fixed levels. In modern exchange

systems these circuits are used

as

— voltage regulators for power units

— sensors of voltage levels

— interface circuits between different

subsystems

— operational amplifiers in MFC filters

etc.

Digital micro circuits

These circuits are predominant among

the micro circuits. Digital circuits carry

out logic operations by means of digital

signals, i.e. voltages on the inputs and

outputs that take up values close to

fixed levels. Many of these circuits belong

to specific so-called circuit

families with a certain type of logic element

and in other respects designed so

that they can interwork in systems.

In addition to these circuit families a

number of digital circuits are used that

do not belong to any particular family.

These can be divided into a number of

groups according to function, such as

registers, adders, arithmetic circuits,

counters, data switches, coders and decoders.

DTL circuits (Diode-Transistor-Logic)

constituted one of the first families in

micro circuit technique. They are no

longer used when designing new

equipments.

TTL circuits (Transistor-Transistor-

Logic) are faster than DTL circuits and

have gradually become the predominant

type.

A large number of circuits are available

on the market in several different variants.

Certain series (e.g. 74S and 74LS)

have integrated so-called Schottky

diodes, whereby the circuits have been

made faster.

CMOS (Complementary-Metal-Oxide-

Silicon) circuits operate within wide voltage

limits and have low power consumption,

but they are not particularly

fast.

Memories constitute an important

group. They can be in the form of random

access memories, where the con-


Fig. 8

Load test

Electrical load tests over a relatively long period (several

thousand hours) constitute an Important part of the type

testing ot components. For these tests the components

are mounted on printed wiring boards placed In racks,

which when necessary are equipped with supervisory

equipment that records component faults. The electrical

load Is often Intermittent, i.e. It Is switched on and off at

certain Intervals In order to Imitate the stresses that can

occur In some operational cases. At certain times the

components are removed In order to measure their

electrical characteristics.

The lead tests provide Information regarding changes In

the component data during operation (ageing), and In certain

cases regarding probable failure rate and life

Fig. 9

Cold test

Exchange equipments do not normally need to work at

temperatures below the freezing point. However, during

transport in cold areas they can be exposed to low temperatures,

which they must be able to withstand without

damage. The electrical components are therefore tested

at temperatures down to at least — 40°C.

In a corresponding way the effect of high temperatures Is

• • . . . . . . - . . - - ••• •

tent can be changed, or read only memories

with fixed content. Both the fast

bipolar semiconductor technique and

the less power-demanding MOS technique

are used for memory components.

Special circuits

The above-mentioned micro circuits are

of standard design and can be bought

from different suppliers. However, for

certain purposes it may be appropriate

to introduce special circuits that satisfy

particular function requirements.

Packaging

Micro circuits are usually packaged in

ceramic cases with the external pins

arranged in two rows, so-called DIL

packages, although certain types of

analogue micro circuits are packaged

in cylindrical metal cans.

Type testing

The purpose of type testing is to determine

whether a certain type of component

from a manufacturer satisfies

the given data and requirements. The

type testing comprises measurements

of data, function checks, environmental

tests and load tests.

The actual type testing is usually preceded

by a preliminary investigation,

which comprises the study of available

99

information concerning the type of

component and a construction analysis

of a small number of test items. Such

methods as X-ray photography, dissection,

microscoping and material analysis

are used to investigate and assess

the packaging and sealing, internal

connections, metal and oxide layers,

diffusion pattern, cooling and mounting

and connection facilities.

Type testing is carried out in accordance

with programs that indicate

which tests and measurements are to be

carried out. As far as possible the type

testing programs are based on the recommendations

issued by the International

Electrotechnical Commission

(IEC). When necessary, additions and

modifications are made in order to

adapt the type testing to the special operational

conditions of telephone exchange

equipments. Thus particular

importance is attached to the verification

of the reliability and stability of the

components during long periods on

load.

The type testing programs normally

comprise cold tests, heat tests, temperature

cycling and humidity tests in a

constant environment and also with

fluctuating air humidity and temperature.

Moreover, the programs generally

include vibration tests, soldering tests,


100

Type of check

Type of component Me- En- El.

chan- viron- param.

ical mental

Resistors, resistor net­

works and potentio­

meters S S

Capacitors

Diodes, transistors

S S

and thyristors S A

Micro circuits S A A

Table 1

Testing of components

A Check of the whole consignment

S Sampling test in accordance with MIL-STD-105

Fig. 10

The solderability tester STE 74 works in accordance

with the solder globule method and is intended

for measuring the solderability of components

and metallized holes in printed boards etc.

The test Item whose solderability is to be measured is lowered

into a molten solder globule that is placed on top of a

heated iron cylinder so that the globule Is divided into two

equal parts. When the solder wets the test item the latter is

completely enclosed by the solder. The wetting time is

measured and Is a measure of the solderability of the test

item.

The lowering speed, solder temperature and quantity of

solder are carefully specified. The solder and test item are

treated with flux and the solder must wet the iron cylinder

hermeticity tests, tension, bending and

torsion tests on the leads and flammabil

ity tests. Electrical tests may com prise

voltage tests, current pulse tests and

power loading tests. Such tests can

continue for periods of 1 000 hours up to

more than 10000 hours depending on

the type of test and the "acceleration

factor", i.e. the size of the load in relation

to specified component data.

Significant component data are measured

before, during and after the

course of the type testing.

Type testing programs for electronic

components also contain instructions

for assessing the test results. However,

the final decision as to whether a certain

type of component should be accepted

is always based on the expert knowledge

of the component specialist.

Quality follow-up

Components delivered by approved

suppliers are inspected on arrival in the

way described in the next section. In

addition a so-called reliability evaluation

is carried out in accordance with a

yearly plan, primarily of recently introduced

components and components

purchased in great quantities.

The reliability evaluation provides a

continuous verification that the com­

ponent quality originally accepted after

type testing is maintained in later component

deliveries.

In this evaluation, which is carried out

on samples taken from the deliveries,

the inner construction of the component

is studied and compared with reference

examples from the type testing.

It can then be ascertained whether the

manufacturer has for example introduced

a new type of silicon chip in a

transistor or changed the connections

to a capacitor foil.

The reliability evaluation also includes

a limited type testing for the purpose

of finding any quality defects in a component

consignment within a few

weeks. It is then possible to prevent the

use of unsatisfactory components in the

production of exchange equipments.

When a component fault is reported in

equipment being manufactured, in the

system testing stage or in operation, a

fault analysis is carried out in order to

determine the cause of the fault and

when necessary to improve the component

quality.

Inspection of components

on arrival

Inspection of purchased components


Fig. 11

on arrival takes place in accordance

with test instructions based on IEC and

MIL standards. The purpose of the inspection

on arrival is to ensure that the

components in the system meet LM

Ericsson's high demands for reliability

and long life.

SCOPE

The inspection on arrival is carried out

on passive components, discrete

semiconductors and micro circuits. It

comprises checks of the mechanical

properties of the components, their

ability to withstand adverse environments

and their electrical parameters.

The checks are carried out either on all

components or on a sample in accordance

with table 1.

101

INSPECTION PROCEDURE

All components are tested mechanically

in the following way:

Mechanical dimensions are measured

with vernier callipers and the solderability

checked by means of the solder

globule method or the solder bath method

at 230 ± 10°C (requirement of IEC 68-

2-20). Fig. 10 shows a solderability tester.

Resistors, resistor networks

and potentiometers

These are tested as follows:

The resistance value is determined with

the aid of a Wheatstone bridge.

The harmonic distortion factor is measured

with a distortion factor meter.


Fig. 12

Computer-controlled test system for memory

circuits, Macro-Data MD 104 M/MC

Here equipped with a handler, which makes possible testing

at Increased temperature

Fig. 13

Test system Tektronix S-3260

Evaluation and checking of complex micro circuits both

require such extensive measurements that special test

systems are necessary. A minicomputer is used tor executing

the test programs, which apply Incoming signals

on certain of the component connections. At the same time

measurements are made on the output connections. The

test results are processed and are then shown on a display

or as a printout

Capacitors (excl. electrolytic

capacitors)

The capacitance value is measured with

a comparison bridge, where the value is

set up and the deviation is read off in

percentage units.

The dissipation factor is measured with

a distortion factor meter.

Voltage tests are carried out using a

special voltage tester, which is set up

for a certain voltage and which records

the insulation resistance and any

breakdowns.

Electrolytic capacitors

Capacitance, dissipation factor and

leakage current are tested with a comparison

bridge, where the capacitance

and dissipation factor values are balanced

out, after which the leakage current

is read off on a special scale.

Diodes and transistors

The electrical parameters of these are

measured using a go-no go tester with

automatic input. SMall consignments

are checked using a curve tracer.

Micro circuits

Micro circuits are subjected to rigorous

checks comprising mechanical, environmental

and electrical tests. The

testing procedure is shown in fig. 11.

The electrical testing of micro circuits

deserves to be described more in detail.

From the point of view of testing, the

micro circuits can be divided into four

groups, namely analogue, simple digital,

complex digital and memory circuits,

which require different types of

advanced test equipment.

Analogue circuits

The parameters concerned are checked

manually in test equipment type General

Radio 1730.

Simple digital circuits

These are tested statically in test

equipments type Teradyne J133 and

Fairchild Q 901 "Qualifier".


Fig. 14

Diagram of the fault ratios for micro circuits distributed

on a manufacturer basis

Leakage faults check position 1

Electrical faults

Leakage faults

Electrical faults

Cneck ,,,„„ 2

Leakage faults

Electrical faults

check pos|tlon , + 2

Different manufacturers

Fig. 15, right

Fault ratios for passive components and discrete

semiconductors, obtained from computer system

"Makon"

Mechanical faults

Electrical faults

Complex digital circuits

The circuits are tested from a functional

point of view and also statically and

dynamically. For this purpose the production

side uses system Tektronix

S-3260, which is shown in fig. 13.

Memory circuits

These are also tested as regards function

and statically and dynamically. The

test equipment used is Macro-Data

M104 M/MC, shown in fig. 12.

THE RESULTS OF INSPECTION

ON ARRIVAL

Inspection reports are kept for each individual

inspection occasion. The reports

are compiled once a month and

the statistical data are processed with

the aid of the LM Ericsson computer

system MAKON (Material Control

Purchase). Some results are shown in

the histogram for micro circuits, fig. 14.

The histogram contains statistics from

two different inspection positions,

where the inspection differs as regards

the hermeticity test. In one place the

trace gas used is krypton 85 and in the

other helium.

Fig. 15 shows the fault ratios for passive

components and discrete semiconductor

components.

103

FAULT TRACING COSTS-A

COMPARISON

Fig. 16 shows a comparison of fault tracing

costs at different check levels. The

figures are based on experience of

actual costs. The diagram shows that it

can be profitable to invest in more effective

fault elimination methods in the inspection

on arrival, forexample burn-in,

in order to eliminate defective components

that whould otherwise cause operational

disturbances in the systems.

FUTURE PROSPECTS

Development of an effective and cheap

method that makes possible a one

hundred per cent check for gross leakages

is desirable. Fine leakages in the

encapsulation are then checked by

means of sampling. Heat storage of

components is replaced by burn-in with

voltage applied and increased temperature.

The increase in the complexity and

speed of micro circuits requires large

investments in systems for testing the

functions and the DC and AC parameters

during the inspection on arrival. The

test system is equipped with a main

computer that controls several check

stations. The check stations for the inspection

on arrival can work as independent

units and utilize centrally prepared

programs. Electrical function

testing will to an increasing extent be

carried out at an elevated temperature.


104

Fig. 16

Comparison of fault tracing costs at various check

levels. (Micro circuits)

Volume checked: 2 000 000

Volume checked: 10000000

Development tendencies

The component development is at present

progressing very rapidly, particularly

in the field of micro circuits. There

are already so many types of circuits for

different purposes that existing demands

for speed, low power consumption,

insensivity to disturbances or voltage

variations can usually be satisfied.

However, because of the rapid development

of micro circuits there has

often been time for improved circuits to

appear on the market during the period

between the selection of components

and the putting into service of the first

example of a new system. It is desirable

that it should be possible to exploit new

achievements in the field of components

in previously completed designs,

for example by changing over to a new

circuit family.

The development of micro circuits leads

to an increasing degree of complexity

and flexibility. This means that the

boundaries between components, units

and subsystems are being wiped out.

Programmable component types, such

as micro processors and memories, will

have a decisive influence on the design

and performance of the systems. This

also means that a greater part of the

"knowledge" and flexibility of the exchange

systems will be transferred from

fixed hardware to changeable software.

As regards memory components the

development is towards greater capacity

and speed. It is likely that the memory

types that retain the information even in

the case of voltage failures will become

very important in future.

It is also likely that selectors with

mechanical contacts will to an increasing

extent be replaced by electronic

switching elements. Opto-electronic

and purely optical components will also

be very important for the transmission

of information.

Development of passive components

follows in the wake of the applicable

material and production engineering

development in the semiconductor

field. The resistors will be able to withstand

higher voltages and will have

smaller dimensions. There are already

resistor networks that are mounted in

micro circuit packages. It is also likely

that plastic foil, oxide and ceramic

capacitors will be improved.


Cross Stranding of

Telephone Cable

Sigurd Nordblad

LM Ericsson have developed a new manufacturing process and constructed new

machines for the manufacture of pair cables. The process, which is called cross

stranding, combines two methods: twinning and stranding of groups in one operation

and repeated changing of the relative positions of the pairs during the stranding.

The changing can either be carried out systematically in accordance with a set

plan or at random, so-called randomized cross stranding. The main purpose of the

cross stranding is to reduce the extreme values of the crosstalk and thus improve

the quality of the cable.

