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 - V O L U M E
54
Copyright Telefonaktiebolaget LM Ericsson
Printed in Sweden, Stockholm 1977
RESPONSIBLE
EDITOR
PUBLISHER
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EDITORIAL
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O.
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TECHN
CHRISTIAN
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FOLKE
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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 1 0 1 - t h e 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
95
BERNDTAGNEUS
Älvsjö Electronics Factory
IVAN B O R G S T R Ö M
Telephone Exchange Division
Telefonaktiebolaget LM Ericsson
Fig. 1
Column 1 (lett)
S o m e 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.
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
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.
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.
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.
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.
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.
Fig. 3
Light m i c r o s c o p e
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
PASSIVE COMPONENTS
Passive components comprise various
types of resistors, capacitors and transformers.
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
l i o n irt r a l n w QjatQ
97
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.
Fig. 4
X-ray c a m e r a
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
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
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-
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,
uses infra-red lights as the transfer
medium between a light-emitting diode
and, for example, a photo transistor.
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
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.
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
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-TransistorLogic) 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-OxideSilicon) 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-
99
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.
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
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
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
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• • •
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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
Mechanical
EnEl.
viron- param.
mental
Resistors, resistor networks and potentiometers
S
S
Capacitors
S
S
Diodes, transistors
and thyristors
S
Micro circuits
S
A
A
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.
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.
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.
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.
Quality follow-up
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.
A
Table 1
Testing of components
A Check of the whole consignment
S Sampling test in accordance with MIL-STD-105
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-
Fig. 10
The solderability tester STE 74 works in accord a n c e 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
ponent quality originally accepted after
type testing is maintained in later component deliveries.
Inspection of components
on arrival
Inspection of purchased components
101
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.
Fig. 11
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 682-20). 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
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
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
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".
103
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.
Fig. 14
Diagram of the fault ratios for micro circuits distributed on a manufacturer basis
Leakage faults
Electrical faults
Leakage faults
Electrical faults
check
Cneck
Leakage faults
check
Electrical faults
Different manufacturers
position 1
,,,„„
pos|tlon
2
,+
2
Fig. 15, right
Fault ratios for passive components and discrete
semiconductors, obtained from computer system
"Makon"
Mechanical faults
Electrical faults
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.
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
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
Fig. 16
Comparison of fault tracing costs at various check
levels. (Micro circuits)
Volume checked: 2 000 000
Volume checked: 10000000
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
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,
Fig. 1
Cross stranded cables
Top, 150-pair cable with 25-pair groups
Bottom, 50-pair cable with 10-pair groups, jelly-
SIGURD NORDBLAD
Sieverts Kabelverk AB
also require cables with
electrical characteristics.
improved
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.
The principle of the cross
stranding technique
Fig. 2
Cable groups with the conventional lay-up
Top, 10-palr group
Bottom, 25-palr group
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
Fig. 3
Cross stranding lines
Top, line lor manufacturing 10-palr groups
Bottom, 25-pair line with drum twister take-up
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
107
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.
Fig. 4
Cross stranding device for a 10-pair line
Fig. 5
Random pulse generator
Fig. 6
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
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.
Length measuring device
Fig. 7 also shows the length measuring
device, including the tachometer which
synchronizes all drive motors of the
whole line.
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.
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.
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.
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
109
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.
Fig. 10
Distribution curves, showing the capacitance unb a l a n c e 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. 1 1 , right
Distribution curves, showing c a p a c i t a n c e unbalance b e t w e e n 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
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,
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
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.
Insulation: Foamed
polyethylene
Conductor diameter: 0.5 mm
Cable length: 500 m
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.
Insulation: Solid
polyethylene
Conductor diameter: 0.7 mm
Cable length: 500 m
Fig. 13
RMS v a l u e s of c a p a c i t a n c e u n b a l a n c e d i s t r i b u t i o n for c r o s s s t r a n d e d c a b l e
Each cross represents the RMS value of the 45 capacitance unbalance values within a 10-pair group
Fig. 12
Distribution curves, showing the capacitance unb a l a n c e for 25 a n d 10-pair g r o u p s
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
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
111
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.
PE insulated, solid cable
Standard
deviation.
