ERICOOL for Cooling Telecommunications Equipment

ERICSSON
REVIEW
2 1986
Cabinet Construction Practice for Electronic Systems
ERICOOL for Cooling Telecommunications Equipment
Operational Experience of ERICOOL for Active Cooling
ERICOOL Systems for Passive Cooling
Automatic Teller Machine E281
Frequency Planning of Digital Radio-Relay Networks
Modulation and Switching Using Optical Components in Lithium Niobate
New Hardware in AXE 10

ERICSSON REVIEW
Number 2 1986 Volume 63
Responsible publisher Gosta
Llndberg
Editor Gosta
Neovius
Editorial staff Martti
Viitaniemi
Address S-126 25 Stockholm, Sweden
Subscription one year $ 16
Published in Swedish, English, French and Spanish with four issues per year
Copyright Telefonaktiebolaget LM Ericsson
Contents
42 • Cabinet Construction Practice for Electronic Systems
49 • ERICOOL for Cooling Telecommunications Equipment
52 • Operational Experience of ERICOOL for Active Cooling
58 • ERICOOL Systems for Passive Cooling
63 • Automatic Teller Machine E281
71 • Frequency Planning of Digital Radio-Relay Networks
80 • Modulation and Switching Using Optical Components in
Lithium Niobate
86 • New Hardware in AXE 10
Cover
One of the first installations of AXE 10 in cabinet
construction practice BYB202, in Sevenoaks just
south of London, England.
Fully built out the exchange will have 16000
subscribers, handle 97000 Busy Hour Call Attempts
and have approximately 500 systems for
2 Mbit/s

Cabinet Construction Practice for
Electronic Systems
Bengt Hellstrom and Dick Ernmark
Digital electronic equipment is subjected to increasingly stringent environmental
endurance requirements, particularly as regards electromagnetic compatibility
(EMC) and the ability to survive earthquakes and high temperatures. New system
components mean demands for greater heat dissipation ability. Cabinet
construction practice BYB202 has been developed in order to satisfy new system
applications as well as these new environmental requirements.
The authors describe the criteria of the design work, the construction of BYB202
and how it is adapted to the functional units and handling units called magazine
modules.
packaging
environmental engineering
Digital technology is a comparatively
new phenomenon in the telecommunications
field. It was introduced into
a branch which already had its own established
operating conditions. The experience
obtained from the use of digital
technology has led to more stringent requirements
as regards the environmental
endurance of the systems. This applies
above all to the electrical environment,
i.e. the electrical and magnetic
effects of the environment on the system
and the corresponding effects of the
system on the environment. However,
the requirements for the equipment to
be able to withstand high temperatures
and mechanical stresses, such as earthquakes,
have also increased. The requirements
vary slightly in different
countries but international standardization
work is well on its way to achieving a
uniform standard.
Magazine
The mechanical building blocks in a
cabinet consist of magazines. Their
height can vary between single and triple
height and their length from 3 to
24 building modules, BM (one
BM = 40.64mm).
A magazine consists of a printed board
frame with a rear plate that constitutes
the wiring unit. The printed board assemblies
are inserted into slots in the
magazine, plugged into the connectors
(usually two for each printed board) in
the wiring unit and locked into place by
a front rail in the frame.
The connectors and frame slots are
placed at fixed distances of six or eight
modules, M, from each other
(M = 2.54mm).
All cabling is connected to the front of
the printed board assemblies or to
cross-connection fields which are situated
in the wiring unit but accessible
from the front of the cabinet. Internal
logic voltages are distributed by the wiring
unit, usually from a plug-in power
unit.
The need for high transmitted power
and low tolerances as regards voltage
drop has led to the use of busbars made
of 0.25mm connecting wire or printed
conductors for the voltage distribution
in the wiring units.
Fig. 1
The modular structure of system AXE 10 has
made it possible to exploit new technology and
new system design for various subsystems. The
figure shows how this has affected the space and
power requirements
ARF (crossbar switches)
AXE10
Greater need for heat
dissipation
The development in the component field
is rapid and the new components have
made it possible to reduce the volume of
the hardware drastically. However, it has
not been possible to reduce the amount
of power per component in step with the
volume. For the new components to be
used with reasonable packing density
the heat dissipation must be made more
efficient. Fig. 1 shows how the volume
and power have gradually been reduced
for an AXE 10 exchange with 10000
lines.
Uniform heat transfer is a main objective
in the thermal dimensioning of a construction
practice. The operating conditions
for a magazine must be the same

43
BENGT HELLSTROM
DICK ERNMARK
Public Telecommunications Division
Telefonaktiebolaget LM Ericsson
regardless of its position in the cabinet.
This has been achieved in BYB 202, and
the limit for cooling by means of selfconvection
has been extended by using
a combination of series and parallel
cooling. The maximum permissible
power dissipation is 1200W per cabinet
and the average power per printed
board assembly 5.5 W with a board spacing
of 8 M. Fig. 2 shows the temperature
differences recorded in the cabinet.
Environmental endurance
requirements and
environmental stresses
Environmental endurance requirements
specify the environmental
stresses a product must be able to withstand
without the function deteriorating.
The requirements span all stages in
the creation and life of a product.
The product is exposed to a number of
environmental factors which interact in
complicated ways. For example, during
handling, storage, transport and operation
the product suffers vibrations and
shocks as well as variations in temperature
and humidity. The effects of the environmental
factors on the product are
dependent on the product design, environmental
control arrangements and
the contributions generated by the
product itself during operation.
To be able to design a product with good
environmental endurance and economy
it is necessary to know both the type and
the magnitude of the environmental
stresses it can be expected to encounter
Once the actual environment and
the requirements for operational reliability
are known the environmental
endurance requirements can be drawn
up. At the same time the environmental
endurance of the product makes demands
on the environment. It is therefore
necessary to specify the environment,
i.e. set environmental requirements.
Various standards are used for
this purpose, and the relations between
environmental endurance and environmental
stresses have to be treated systematically.
Standards of importance in this context
are various rules, regulations and instructions
that specify parameters, values,
materials, methods etc.
Fig. 3 gives a summary of environmental
concepts that concern the environmental
endurance of the products.
Spread within the magazine
5 W/board with a spacing of 8 M
Fig. 2
Excess temperature at printed board assemblies
with power evenly distributed in the magazines.
The excess temperature is the increase in temperature
above the ambient temperature. The
magazines must be given equivalent conditions
regardless of their position in the cabinet