In the article the cross stranding technique is described with the emphasis on the

manufacture of pair cables with randomized changing, but cross stranding can also

be used with advantage for stranding single conductors, triples, quads, quintuples

etc.

The cross stranding technique has now been introduced at most of the telecommunication

cable factories owned by the Ericsson Group. At the Piteå plant, which

wasstartedin 1972, the entire production is based on this technique. Manufacturers

outside the Group also use the technique.

UDC 621.315.2

621.391.31

Fig. 1

Cross stranded cables

Top, 150-pair cable with 25-pair groups

Bottom, 50-pair cable with 10-pair groups, jelly-

In addition to line attenuation, characteristic

impedance and line resistance,

the crosstalk characteristics of a cable

have a very great influence on its field of

use. This applies particularly in the case

of trunk cables but also for subscriber

cables.

One reason why the subscriber cables

of today should have a low level of

crosstalk is that modern telephone sets

can then be utilized more efficiently.

The usefulness of a telephone set is limited

by such factors as the crosstalk

level in the cable network. A reduction

of the crosstalk means that greater distances

can be spanned or that the conductor

size can be reduced.

High frequency systems, which are used

nowadays to an ever increasing extent,

SIGURD NORDBLAD

Sieverts Kabelverk AB

also require cables with improved

electrical characteristics.

Previously the pairs, single conductors,

quads etc. of a cable have usually been

assembled in concentric layers. The

pairs were then parallel in each layer

and were adjacent to the same pairs

along the whole length of the cable.

Subsequently the unit cable was introduced,

but the units were still built up of

concentric layers. Efforts to improve the

cable characteristics have been concentrated

on improving the precision of

the wire drawing, insulation etc. and on

suitable selection of lay lengths, i.e. improvements

within the pairs, and very

little attention has been paid to the effect

of the cabling method on the

electrical characteristics.

Crosstalk occurs mainly between adjacent

pairs and it is obvious that the

crosstalk increases when the pairs are

adjacent over a long distance. Using the

conventional layer stranding technique

the pairs are placed adjacently and as

close as possible along the whole

length of the cable. The crosstalk level

between pairs varies in a cable; high

level between adjacent pairs and very

low level between separated pairs.

However, in a telephone system the

worst values often constitute a technical

limit and a number of very good values

does not alter this fact.


Fig. 2

Cable groups with the conventional lay-up

Top, 10-palr group

Bottom, 25-palr group

Fig. 3

Cross stranding lines

Top, line lor manufacturing 10-palr groups

Bottom, 25-pair line with drum twister take-up

The principle of the cross

stranding technique

Cross stranding differs from the other

stranding methods inasmuch as the

pairs or other elements in question are

assembled to form a group with the

pairs continuously changing their relative

positions during the assembly. This

can be carried out in different ways. The

elements can be assembled in groups

either in accordance with a set pattern,

systematic cross stranding, or at random,

randomized cross stranding.

Systematic cross stranding has the disadvantage

that two elements meet at

fixed intervals. In high frequency

systems the intervals can correspond to

wavelengths in the frequency range

concerned, which can give rise to a resonance

phenomenon that is difficult to

eliminate. With randomized cross

stranding the elements are crossed at

random, which eliminates this resonance

phenomenon.

Randomized cross stranding

Capacitance unbalance has a predominant

effect on the value of the crosstalk,

particularly at low frequencies. If

we consider a conventional, concentric

10 or 25-pair group, fig. 2, it is well

known that unbalances arise mainly between

adjacent pairs, 1—2, 2 — 3, 3 — 4

etc. Unbalances also occur to some extent

between the center pairs and the

pairs in the first layer, sometimes also

between pairs in neighbouring layers.

Unbalances between any other com­

binations are almost non-existent. It has

also been established that at least the

highest unbalances increase approximately

in direct proportion to the length

of the cable.

In cross-stranded cables the random

mixing ensures that two pairs are adjacent

only for a limited part of the cable

length and thus the high capacitance

unbalance values are reduced.

The ten pairs in a 10-pair group (fig. 2)

occupy ten different positions. If, for

example, we consider pair no. 1, wefind

that two other pairs can be considered

as adjacent. Two other positions (in the

centre of the group) are slightly further

away but can still be considered as

adjacent. If the positions of the pairs in

the group are changed at random along

the length of cable, we find that two

arbitrarily chosen pairs will be adjacent

for only about 4/9 of the cable length.

The capacitance unbalances contribute

to the crosstalk mainly during this minor

part of the cable length.

Cross stranding of groups that contain

more than ten pairs gives an even greater

reduction of the unbalances. In a

cross-stranded 25-pair group two pairs

are adjacent for only 3/24 to 4/24 of the

total cable length, which gives a corresponding

reduction of the unbalances.

This calculated reduction is

approximate, but the tendency is that a

random mixing of an increasing number

of pairs gives a corresponding

reduction of the capacity unbalances


Fig. 4

Cross stranding device for a 10-pair line

Fig. 5

Random pulse generator

Fig. 6

between the pairs. For example, in a

100-pair group the unbalances would

hardly reach measurable values.

On the other hand the 10-pair group

must be considered as the smallest unit

for which cross stranding gives a

reasonable reduction of the unbalances.

For practical reasons, such as

colour coding, the cross stranding

technique is considered suitable for

groups with between 10 and 30 pairs.

Cross stranding, both randomized and

systematic, gives the group a certain

mechanical flexibility. Thus in this respect

it can be compared with such processes

as the braiding operation used

when making flexible cables.

The most suitable mixing ratio for cross

stranded 10-pair groups is approximately

two crossings per metre, and

these crossings have proved to make

the cable core looser. This results in

greater separation of the pairs and thus

a lower mutual capacitance compared

with the conditions prevailing in a layer

stranded cable. When changing over to

cross-stranded cable the insulation

thickness can therefore be reduced, for

the same value of capacitance, which

means a reduction in cost. This will be

illustrated later on in the article.

Process and machines

107

The most common pair cable specifications

prescribe groups containing between

10 and 25 pairs. Small fixed

groups are used when the cross stranding

technique is applied. It is then possible

to carry out pair twinning and

stranding of groups in one and the same

operation.

A cross stranding line, fig. 3, consists of

the following main components:

1. group twinner

2. random pulse generator

3. mixer, the cross stranding device

4. binding head

5. length measuring device

6. take-up stand

Group twinner

The group twinner is basically a number

of twinning machines assembled to

form a unit, fig. 6. The design of the

twinning machines has intentionally

been kept uncomplicated. The reason

for this is that the process is duplicated

10, 12, 13 or 25 times in each machine.

There is greater risk of faults in sophisticated

machines and the efficiency is

reduced because of the greater number

of repairs.


108

Fig. 9

Take-up stand lor connection wire

Fig. 7

Binding head and length measuring device

Fig. 8, right

Take-up stands for 10-pair groups

Random pulse generator

The random pulse generator, fig. 5,

utilizes the white noise in a transistor to

generate randomly distributed pulses

for the mixer.

Mixer, cross stranding device

Fig. 4 shows the cross stranding of a

10-pair group. The pairs are taken

through dies which move sideways in

the cross stranding device. The movements

of the dies —the mixing of the

pairs —are controlled by a motor that is

started and stopped by pulses from the

random pulse generator. The pairs are

fanned out over rollers, after which they

are assembled and bunched together.

There is no systematic order between

the pairs because their positions on the

rollers are changed at random.

Binding head

The purpose of the binding head is to fix

the pairs in the same order that they

have when leaving the mixer, fig. 7. The

binding yarn can be used for identification

purposes. A binding head usually

has an electromechanical binder yarn

break detector. The mechanical part of

the detector has a sensing finger which

is easily broken, thereby causing the

machine to stop. The break detector in

the cross stranding line binding head

has therefore been redesigned and is

fully electronic. The binder yarn tension

can be adjusted during operation.

Length measuring device

Fig. 7 also shows the length measuring

device, including the tachometer which

synchronizes all drive motors of the

whole line.

Take-up stand

Any type of take-up stand can be used

for 10-pair groups. Fig. 8 shows a type of

take-up stand where all drive equipment

is placed on a frame above the drum

which leaves the floor free for the transportation

of drums. A drum twist takeup

is recommended for 25-pair groups.

Final assembling

A conventional stranding machine with

a drum twist take-up can be used for the

final assembly. It need only be equipped

with a few stands for pay-off reels and

can thus be simple. No back-twist of the

individual groups is required.

Supplementary equipment

Fig. 3 shows an ordinary cross stranding

line. Accessories for various

purposes can be included in the line,

such as taping heads for different taping

materials.

If the group twinner is supplemented

with a specially designed pay-off and

take-up device it will be suitable for

simultaneous twinning and coiling of

connecting wire on small bobbins. Ten


Fig. 10

Distribution curves, showing the capacitance unbalance

of 10-pair groups

Insulation: Solid polyethylene

Conductor diameter: 0.5 mm

Cable length: 500 m

Curve A represents approximately 1000 capacitance unbalance

values within 10-pair groups in cross stranded

cables manufactured In the Plteä plant during 1976.

Curve B represents approximately 1000 capacitance unbalance

values within concentric (2 + 8) 10-pair groups.

The shaded area shows the reduction of high capacitance

unbalance values obtained by introducing the cross

stranding technique. The expected reduction for other

curves B (due to the techniques used tor the wire drawing,

twinning etc.) can be calculated approximately by shifting

the shaded area

Fig. 11, right

Distribution curves, showing capacitance unbalance

between and within 10-pair groups

Insulation: Solid polyethylene

Conductor diameter: 0.5 mm

Cable length: 500 m

Curve A represents the capacitance unbalance between

10-pair groups In cross stranded cables

Curve B represents the capacitance unbalance within 10pair

groups in cross stranded cables

bobbins with pairs and triples or five

bobbins with quadruples and quintuples

can be manufactured in one operation.

The take-up device is shown in fig.

9.

Cross stranding line

It has already been stated that since the

group twinner consists of several individual

twinning machines, special care

was devoted to making the design reliable

and simple. Thus the 10-pair group

twinner has twenty pay-off shafts, each

with its own brake. The risk of a

breakdown because of a brake fault is

then multiplied by twenty and hence the

group twinner is equipped with reliable,

simple rope-brakes.

Size of reels

It is generally considered that large

pay-off reels give high efficiency, but

experience shows that there is an

optimum size. Too large reels give rise

to such disadvantages as conductor

elongation, long acceleration and retardation

times etc.

Most factories in which the introduction

of cross stranding lines is contemplated

are already provided with pay-off and

take-up drums. It must therefore be

possible to adapt the cross stranding

equipment for use with a wide range of

such drums.

Space requirements

A cross stranding line requires less floor

space than conventional equipments,

109

owing to the fact that the pair twinning

and group stranding is carried out in a

single operation. The group twinner

alone requires much less space than the

corresponding number of single twinners

even if these are of the high-speed

type.

Operation

In the group twinner all twinning heads

are idle during reloading. This factor

has a negative effect on the efficiency

compared with production using the

corresponding number of single twinning

machines. A loading table for

pay-off reels has therefore been included

in the cross stranding line in order

to reduce the loading time. A 10-pair

line has to be reloaded every third to

fourth hour and the reloading time is

only ten minutes. Owing to the compactness

of the line and the smooth operation

one operator is sufficient for the

supervision of three 10-pair lines. However,

it is desirable that two operators

work together when reloading.

Electrical characteristics

of cross stranded cables

Capacitance unbalance

The cross stranding technique reduces

the high unbalance values between the

pairs and the crosstalk characteristics

are improved to a corresponding degree

since no pair combinations are

permitted to be systematically adjacent

during any large part of the cable

length. This is shown in fig. 10.


Insulation: Solid

polyethylene

Conductor diameter: 0.5 mm

Cable length: 500 m

Insulation: Foamed

polyethylene

Conductor diameter: 0.5 mm

Cable length: 500 m

Insulation: Solid

polyethylene

Conductor diameter: 0.7 mm

Cable length: 500 m

Fig. 13

RMS values of capacitance unbalance distribution

for cross stranded cable

Each cross represents the RMS value of the 45 capacitance

unbalance values within a 10-pair group

Fig. 12

Distribution curves, showing the capacitance unbalance

for 25 and 10-pair groups

Insulation: Solid polyethylene

Conductor diameter: 0.5 mm

Cable length: 500 m

Curve A represents the capacitance unbalance values

within 25-pair groups In cross stranded cable

Curve B represents capacitance unbalance values within

10-pair groups in cross stranded cables

The characteristics of completed cables

are naturally also dependent on the

quality of the individual pairs as regards

the uniformity of conductors and insulation,

lay lengths etc.

As can be seen from fig. 11 the unbalances

between groups is much less

than the unbalances within groups.

Fig. 12 shows that the unbalances in

25-pair groups are lower than the corresponding

values in 10-pair groups.

The quality of a cable as regards capacity

unbalance is given as the RMS (root

mean square) value. The distribution

diagrams in fig. 13 represent the RMS

values obtained for different types of

cables.

As can be seen from the diagrams, the

spread is relatively large and thus a

reasonably large number of measured

values will be required in order to be

able to establish differences in the quality

of cables that have been manufactured

in different ways.

Mutual capacitance

In cross stranded cables there is no

systematic difference in mutual capacitance

between pairs, caused by their

positions in different layers. There are,

however, some small differences in

mutual capacitance because of the different

lay lengths and manufacturing

tolerances of the pairs. This is shown in

table 1.

Cross stranded, PE insulated 10-pair

group cables without jelly filling have a

lower mutual capacitance than the corresponding

10-group layer cables

(2 + 8). The reason for this is that the

cross stranded cables contain more air

because of the stranding method. A reduction

in mutual capacitance of about

3 % has been noted.