.1, of the
mutual
capacitance.
percentage
10-pair
groups.
|aid u p in
|ayers
10-pair
groups.
cross
stranded
(2 + 8)
1.4
The suitability of a particular cable for
PCM transmission is dependent on the
following four parameters:
0.75
Table 1
Near-end crosstalk
at 1 MHz
Within groups
Between adjacent
groups
Between groups separated by one group
Far-end crosstalk
at 150 kHz
RMS
m
a
L
N
25-pair
groups
m
o
10-pair
groups
m
o
dB
63
dB
58
dB
6
dB
6
80
6
68
6
97
6.6
78
6
dB
dB
78
70
Table 2
Typical crosstalk values for cross stranded cables
m
Mean value
a
Standard deviation
RMS Root mean square
Mean value, crosstalk
Standard deviation, crosstalk
Attenuation over a repeater section
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
Fig. 14
The number of permissible 30-channel PCM
systems, N, can be read off from the diagram for
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 1 0 - 1 5 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
113
ARNE BOERYD
GUNNAR WIKLUND
Division for Subscriber Equipments
Telefonaktiebolaget LM Ericsson
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.
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
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
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.
System aspects
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
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 generation2 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 earlier2. 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-
115
JUHO ARRAS
ÖRJAN M A T T S S O N
T r a n s m i s s i o n Division
T e l e f o n a k t i e b o l a g e t L M Ericsson
Fig. 2
C o m p a r i s o n of t h e a t t e n u a t i o n c h a r a c t e r i s t i c s of
p a p e r - i n s u l a t e d star q u a d c a b l e (1.2 m m , 25
nF/km) and polythene-insulated cable based on
the a s s u m p t i o n t h a t t h e a t t e n u a t i o n of b o t h
c a b l e s at 4.224 M H z is 60 d B . T h e f r e q u e n c y
d e p e n d e n c e of t h e p a p e r - i n s u l a t e d c a b l e c o r r e s p o n d s to \ 7 + 0 . 6 f a n d t h a t of t h e p o l y t h e n e i n s u l a t e d c a b l e to \ T.
^""
^™
Paper-insulated
Polythene-insulated
Fig. 3
a) Overvoltage p r o t e c t i o n for t h e ZAD 2 — 3 l i n e
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
article3, 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
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
2 0 % 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 - 2 5 dB (4.224 MHz) pair cable. The variable
resistance R is controlled by the peak amplitude
of the signal after the equalization
Digital line repeaters for
ZAD8-2andZAD2-3
The f u n c t i o n and block diagram for the
repeaters in ZAD 8 - 2 and ZAD 2 - 3
are similar and are s h o w n in fig. 4.
However, in the case of the 8 M b i t / s
repeater the detailed design is more
comprehensive and requires
more
space because of the more c o m p l i c a t e d
equalization conditions. C o m m o n tasks
for the two line repeaters are equalization, t i m i n g recovery and pulse regeneration.
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 A d = \ T + a f where (K-a^-0.6
I.e. the cable parameters3 can be selected independent
of each other
Fig. 4
Block diagram of the 8 Mbit/s digital repeater
and the associated signal diagram
The purpose of the equalization is to
compensate for the frequency-dependent attenuation introduced by the
cable. An o p t i m u m 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 d i mensioned with the aid of a computer,
and the goodness criterion was the
smallest possible signal/noise ratio at
the repeater input, i.e. m a x i m u m n u m ber of disturbing systems for a given
bit error rate. For the purpose of d i m e n sioning it was assumed that the line
signal code was one of the internationally standardized transmission codes,
H D B - 3 o r A M I , and that the disturbances
had crosstalk characteristics. The effect
of thermal noise has been investigated
and has been f o u n d 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 f o l l o w i n g parts:
— a fixed part that equalizes the maximum attenuation 65 dB of paperinsulated pair cable with the attenuat i o n / f r e q u e n c y characteristic Vf~+
0.6 f.
— a fixed line b u i l d i n g - o u t (LBO) network w h i c h simulates a 15 dB cable
(at 4.224 MHz) and w h i c h can be connected in for short repeater sections.
— a variable equalizer (ALBO) network
for 0 - 2 5 d B cable (at 4.224 MHz).