44
The actual product environment
Environmental factors and characteristic
environments during the life of the products
Climatic
environment
Handling
environment
Chemical
environment
Storage
environment
Mechanical
environment
Transport
environment
Biological
environment
Operating
environment
Fig. 3
Summary of the different concepts that affect the
environment and environmental endurance of the
products
Electrical
environment
Fig. 4
An example of electrical environmental
requirements (from FCC).
uV refers to a terminal voltage (conducted) and
uV/m to field strength (radiated)
Class A (industrial equipment), measured at a
distance of 30 m
Class B (consumer equipment), measured at a
distance of 3 m
Temperature and humidity
requirements
The upper temperature limit for safe
function is determined by the equipment
installed and is normally 45°C.
This upper limit is primarily intended to
safeguard operation in the case of a
breakdown of the air conditioning
equipment. Administrations exploit this
feature for various purposes, for example
to repair cooling equipment without
standby. The room temperature and relative
humidity are measured at a point
0.4m from the equipment and 1.5m
above the floor.
Electrical environment
Electronic equipment works with the aid
of electromagnetic energy, which is
transported over signal conductors between
the circuits in a specified way. In
addition to the desired electromagnetic
energy unwanted energy can appear,
so-called electromagnetic interference,
EMI. The interference can be divided
into two basic categories:
- Interference caused by the equipment:
emission
- Interference imposed on the equipment:
reception.
Some countries with requirements fixed
by law are:
- West Germany (VDE, Verband Deutscher
Elektrotechniker)
- the United States (FCC, Federal Communications
Commission).
The requirements of different countries
are often based on recommendations by
CISPR (Comite International Special
des Perturbations Radioelectrique).
This is the committee that, under the
International Electrotechnical Commission,
works on the standardization of
matters concerning interference of
broadcasting and television. Fig.4
shows an example of such requirements.
When designing the BYB202 cabinets
an electrically screened version was
also developed. Measurements show an
attenuation factor of 50 dB in the frequency
range 30-500 MHz, fig. 5. The
screened version consists of a basic
cabinet equipped with screening strips,
rear doors and screens at the top and
bottom.

Fig. 5
The screening properties of cabinet construction
practice BYB. The diagram shows that the
screening factor is 50 dB in the frequency range
30—500 MHz. The interference source used is a
10 MHz oscillator and a number of loaded current
loops
The screened cabinet can be supplemented
by special cable runs with similar
attenuation properties.
stand discharges of 15kV against the
cabinet casing.
Fig. 6
Typical time sequence for an earthquake in the
most severe of the four zones specified for the
US. The earthquake strength specification has
been given as a frequency domain with its
response spectrum. In this illustration the
earthquake tremors are shown in the time
domain, which gives a clearer picture
All electronic equipment is to a greater
or lesser degree sensitive to electrostatic
discharge, ESD. Low relative humidity,
combined with insulated flooring,
contributes to an impaired operating environment
for the equipment. A general
recommendation for flooring is that it
should have good antistatic properties
and a volume resistivity of 10 7 -10 9 ohms
in order to prevent ESD. When preparing
the requirements specification for
cabinet construction practice BYB 202
consideration was paid to its ability to
withstand ESD. Verification tests have
shown that the equipment can with-
Mechanical environment
BYB 202 has been designed to meet new
requirements for mechanical environmental
endurance during transport and
operation. Transport can entail great
stress for cabinets. Special packing and
transport securing requirements had to
be met to make it possible to transport
fully equipped cabinets. The mounting
of magazines and printed board assemblies
has also been adapted to meet
these requirements. This has resulted in
a robust construction practice which
can also withstand earthquakes.

Fig. 7
The ceiling height required is basically
determined by two factors.
It must not be so low that it is a risk to the heat
dissipation and there must be a reasonable
working space between overhead cable ducts and
the ceiling. The figure shows the recommended
ceiling height and the cable running, using
overhead ducts as well as floor ducts together
with Ericsson's cable floor
Technical data
BYB202 is a modular cabinet construction
practice for systems with magazines as the
basic units. The external dimensions of the cabinet
are
height 2120 mm
depth
400 mm
width 1 720 mm
width 2 1 200 mm
Its main features are
- high ability to withstand ESD
- good electrical attenuation properties
- efficient heat dissipation through self-convection
- robust mechanical construction which
makes it possible to deliver cabinets fully
equipped and enables them to be installed in
earthquake zones.
Fig. 8
Cabinet BYB202
Certain countries make special demands
as regards mechanical stress, for
example the US where four earthquake
zones have been specified. Fully equipped
cabinets have undergone a number
of tests based on the American requirements.
The results show that the requirements
were met, fig. 6. During the
tests the equipment was fixed to a
vibrating table by means of angle
brackets. The same type of bracket is
used for installing the equipment.
Installation and layout
criteria
A construction practice must be flexible
enough to be adapted to different customer
requirements within certain limits.
For example, the cable running differs,
with cables laid in ducts on top of
the equipment or in ducts on the floor. In
the latter case the cabinets are mounted
on raised or cable floor. BYB202 cabinets
can be installed singly and the
layout can be adapted to suit local conditions,
such as previously installed
equipment and pillar spacing.
Other basic principles of the row construction
practice have been maintained,
such as full frontal accessibility
for magazines, printed board assemblies,
connection blocks and cables.
This means that very compact layouts
can be obtained by placing cabinets
back to back.
Two steel profiles have been chosen for
the cabinet base in order to compensate
for any unevenness in the floor of the
exchange room. They have a bearing
surface of 400x40 mm and are adjustable
vertically by 10mm. This construction
spreads the load over a large
surface and avoids the pressure normally
exerted by supports.
Ericsson has designed a cable floor as
an alternative to the conventional raised
floor. This floor is recommended for
new exchange buildings. The equipment
is mounted on a floor framework
having the same dimensions as the base
of the cabinet. The cable floor covers
only the space between cabinets and the
immediate surroundings. This means
that the equipment is earthquake-resistant,
since the strength of the cable floor
is no longer a crucial factor. The floor is
180 mm high, sufficient for screened cable
ducts. The cable ducts, with their
close-fitting lids, also provide good fire
protection.
Overhead cabling can also be used with
BYB 202, and optional assembly kits can
be used to adapt the height of the cabinets
to existing cable routes and Ericsson's
water-based cooling system
ERICOOL. 1
Fig. 7 shows the recommended ceiling
height.