The mutual capacitance relationships

are different for cables with other types

of insulation material.

The cables are generally specified for a

fixed mutual capacitance and hence the

conductor insulation in cross stranded

cables can be reduced with a consequent

reduction in material consumption.

High frequency characteristics

The high frequency characteristics of

symmetrical cables are becoming increasingly

important. This applies

wherever the cables are situated in the

network and particularly when they are

to be used for PCM systems. Typical

crosstalk values for cross stranded cables,

given as the mean value m and the

standard deviations, are shown in table

2.

The standard deviation, o, for near-end

crosstalk is of particular interest. The


PE insulated, solid cable

10-pair 10-pair

groups. groups.

Standard |aid up in cross

deviation. |ayers stranded

.1, of the (2 + 8)

mutual

capacitance.

percentage 1.4 0.75

Table 1

Near-end crosstalk 25-pair 10-pair

at 1 MHz groups groups

m o m o

dB dB dB dB

Within groups 63 6 58 6

Between adjacent

groups 80 6 68 6

Between groups separated

by one group 97 6.6 78 6

dB dB

Far-end crosstalk

at 150 kHz

RMS 78 70

Table 2

Typical crosstalk values for cross stranded cables

m Mean value

a Standard deviation

RMS Root mean square

Fig. 14

The number of permissible 30-channel PCM

systems, N, can be read off from the diagram for

cr-value for conventional cables with 10

or 25-pair groups laid up in concentric

layers is 8 - 10 dB and, as shown in table

2, the corresponding value for cross

stranded groups in approximately 6 dB.

The suitability of a particular cable for

PCM transmission is dependent on the

following four parameters:

m Mean value, crosstalk

a Standard deviation, crosstalk

L Attenuation over a repeater section

N Possible number of PCM systems

The possible number of 30-channel

PCM systems can be determined with

the aid of fig. 14 with a certain degree of

statistical reliability at given m, L and a

values. The diagram is based on singlefrequency

measurements.

Example

Two cables with two 10-pair groups

each, one cross stranded and the other

with concentric layers, have the following

typical near-end crosstalk values.

m = 68 dB

a = 6 dB for the cross stranded cable

a = 9 dB for the cable with concentric

layers

L = 29dB(m - L =39 dB)

Fig. 14 shows that the cable with o = 6

dB can be filled (10 systems) whereas

the second cable permits only one

system although the mean value of the

crosstalk attenuation is the same (68

dB) for both. As can be seen the lower

111

spread of the cross stranded cable is of

great importance.

The crosstalk level between 10-pair

groups in cross stranded cable is 10 dB

better than the level within groups and

this ratio is very constant. For groups

separated by one group there is an additional

improvement of 10 dB. In the case

of 25-pair groups the corresponding difference

is 17 dB.

These good and well defined values and

the well organized cable lay-up make

cross stranded cables very suitable for

PCM systems.

Summary

The method and machines for telecommunication

manufacture which

have been described above have resulted

in

— improved cable quality

Owing to the cross stranding of the

groups the number of high capacitance

unbalance values between

pairs is reduced. The capacitance

level and standard deviation of the

cable are also reduced.

- reduced production costs

Since twinning and group stranding

are carried out in one single operation,

the amount of space required is

reduced and also the investment,

operation and maintenance costs. In

addition the planning and supervision

of the production are simplified.


New Telephone Set

Arne Boeryd and Gunnar Wiklund

New standard telephone sets have been introduced on the market at intervals

of 15-20 years. DIALOG was introduced in 1963 and soon attracted attention and

appreciation because of its excellent transmission characteristics and high overall

quality.

During the second half of 1974 work on developing a new telephone set was started

in order to meet the demands of the future as regards for example push-button

dialling and more stable long-distance characteristics. As a result of this work

LM Ericsson will start production of a new table set, designated DBA 100, during

the autumn of 1978.

UDC 621.395.721

Fig. 1

Telephone set DBA 100

Telephone set DBA 100 has been developed

with the aim of providing a telephone

set

— that gives the best possible overall

economy and which remains up-todate

for 10-15 years after its introduction

— which is suitable for both office and

domestic environments and which

will meet the demands of the 1980s

as regards appearance and quality

— with a simple and reliable construction

and which lends itself to rational

production

— with an entirely modular structure

that facilitates servicing

— that is suitable as the basic product

for a family of telephone sets.

Work on developing and designing a

new standard telephone set was started

jointly by LM Ericsson and the Swedish

Telecommunications Administration

during the autumn of 1974, and a development

assignment was placed with

ELLEMTEL The work was based on

jointly prepared specifications and with

active participation by specialists from

the Administration and LM Ericsson.

LM Ericsson's new telephone set, DBA

100, will be put on the market during

the autumn of 1978 and will gradually

replace DIALOG.

Design

The requirements that are of prime importance

for a telephone set relate to

— the appearance

— the design of the handset with regard

to handling and transmission performance

— the design of the impulsing device

and its location.

A number of industrial designers were

given the task of making suggestions

for the external design of the set. The

resultant design models were examined

from an aesthetical point of view, and

at the same time the possibilities of rational

construction were assessed.

In the design selected, fig. 1, the exterior

of the set is built up of four units,

namely the base, rear and front covers

and the handset.

Mechanical construction

When developing the set the possibilities

provided by the exterior design

have been exploited in order to limit

the number of coloured details. This is

advantageous from the point of view of

manufacture, stocking sparesand maintenance,

and at the same time there is

considerable scope for varying the

colour of the front cover.

The base, rear cover and handset are

manufactured in one colour, preferably

black.

The handset has been designed so that

it rests easily in the hand, reaardless of


ARNE BOERYD

GUNNAR WIKLUND

Division for Subscriber Equipments

Telefonaktiebolaget LM Ericsson

Fig. 2

Exploded view of telephone set DBA 100

1. Rear cover

2. Base

3. Printed board assembly

4. Front cover

Fig. 3

Transmission properties of DBA 100 when using

whether the user grasps it in the middle

or at the microphone end. The handset

also rests on the body of the set in such

a position that it can easily be picked

up from any side of the set.

The set is designed primarily for pushbutton

dialling.

One of the basic design aims was to

create sufficient space in the set for

printed boards. This means that the necessary

mechanical components, primarily

the push-button set and the cradle

switch, have been designed for

mounting on the printed board. The

basic design of the set is shown in fig.

2.

A standard set holds one printed board

assembly that contains the push-button

set, cradle switch, electronic components

for impulsing and current feeding,

and terminals for the handset and

telephone instrument cords.

The ringing device used is a conventional

bell. The base has been equipped

with the resonators that are required

for amplifying the sound from the gongs

within the frequency range 1000-2000

Hz.

The construction described here has

the following advantages from the

points of view of manufacture, installation

and maintenance:

— the front cover is a simple detail without

any fitting problems or special

tolerance requirements

— the set can be tested, packed and

transported without the front cover.

The front cover can easily be fitted

on site, when the customer has chosen

a colour

— the weight distribution of the set is

such that it is easy to carry

— the number frame is placed on top of

the rear cover in front of the handset.

This makes the subscriber number

easy to read

— the push-button set is placed on the

right-hand side of the set, with is

both convenient and attractive. It is

placed in an indentation in the cover.

In this way the set and the printed

board assembly are protected

against shocks if the set should fall

>n to the floor.

Circuits and components

113

All the components are mounted on a

single printed circuit board. It is therefore

possible to take full advantage of

component development and market

requirements. This can be especially

worthwhile with regard to pushbutton

dialling. The design implementation of

these functional elements meets applicable

CCITT recommendations, CEPT

specifications and any additional requirements

imposed by the telecommunications

administrations.

The set will be available either with

a linear microphone and electronic

speech circuit or with a carbon microphone

and a traditional hybrid circuit.

Identical components will be used as

receiver and microphone elements in

the version with an electromagnetic

microphone. Identical electroacoustic

components for transmitting and receiving

are an advantage from the point

of view of maintenance and stocking

spares.

The version with an electret microphone

provides the maximum quality

as regards sound reproduction of the

speech signal.

The reference attenuation of the set

relative NOSFER will be the same irrespective

of whether an electromagnetic

or electret microphone is used.

Fig. 3 shows an example of these transmission

properties when using an electronic

speech circuit.

Summary

LM Ericsson's new telephone set DBA

100 will be the basic set in a range that

will cover such applications as:

— loudspeaking telephone

— executive-secretary system

office telephone systems with a various

number of exchange lines being

available to the set.

This range of telephone sets will be

introduced successively during 1979.


Digital Line Equipments for

8 Mbit/s and 2 Mbit/s

Juho Arras and Örjan Mattsson

This article presents the digital line equipments included in LM Ericsson's new

family of PCM systems in the M5 construction practice. PCM multiplex and

signalling conversion equipment has been described earlier\ The two line equipments

are intended for transmitting 8.448 Mbit/s and 2.048 Mbit/s over pair and

quad cables. A unique strapping network has been introduced in the repeater

equalizers which makes it possible to use existing paper-insulated cables for

transmitting 8.448 Mbit/s.

When designing the equipments the latest CCITT and CEPT recommendations

have been taken into consideration and also the experience gained from the

earlier generation of 2 Mbit/s line equipment. The equipments are characterized

by high reliability with generously dimensioned lightning protection, good transmission

characteristics and a high degree of flexibility in combination with a

design that makes installation and maintenance easy. The two systems are

closely related as regards their design.

UDC 621.395 343

621.3152:

621.391.31

Fig. 1

Block diagram and interfaces for digital line

equipment

MUX PCM multiplex equipment tor 30 circuits

LTE Line terminating equipment lor a PCM system

In the terminal station

Two-way intermediate repeater in a dependent

repeater station

D Digital line interface 75 Q

S Line Interface

RS Repeater section

PFS Power feeding section

FLS Fault location section for repeaters

CS Cable section

1) Interface cable (coax. 75 Q)

2) Line (pair or quad cable)

~ ~ Signal path

System aspects

The new family of digital line equipments

in the M5 construction practice

for transmission over pair and quad

cables consists of

- ZAD 8-2, with a bit rate of 8.448

Mbit/s corresponding to PCM transmission

of 120 telephony channels

- ZAD 2-3, with a bit rate of 2.048

Mbit/s corresponding to PCM transmission

of 30 telephony channels.

There are great similarities between the

two systems as regards design and

equipment. The article will deal mainly

with ZAD 8-2. The description of ZAD

2 — 3 is restricted to the parts that differ

from the previous generation 2 or are

common for ZAD 2 - 3 and ZAD 8-2.

Fig. 1 shows the structure of a digital

line equipment. The basic principles of

its function have been described in detail

earlier 2 . The connection to the line

is via the internationally standardized

coaxial D interface. The matching between

the interface and the cable takes

place in the bay-mounted line terminating

equipment. The bipolar line

signal is regenerated in dependent twoway

regenerative repeaters placed in re

peater housings along the cable. Two

line terminating equipments and the intermediate

line repeaters form a digital

line section, which is designed as an

independent functional block with its

own power and alarm systems. Fault

location equipment, which is usually

common for several digital line sections,

is normally included so that any

faulty repeaters can be located. The

transmission takes place over symmetrical

pairs, one pair for each direction of

transmission. The two pairs can be in

the same cable — single-cable operation

— or in separate cables —two-cable

operation. Single-cable operation

means simpler system design. Twocable

operation has transmission advantages

since near-end crosstalk,

which is often the predominant source

of interference, is eliminated.

8 Mbit/s on existing cables

First-order PCM systems were introduced

in the telecommunication network

mainly because of the increase in

the capacity of existing cables that was

thereby obtained. Experience has

shown that these systems have provided

good technical performance and

good economy. In the case of second-


JUHO ARRAS

ÖRJAN MATTSSON

Transmission Division

Telefonaktiebolaget LM Ericsson

Fig. 2

Comparison of the attenuation characteristics of

paper-insulated star quad cable (1.2 mm, 25

nF/km) and polythene-insulated cable based on

the assumption that the attenuation of both

cables at 4.224 MHz is 60 dB. The frequency

dependence of the paper-insulated cable corresponds

to \ 7+0.6 f and that of the polytheneinsulated

cable to \ T.

^"" Paper-insulated

^ Polythene-insulated

Fig. 3

a) Overvoltage protection for the ZAD 2 — 3 line

repeaters

Longitudinal overvoltages build up a voltage across R1

and T so that the gas tube G strikes. During this process

the repeater equipment and feeding diode D are protected

by an effective current division between the power

diode T and R2.

b) A test pulse used for overvoltage testing. The shortcircuit

current of the surge voltage generator has been

varied over the range 200 A to 1300 A.

order PCM systems it has been assumed

that special cables with polythene

insulation will be used. These often

contain screened groups in order to

keep the near-end crosstalk at an acceptable

level with single-cable transmission.

The 8 Mbit/s system makes

much greater demands than the 2

Mbit/s system as regards the separation

between the transmission directions.

Considerable financial advantages

would be attained if existing paper-insulated

cables could also be used for

second-order systems. In many cases

two-cable operation can be arranged or

a large cable can be utilized so that it is

possible to achieve the necessary separation.

As has been mentioned in a previous

article 3 , at the frequencies of interest

when transmitting at 8 Mbit/s, paperinsulated

cables have an attenuation

curve that deviates from that of polythene-insulated

cables. There are also

considerable differences between different

types of paper-insulated cables.

The article mentioned above gives the

theoretical background for the method

whereby the 8 Mbit/s line repeater can

be adjusted optimally to suit different

types of cables, by means of straps in

the equalizer. ZAD 8 —2 therefore offers

the attractive possibility of working

with existing paper-insulated cables

and also polythene-insulated ones. The

use of only one type of repeater is advantageous

from the point of view of maintenance

and the stocking of spares.