— a strappable network w h i c h can be
used to adapt the equalization to different types of paper and polytheneinsulated cable.
The c o n f i g u r a t i o n of the last two of
these networks are s h o w n 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-
117
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.
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
( - 4 0 " 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 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
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
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 e q u i p m e n t
inZAD8-2
Electronic switch
Resonant circuit
Pulse regenerating circuit
Strapping field
Transformer
Line bullding-out network
DC-DC converter
Signal path
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.
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.
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.
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.
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
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
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
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-
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-
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
equipment1 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 - 2 4 to - 6 0 V.
The alarm circuits are fed from —12 V.
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.
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
— 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.
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
- 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
121
2 Mbit/s two-way
repeater
8 Mbit/s one-way
repeater
8 Mbit/s one-way
repeater
Filter and
service unit
Fault d e t e c t o r
and service unit
Side c i r c u i t
l o a d i n g coil unit
Phantom circuit
l o a d i n g coil unit
Phantom circuit
l o a d i n g c o i l unit
Measuring box
Through-connection block
Loop connection
adapter
Fig. 14
Unit connection c a b l e s are u s e d for connecting
the units to the stub cable. This a r r a n g e m e n t
gives great flexibility and simple conversion
between different equipment alternatives
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-
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
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
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
Fig. 16
Fault detector shelf and fault detector and service unit. The instrument units are placed to the
left in the shelf
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 filter2
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.
123
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-
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
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
and the possibilities offered by c o n struction practice M5, c o m p o n e n t development etc. The t w o systems have
much in c o m m o n . The use of the same
housing admits c o m m o n e q u i p p i n g
and facilitates future conversion. ZAD
8 - 2 has several unique characteristics,
for example the possibility of using
both polythene and existing p a p e r - i n sulated cables, and a fault location
system that permits measurements during operation. Compared with the previous generation of 2 M b i t / s line systems ZAD 2 - 3 has lower power cons u m p t i o n per repeater, i.e. larger power
feeding distance, better lightning protection and a more advanced alarm system. Furthermore the volume of the terminal e q u i p m e n t is only half that of the
previous generation.
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
ZAD2-3
ZAD 8 - 2
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
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
5 - 3 5 dBat 1 MHz
4 0 - 6 5 dB strappable
2 5 - 5 0 dBat 4.2 MHz
8 2 V/48 mA
- 4 0 ° C t o + 70"C
15.5 V/48 mA
- 4 0 ' C t o + 70"C
Battery 24. 36, 48, 60 V
Rectifier tor 110, 127, 220 V ( 4 5 - 6 5 Hz)
Series feeding via the phantom circuit
48 mA DC
±106 V bal.
Mechanical data
Terminal repeater station
Shelf dimensions
Capacity per line terminating
shelf
Bay height
Capacity per bay
References
1. Lindquist, S. and Widl, W.: 30Channel 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. 4 7 - 5 5 .
3. Fredricsson, S.: Transmission Properties of Paper-Insulated Twin
Cables at High Frequencies. Ericsson Rev. 54 (1977):1, pp. 2 8 - 3 1 .
4. Axelson, K., Harris, P.-O. and Storesund, E.: M5 Construction Practice
for
Transmission
Equipment.
Ericsson Rev. 52 (1975):3/4, pp.
94-105.