Fig. 9
The space required for functional unit ETC has
been reduced from two six-shelf magazine groups
to a single-shelf magazine module
Characteristics of a magazine
module
- is a handling unit for the optimum arrangement
of magazines in a cabinet
- is a functionally delimited unit
- can occupy one or more shelves or comprise
more than one cabinet
- does not include cables or cabinets
- is documented in the form of rules.
Mechanical construction
The cabinet, which mechanically is a
self-supporting unit, is built up of a sturdy
top and bottom frame. Brackets for
the sides are welded to the frames, and
the sides are screwed to the brackets.
The fittings, which consist of a cable
chute, earth bars, shelves and ducts for
internal cabling, are screwed to the framework.
The cabinet front consists of
two doors, which can be opened 180°
and lifted off the hinges if necessary.
The cabinet can also be fitted with supplementary
equipment, for example
rails for 19" equipment.
The earthing, which is an important
function in the cabinet, is supplied by
two vertical aluminium rails, which via
contact plates are connected to the horizontal
shelf earth rails. Earth wires are
used for the earthing between cabinets
and between cabinet rows. The earth
system meets the requirements for
1000 A short-circuit current, which gives
a maximum voltage drop of 0.5V.
Functional units
One or more magazines equipped with
printed board assemblies form a functional
unit, which constitutes the building
block in the cabinet in AXE 10. Previously
the functional units were assembled
in standardized magazine
groups which included the associated
row mechanical structure and internal
cabling. The great reduction in the volume
of AXE 10 has facilitated new dispositions
for optimum utilization of the
construction practice. For example, the
functional unit ETC (Exchange Terminal
Circuit) for 512 channels, with the associated
control equipment and power
unit, previously comprised two row sections
having a height of six shelves. Today
the corresponding functional unit
occupies just one shelf, fig.9.
Magazine modules
By treating the functional units separately,
not associated with the cabling
and mechanics, a handling unit is obtained
which gives more versatile use of
Fig. 10
The number of cabinets required for a local
exchange with 11 000 subscribers, of which 6000
are connected to the parent exchange. The
remaining 5000 are connected to six remote
subscriber stages. The figure also shows the
number of magazine modules per subsystem. The
traffic intensity is 0.12Erlang per subscriber
IOS
CPS
GSS
TSS
CCS
Input/Output Subsystem
Central Processor Subsystem
Group Switching Subsystem
Trunk and Switching Subsysten.
Common Channel Signalling Subsystem
• I Subscriber Switching Subsystem

48
Magazine module
document
(positioning rules)
Fig. 11
Flow from the choice of product to the
installation.
The magazine module documentation is an aid for
planning the positioning of magazines in the
cabinets. Standard arrangements of magazines in
cabinets can be prepared if customers so desire
and be productized with all internal cabling
Technical data
Cabinet
Height
2133 mm
Width
1 200and 720 mm
Depth
400 mm
Required ceiling height 2650mm
Aisle width
800 mm
Load on the floor 4 kN/m 2
Magazine
1M
0.1" (2.54mm)
1 BM 1.6" (40.64 mm)
Height
6 BM (234.8 mm)
Width
Nx3BM
N 1-8
Depth
220 mm
Printed board spacing 6 M or 8 M
Printed board
Height
Depth
2 or 4 layers
222 mm
178 mm
Wiring unit
Wrapped or printed board
2 or 6 layers
Pin spacing
1 M
Operating conditions
Temperature
Normal range
5-40°C
Safe function
0-45°C
Relative humidity
Normal range 20-80%
Safe function 5-90%
the mechanics while retaining standardization
and rational handling. This handling
unit is called a magazine module.
The magazines in a magazine module
can fill a shelf, several shelves or several
cabinets. The documentation for magazine
modules can be considered as
menus, describing which magazines are
included, and giving disposition examples
and any layout restrictions. The
documents are used in the project planning
and design of exchanges. When an
exchange has had its functional content
defined and has been converted to hardware
with the aid of a computer program
it is time to position the magazines in
cabinets.
Magazine modules are the basic units
used in the positioning, which can be
manual or computer aided. Fig. shows
the arrangement of magazine modules
for a whole exchange. The next stage is
to plan the layout and prepare a floor
plan. When this has been completed, cable
types are chosen and cable lengths
are calculated forthe cabling within and
between cabinets. At this stage basic
data for the production can be prepared,
so that the cabling can either be manufactured
in the factory and delivered
ready-made to the exchange or prepared
on site by the installation staff.
Computer aids are available for the
whole process, from the choice of product
to the production documentation,
see the flow chart in fig. 11.
Summary
BYB202 is a versatile, modular cabinet
construction practice for systems
whose construction is based on magazines.
Its first application is for AXE 10.
The construction practice is characterized
by good heat dissipation, high
ESD endurance and ability to withstand
great mechanical stresses.
Supplemented with EMI protection and
earthquake security devices it will meet
the most stringent customer demands.
References
1. Almquist, R.: A Cooling System for
Electronic Telephone Exchanges.
Ericsson Rev. 58 (1981):4, pp. 188-
195.

ERICOOL for Cooling
Telecommunications
Equipment
Erik Albertsson
Ericsson has developed an extensive product range for cooling electronic
equipment in both small and large premises. The ERICOOL cooling systems have
been designed and dimensioned to maintain the stipulated component and plant
temperatures in all existing types of climate.
The author emphasizes the importance of uninterrupted cooling function and
describes the two basic cooling principles, active and passive cooling, and the
conditions that determine which principle should be chosen for a certain plant.
ERIK ALBERTSSON
Ericsson Power Systems
RIFA AB
sures low maintenance costs for the
ERICOOL cooling systems. Periodic
preventive maintenance is usually sufficient.
cooling
telecommunication equipment
The requirements for operational reliability
of telecommunications equipment
are very exacting. A reliable system
requires reliable subsystems and
components. These requirements have
led to the development of uniquely reliable
computers for controlling sophisticated
telecommunications systems.
However, modern electronic circuits,
with their high component density, have
much higher heat dissipation. Efficient
cooling has therefore become a prerequisite
for satisfactory operation of the
systems. Ericsson's product range for
uniquely reliable cooling is called
ERICOOL.
Uninterrupted cooling function -
matching the high exchange reliability
- is ensured by means of energy storage,
a system structure with parallel circuits
and duplication of vital components.
The use of reliable components
and dependable system designs also en-
Low maintenance costs, low energy
comsumption and a long life are three
important factors that contribute to the
good overall economy of the ERICOOL
cooling systems.
ERICOOL cooling systems work according
to two main principles:
- Active cooling, which means that the
system is equipped with a special
cooling unit and a pump or fan that
ensures circulation in the system.
- Passive cooling, which means that
natural convection is used for the
transfer of heat and that the cooling
system uses and stimulates spontaneous
thermal processes.
Several factors influence the choice of
the main cooling principle.
The advantages of the purely passive
systems are most apparent in the case of
remote and unattended units. The deci-
Active ERICOOL Passive
Low Local energy costs High
Standard of comfort Temperature requirements Component standard
Fig. 1
Choice of cooling principle, general guidelines.
The size of the exchange, environmental requirements
and the local power costs are some of the
factors that determine the choice of basic cooling
principle. A remote link unit which is driven by
relatively expensive power, for example from
solar cells, is best cooled passively, whereas a
large exchange with a good mains supply is
normally cooled actively
Large Exchange size Small