On the island of Funen in Denmark some

fifty two-way repeaters have successfully

been installed and put into operation

on paper-insulated cable, conductor

diameter 1.2 mm, capacitance 25

nF/km. The repeaters work with twocable

operation, with a repeater spacing

corresponding to 60 dB attenuation

at 4.2 MHz. In order to give an idea

of the difference in the attenuation

characteristics, the attenuation curves

of paper and polythene-insulated cables

are compared in fig. 2. The difference

in attenuation is as much as ±10 dB

within the frequency range of the repeater.

Reliability, overvoltage

protection, maintenance

-High reliability is a prerequisite for a

115

line equipment. This applies particularly

for the cascade-coupled line repeaters,

which are often located in inaccessible

places. In the design stage great efforts

have therefore been made to choose

the most suitable components, and to

dimension the circuits with ample safety

margins. In addition the burn-in method

is used during manufacture in order to

eliminate unreliable components.

In rural areas PCM transmission is often

used in cables where the repeaters

can be subjected to very severe stress

in connection with lightning and short

circuit to earth in nearby power lines.

Extensive work has been devoted to

equipping repeaters and other equipment

with efficient overvoltage protection.

Fig. 3 shows how such protection

is arranged in the ZAD 2 — 3 line repeaters.

The dimensioning, which can cope

with pulses far in excess of the CCITT

requirements, has been tested in field

trials in Norway with both aerial and

buried cable.

The repeater protection occupies about

20% of the area of the printed wiring

board. The volume of the components

concerned must be large, among other

reasons because they have to be able

to withstand the high powers that arise

with induced currents of some tens of

amperes and of long duration. The

overvoltages are as far as possible

leaked away via overvoltage tubes before

they reach the printed board. Exposed

conductors are made wide, with

a large distance to adjacent conductors.

Efficient methods for locating repeater

and cable faults are essential from

the point of view of maintenance. A new

fault locating system for repeaters has

been developed for ZAD 8 — 2. It is based

on remotely controlled fault detectors

in each repeater housing and permits

measurements during traffic. The line

terminating equipment includes alarm

circuits for supervising transmitted and

received signals and the remote power

feeding, so that the type of fault can

easily be determined. The equipment

at the terminal can be provided with a

unit that carries out automatic changeover

to a standby system if a fault

occurs in the working system.


Fig. 5

ALBO network for automatic equalization of

0-25 dB (4.224 MHz) pair cable. The variable

resistance R is controlled by the peak amplitude

of the signal after the equalization

Vf+0.6f

characteristic

vT characteristic

Fig. 6

Strappable correction network and its frequency

characteristic

a) network configuration

b) attenuation

The network can be strapped to compensate for all cable

attenuations of the form Ad=\T+af where (K-a^-0.6

I.e. the cable parameters 3 can be selected independent

of each other

Fig. 4

Block diagram of the 8 Mbit/s digital repeater

and the associated signal diagram

Digital line repeaters for

ZAD8-2andZAD2-3

The function and block diagram for the

repeaters in ZAD 8-2 and ZAD 2-3

are similar and are shown in fig. 4.

However, in the case of the 8 Mbit/s

repeater the detailed design is more

comprehensive and requires more

space because of the more complicated

equalization conditions. Common tasks

for the two line repeaters are equalization,

timing recovery and pulse regeneration.

The purpose of the equalization is to

compensate for the frequency-dependent

attenuation introduced by the

cable. An optimum selection of attenuation/frequency

characteristic for the

equalizer means that the effect of disturbance

is minimized. The line repeaters

in ZAD 8-2 and ZAD 2-3 were dimensioned

with the aid of a computer,

and the goodness criterion was the

smallest possible signal/noise ratio at

the repeater input, i.e. maximum number

of disturbing systems for a given

bit error rate. For the purpose of dimensioning

it was assumed that the line

signal code was one of the internationally

standardized transmission codes,

HDB-3orAMI, and that the disturbances

had crosstalk characteristics. The effect

of thermal noise has been investigated

and has been found to have no significance

for the cable attenuations encountered

in ZAD 8-2. The maximum

cable attenuation that can be equalized

in the repeaters is 65 dB at 4.224 MHz

for ZAD 8-2 and 35 dB at 1.024 MHz

for ZAD 2-3.

The repeaters in the ZAD 8-2 system

each contain an equalizer consisting of

the following parts:

— a fixed part that equalizes the maximum

attenuation 65 dB of paperinsulated

pair cable with the attenuation/frequency

characteristic Vf~+

0.6 f.

— a fixed line building-out (LBO) network

which simulates a 15 dB cable

(at 4.224 MHz) and which can be connected

in for short repeater sections.

— a variable equalizer (ALBO) network

for 0-25 dB cable (at 4.224 MHz).

— a strappable network which can be

used to adapt the equalization to different

types of paper and polytheneinsulated

cable.

The configuration of the last two of

these networks are shown in figs. 5 and

6. This equalizer design means that line

equipment ZAD 8-2 can be adapted for

use with all pair and quad cables en-


Fig. 7

Line repeaters in system ZAD 2-3 (left) and

ZAD 8-2 (right). The cassettes, with the dimensions

245X100X45 mm including connectors,

accommodate one two-way 2 Mbit/s repeater and

- --L!»/ *~*nAfinnntiunhi

countered in practice that have an attenuation

of between 25 dB and 65 dB

at 4.224 MHz.

The digital line repeater for ZAD 2-3

contains an equalizer of the same general

design as that described above, but

simpler. In this case there is no need to

adapt the equalizer for different types

of cables, since the attenuation/frequency

characteristic of pair cables is

affected only slightly by material parameters

at frequencies less than 1 MHz.

The timing recovery is carried out by

filtering the line signal in a resonant

circuit (Q~80) followed by extraction of

the zero transitions of the sinusoidal

signal. The circuit design is such that

codes with very low pulse density can

be transmitted, at the same time that

considerable deviations from the nominal

bit rate can be tolerated on the lines.

The reconstruction of the received

pulse train takes place in two decision

circuits, which then control the transmission

of a new regenerated pulse.

The sequence is illustrated in fig. 4.

In both systems the power feeding of

the repeaters takes place with constant

current over the signal transmitting

wires. The feeding voltage for the ZAD

117

2-3 repeaters has been reduced in relation

to that used for the repeaters of

the previous generation. However, attention

has been paid to the requirement

that the repeaters must be reliable

over a large range of temperatures

(-40"C to + 70°C).

The mechanical construction of the line

repeaters is shown in fig. 7. As can be

seen, a two-way repeater in system ZAD

2 — 3 is fitted in the same size of cassette

as a one-way line repeater in ZAD 8 — 2.

The latter repeater makes great demands

as regards internal crosstalk because

of the great differences in levels

and the mixing of analog and digital

functions on the same printed board

assembly. Possible crosstalk paths

have been eliminated by means of a

carefully designed layout and the use

of screening.

Line terminating equipment

The main tasks of the line terminating

equipment are

- to adapt the signal in the send and

receive direction between the digital

link interface D and the symmetrical

line interface S

- to power feed the dependent repeaters

via the cable

- to detect and indicate alarm conditions.


Fig. 8

Block diagram of the line terminating equipment

inZAD8-2

Electronic switch

Resonant circuit

Pulse regenerating circuit

Strapping field

Transformer

Line bullding-out network

DC-DC converter

Signal path

Fig. 9

Alarm functions in the line terminating equipment

Absence of pulses, send direction

Remote power feeding fault

Absence of pulses, receive direction

High error rate, receive direction

Strappable combinatory logic

Transmission path

Fig. 8 shows the block diagram for the

line terminating equipment in system

ZAD 8-2. In the send direction the bipolar

signal is converted from unbalanced

to balanced form in the send

transformer of the transformer unit. In

the receive direction the signal is regenerated

in the terminal repeater,

which is identical to a one-way dependent

repeater. If the repeater section

is short, LBO networks with an attenuation

of 30 dB at 4.224 MHz are

connected in.

The description above also applies for

ZAD 2-3. In this case no LBO network

is required, but a 6 dB flat attenuator

can be strapped in the send direction,

for example to reduce the cable crosstalk.

Leaving out the LBO network has

made it possible to incorporate the

alarm circuit in the transformer unit.

Remote power feeding

The dependent repeaters along the line

are power fed in series over the phantom

circuit from the remote power feeding

unit in the line terminating equipment.

The same type of unit is used in

both ZAD 8-2 and ZAD 2-3. The

power feeding takes place at a constant

direct current of 48 mA and a voltage of

up to ±106 V balanced to earth. The

distance between power feeding stations

varies from about 20 to 40 km in

the case of 8 Mbit/s and from about 40

to 60 km for 2 Mbit/s, depending on the

repeater spacing and the voltage drop

in the cable. This distance can almost

be doubled by using extended feeding

via separate pairs or by series connection

of power feeding units. In order to

ensure personal safety it is possible, by

strapping, to limit the maximum output

voltage to approximately 10 V if a break

should occur in the powerfeeding loop,

for example a cable break.

Alarm, automatic changeover

The line terminating equipments in ZAD

8-2 and ZAD 2-3 have the same alarm

functions, fig. 9. Plug-in U-links are

used to set up the desired connections

between primary and derived alarms.

The alarm state of the system is indicated

by light-emitting diodes, which can

be seen through the front plate of the

unit.

The line terminating equipment can be

provided with an auxiliary unit which,

in the case of an alarm in the receive direction,

provides automatic changeover

to another, predetermined system that

serves as a standby, fig. 10. The automatic

changeover, which is tied to

single-cable working, is particularly attractive

if the standby system goes via

another cable or a radio relay link.


Fig. 10

Automatic changeover between two systems that

operate as the working and standby system

respectively. The changeover is initiated by the

absence of a signal in the receive direction or too

high an error rate on the received signal

Line terminating equipment, system 1

Two-way dependent repeater

Control logic

Fig. 11

Line terminating shelves for ZAD 8-2 (top) and

ZAD 2-3. The top shelf is equipped with two

8 Mbit/s line terminating equipments, the bottom

shelf with four 2 Mbit/s line terminating equip-

Mechanical construction

The line terminating equipments are

placed in M5 single shelves", fig. 11. A

shelf holds four systems in ZAD 2-3

and two systems in ZAD 8-2. The same

type of shelf is used for both single and

two-cable operation and for different

power feeding alternatives. In the 8

Mbit/s system, with its stringent demands

as regards crosstalk between

different parts, a one-way dependent repeater

is used as the terminal repeater,

which has been made possible by adapting

the shelf.

The interface connections are assembled

at the left end of the shelf. Eight

easily accessible coaxial contacts, the

D interface, are mounted on the inside

and outside of the left side member. The

first contact position at the left end of

the shelf is reserved for the L interface.

This is used for connecting the line terminating

shelf to the fault location

equipment in the bay and for connect­

ing in the system alarm. The interface

cables are placed in the left bay side

member. The station cable is brought

in to the following contact positions in

the shelf via connection units.

As regards the bay construction reference

should be made to the description

of the 30 channel PCM terminal

equipment 1 and the M5 construction

practice 4 .

The flexible bay design permits mixed

equipping of 2 and 8 Mbit/s line equipments,

PCM multiplex, digital multiplexors

and signalling equipments.

When the bay is equipped with only line

equipment it holds, apart from fault location

equipment, 64 line terminating

equipments type ZAD 2 — 3 or 36

line terminating equipments type ZAD

8-2. The line equipment is fed direct

from the station battery -24 to -60 V.

The alarm circuits are fed from —12 V.


Fig. 13

Small repeater housing of the loading coil box

type for one 2 Mbit/s system plus fault location

and speaker circuit equipment. Alternatively

the housing can be equipped with two 2 Mbit/s

two-way repeaters

Fig. 12

A repeater housing equipped with eight 2 Mbit/s

two-way repeaters and equipment for fault location

and speaker circuit. Alternatively the housing

can be equipped with eight 8 Mbit/s one-way

repeaters. The housing can also be used to

accommodate combinations of these repeaters

Housing for intermediate

repeaters

The development of ZAD 8-2 and

ZAD 2 — 3 has also meant a new generation

of repeater housings. This work

has taken place in close collaboration

between the Nordic Telecommunications

Administrations and installation

staff from LM Ericsson. The following

types of housings are available.

— Two rectangular housings with capacities

of 23 and 8 2 Mbit/s two-way

repeaters or 23 and 8 8 Mbit/s oneway

repeaters in addition to equipment

for fault location and a speaker

circuit. The housings are made of

steel and silumin respectively and

are identical to those of the previous

system generation. The compact

external dimensions make these

housings particularly suitable for installation

in manholes and on poles,

but they can also be buried. Fig. 12

shows the smaller of the two housings.

— A cylindrical steel housing with the

same fittings and capacity as the

small rectangular housing. The housing

is identical with the one used in

FDM line equipment and is particularly

suitable for direct burial in the

ground.

- A small cylindrical housing made of

stainless steel. The housing is in principle

a loading coil box which can be

opened, fig. 13. It is intended only for

2 Mbit/s and has a capacity of two

systems or alternately one system

plus fault location and speaker

circuit equipment. The housing is

intended mainly for easily accessible

places, for example on poles or in

manholes, and constitutes a financially

attractive solution in, for example,

sparsely populated areas.

As has already been mentioned, the

first three types of housings can be

used for both ZAD 8-2 and ZAD 2-3.