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
Intermediate repeater station
ZDD 532
ZDD 533
ZDD 534
Dimensions h x w x l or hx®
310*280x430 mm 700x510 mm 320x480x610 mm
Weight
40 kg
110 kg
80 kg
Number of two-way 2 Mbit/s
repeaters or one-way 8 Mbit/s
repeaters (incl. fault location and speaker circuit
equipment)
8
8
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
Country
Australia
National
International
Helsinki, PLH (1974)
H e l s i n k i , PLH
Helsinki, H T ( 1 9 7 6 )
T u r k u (1974)
X
X
X
X
Bari (ASST)
X
Napoli(SIP)
P a l e r m o (SIP) (1975)
Padova(SIP)
Verona (SIP)
Salerno (SIP)
X
Guadalaiara (1975)
M e x i c o D F (1973)
Monterrey (1975)
x
D o r d r e c h t (1976)
R o t t e r d a m DC (1971)
R o t t e r d a m INT (1976)
X
Bergen
Drammen
Oslo (1976)
Skien
Stavanger
x
G o t h e n b u r g , Vrr
S t o c k h o l m , FRE (1974)
Stockholm, HY(1976)
X
England
Total:
London-Thames
X
X
9600
12 000
X
20 400
6 000
X
9 600
X
7 200
6 000
X
X
15 000
4 000
8 000
X
X
3 600
X
X
X
X
X
X
X
•
x
X
X
8 400
18 600
6 000
3 600
9600
3 600
X
6
6
3
3
4
4
000
600
600
600
800
800
7 200
1 200
3 600
9600
3 600
3600
X
X
4 800
X
X
29 400
8 000
3 200
3 600
2 400
X
X
3 600
7 200
9600
X
X
Oil
order
18 000
X
X
Sweden
in
operation
*
Å l b o r g (1974)
Arhus (1977)
Albertslund
C o p e n h a g e n (1974)
Hillerod
Odense (1976)
Slagelse
Virum
Norway
Multiple-capacity
2 400
Sydney (1974) - B r o a d w a y
Sydney - P a d d i n g t o n
Denmark
Holland
k ~ 1cl 1077
Exchange
X
Mexico
•
As can be seen from table 1, 18 AKE 13
exchanges have been put into operation
in eight countries in three continents
Prag
Italy
o
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 .
Czechoslovakia
Finland
Table 1
AKE 13 exchanges in operation or on order on
multi-processor exchange1. 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
19682.
X
X
2 400
12 000
16800
174 400
158 400
332 800
LARS G ERICSSON
AKE PERSSON
Telephone Exchange Division
Telefonaktiebolaget LM Ericsson
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.
Fig 1
Block diagram of the h a r d w a r e . An A K E 13 exchange c a n 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
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
Helsinki
Copenhagen
Mexico City
Mexico City
Rotterdam DC
Rotterdam DC
Rotterdam INT
Turku
Turku
Ålborg
Ålborg
Size of the extension
Time
Jan -77
Nov -75
Sept -75
Sept -76
Mar -73
July-74
May -76
Feb -75
April -77
Aug -74
Feb -77
4 processors
2
„
2
„
1
„
1
1
,,
„
9 600 multiple pos.
7 200
7 200
3 600
1 200
3 600
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-
Fig.2
Size of the exchange after
the extension
6 processors
6
,,
4
„
5
..
2
„
3
„
2
,,
2
„
2
„
4
„
4
„
15 000 multiple pos.
20 400
15 000
18 600
6 000
9 600
3 600
6 400
8 000
8 400
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
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
Fig. 3
Standardization of program packages
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
129
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.
Software f o r / h e
s w i t c h i n g system
(APT)
Standard p r o d u c t s
36 %
Software for the
s w i t c h i n g system
New p r o d u c t i o n
4 %
Fig. 4
Distribution of the software volume between
standard and new production
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-
Fig. 5
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
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
Fig. 6
The control room in an AKE 132 exchange with
maintenance panel, magnetic tape units and
other I/O devices
— 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
131
- 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
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
Fig. 7
Test d e s k 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
Table 3
Number of component faults per rack and operating year in the Rotterdam DC
Type of e q u i p m e n t
Central data p r o c e s s i n g e q u i p m e n t
Test and c o n t r o l e q u i p m e n t
I/O e q u i p m e n t
Code switches
Other s w i t c h i n g devices
No. of
racks
30
17
2
64
90
change is small c o m p a r e d with one in a
conventional exchange because the
logic f u n c t i o n s are carried out by the
software.)
Route supervision panel with lamps for
indicating route congestion and various
types of b l o c k i n g .
A typewriter that provides access to all
supervisory functions in the system.
The design of ITMC can vary d e p e n d i n g
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 r o o m .
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 c o n s i d erably less resources and can be carried out in very m u c h 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 f u n c t i o n al changes since the majority of the
Fig. 8
Connection of the ITMC test desk to the switching
network
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
f u n c t i o n s 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 c o n n e c t i o n 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
f o l l o w i n g 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 a m o u n t 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
133
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.