Fig. 2
The ERICOOL passive cooling systems are extremely
reliable. In this container for small telecommunications
units the heat dissipated by the
electronic circuits is used as the driving power.
The cooling system has no moving parts, which
makes it maintenance-free.
The standby cooling capacity is unlimited since
the system is not dependent on any external
power sources
Fig. 3
ERICOOL offers several cooling alternatives for
equipment installed in containers. This active
system can be extended in stages to a total
cooling power of 5-10kW
Fig. 4
ERICOOL Comfort offers silent and draught-free
cooling of modern work premises - laboratories,
conference rooms, banks and offices.
The pleasant climate is obtained by natural convection
whereby the air circulates through cooling
coils and by maintaining a fairly high water
temperature in the collectors (13-15'C).
ERICOOL Comfort is available as a complete
system including the cooling unit or as a supplement
to an existing cooling system

Fig. 5
ERIC00L cooling systems for large exchanges
work with self-convection at the heat source. Heat
Is transferred from the exchange room by means
of the active method. These systems offer
uniquely reliable cooling of exchanges having a
cooling requirement of up to several hundred
kilowatts.
There is no capacity limit for the ERICOOL
cooling systems
sive factors are then the extremely high
operational reliability and independence
of external power sources.
Large attended exchanges with a good
power supply are usually cooled actively.
In the power range up to 10kWthe
factors that decide the choice of cooling
method are the climate, comfort requirements
and access to power. A
mainly passive system supplemented by
a simple circulation device may be a
suitable solution in such cases.
Some ERICOOL systems of different
size and design are shown here. The following
two articles describe the latest
development of each main principle and
recent operational experience from
some plants.
Summary
ERICOOL cooling systems are characterized
by extremely high reliability with
uninterrupted operation also in case of
mains failure. Low maintenance cost,
low or no power consumption and long
life are other characteristics of the
ERICOOL cooling systems which ensure
a low life cost and good overall
economy.
Fig. 6
Modular structure with a capacity range of 2 to
10 kW (illustrated here) makes it possible to
design reliable and economical cooling systems
for small and medium-sized exchanges
References
1. Almquist, R.: A Cooling System for
Electronic Telephone Exchanges.
Ericsson Rev. 58 (1981):4, pp. 188-
195.
2. Alexandersson, R., Junborg, A. and
Vesterberg, H.-J.: Passive Cooling of
Premises for Electronic Equipment.
Ericsson Rev. 61 (1984):3, pp. 128-
131.

Operational Experience of ERICOOL for
Active Cooling
Ragnar Almquist
Since its introduction in 1980, ERICOOL has become a familiar concept in
telecommunications administrations around the world. Its main features are
uninterrupted cooling and good environment for both eguipment and staff.
The author describes the experience gained from ERICOOL and the further
development of the systems. Finally, new applications are discussed.
cooling
telecommunication equipment
Since the introduction of electronictelephone
systems, the thermal density has
increased from 100 to 500 W/m 2 floor
area. There are no signs today that this
trend will be broken; the density instead
seems likely to increase.
When AXE 10 was introduced it was realized
within Ericsson that the amount of
heat dissipated from the system would
create problems. The company faced up
to the fact and decided to develop a
cooling system that met all the requirements
telecommunications make on climate
regulation. So far Ericsson is the
only manufacturer of telecommunications
equipment to develop its own cooling
system.
Brief system description
ERICOOL has been described in a previous
issue of Ericsson Review 1 , and
hence only a brief description will be
given here.
The system is based on self-convection.
The heat from the telephone system is
dissipated into the air which rises, transfers
the heat to the cooling coils and
then flows down into the aisles, fig. 1.
Fig. 2 shows the full system function.
The temperature in the exchange room
is kept constant by means of the mixer
valve (MV), which controls the ratio of
returning water to cold water. During a
power failure the cold water comes from
tanks having a volume that ensures a
coolant backup which corresponds to
the power backup period provided by
the exchange battery.
Experience from five years of
operation
ERICOOL was designed to meet the following
requirements:
Fig. 1
The telephony equipment is cooled by means of
self-convection. This method gives efficient cooling
and a quiet and draught-free environment