The accommodation not used can be

equipped with loading and phantom

coil units. In general the housings have

great flexibility as regards equipping

Movable dividing walls permit varying

unit dimensions and the connection to

the stub cable is via plug-in unit connection

cables, fig. 14. Strapping for

the power feeding alternative is done in

these cables in orderto simplify installation

and change of repeaters. The stub

cables are made up of screened cable

units in order to obtain the required separation

between the transmission directions

for 8 Mbit/s.

The repeater housings, which are pressure-tight

towards the cable and the en-


Unit

connection

cable

Connection

strip

Fig. 14

Unit connection cables are used for connecting

the units to the stub cable. This arrangement

gives great flexibility and simple conversion

between different equipment alternatives

Fig. 15

Block diagram of the fault location system

with remotely controlled bipolar error detectors

Transformer unit

One-way repeater

Electronic switch

(built Into the one-way repeater)

Address generator

Error analyzer

Address counter

2 Mbit/s two-way

repeater

8 Mbit/s one-way

repeater

8 Mbit/s one-way

repeater

Filter and

service unit

Fault detector

and service unit

Side circuit

loading coil unit

Phantom circuit

loading coil unit

Phantom circuit

loading coil unit

Measuring box

Through-connection

block

Loop connection

adapter

vironment, can be pressurized via the

stub cable by means of a pneumatic

resistance or an external valve. The lid

is sealed with a toroidal ring seal, which

has proved to be very efficient.

Location of repeater

and cable faults

Fault location equipment ZAD 8 — 2

A new fault location system for repeaters

has been devised in connection

with the development of ZAD 8-2. It

has a number of advantages compared

with other systems, such as

— well defined fault criterion in the

form of error rate

— the fact that measurements can be

carried out during operation, i.e. that

preventive maintenance is permitted

— fault location from one supervising

station

— identical fault location equipment in

each housing.

A characteristic feature of the fault location

system, fig. 15, is that each inter­

121

mediate repeater station contains a bipolar

error detector, which can be used

to measure the error rate at the output

of an arbitrary repeater in the housing.

The supervising terminal station can

indicate the repeater to be tested via a

loaded pair, the fault location pair,

which is common for all intermediate

repeater stations. The indication is carried

out by sending a pulse train that

contains housing and repeater addresses.

The same fault location pair is used

for sending the error detector result

back to the supervising station. The

communication over the fault location

pair takes place via data modems

of the FM type. A transmission speed of

750 error pulses/s has been chosen as

giving a suitable compromise between

information speed, modem complexity

and demands on the transmission medium.

It corresponds to a maximum

transmitted error rate of approximately

10" 4 . Addressing takes place at the low

speed of 100 bauds in order to ensure

that the addressing is reliable. The

range is limited by the power fed out


122

Fig. 16

Fault detector shelf and fault detector and service

unit. The instrument units are placed to the

left in the shelf

and the attenuation of the fault location

pair. A maximum of 32 housings can be

connected, on condition that the attenuation

is less than 40 dB. The power

feeding is carried out from the supervising

station using parallel feeding. This

permits branching of the fault location

pair.

The fault location equipment in the repeater

housing consists of the fault detector

and service unit, which also contains

the speaker circuit equipment. All

housings are equipped with identical

units and the address identity is determined

by means of straps.

At the terminal the fault location equipment

is assembled in a fault detector

shelf of the M5 single shelf type, fig. 16.

The shelf can accommodate the abovementioned

unit for supervising the terminal

repeaters in the bay. In the supervising

terminal the shelf is also equipped

with the instrument units, including

power equipment, required for the fault

location. The received error rate is indicated

by a light-emitting diode strip.

The error pulses are also available on a

counter and a recorder output. The

housing and repeater addresses are set

up with thumb-wheel switches. Each

fault detector shelf can terminate and

monitor six fault location pairs.

The unit is prepared for control from an

external computer which makes possible

automatic supervision.

Fault location equipment ZAD 2 — 3

The fault location method with filter 2

used in the previous system generation

has been retained in the 2 Mbit/s equipment.

A mechanical adaptation to the

new system has been carried out. In the

intermediate repeater stations the fault

location filter has been combined with

the speaker circuit unit, and this unit

can also be placed in the terminal in a

fault location shelf. The fault location

shelf, a M5 single shelf, can accommodate

two fault localisation filters,

and terminate up to six fault location

pairs. The shelf can also accommodate

one line terminating equipment, a facility

that has been provided to cater for

small stations where there is only one

PCM system.

The reasons for retaining the filter

method were that it is simple and that

many administrations have access to

the required measuring instruments. It

is, however, possible to adapt ZAD 2-3

to the fault location system of ZAD

8-2.


Fig. 17

The instrument "2 Mbit/s line test set" lor investigating

whether cables are suitable tor PCM

transmission. Practical operating conditions can

be simulated and evaluated with the aid of this

instrument

Locating of cable faults in

ZAD8-2andZAD2-3

In the case of cable breaks it is possible

to locate the fault in the cable with the

aid of the power feeding. The power

feeding unit is then switched over to

voltage feeding with reversed polarity.

A current contribution is obtained from

each repeater before the break point

and the faulty repeater section can be

singled out by measuring the sum current

at the terminal. If the cable fault

consists of a short circuit between the

two pairs in the power feeding loop the

fault can be located by measuring the

output voltage.

Line test sets

LM Ericsson have developed special

instruments, line test sets, for 8 Mbit/s

and 2 Mbit/s digital line systems,

in order to simplify planning, installation

and fault tracing. The two instruments

have the same general structure

and each consists of a transmitter, receiver

and accumulator with a charging

device. Fig. 17 shows the 2 Mbit/s

line test set, which is now in production.

The various parts are combined

into one robust mechanical unit.

The transmitter can generate bipolar

pulse trains, one of which is crystal

controlled. The receiver consists of a

modified one-way repeater, supple­

123

mented by a bipolar error detector and

a counter. The modification makes it

possible to control the equalizer and

the position of the decision thresholds

manually. The transmission quality of

the cable can be checked with the instruments

by measuring the error rate,

cable attenuation and eye opening. The

last test provides a measure of the efficiency

of the equalization and of any

reflections. With the 8 Mbit/s instrument

it is also possible to check the

strapping chosen in the equalizer with

regard to the type of cable. The instruments

can also be used for crosstalk

measurements or for checking the effect

of external disturbances such as

signalling disturbances. During these

measurements it is often only the end

points of the cable that are accessible,

i.e. no working signal can be applied to

the receiver. Through a unique property

of the instruments the result can be

obtained in the form of an equivalent

error rate. Alternatively the noise power

at the decision point can be measured.

The interpretation then assumes a

knowledge of its amplitude distribut ion.

Summary

When developing the digital pair cable

systems ZAD 8-2 and ZAD 2-3 experience

from the previous generation of

2 Mbit/s line systems has been utilized


124

References

1. Lindquist, S. and Widl, W.: 30-

Channel PCM Terminal Equipment

in the M5 Construction Practice.

Ericsson Rev. 53 (1976):1, pp.

38-49.

2. Arras, J. and Tarle, H.: PCM Line

Equipment ZAD 2. Ericsson Rev.

49(1972):2, pp. 47-55.

3. Fredricsson, S.: Transmission Properties

of Paper-Insulated Twin

Cables at High Frequencies. Ericsson

Rev. 54 (1977):1, pp. 28-31.

4. Axelson, K., Harris, P.-O. and Storesund,

E.: M5 Construction Practice

for Transmission Equipment.

Ericsson Rev. 52 (1975):3/4, pp.

94-105.

and the possibilities offered by construction

practice M5, component development

etc. The two systems have

much in common. The use of the same

housing admits common equipping

and facilitates future conversion. ZAD

8-2 has several unique characteristics,

for example the possibility of using

both polythene and existing paper-insulated

cables, and a fault location

Technical data

Electrical data

Line signal

Bit rate/symbol rate

Code

Impedance

Pulse amplitude

Intermediate repeater

Equalization range

Power consumption per oneway

repeater, max.

Temperature range

Power supply

Primary current source

Feeding of intermediate

repeaters

Nominal regulated current

Output voltage, max

Mechanical data

Terminal repeater station

Shelf dimensions

Capacity per line terminating

shelf

Bay height

Capacity per bay

Intermediate repeater station

Dimensions hxwxl or hx®

Weight

Number of two-way 2 Mbit/s

repeaters or one-way 8 Mbit/s

repeaters (incl. fault location

and speaker circuit

equipment)

ZAD2-3

D1 interface S1 interface

2.048 Mb/s 2.048 Mbaud

Bipolar HDB-3 or AMI

75Q unbal 120L> bal.

±2.37 V

+ 3.0 V

5-35 dBat 1 MHz

8 2 V/48 mA

-40°Cto + 70"C

ZDD 532

310*280x430 mm

40 kg

8

system that permits measurements during

operation. Compared with the previous

generation of 2 Mbit/s line systems

ZAD 2-3 has lower power consumption

per repeater, i.e. larger power

feeding distance, better lightning protection

and a more advanced alarm system.

Furthermore the volume of the terminal

equipment is only half that of the

previous generation.

ZAD 8-2

D2 interface S2 interface

8.448 Mb/s 8.448 Mbaud

Bipolar HDB-3 or AMI

75Q unbal. 150Q bal

±2.37 V + 3.3 V

40-65 dB strappable

25-50 dBat 4.2 MHz

15.5 V/48 mA

-40'Cto + 70"C

Battery 24. 36, 48, 60 V

Rectifier tor 110, 127, 220 V (45-65 Hz)

Series feeding via the phantom circuit

48 mA DC

±106 V bal.

122x225-473 mm

ZAD 2-3: 4 systems

ZAD 8-2: 2 systems

Max. 2743 mm

ZAD 2-3: 64 systems

ZAD 8-2: 36 systems

ZDD 533

700x510 mm

110 kg

8

ZDD 534

320x480x610 mm

80 kg

23

ZDD 535

280x195 mm

10 kg

1 (2 Mbit/s)


Operation and Maintenance

Characteristics of AKE 13

Lars G. Ericsson and Åke Persson

This article is devoted primarily to a description of the operation and maintenance

characteristics of AKE 13. The article also gives some examples of operational

experience, but this will be described in more detail in a later issue of Ericsson

Review. Certain of the facilities offered by AKE 13 as regards international and

intercontinental traffic are also touched upon.

UDC621 395 343 AKE 13 is an SPC system intended for

medium-sized to very large transit exchanges

for national as well as international

and intercontinental traffic. The

first version of AKE 13, AKE 131 with

control system APZ 130, was taken

into service in Rotterdam in 1971 and

was then the first SPC transit exchange

in the world and also the first

Table 1

AKE 13 exchanges in operation or on order on

o • k~ 1cl 1077

Country

Australia

Czechoslovakia

Denmark

Finland

Italy

Mexico

Holland

Norway

Sweden

England

Total:

Exchange

Sydney (1974) - Broadway

Sydney - Paddington

Prag

Ålborg (1974)

Arhus (1977)

Albertslund

Copenhagen (1974)

Hillerod

Odense (1976)

Slagelse

Virum

Helsinki, PLH (1974)

Helsinki, PLH

Helsinki, HT(1976)

Turku (1974)

Bari (ASST)

Napoli(SIP)

Palermo (SIP) (1975)

Padova(SIP)

Verona (SIP)

Salerno (SIP)

Guadalaiara (1975)

Mexico D F (1973)

Monterrey (1975)

Dordrecht (1976)

Rotterdam DC (1971)

Rotterdam INT (1976)

Bergen

Drammen

Oslo (1976)

Skien

Stavanger

Gothenburg, Vrr

Stockholm, FRE (1974)

Stockholm, HY(1976)

London-Thames

multi-processor exchange 1 . However,

Rotterdam was not LM Ericsson's first

SPC exchange. AKE 13 was based on

experience gained from the combined

local and transit exchange system AKE

12, which was put into operation in

Tumba, outside Stockholm, as early as

1968 2 .

The latest version of the system, which

is designated AKE 132 and which contains

the new control system APZ 150,

has been described previously 3,5 .

As can be seen from table 1, 18 AKE 13

exchanges have been put into operation

in eight countries in three continents

National

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

x

X

X

X

x

x

X

X

X

X

X

X

X

International

*

X

X

X

X

X

X


X

X

X

X

X

Multiple-capacity

in

operation

2 400

9600

12 000

20 400

9 600

15 000

4 000

8 000

3 600

8 400

18 600

6 000

3 600

9600

3 600

9600

2 400

12 000

Oil

order

3 600

7 200

18 000

9600

6 000

7 200

6 000

29 400

8 000

3 200

6 000

6 600

3 600

3 600

4 800

4 800

7 200

1 200

3 600

3 600

2 400

3 600

3600

4 800

16800

158 400 174 400

332 800


LARS G ERICSSON

AKE PERSSON

Telephone Exchange Division

Telefonaktiebolaget LM Ericsson

Fig 1

Block diagram of the hardware. An AKE 13 exchange

can be equipped with up to 8 data processing

blocks (DPB)

Each DPB is synchronously duplicated, i.e. consists of

two sides, each with a complete processor with stores

and a transfer unit. Both sides normally work In synchronism,

which Is continuously monitored. However, only one

side Is executive. When there Is a discrepancy between

the sides the faulty unit Is disconnected. The duplication

can be utilized, for example, when changing programs

and a further 18 exchanges are on order.

Thus the further development of the

system that is continuously being carried

out is founded on long and extensive

experience.

System characteristics

The telecommunications administrations'

need of transit exchanges with

high capacity increases with the expansion

of the long-distance traffic. Previously

it has not always been possible to

satisfy the need for such large exchanges,

and hitherto it has been a fairly

common practice to combine a number

of exchange units, each with a relatively

low maximum capacity, to form what is,

from the point of view of the network,

one common switching point.