N u m b e r of a u t o m a t i c
restarts per month
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-
Fig. 9
S y s t e m r e s t a r t f r e q u e n c y in t h e AKE 13 e x c h a n g e
in the Rotterdam DC with 3 DPBs a n d 9 600
multiple p o s i t i o n s
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
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
r a n a r i t u n f t h o QvQtpm
135
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 - 1 0 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 1 0 - 1 5 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. 4 2 - 4 9 .
3. Meurling, J., Norén, L.-O. and
Svedberg, B.: Transit Exchange
System AKE 132. Ericsson Rev. 50
(1973):2. pp. 3 4 - 5 7 .
4. Norén, L.-O. and Sundström, S.:
Software System for AKE 13. Ericsson Rev. 5? (1974):2, pp. 3 4 - 4 7 .
5. Nilsson, R. and Norén, L.-O.: InPlant System Testing. Ericsson
Rev. 53 (1976):1, pp. 1 9 - 2 7 .
6. Norén, L.-O. and Sundström, S.:
Development,
Production
and
Maintenance of Software for AKE
13. Ericsson Rev. 53 (1976):3, pp.
152-160.
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
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.
Fig. 1
ABJ 101 e q u i p p e d for 40 m a g n e t o l i n e s , 4 CB
junction l i n e s a n d 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 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.
137
LENNARTALDESTAM
Telephone Exchange Division
Telefonaktiebolaget LM Ericsson
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
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
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 m a g n e t o lines
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
Fig. 4
Cord pair unit
AP
A n s w e r i n g cord
RP
Calling cord
SK-RK 3-posltlon switch with speech position SK and
ringing position RK
SL
Clearing drop indicator
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
139
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.
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
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
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
Base unit
+ 1 line box
Base unit
+ 2 line boxes
80
18
160
18
70 60
4 8
18 18
150 140
4
8
18
18
Base unit
+ 3 line boxes
240
230 220
4
8
18
18
18
Dimensions in cm
Width
Height
Depth
62
41
53
62
59
53
62
77
53
Approx. weight, kg
40
55
70
Operating voltage
6VD.C.
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.
ABJ 101
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.
ECUADOR
Quito
2. Teléfonos Ericsson C A
IRAQ
Baghdad
7. Teletonaktiebolaget LM Ericsson
GUATEMALA
Guatemala City
7. Teletonaktiebolaget LM Ericsson
IRAN
Teheran
3. Simco Ericsson Ltd.
4. Aktiebolaget Erifon
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
LATIN AMERICA
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.
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
URUGUAY
Montevideo
2. Cia Ericsson S.A.
THAILAND
Bangkok
2. Ericsson Telephone Corporation
Far East AB
VENEZUELA
Caracas
1. Cla Anonima Ericsson
TURKEY
Ankara
2. Ericsson Turk Ticaret Ltd Sirketi
Representatives in:
Bolivia. Costa Rica, Dominican Republic,
Guadeloupe, Guatemala. Guyana, Haiti,
Honduras. Martinique, Netherlands Antilles,
Nicaragua, Panama, Paraguay, El Salvador,
Surinam, Trinidad. Tobago
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
AFRICA
UNITED STATES and
CANADA
ALGERIA
Algiers
7. Telefonaktiebolaget LM Ericsson
EGYPT
Cairo
7. Telefonaktiebolaget LM Ericsson
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.
KUWAIT
Kuwait
7. Telefonaktiebolaget LM Ericsson
MOROCCO
Casablanca
4. Société Marocaine des Telephones et
Telecommunications "SOTELEC"
UNITED STATES
Woodbury NY.
2. LM Ericsson Telecommunications Inc
New York, NY.
5. The Ericsson Corporation
CANADA
Montreal
2. LM Ericsson Limitée/Limited
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.
AUSTRALIA and
OCEANIA
Melbourne
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1. Rifa Pty. Ltd.
5. Telenc Pty Ltd
Sydney
3. Conqueror Cables Ltd.
Representatives In:
New Caledonia, New Zealand, Tahiti.
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
T p l f f n n a k t i p h n l f l n o t I M EricSSOn
ASIA
INDIA
Calcutta
2. Ericsson India Limited
INDONESIA
Jakarta
2. Ericsson Telephone Sales
Corporation AB
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
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