53
RAGNAR ALMQUIST
Ericsson Power Systems
RIFA AB
Fig. 2
The modular structure makes for simple installation
and enables the equipment to be extended in
step with the telephone system
W
v'
CC
PU
MV
WT
CU
Circulation during normal operation
Circulation during a mains failure
Cooling coil
Pump unit
Mixer valve
Water tank
Cooling unit
High reliability
The availability of a telephone system is
very much dependent on the reliability
of its auxiliary systems for power supply
and cooling. 2 3 The auxiliary systems are
integrated subsystems and their reliability
should be on par with that of the
exchange system.
Simple installation
The telecommunication projects of today
are usually turn-key projects. It is
important that all subsystems should be
designed for rapid installation. As far as
possible the installation should not require
specially trained staff.
Simple extension
It may be difficult to forecast the final
capacity and extension rate of a telephone
system. It should therefore be
possible to build cooling systems with
the required initial capacity and then extend
them to suit future demands.
A minimum of maintenance
Modern telecommunications networks
consist to an increasing extent of a large
number of small, unattended exchanges
and only a few large ones, from
which all network supervision is managed.
The maintenance of a cooling system
must be kept to a minimum and performed
periodically, for example once a
year. Staff should not need special training
in cooling engineering to carry out
maintenance.
These requirements are related to the
experience obtained during five years of
operation.
ERICOOL now in more than
20 countries
Since its introduction in 1980, ERICOOL
has been installed and is in operation in
more than 20 countries in all parts of the
world and in most climate types (Nordic
climate, desert climate and warm and
humid tropical climate). There are now
approximately 80 systems in operation
(October, 1985).
Most installations are complete systems
according to fig.2, or the compact version
tailor made primarily to meet the
space requirements of telephone systems
in containers. In some cases only
parts of ERICOOL have been installed
and combined with existing cooling systems.
For example, in one case ERICOOL was
to be installed in a building which already
had a cold water system for the air
conditioning of offices. The cooling
coils and pump rack from the ERICOOL
system were used, the cold water being
supplied from the existing system.
High reliability, interruptionfree
One of the unique properties of
ERICOOL is that the cooling function
can be maintained during a power
failure. Experience obtained on several
markets - Saudi Arabia, Egypt and
Pakistan - confirms the importance of
this function. Fig. 3 shows the temperature
curve for an exchange in Cairo exposed
to a prolonged mains failure.
During the years ERICOOL has been in
operation temperature curves obtained
during mains failures have also been reported
for exchanges without a standby,
i.e. where conventional air conditioning
systems have been used. These reports
verify that the temperature exceeds the
permissible limit shortly after the loss of
the cooling function. Fig.4 shows the
temperature increase with different
thermal densities. 4
With only five years of operational experience
it is difficult to obtain a complete
evaluation of the characteristics and
performance of the system. However, it
is clear that the objectives set out during
the development of ERICOOL - high reliability,
simple installation, and low
maintenance costs - have been reached.
The concern expressed regarding the
risk of water leakage into the electronic
system has not been justified. No leakage
has been reported from any system
in operation.
The features of ERICOOL that are most
highly regarded by the users are, in addition
to the high reliability, the low energy
costs and the quiet environment, free
from draughts.

Fig. 3
Correctly dimensioned ERICOOL provides good
protection against overheating during long mains
failures. The temperature falls to the normal value
when the mains power is restored
Temperature during a mains failure
Temperature after the mains power has been
restored
Comments from customers
ERICOOL has met with interest from
telecommunications administrations
around the world. Some of the administrations
that have installed the system
have made their own evaluations which
have formed the basis of published articles.
Some excerpts are given here:
Comments from Finland
"ERICOOL was installed in Jyvaskyla in
1984. 3 The system was easy to install.
The telephone exchange (AXE 10) is
placed in a600 m 2 room in rock, of which
the telephone system occupies 80m 2 .
The space requirements would have
been reduced by 200 m 2 if ERICOOL had
been chosen at the start. The building
costs would then have been reduced
from 4.5 to 3 million Finnish marks.
The modular structure of ERICOOL permits
extensions. As a consequence the
initial investment was low, which has
kept the capital cost low. A minimum of
maintenance, together with low energy
consumption and heat recycling, gives
low operating costs."
Fig. 4
With no cooling the temperature in the exchange
room rises. The rise in temperature is mainly
determined by the thermal density of the telephone
system. The curves refer to an outdoor
temperature of 25°C
Temperature, °C
A
Comments from Singapore 6
"In 1984 ERICOOL was installed in the
Tampineo exchange building to cool an
SPC exchange of the FETEX type. Telecom's
annual electricity bill for the cooling
of telecommunications equipment
is 10 million Singapore dollars. Telecom
is therefore continually seeking new,
less energy-demanding cooling systems.
The new system, ERICOOL, is
more efficient than the systems used
previously. An energy saving of 20% is
expected. Other advantages of
ERICOOL are uninterrupted operation
and the absence of air ducts and raisedfloor
systems."
New system design gives
even lower energy
consumption
The design work on the ERICOOL system
started in 1979. The experience
gained since then has been collated and
discussed. Only a few modifications
have been necessary since the first generation
of the system was launched.
Other possible improvements sugaested
bv the onerational pxnprience

55
kept at a suitable temperature by cooling
unit CU1.
The standby circuit consists of cooling
unit CU2, tank WT2 and mixer valve
MV2. CU2 keeps the water in the tank at
8°C.
In case of a mains failure or CU1 being
out of operation, standby mixer valve
MV2 is activated and regulates the ratio
of water from WT1 and WT2 in such a
way that the water flow to pump unit PU
is kept at a temperature of 17°C.
Apart from the features described
above, the new system works in the
same way as the earlier ERICOOL system.
Cooling units CU1 and CU2 are identical
except that they work with different
water temperatures.
Having CU1 working at a higher temperature
increases its capacity by 30%.
Fig. 5
The second generation of ERICOOL. The system
design facilitates low energy consumption
l» Circulation during normal operation
Hi
Circulation during a mains failure
CC Cooling coil
PU Pump
MV1 Mixer valve 1
MV2 Mixer valve 2
WT1 Operating tank
WT2 Standby tank
CU1 Operating cooling unit
CU2 Standby cooling unit
DC Cooler (heat exchanger)
are now forming the basis of the second
generation of ERICOOL.
The most important features, the high
reliability and energy saving, have been
extended further through different system
designs, fig. 5.
The temperature of the water to the
cooling coils must not fall below 17°C.
This limit gives a safe margin between
the ambient temperature of the room
and the dew point.
The way the system functions in the exchange
room has not been altered.
However, the cooling of the water in the
system has been divided into two separate
circuits: one for water at a temperature
of 17°C (operating circuit) and one
for water at 8°C (standby circuit).
In normal operation the pump unit (PU)
is fed with water at 17°C from the operating
water tank (WT1) via the mixer valve
(MV1). The water in the operating tank is
The system is dimensioned to give the
desired capacity at a water temperature
of 17°C. The previous system was based
on 8°C from both units. The curve of
fig.6 shows that the relationship between
cooling capacity, supplied power
and water temperature is not linear,
which means that the energy consumption
has been reduced by approximately
15%.
Alternative system designs
Outdoor air can be used to cool the
water in areas where the mean daily temperature
falls below 15°C for eight
months of the year. This method gives a
considerable energy saving and higher
system reliability.
Cooling by outdoor air requires a cooler
(DC) that supplements or replaces CU1
in the system, fig. 5. DC consists of a
cooling coil and a fan, is placed outdoors,
and works as a heat exchanger
between the water and the outdoor air.
During the part of the year when the
temperature is lower than 15°C,all cooling
is done by DC.
During periods with high outdoor temperatures,
CU1 or the standby circuit are