A way of solving these problems that is

often more economical for the telecommunications

administrations and

also technically more suitable, not least

from the point of view of operation and

maintenance, is to install a single exchange

having the required capacity.

AKE 13, with the following inherent

properties, is able to satisfy all reasonable

demands as regards lines and traffic:

— maximum number of incoming lines,

30000

— maximum number of outgoing lines,

30 000

— maximum number of switched calls

per hour for the control system APZ

150, 750 000

— maximum traffic capacity of the

switching network with an internal

congestion of 0.2 %, 25 000 erlangs

The switching capacity is among the

largest in the world. The system also

meets very stringent demands as regards

reliability and operating

characteristics.

Synchronously duplicated

multi-processor system

The AKE 13 control system is built up of

a suitable number of synchronously duplicated

data processing blocks (DPB),

with a maximum of eight blocks. The


Table 2

Extended AKE 13 exchanges Exchange

Fig.2

Helsinki

Copenhagen

Mexico City

Mexico City

Rotterdam DC

Rotterdam DC

Rotterdam INT

Turku

Turku

Ålborg

Ålborg

Time

Jan -77

Nov -75

Sept -75

Sept -76

Mar -73

July-74

May -76

Feb -75

April -77

Aug -74

Feb -77

Size of the extension

4 processors 9 600 multiple pos.

2 „ 7 200

2 „ 7 200

1 „ 3 600

1 200

1 ,, 3 600

1 „ 1 200

800

1 600

3 000

1 200

data processing capacity of the system

can thus be extended in step with the

increase in the number of lines, fig. 1.

This means that the central, most complex

and, for the operation most important

part of the system need never be

larger than what is required for handling

the traffic on the lines connected at the

time.

The factor that is most important for the

reliability is the synchronous duplication

of the control system. It provides

— the fastest possible fault detection

through continuous comparison of

the function of the duplicated units

— the possibility of easily separating

software faults and hardware faults

— simple and reliable fault localization

— the minimum loss of traffic handling

capacity when a fault occurs

— the possibility of introducing new

functions without disturbing the

traffic

Thanks to the duplication it is possible

to reload the whole system without disturbing

the traffic. The two sides in the

system, A and B, which normally work in

synchronism, are separated by means

of a command, fig. 2. Side A is then

loaded with exchange programs and

data from a tape unit. Side B continues

the traffic handling without interruption.

When the loading is completed, the

newly loaded side A takes over the traf­

Size of the exchange after

the extension

6 processors 15 000 multiple pos.

6 ,, 20 400

4 „ 15 000

5 .. 18 600

2 „ 6 000

3 „ 9 600

2 ,, 3 600

2 „ 6 400

2 „ 8 000

4 „ 8 400

4 „ 9 600

fic handling and side B is put in the

standby state. If any operational disturbance

should then occur because of

faults in the newly loaded software,

there will be an automatic changeover

to side B and the traffic handling will

again be carried out by the original

software. When it has been proved that

the newly loaded side A works

satisfactorily, updating of side B is

ordered and also a return to synchronously

duplicated operation. The updating

is carried out by copying the contents

of the A-side stores.

This facility, which through separation

of the system sides enables programsto

be loaded and verified without interruption

of the traffic handling, can also be

used when making major changes in the

software.

The possibilities offered by the synchronous

duplication and multi-processor

arrangement have been utilized

in the methods for installation and testing

of extensions that have been used

successfully in AKE exchanges already

in operation, table 2.

The system can be extended by the

addition of new data processing blocks

without it being necessary to change

the contents of the program stores

already in service. If the extension does

not include any new functions it is sufficient

to make certain minor adjust-


128

Fig. 3

Standardization of program packages

merits in the data stores of the data processing

blocks in service, in order to

show the changed configuration of the

control system.

When extending an exchange, the additional

data processing block and

switching equipment are tested by

means of special installation test programs,

which are run in the new processor

before the new units are connected

to the data processing blocks that are

already in service.

Division into function blocks

Several of the basic characteristics of

AKE 13 have been obtained by dividing

the system into function blocks. The

blocks contain program sequences with

functionally associated data and also

hardware units. The interfaces between

the various blocks are clearly defined

and the interworking between blocks is

carried out with the aid of special signals.

Experience has shown that this structure

is essential for the design, maintenance

and production of such a large

and complex SPC system as AKE 13. To

develop clear, lucid and well adapted

documentation for a large program

system is generally considered as one of

the most difficult and resource-demanding

tasks in the production of

software. However, thanks to the division

into blocks it has been possible to

apply the same product handling and

documentation rules for the AKE 13

software as have long been used successfully

for LM Ericsson's earlier exchange

systems. This has been

advantageous both for the operation

and the maintenance of the AKE 13

systems.

Standardized software

When designing software a natural aim

is to create software that can be used

for as many exchanges as possible.

Standardization means simplified document

handling and improved program

quality because of the wider field of

application. This has a favourable

effect on both exchange and product

maintenance.

Thanks to the division into function

blocks it has been possible to build up

an extensive program library over the

years. As regards the switching system

this library comprises approximately

200 blocks with standard functions and

a further 200 blocks containing market-dependent

functions. Altogether

this means a total program volume of

approximately 700 000 words for the

switching system. The standard blocks

cover all signalling systems that have

been specified by CCITT, including No.

6, and a comprehensive operation and

maintenance system for the exchange

switching system. The operating system

in APZ 150 is general for all exchanges,

and it has therefore been possible to

create a standardized system file forthis

system that applies for all exchanges,

both as regards the revision status of

the blocks and their placing (allocation)

in the program store. The operating system

is handled as a superior product

and its status is marked with a revision

state indication for the whole operating

system. The revision state is changed

when functions are added to the operating

system. The operating system in

service can be exchanged for a more

modern one without the environment,

i.e. the software in the switching system,

being affected.

It is also possible to standardize the

switching system software in the same

way. This has been done for several

administrations. The aim has been to

create, for each administration, as large

a share of standard allocated program

volume as possible. The blocks that are

uniaue for a particular exchanqe are


Software for/he

switching system

(APT)

Standard products

36 %

Software for the

switching system

New production

4 %

Fig. 4

Distribution of the software volume between

standard and new production

Fig. 5

then added, fig. 3. Thanks to the block

structure of the software it has thus

been possible to create standard allocations,

despite functional differences between

different exchanges, a fact which

has been a considerable help in reducing

an administration's costs.

The far-reaching standardization has

meant that nowadays when LM Ericsson

deliver an exchange in a new market

it is only necessary to design on average

4% of the total amount of software

to be included in the exchange.

The remainder can be collected as verified

standard products from a library,

fig. 4, without any changes being

necessary.

AKE 13 in the international

network

When AKE 13 was designed, one of the

prerequisites was that the system

should be suitable for the handling of

international and intercontinental traffic

with particularly complex demands.

The large traffic handling capacity,

adaptability to different signalling sys­

129

tems and traffic routing requirements

and the comprehensive maintenance

functions are examples of characteristics

that are important for the international

traffic and which it has been possible

to realize through the SPC technique.

Of the 36 AKE 13 exchanges which

have hitherto been put into operation or

ordered, no less than 14 are international

exchanges (table 1).

System AKE 13 is able to provide all traffic

facilities that have been agreed internationally,

and the system is suitable

for all levels in the international

hierarchy. Today practically all the international

signalling systems are in

operation in AKE 13 exchanges, namely

R1, R2, CCITT 4, CCITT 5 and CCITT 6.

Facilities for connecting echo suppressors,

individual ones or from a common

group, and for automatically connecting

in and disconnecting attenuators

are built into the system. All current

forms of international accounting are

catered for. Charging can be carried out

by means of repeated metering pulses

or toll ticketing. For example, pulse

charging can be used for the national

traffic and toll ticketing for the international

traffic.


130

Fig. 6

The control room in an AKE 132 exchange with

maintenance panel, magnetic tape units and

other I/O devices

International maintenance centre, IMC

In an international exchange it is naturally

particularly important that the

maintenance of the exchange and lines

can be carried out efficiently and that

suitable aids are available. CCITT recommend

that the supervision measurement

and testing of international

lines and the associated telephone exchange

equipment should be carried

out at an international maintenance

centre, IMC, in the international exchange.

IMC comprises the following

parts:

ISMC Maintenance centre for the international

exchange

ITMC Maintenance centre for the international

lines

ISCC Administrative centre for coordination

of the maintenance of exchange

and lines. ISCC does not

require any special equipment

and will therefore not be discussed

here.

ISMC

ISMC has access to functions for

— supervising the operation

— testing devices and localizing faults

— carrying out traffic recording

In AKE 13 these functions are built into

the system and are reached via

typewriters. The ISMC activities are

therefore usually carried out in the control

room of the AKE exchange, fig. 6.

The AKE system provides ISMC with

some fifty operation and maintenance

functions for the switching equipment

Some of these are:

— supervision of fuses and control

circuits

— supervision of traffic disturbances,

congestion and blocking. An alarm

and printout are obtained when a certain

threshold value is exceeded. The

system also contains functions for a

more detailed study of each disturbance

— automatic and semi-automatic

supervision of the quality of connections

and calls through observation

of randomly selected connections

— automatic checking that each line

has at least one call every 24 hours

— automatic signalling check on outgoing

lines


Fig. 7

Test desk for ITMC

The desk contains, among other things,

— a level meter

— a variable oscillator

— a frequency meter

— a psophometer

The desk can be connected to the lines either automatically

via the switching stages In response to a command

from the typewriter, or manually, via the U-link racks In

- tracing of the connection path

through the exchange for a certain

connection

- recording of changes in the state of

devices in a certain connection

- circuit tester for code receivers and

code senders. The testing is initiated

by a command or automatically from

the disturbance supervision

— periodic testing of the speech paths

through the switching network

— blocking of lines, devices and links

by means of commands

— traffic recording and the collection of

statistics on line routes, device

groups and link routes. There is a

wide range of measurement types

available in addition to those recommended

by CCITT.

ITMC

Extensive equipment is placed at the

disposal of ITMC for the maintenance of

international lines:

Measuring equipment for making fully

automatic transmission measurements

in accordance with CCITT recommendations.

The measuring equipment is of

two types. One type is designated ATME

(Automatic Transmission Measuring

Equipment) and carries out level and

noise measurements on international

131

lines in accordance with CCITT recommendation

No. 2. The other type consists

of automatic test equipments;

CCITT 12 which uses CCITT measuring

methods Nos. 1 and 2 for routine checks

of the transmission quality on international

lines with signalling in accordance

with CCITT system No. 4, and

STC (Simplified Transmission Check)

for routine checks on international lines

with signalling in accordance with

signalling system R2. The measurements

are controlled by a previously

stored program that indicates when the

measurements are to be made and on

which lines.

A test desk with instrument for making

manual or semi-automatic transmission

measurements, fig. 7. As can be seen

from fig. 8, these desks can be connected

both to the station side of the

junction line relay sets, via the selector

network, and to the line side, via U-link

racks (jack racks that give access out

towards the line or in towards the station).

U-link racks for connecting lines to the

test desk. (Certain telecommunications

administrations, however, consider that

the U-link racks can be omitted, since a

junction line relay set in an SPC ex-

WilH UiUdl/r

IP ,1


Table 3

Number of component faults per rack and operating

year in the Rotterdam DC

Fig. 8

Connection of the ITMC test desk to the switching

network

Type of equipment

Central data processing equipment

Test and control equipment

I/O equipment

Code switches

Other switching devices

No. of

racks

30

17

2

64

90

change is small compared with one in a

conventional exchange because the

logic functions are carried out by the

software.)

Route supervision panel with lamps for

indicating route congestion and various

types of blocking.

A typewriter that provides access to all

supervisory functions in the system.

The design of ITMC can vary depending

on the size of the exchange and the

number of international lines. The

equipment is normally placed in a separate

room. It is then often most convenient

to put the U-link racks in the same

room. For small international exchanges,

the ITMC equipment can be

placed in the maintenance desk in the

control room.

Operational experience

The SPC technique has made it possible

to rationalize the operation and maintenance

work to a very great extent. The

administrations have pointed out many

advantages, for example:

- that changes of traffic routing data,

route information and also charging

and accounting data require considerably

less resources and can be carried

out in very much shorter time in

AKE 13 than in conventional systems.

A comparison is made on the last

page of this article

— that it is easier to introduce functional

changes since the majority of the

1972

No. of faults

per rack

04

1 82

2.0

0.047

0.28

No. of

racks

47

32

4

128

158

1975

No. of faults

per rack

0.28

1.53

0.25

0056

0082

functions are realized in software

— that the efficient supervision and

fault localization functions have

meant that in AKE 13, more often than

in previous systems, faults are detected

and cleared before the subscribers

complain

— that the connection and testing of

lines is greatly facilitated by the

maintenance panel and typewriter

provided.

Extension of exchanges in operation

It has already been mentioned that several

AKE 13 exchanges in operation

have been extended, table 2. The great

flexibility of the system offers an almost

unlimited variety of extension configurations,

but experience from the extensions

that have been carried out

shows that it is possible to limit and

standardize the number of extension

configurations and still meet all requirements

that the administrations

may have. This standardization has the

following advantages:

— it admits the development of standardized

methods and aids

— it gives short installation and testing

times

— extensions can be carried out without

specialist aid

— it reduces the amount of resources

required in all handling stages

— it gives high reliability

Component reliability

In a previous article on the first AKE 13

exchange, Rotterdam DC 1 , the number


Fig. 9

System restart frequency in the AKE 13 exchange

in the Rotterdam DC with 3 DPBs and 9 600

multiple positions

1. The switching stages and data store were extended at

the beginning of 1973

2 The exchange was extended by the inclusion ot a new

data processing block and new switching stages at the

beginning ot 1974

3. An inverter fault occurred in June 1975

— Mean value tor 4 months

of component faults per rack was given

for the various parts of the system during

the first year of operation, 1972.