Fig. 6
ERICOOL operates at high water temperatures.
This ensures better utilization of the cooling units
and leads to energy savings
Coefficient of performance (cooling capacity/supplied
power),% of nominal operating data
Fig. 8
ERICOOL for the modern computerized office.
Here features such as high capacity and quiet and
draught-free environment are very important
used. A suitable dimensioning of the
combination of DC, CU1, CU2 and WT2
gives the optimum design for low energy
consumption, fig. 7.
New applications
The unique ERICOOL properties of silent
and draught-free operation have
now become even more important with
the increased use of computers and terminals
in offices.
A normal office in Sweden has a thermal
load of 20-30W/m 2 . This value increases
to 50-200W/m 2 when computer
and terminal equipment is installed.
By comparison it should be mentioned
that computer centres have thermal
loads of over 300 W/m 2 .
To ensure the comfort of the office staff,
the air conditioning system has been divided
so that cooling is arranged by
means of cooling coils for self-convection
(often placed on a suspended
ceiling), whereas the fresh-air ventilation
is arranged in the traditional way,
fig.8.
The use of conventional air-conditioning
systems to handle the new
cooling problems would produce an environment
that would be considered

Fig. 9
ERICOOL for telephony equipment. A first step
towards an integrated system
Fig. 7
In a temperate climate a cooler, DC In fig. 5, can
be used during the greater part of the year. The
cooling unit is only used for peak loads during
the warmest period of the year and as a standby
for the cooler. This system version has an extremely
low power consumption, t = °C outdoors
Top: The capacity of DC Is high when the outdoor
temperature Is low but falls to zero at 17 C. CU2 provides
the extra cooling that DC cannot manage.
Centre: Up to 15 C only DC consumes energy. At higher
temperatures the consumption Increases as CU2 starts
operating.
Bottom: During the greater pari of the year only DC Is In
operation. The figure shows the number of hours during
which the temperature exceeds a certain value. The
climate Is Central European. The curve refers to Zurich.
-Capacity of the cooler, DC
Energy consumption
Capacity of the cooling unit, CU2
Only DC consumes energy
Both DC and CU2 consume energy
Only CU2 consumes energy
Conclusion
The telephone systems of today have a
heat dissipation factor corresponding
to approximately 500 W/m 2 . The trend is
rising, and in a not too distant future it
will reach 1000 W/m 2 . Tests in ERICOOL
laboratories show that self-convection
can be used in both telephone packaging
structures and cooling systems to
dissipate these thermal loads.
Fig. 9 shows a joint construction of telephone
and cooling systems.
The next stage in the development is
most likely that the cooling system will
be integrated in the telephone packaging
structure, so that the heat will be
taken directly from the source instead of
being transferred first to the air and then
to the cooling coils for removal.
References
1. Almquist, R.: A Cooling System for
Electronic Telephone Exchanges.
Ericsson Rev. 58 (1981):4, pp. 188-
195.
2. Wolpert, T.: The Reliability of Power
and Cooling Systems. Intelec 1982
Proceedings, pp. 181-186.
3. Wolpert, T.: The Reliability of Auxiliary
Systems - Power and Cooling; Further
Insights. Intelec 1983 Proceedings,
pp. 109-116.
4. livarinen, R.: The Effect on Telephone
Modernization on Buildings. CEPT AP/
GT6 1984, pp. 76-83.
5. Hakkinen, M.: Water Cooled Telephone
Exchange, a New Concept.
Puhelin 6/84 (Finland), pp. 26-27.
6. Boon, O. E.: Towards Cooling Exchanges
at Less Cost. Hello - Newsletter
for Employees of Telecoms. July
1984 (Singapore), pp. 5.

ERICOOL Systems for Passive Cooling
Rune Alexandersson and Anders Junborg
Ericsson has developed methods for dimensioning systems for passive cooling of
electronic equipment. Detailed studies of flows in and around heat sources and
exchange rooms have provided the experience that forms the basis of optimum
dimensioning of components and complete systems for passive cooling.
The authors describe three ERICOOL systems for interruption-free cooling of
small telephone exchanges and give a summary of the calculation methods.
er functional density and high heat dissipation.
A holistic approach to the phenomenon
of heat being conveyed from a
component, through the room and out
to the environment, provides new possibilities
of efficient cooling of the electronic
equipment. Cooling is being introduced
closer and closer to the heat
source.
cooling
calculation
telecommunication equipment
Fig. 1, left
Container 500, basic diagram.
The heat in the primary cooling circuit is transferred
out to the secondary cooling circuit
through the walls of the container
Fig. 2, centre
Cooling module 700, basic diagram.
The liquid thermosyphon has two heat exchangers,
an internal heat collector and an external
cooler
Fig. 3, right
Container 3500, basic diagram.
The liquid thermosyphon has been equipped with
a thermal mass that provides cooling reserves
and reduces the daily temperature variations
The following three examples have been
chosen to illustrate the application of
passive cooling:
- Air-cooled container for small exchange
units that dissipate up to
500 W.
- Liquid thermosyphon for cooling an
existing exchange building.
- 20-foot container with liquid cooler
for a temperate climate and 3500W
dissipated power.
The common denominator of these
ERICOOL systems is that they work
without any external power supply and
therefore offer extremely high operational
reliability - in practice interruption-free
cooling.
The development of systems and components
in the telecommunications
field tends towards structures with high-
Modern telecommunications networks,
with an increasing number of small remote
system units, require very high operational
reliability and maintenancefree
equipment. Special consideration
should be paid to the requirement for
balance between battery reserves and
cooling reserves. Passive cooling systems,
which in most cases work without
any moving parts and any energy consumption,
are an attractive choice for
such applications.
The systems described in this article are
based on natural convection in air and
liquids. The heat dissipated by the electronic
equipment provides the driving
force in the cooling systems.
When the hot air leaves the electronic
equipment it passes an adjacent heat
exchanger, which absorbs the heat and
lowers the air temperature, whereby the
airflow isturned down, recirculated into
the room and onwards through the
equipment. This air flow is the primary
circuit in the passive cooling system.

59
RUNE ALEXANDERSSON
ANDERS JUNBORG
Ericsson Power Systems
RIFA AB
The heat exchanger that lowers the temperature
also forms part of the subsequent
system circuit, which in the simplest
case consists of the air flows
around the exchange room, for example
a cabinet or a container. Container 500
is one example of this type of system,
fig. i •
The heat exchanger often consists of a
collector that forms part of a liquid thermosyphon,
which transfers the heat to
the cooling coils placed on top of the
container. The heat dissipated by the
electronics is used as the driving force
also for the second circuit.
The thermosyphon has closed circulation.
The liquid takes up heat in the collector,
and the heat rises through pipes
up to the cooling coils, where it is transferred
to the surrounding air through
the flanged coils. The cooled liquid is
piped down to the collector to be heated
again and keeping the circulation going.
Cooling module 700 consists of such a
simple thermosyphon, fig.2.
Systems for exchanges that require redundant
capacity or which experience
large daily variations in the heat dissipation
and outdoor temperature are equipped
with a thermal mass in the form of a
water tank. The thermal mass evens out
the daily variations and acts as a buffer
in case of unexpected events. The cooling
system in Container 3500 is of this
type, fig. 3.
Container 500 for tropical
climate
The cooling system for Container 500 is
built up around a sturdy metal minicontainer.
The internal collector circuit consists
of air conduits specially designed
for the packaging structure, which
guide the heat from the electronic circuits
out to the container walls. The external
cooling circuit consists of the air
conduits between the sun screens that
surround the container and the outer
walls of the container. Container 500 is a
purely passive cooling system without
any power consumption and with extremely
high reliability.
Passive cooling system for
small buildings
ERICOOL also provides facilities for
passive cooling in connection with the
extension and modernizing of existing
exchanges. A flexible component program
makes it possible to adapt the
cooling systems to local requirements
and conditions.
Fig. 4
Container 500
Fig. 5
The diagram illustrates the thermal properties of
Container 500. The blue curve shows the outdoor
temperature, the other curves the indoor temperature.
Passive cooling systems are often dimensioned
in accordance with component requirements.
Higher temperatures and larger temperature
variations are permitted than for attended
premises with comfort requirements. For example,
Ericsson's environmental specification allows
the room temperature to vary between 5 and
40°C

Fig. 7
The two diagrams show the daily temperature
variations of the thermosyphon system in Brobyvaerk
during one week in the summer (top) and
winter (lower diagram).
During summer all four thermosyphons are in
operation, the outdoor temperature varies between
7 and 22 C, the indoor temperature is
slightly above 20 C. Sunshine is indicated on the
diagram by a separate curve.
One or more thermosyphons can be shut off
during the cold season. The second diagram
shows the outdoor and indoor temperatures during
a week in December. Only one thermosyphon
is in operation and gives sufficient cooling
Fig. 6
Chimneys and air conduits at collectors and
coolers improve the performance considerably.
This system with four thermosyphons has been
equipped with chimneys around the cooling coils
on the roof
In Brobyvaerk, Denmark, an exchange
has been modernized and supplemented
by electronic equipment which
dissipates approximately 3kW. The
building is an insulated brick house. The
cooling system consists of four simple
thermosyphons. The collectors in the
house are connected to the external
cooling coils by means of pipes straight
through the roof.
The cooling coils are supplemented by
chimneys, fig. 6, which improve the efficiency
considerably. The basic cooling
system is not equipped with any special
regulators for continuous control of the
circulation. However, the thermosyphons
can be regulated individually by
means of manual valves for seasonal adjustment
of the system.
Container 3500 for general
use
Container 3500 is built up around a 20-
foot container and is cooled by a thermosyphon
system with several circuits.
The collectors are placed on the ceiling
and the cooling coils are situated outside,
on top of the container. The cooling
system also contains a thermal
mass. The container can be equipped
with external sun screens, which in certain
types of climate prevent heating by
radiation and stimulate the external
cooling air flows.

61
Fig. 8
Container 3500 can be equipped with a maximum
of four cooling modules comprising heat collectors,
coolers and tanks for thermal mass
Fig. 9
Cooling module for Container 3500
In the basic version the thermal mass is
placed in complete cooling modules on
the roof. Each module then comprises
two thermosyphons with collectors,
tanks and cooling coils.
Container 3500 has the tanks placed below
the container, which has some advantages
as regards installation. For example,
it gives great flexibility in the
positioning of the collectors. However,
this design must be supplemented by
small circulation pumps, powered by
the exchange battery. The temperature
reduction process is still entirely passive.
Calculation method
One characteristic of all calculations for
systems working with natural convection
is that temperatures and flow
rates are coupled and interact in a complex
manner. This applies to everything
from individual components to the entire
cooling system, including the room
and peripheral equipment. It istherefore
necessary to start with detailed studies
of, for example, the process between
two flanges in a cooling coil and successively
work towards a whole, balanced
unit.
This is done gradually by switching from
the narrow to the wide perspective -
making detailed calculations that are
then matched to the environment. There
are no shortcuts or simple solutions. Numerical
methods must be used.
The basic data that govern the calculations
for a passive cooling system are
the heat dissipation of the electronic
equipment, environmental requirements,
the thermal properties of the
building and the local climate. For example,
the dimensioning of a system
with a cooling circuit, collector circuit
and thermal mass for a container involves:
- Flow calculations for the cooling circuit
in order to obtain a balance between
two coupled equations: the
momentum equation and the equation
of energy. Expressed in a simplified
way it is a question of achieving
a balance between the heat dissipation
ability of the cooling coils,
Fig. 10
Container 3500 B gives flexibility in the location of
the heat collectors in the container room. The
cooling coils are placed on the roof and the tanks
underneath the container

62
Fig. 11
Ericsson's dimensioning program for passive
ERICOOL systems gives good precision in the
design work. The diagram shows the relationship
between the outdoor temperature and the calculated
and measured temperature in the container
"the motor", and the internal friction
in the circulation, "the brake". Some
factors that affect the efficiency of the
system are the size and shape of the
cooling coil walls, the running of the
pipes and the use of chimneys. The
calculations are iterative. Qualified
guesses give suitable starting values,
and repeated application of the calculation
programs provides the data
for a preliminary assessment of the
cooling circuit.
• The collector circuit is then dimensioned.
This stage includes the important
preliminary work of calculating
how much of the heat dissipated by
the electronics will immediately disappear
through the floor, walls and
ceiling. It is then important to have
access to reliable climate data. Apart
from this the collector circuit is dimensioned
in the same way as the
cooling circuit.
- The thermal mass is calculated with
the aid of special subprograms. The
input data comprises critical component
temperatures, daily variations in
the outdoor temperature and in the
heat dissipated by the electronics and
any special requirements on the duration
of cooling reserves, for example
in the case of mains failures.
Development trends
Important subprograms in the calculation
system concern individual components
in the cooling equipment. The interface
between the heat exchanger and
the electronic equipment is now a subject
of great interest. Chimneys of different
types and special collectors for
small temperature differences and low
air velocities offer new solutions for efficient
cooling systems.
Modern electronic cooling is on the
threshold of a new and interesting
stage. The next generation of cooling
systems will constitute an integral part
of the electronic packaging structure.
References
1. Alexandersson, R., Junborg, A. and
Vesterberg, H.-J.: Passive Cooling of
Premises for Electronic Equipment
Ericsson Rev. 61 (1984):3, pp. 128-
131.
2. Wolpert, T.: The Reliability of Auxiliary
Systems - Power and Cooling; Further
Insights. Intelec Proceedings
(1983), pp. 109-116.