These figures are given in table 3, supplemented

by the corresponding figures

for 1975. It should be noted that the

exchange has been extended in the

meantime. The table verifies the high

component reliability, which has proved

to be very stable and has even improved

during the time the exchange has been

in operation.

System restart

The system restart is such a basic function

in the fault clearing operations that

it deserves a special description.

A software or handling fault can manifest

itself in several ways, for example

through

— the normal program handling ceasing

wholly or partly

— an unauthorized attempt to write

data in a specially protected area

— a jump in the software being addressed

to an unequipped part of the

store.

Number of automatic

restarts per month

133

Restart takes place when any of the

above fault situations occur.

A hardware fault in a processor side is

detected by the system maintenance

unit and can usually be located and isolated

without affecting the operation. In

the exceptional cases when this is unsuccessful,

for example if a double fault

occurs, restart also takes place. Such a

restart means that temporary data are

cleared, whereby any faulty data are removed.

The system is then set to an initial

state where it can start handling

traffic again.

In the first place a normal system restart

takes place, in which calls in the register

state (i.e. connections in the process of

being set up) are disconnected. This

takes approximately 30 seconds and

during this time no new calls can be accepted.

Calls that have already been

established are not affected.

If repeated normal restarts do not have

the desired effect, or if the number of

restarts during a short period of time

exceeds a preset value, a major system

restart takes place. This means that

established calls are also disconnected.

Such restarts are relatively few and are

carried out in approximately 15 seconds.

The exchange staff may sometimes

want to "clean up" the exchange and

they then carry out a manual restart,

normal or major. A manual system restart

is also carried out in connection

with function changes and when a data

processing block is put into operation

or taken out. These manual restarts are

usually carried out during periods of

low traffic.

Subscribers who happen to call the exchange

during a system restart experi-


134

ence this as congestion or a "silent

connection". They then make a new and

normally successful call attempt, and

thus the traffic handling disturbances

must be considered as negligible.

Fig. 9 shows the system restart rate for

the very first AKE 13 exchange, Rotterdam

DC, from when it was first put

into operation until the end of 1976. The

great reduction in the number of restarts

is a result of the successive improvement

and stabilization of the

system and also the clearance of faults

in the exchange itself. A number of

faults were revealed during the period

immediately after the system had been

put into operation, when new programs

were taken into use and more lines connected

in. Hence the number of system

restarts per month increased until

March 1972, and then started to decrease.

When a system restart is carried out a

printout is obtained, stating the type of

fault. Atthesametime data are recorded

on magnetic tape that define the system

statewhen thefaultoccurred. Thisgives

valuable information for further fault

tracing.

In conclusion it can be said that the

system restart function is an excellent

aid for maintaining the operational reliability

of the system, since it limits the

effects of a fault and also provides the

basic data for clearing program and

handling faults. Furthermore the possibility

of initating a system restart manually

means that the operating staff

have been given a tool that enables

them to clear up a complex fault situation.

Successive improvements

The AKE 13 system has been delivered

to some of the most technically

advanced administrations in the world.

In meeting their different requirements

AKE 13 was successively supplemented,

so that it now constitutes a

system that meets the most divergent

demands, especially as regards operation

and maintenance. The administrations'

experience of AKE 13 has also

provided views that have resulted in

new facilities and improved handling

methods.

As new techniques become available

the possibility arises of adding new system

components, which increase the

capacity of the system, enlarge its field

of use, improve its operational reliability

and simplify its handling. Processor

APZ 150 is one example of this development.

This modern processor was

used for the first time in Stockholm

(Hammarby exchange) in June 1976.

Three more exchanges with APZ 150

were taken into service in 1976, in

Odense (Denmark), Oslo (Norway) and

Helsinki (Finland). By using integrated

circuit engineering and semiconductor

memories it has been possible, for

example, to reduce the space requirements

and increase the traffic handling

capacity. A list of the most important

improvements that APZ 150 has brought

the AKE 13 system is given on the opposite

page.

Another example of the continuous development

of the AKE system is the introduction

of regional computers. Thus

the LM Ericsson type APN 163

minicomputers are used in AKE 13 for

several applications, for example forthe

signalling terminals in the latest AKE

generation of the CCITT signalling system

No. 6, and for the display-based

operator system ANE 403. Minicomputer

APN 163, which is also used in several

applications outside the telecommunications

field, has been designed with

special regard paid to the stringent demands

on reliability that a telephone

exchange makes. The list of instructions

for APN 163 has also been designed

to meet the requirements of SPC

exchanges. Since the minicomputer

has been designed by LM Ericsson it

has been possible to integrate its operation

and maintenance with that of the

remainder of the exchange.

The use of regional computers provides

valuable flexibility at the interface between

the central functions in the control

part of the AKE system and the functions

of the peripheral units, which are

often affected by external conditions. In

certain cases it has also been possible

to relieve the central control system of

routine but capacity demanding functions,

which would otherwise have reduced

the overall traffic handling

ranaritu nf tho QvQtpm


Comparison of the amount of work required for installing a new

route in a conventional exchange and in an AKE 13 exchange

Assume that a new outgoing line route of 30 lines is to be connected in. The exchange

has 3 000 incoming and 3 000 outgoing lines.

In a conventional transit exchange the

work includes the following work operations:

I.New number analysis wirings, route

type markings and wires for idle marking

must be included in the route marking

devices.

2. In the line selection devices the line test

wires must be strapped to connection

relays.

3. Straps must be made in the exchange

intermediate distribution frames (IDF)

for connecting the idle marking, test,

control and statistics wires of the new

junction line relay sets.

4. The speech and control wires of the

junction line relay sets must be connected

in the IDF to the correct position

in a selector stage multiple (in AKE 13

this is normally done by means of fixed

exchange wiring).

The work is carried out in different parts

of the exchange rack room and is concluded

by deblocking the lines with the

aid of the deblocking button on each

junction relay set in the relay set rack in

question.

The exchange is assumed to comprise 22

central route marking devices and 25 line

selecting devices.

A total of approximately 740 straps or IDF

wires must be connected. Assuming that

the work is carried out by experienced

staff, a total of approximately 31 work

hours is required (8 hours of which are

required for connecting the lines to the

switching stages).

APZ 150 compared

with APZ 130

- The capacity approx. 3 times larger

- The amount of space required for

the control part is reduced to 1/3

for the same capacity

- The power required for the control

part is reduced to 1/3 for the same

traffic handling capacity

- The use of integrated circuits instead

of discrete components increases

the reliability

- More efficient fault localization

system

- Automatic restart with reloading

and safeguarding of certain data

when the system restart function

cannot restore the exchange to

traffic handling

- Improved aids in the system for

functional changes and changes in

size

- Improved facilities for tracing

program faults

- Advanced system for safe introduction

of program changes during

operation

In an AKE 13 exchange all operations are

carried out from the control room with the

aid of commands, which are either typed

on a typewriter or punched and read in

via a punched tape reader

1. A command that creates the new route

and gives it the correct characteristics

5-10 minutes

2. One command per line to include it in

the new route

approximately 30 minutes

3. Commands for dimensioning supervision

of congestion, disturbance and

blocking for the route 10-15 minutes

4. Changing the digit analysis tables

approximately 30 minutes

Consists of the following operations:

- punching the analysis command

- mounting the magnetic tape for the

change in the analysis table and writing

the command

- read-in of the control commands

- read-in of the analysis commands

- read-in of the loading tape

5. One deblocking command per line

approximately 30 minutes

A total of 11/2-2 hours is required, including

the punching of the command

tapes.

References

1. Hamstad.O. and Norén, L.-O.AKE

131 Rotterdam Exchange and Experience

from First Year of Operation.

Ericsson Rev. 50 (1973):2, pp.

58-64.

2. Sundblad, A.: Operating Experience

from AKE 120, Tumba. Ericsson

Rev. 47 (1970):2, pp. 42-49.

3. Meurling, J., Norén, L.-O. and

Svedberg, B.: Transit Exchange

System AKE 132. Ericsson Rev. 50

(1973):2. pp. 34-57.

4. Norén, L.-O. and Sundström, S.:

Software System for AKE 13. Ericsson

Rev. 5? (1974):2, pp. 34-47.

5. Nilsson, R. and Norén, L.-O.: In-

Plant System Testing. Ericsson

Rev. 53 (1976):1, pp. 19-27.

6. Norén, L.-O. and Sundström, S.:

Development, Production and

Maintenance of Software for AKE

13. Ericsson Rev. 53 (1976):3, pp.

152-160.

135


ABJ 101-the Modern Public

Magneto Switchboard

Lennart Aldestam

The demand for manual magneto switchboards has increased considerably during

recent years. There are large areas where conditions are such that magneto switchboards

offer a satisfactory and economical solution to the telecommunication

problems as also long lines of not very high quality can be connected.

In order to meet this growing demand LM Ericsson, in close cooperation with

many of their customers, have developed a modern, single-position magneto

switchboard designated ABJ 101. ABJ 101 can operate either as an independent

exchange or in combination with an automatic exchange (PAX), AKD 860.

UDC 621.395 343

Fig. 1

ABJ 101 equipped for 40 magneto lines, 4 CB

junction lines and 10 cord pairs

1. Base unit

2. Line shelf

3. Line unit for magneto lines

4. Line unit for CB junction lines

5. Supervision unit

6. Cord pair unit

7. Position unit

ABJ 101 -a compact and

flexible switchboard

ABJ 101 is a compact and modern

magneto switchboard with all equipment

built into the chassis. The

switchboard has a modular structure,

fig. 1, and the units are connected via

plugs and jacks, which means simple

and fast installation.

This construction gives a low initial cost

and permits extension in stages. No

special tools are required for assembling

and installing the switchboard.

Owing to the fact that the switchboard is

built up of such components as miniature

relays and cord winders it has very

small dimensions and thus requires

only a third of the volume of space required

for traditional floor switchboard.

ABJ 101 can be placed on a desk, counter

etc. and merges well with different

surroundings. The small dimensions

mean that it is usually very easy to find

a suitable place for the switchboard.

Can be extended from 10 to 240 lines

The switchboard can be extended in units

of ten magneto lines, four CB junction

lines and one cord pair.

The final capacity is 18 cord pairs and

either 240 magneto lines or 220

magneto lines and 8 CB junction lines,

fig. 2. Thus the system covers a very

wide capacity range. The switchboard is

already wired for full capacity when delivered.

All apparatus is inserted from

the front.

Administrations with several switchboards

may find it advantageous to

stock extension equipment themselves.

The cost of this will be small.

High operator efficiency

A summary of the most important

characteristics of ABJ 101 is given at the

end of the article. Many of these

characteristics are such that they enable

the operator to handle a larger

amount of traffic and provide better

service for the subscribers.


LENNARTALDESTAM

Telephone Exchange Division

Telefonaktiebolaget LM Ericsson

Fig. 2

ABJ 101 with two line boxes equipped for 130

magneto lines and 14 cord pairs (maximum 160

magneto lines with two line boxes). The capacity

is extended to the final number of 240 magneto

Some examples of such aids are automatically

generated ringing (transistorized),

ring-back tone to the calling

subscriber and supervision of a junction

line when other calls are being handled.

The switchboard can also be equipped

with a push-button set for decadic impulsing

when required. Furthermore

control devices have been positioned

and the colour scheme selected with the

aim of making the work of the operator

as easy and pleasant as possible.

Independent exchange

ABJ 101 can be included in a network as

an independent exchange and then interwork

with all types of manual and automatic

public systems.

Mechanical design

From the points of view of construction

and function the switchboard consists

of two main parts, namely the basic unit

and line boxes. The basic unit contains

a central wiring unit to which all wiring

between different equipment has been

concentrated. Position and cord pair

equipment is mounted in the basic unit.

The line boxes contain magneto line

and CB junction line units. The first line

box also contains a supervision unit.

Incoming lines are connected to the

137

equipment in the line boxeseitherdirect

or via a wall-mounted connection box.

(Magneto lines are connected via 10pair

cables and CB junction lines via 4pair

cables.)

The sides of the switchboard are made

of teak in natural colour with a plastic

finish. The plates for mounting the line

units and the top and rear plates of the

exchange are finished in green. The

cord pair and position units are framed

by anoidized light metal sections. Vacant

positions are covered by green plastic

strips.

All components meet the requirements

for good insulation, shape permanence

etc. even during extreme climatic conditions.

Cord pair equipment

The components for a cord pair have

been made up into a cord pair unit, fig.

4.

The unit, the front of which is covered

with green plastic, contains two cord

winders with 3-pole cords and plugs.

The plugs have covers and protective

spirals made of grey plastic, which together

with the design of the cord winder

considerably reduce the mechanical

stress on the cord.


Fig. 3

Line unit for 10 magneto lines

Fig. 4

Cord pair unit

AP Answering cord

RP Calling cord

SK-RK 3-posltlon switch with speech position SK and

ringing position RK

SL Clearing drop indicator

LM Ericsson have long operational experience

of cord winders obtained from

the portable switchboards ABM 10,

which have withstood severe trials under

field conditions. The cord winder is

a corner stone in the ABJ construction

and has greatly contributed to the reduction

of the switchboard volume.

The cord pair unit also includes a 3position

switch and a clearing drop indicator.

The switch, which has small

dimensions, has a frame and lever arm

made of grey plastic.

Line equipment

The line units are available in two variants,

one for magneto lines, fig. 3, and

one for CB junction lines. Among other

things the line units contain a drop indicator

jack strip. The CB junction line

units also contain a printed board assembly

with line components.

Position equipment

The dial and other control devices that

are common for the whole of the exchange

have been assembled in a position

unit. The front of the unit is covered

with a plate of green plastic.

Supervision equipment

A flag indicator, battery indicator and

jacks for checking cords etc. are assembled

in a supervision unit.

ABJ 101 in combination with

automatic exchange AKD 860

For certain telecommunication requirements

in rural areas LM Ericsson

can offer a new, economical system

consisting of the magneto switchboard

ABJ 101 in combination with an automatic

exchange (PAX) AKD 860, fig. 5.

This system is intended for very small

communities and can be used while

waiting for the demand to increase sufficiently

to justify a changeover to a fully

automatic rural exchange system. The

combination of these two standard


Fig. 5

ABJ 101 in combination with automatic exchange

AOK 860 gives dialled calls in a the densely populated

area and manually extended calls in the

surrounding rural area. Both subscriber categories

have the possibility of national and international

calls via the operator in the manual

switchboard

products gives subscribers in densely

populated areas many of the

advantages of automatic calls and at the

same time offers remote subscribers in

the surrounding areas telephone

service via the modern manual

switchboard.

All subscribers have the possibility of

national and international calls via the

operator at the manual switchboard. A

subscriber in AKD 860 calls the operator

by dialling a single-digit number. Calls

within AKD 860 are set up automatically

and within ABJ 101 manually. Calls between

subscribers in ABJ 101 and AKD

860 are set up by the operator.

Exchange AKD 860 is built up of plug-in

units, which means simple and fast installation

and low maintenance costs.

This construction permits extension in

stages and facilitiates any future move

of the equipment to another location.

The small dimensions enable the

system to be installed in suitable existing

premises, and thus no special building

is required.

The operator at the manual switchboard

handles the charging for trunk calls and

in certain cases this is done in cooperation

with the trunk operator in the

superior exchange.

Accessories for ABJ 101

139

Power equipment

For power supply four dry-cell batteries

BKA 1002 for 1.5 V and 50 Ah are recommended.

These are placed in battery

box BKY 1012.

Main distribution frame

Main distribution frame NBA is recommended

for switchboards with more

than 40 lines. A main distribution frame,

but without line fuses, can also be

obtained through using double the

number of connection boxes.

Telephone sets

Ordinary magneto telephone sets are

connected to the exchange, for example

LM Ericsson's model DAG 11102/8.

External bell

When an acoustic signal is needed outside

the switchboard, a bell KLD 1303,

can be connected. Various outdoor

bells can also be used.

Wooden sides

ABJ 101 can be adapted to the environment

at the installation site. The switchboard

is delivered with teak sides. Sets

of side pieces made of jacaranda,

natural pine, walnut or other types of

wood can be supplied on special request.


" The maximum number of lines that can be connected

to a certain switchboard is dependent on a

number of factors, such as the amount of traffic,

type of traffic, the efficiency of the operator, calling

habits, local tradition etc. Under normal circumstances

an operator in a single-position magneto

switchboard can handle a maximum of 100-140

magneto lines and 8 CB lines. However, if the

amount of traffic is very small it is possible in some

cases to handle more than 200 lines

Technical data

Maximum number* of

magneto lines

CB junction lines

Cord pairs

Dimensions in cm

Width

Height

Depth

Approx. weight, kg

Operating voltage

6VD.C.

Base unit

+ 1 line box

80 70 60

- 4 8

18 18 18

62

41

53

40

Line resistance

The maximum value of the line resistance

for magneto lines is dependent on

the line attenuation, which may amount

to 15 dB. The leakage resistance must

not be less than 10000 ohms. The indicators

drop at 9 mA. The resistance and

leakage values for CB junction lines are

primarily dependent on the limit values

of the main exchange. Thus the maximum

values for these lines must be

calculated on the basis of data from the

main exchange.

Base unit

+ 2 line boxes

160 150 140

- 4 8

18 18 18

ABJ 101

62

59

53

55

Base unit

+ 3 line boxes

240 230 220

4 8

18 18 18

62

77

53

70

Advantages

The exchange has been given all the

characteristics that can be demanded

from a modern manual magneto

switchboard which means that

— CB junction lines from manual or automatic

exchanges can be connected

— magneto junction lines can be connected

to the ordinary magneto units

— supervision of a junction line can be

carried out by the operator while

handling other calls

— line splitting gives the operator the

possibility of talking to one party

without the other being able to overhear

the conversation

— the ringing is generated automatically

(transistorized)

— a flag indicator indicates that a signal

is being sent out

— a ring-back tone is sent to the caller

— backward ringing can be carried out

via the answering cord

— acoustic signals can be obtained

concurrently with incoming seizure

and clear-forward signals

— a fixed acoustic signal can be connected

in by means of a switch

— dropped indicators are automatically

reset during the handling of the calls

— a battery indicator indicates when it

is time to check the condition of the

battery

— testing of the cords can be performed

— an automatic fuse eliminates fuse

changes

— anextrajack is provided for connecting

in a handset for an assistance

operator

— space is provided forthe memoranda

that the operator needs to have readily

accessible in order to be able to

work rapidly and efficiently.


The Ericsson Group

With associated companies and representatives

EUROPE

SWEDEN

Stockholm

1. Teletonaktiebolaget LM Ericsson

2. LM Ericsson Telematenel AB

1. ABRrfa

1. Sieverts Kabelverk AB

5. ELLEMTEL Utvecklings AB

1. AB Transvertex

4. Svenska Elgrossist AB SELGA

1. Kabmatik AB

4. Holm & Ericsons Elektriska A8

4. Mellansvenska Elektriska AB

4. SELGA Mellansverige AB

Alingsås

3. Kabeldon AB

Gävle

2. Vanadts Entreprenad AB

Gothenburg

4. SELGA Västsverige AB

Kungsbacka

3. Bota Kabel AB

Malmö

3. Bjurhagens Fabrikers AB

4. SELGA Sydsverige AB

Norrköping

3. AB Norrköpings Kabelfabrik

4. SELGA östsverige AB

Nyköping

1. Thorsman & Co AB

Spånga

1. Svenska Radio AB

Sundsvall

4. SELGA Norrland AB

Växjö

1. Widells Metallprodukter AB

EUROPE (excluding

Sweden)

DENMARK

Copenhagen

2. LM Ericsson A/S

1. Dansk Signal Industri A/S

3. GNT AUTOMATIC A/S

1. I. Bager&Co A/S

Tfistrup

2. Thorsman & Co Aps

2. LM Ericsson Radio Aps

FINLAND

Helsinki

2. Oy Thorsman & Co Ab

Jorvas

1. Oy LM Ericsson Ab

FRANCE

Colombes

3. Société Francaise des

Telephones Ericsson

Paris

2. ThorsmansS.a.r.l.

Bologne sur Mer

1. RIFAS.A.

Marseille

4. Etablissements Ferrer-Auran S.A.

IRELAND

Athlone

1. LM Ericsson Ltd.

Drogheda

2. Thorsman Ireland Ltd.

ITALY

Rome

1. FATMESoc. per Az

5. SETEMERSoc per Az.

2. SIELTESoc. perAz

The NETHERLANDS

Rijen

1. Ericsson Telefoonmaatschappij B.V.

NORWAY

Nesbru

Oslo

2. SRA Radio A/S

4. A/S Telesystemer

4. A/S Installatör

Drammen

3. A/S Norsk Kabelfabrik

POLAND

Warszaw

7. Telefonaktiebolaget LM Ericsson

PORTUGAL

Lisbon

2. Sociedade Ericsson de Portugal Lda

SPAIN

Madrid

1. Irtdustrias de Telecommunicact6n S.A.

(Intelsa)

1. LM Ericsson S.A.

SWITZERLAND

Zurich

2. Ericsson AG

UNITED KINGDOM

Horsham

4. Thorn-Ericsson Telecommunications

(Sales) Ltd

2. Swedish Ericsson Rentals Ltd.

5. Swedish Encsson Company Ltd.

3. Thorn-Ericsson Telecommunications

(Mfg) Ltd.

London

6. Thorn-Encsson Telecommunications

Ltd

4. United Marine Leasing Ltd.

4. United Marine Electronics {UK) Ltd

WEST GERMANY

Frankfurt-am-Maln

2. Rifa GmbH

Hamburg

4. UME Marine Nachnchtentechnik, GmbH

Hanover

2. Ericsson Centrum GmbH

Ludenschetd'Ptepersloh

2. Thorsman & Co GmbH

Representatives In:

Austria, Belgium, Greece, Iceland, Luxembourg.

Yugoslavia.

LATIN AMERICA

ARGENTINA

Buenos Aires

1. Cia Ericsson S.A C.I.

1. Industrias Eléctricas de Quilmes S.A.

5. Cia Argentina de Teléfonos S.A

5. Cia Entrernana de Telétonos S.A.

BRAZIL

Säo Paulo

1. Ericsson do Brasil Comércio e

Industria S.A.

4. Sielte SA. Instalacöes Elétricas e

Telefönicas

4. TELEPLAN, Projetos e Planejamentos

de Telecommunicates S A

Rio de Janeiro

3. Fios e Cabos Plåsticos do

Brasil S.A

Säo José dos Campos

1. Telecomponentes Comércio e

Industria S.A.

CHILE

Santiago

2. Cla Ericsson de Chile S.A.

COLOMBIA

Bogota

1. Ericsson de Colombia S.A.

Call

1. Fåbricas Colombianas de Materiales

Eléctricos Facomec S.A

COSTA RICA

San José

7 Tplffnnaktiphnlflnot I M EricSSOn

ECUADOR

Quito

2. Teléfonos Ericsson C A

GUATEMALA

Guatemala City

7. Teletonaktiebolaget LM Ericsson

HAITI

Port-au-Prince

7. LM Encsson

MEXICO

Mexico D.F.

1. Teleindustna Ericsson, S.A

1. Latinoamericana de Cables S A

de C V

2. Teléfonos Ericsson S.A.

2. Telemontaje, S.A. de C.V.

PANAMA

Panama City

2. Telequipos S A

PERU

Lima

2. Cia Ericsson S A

EL SALVADOR

San Salvador

7. Teletonaktiebolaget LM Encsson

URUGUAY

Montevideo

2. Cia Ericsson S.A.

VENEZUELA

Caracas

1. Cla Anonima Ericsson

Representatives in:

Bolivia. Costa Rica, Dominican Republic,

Guadeloupe, Guatemala. Guyana, Haiti,

Honduras. Martinique, Netherlands Antilles,

Nicaragua, Panama, Paraguay, El Salvador,

Surinam, Trinidad. Tobago

AFRICA

ALGERIA

Algiers

7. Telefonaktiebolaget LM Ericsson

EGYPT

Cairo

7. Telefonaktiebolaget LM Ericsson

MOROCCO

Casablanca

4. Société Marocaine des Telephones et

Telecommunications "SOTELEC"

TUNISIA

Tunis

7. Teletonaktiebolaget LM Ericsson

Zambia

Lusaka

2. Ericsson (Zambia Limited)

2. Telefonaktiebolaget LM Ericsson

Installation Branch

Representatives In:

Angola, Cameroon, Central African Republic,

Chad, People's Republic of the Congo,

Dahomey, Ethiopia, Gabon, Ivory Coast,

Kenya, Liberia, Libya, Malagasy, Malawi,

Mali, Malta, Mauretania, Mozambique,

Niger, Nigeria, Republic of South Africa,

Reunion, Senegal, Sudan, Tanzania. Togo,

Tunisia, Uganda, Upper Volta, Zaire.

ASIA

INDIA

Calcutta

2. Ericsson India Limited

INDONESIA

Jakarta

2. Ericsson Telephone Sales

Corporation AB

IRAQ

Baghdad

7. Teletonaktiebolaget LM Ericsson

IRAN

Teheran

3. Simco Ericsson Ltd.

4. Aktiebolaget Erifon

KUWAIT

Kuwait

7. Telefonaktiebolaget LM Ericsson

LEBANON

Belrouth

2. Société Libanaise des Telephones

Ericsson

MALAYSIA

Shah Alam

1. Telecommunication Manufacturers

(Malaysia) SDN BHD

OMAN

Muscat

7. Teletonaktiebolaget LM Encsson

SAUDIARABIA

Riyadh

7. LM Ericsson

THAILAND

Bangkok

2. Ericsson Telephone Corporation

Far East AB

TURKEY

Ankara

2. Ericsson Turk Ticaret Ltd Sirketi

Representatives in:

Bahrein, Bangladesh. Burma, Cyprus, Hong

Kong, Iran, Iraq. Jordan, Kuwait, Lebanon,

Macao, Nepal, Oman. Pakistan, Phillippines,

Saudiarabia, Singapore, Sri Lanka,

Syria, United Arab Emirates

UNITED STATES and

CANADA

UNITED STATES

Woodbury NY.

2. LM Ericsson Telecommunications Inc

New York, NY.

5. The Ericsson Corporation

CANADA

Montreal

2. LM Ericsson Limitée/Limited

AUSTRALIA and

OCEANIA

Melbourne

1. LM Ericsson Pty Ltd

1. Rifa Pty. Ltd.

5. Telenc Pty Ltd

Sydney

3. Conqueror Cables Ltd.

Representatives In:

New Caledonia, New Zealand, Tahiti.

1. Sales company with manufacturing

2. Sales and installation company

3. Associated sales company with manufacturing

4. Associated company with sales and

installation

5. Other company

6. Other associated company

7. Technical office


TELEFONAKTIEBOLAGET LM ERICSSON

ISSN 0014-0171 fltinlnri in Cuiflrian I uinnlnra^non OrebfOl97!

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