Automatic Teller Machine E281
Weine Bernfordt and Bertil Olsson
Automatic teller machine E281 has been developed jointly by Ericsson
Information Systems AB and the Japanese company Omron Tateisi Electronics in
close collaboration. The main objective was to create a product that met exacting
requirements as regards availability, security and ergonomics. These
requirements tend to grow even more exacting, particularly in the Nordic market.
Ericsson E281 has already been chosen by the savings banks as well as several
commercial banks in Sweden.
The authors give a summary of the development of automatic teller machines
and describe the system components in E281.
history
point of sale systems
etts
The work on automatic teller machine
E281, fig. 1, started early in 1983 as a
part of the continual product development
work. At the same time Ericsson
received an enquiry from the Swedish
savings banks regarding the development
of a new generation of cash dispensers.
The requirements were found to conform
in all essentials to the general market
requirements and the trends that
were apparent for the next generation of
cash dispensers. In certain aspects the
requirements were even more far-reaching
and would require a large investment
in development if they were to be
met.
When contemplating such a large development
project the possibility of establishing
close collaboration with another
manufacturer of cash dispensers
had to be considered. This manufacturer
should above all have experience
of the dispensing of notes and automatic
service. Such experience, combined
with Ericsson's knowhow as regards
system structure, communications, security
and ergonomics, was considered
a prerequisite for the success of the project.
Fig. 1
Automatic teller machine E281 as seen by the
customer
Ericsson already had an established
project organization which was responsible
for the company's previous generation
of cash dispensers. The project organization
was given the task of studying
the requirements specification from
the savings banks and recommending a
suitable action plan.
During the spring of 1983 possible partners
around the world were studied and
evaluated. In the autumn of 1983 the decision
was made to initiate negotiations
with the Japanese company Omron Tateisi
Electronics for a cooperation
agreement concerning the development
of an automatic teller machine.
Omron is one of the leading manufacturers
of cash dispensers in the Japanese
market and since the end of 1984
the company has also established itself
in the US market.
A cooperation agreement was concluded
with Omron and work started on
adapting Omron's units to European requirements,
primarily as regards function
and security. Ericsson had to adapt
the basic system of the machine to facilitate
a wider use of public communication
networks. Data communication in
connection with financial transactions
is a basic requirement for modern bank
terminal systems, of which automatic
teller machines are an integral part.
History and trends
Automatic teller machines, ATM, have
increased rapidly in number during the
last ten years. Approximately 150000
ATMs have been installed, with about 1/3
in the US, 1/3 in Japan and 1/3 in the rest
of the world.

WEINE BERNFORDT
BERTIL OLSSON
Ericsson Information Systems AB
Fig. 2
The growth rate of automatic teller machines,
ATM, in the US and Europe
the US
Europe
In the US the growth started in earnest
towards the end of the 1970s and has
continued along the same trend. In Europe
the growth has taken place in
waves dependent on local restrictions
and the times when collaboration has
been established between different ATM
networks, fig. 2. However, at present the
curve shows a smooth development
trend for Europe.
In Japan the growth has also been rapid,
and the number of installed units iseven
slightly larger than the number in the
US.
In Europe there are considerable differences
between different countries.
Sweden has the highest ATM density
with approximately 150 machines per
million inhabitants, a number exceeded
only by the US, Japan and Hongkong, all
with about 200. Sweden is followed by
France, England, Finland and Norway
with 110-130, whereas for example
Germany and Italy only have approximately
40 machines per million inhabitants.
In countries with a high ATM density the
number of transactions, mainly cash
withdrawals, is also high. An average of
5000-6000 transactions per month and
ATM is common. Some machines can
have over 20000 transactions per
month.
Cash dispensers have been accepted by
the customers in most countries, and
the transaction frequency increases in
line with the installation density. Thefollowing
trends are apparent:
- A changeover to pure on-line communication
with the host computerof
the bank in question.
- Increasing number of functions for
customer self-service.
- Greater collaboration between
banks, otherfinancial institutionsand
card companies.
- More and more machines are being
installed in public places, e.g. in shopping
centres, stations and on company
premises.
- Greater demands on the availability of
ATMs and associated communications
networks.
- Demands for larger note capacity.
- More stringent requirements as regards
both logical and physical security.
- Greater demands for good ergonomic
properties, both for the customers
and the operators.
There are two main reasons why banks
and financial institutions invest large
amounts in cash dispensers and associated
communication networks:
- Competition, which is met by expanded
service in the form of new facilities
and extended opening hours,
sometimes a 24-hour service.
- Rationalization, with a desire to take
the load off the cashiers.
In both cases it is important that the machine
has high availability and also that
the customers' attitude to it is positive,
since it is often their main direct contact
with the bank.
At present there are approximately ten
major ATM manufacturers, the largest
being American and Japanese. With
E281 Ericsson will be one of the three
largest in Europe.
Automatic teller machine
E281
An automatic teller machine is seen by
most customers as a machine from
which one can conveniently obtain cash
by using one's cash card, state the desired
amount and key one's personal code
The fact that the machines also work
outside ordinary banking hours, and are
sometimes installed conveniently close,
increase their popularity even further.
Since the banks will in future also increase
the facilities offered by the machines
by, for example, balance enquiries,
statement requests and transfer of
money between accounts, the availability
of the machines must be very
high. The rationalization work of the
banks includes efforts to enable the customers
to carry out an increasing number
of simple and uncomplicated transactions
themselves, using automatic
teller machines.
Not many people are likely to realize that
the above-mentioned customer service
without any manual supervision requires
a very sophisticated system design.
The "customers" who are not satisfied
with the amount of money they
can legally obtain from the machine

Outdoor climate
- Temperature
- Humidity
- Air pollution
- Sunlight
- Rain
- Snow
Ergonomics
and
design
Security
Protection against
• burglary
• fraud
Availability
Indoor climate
- Temperature
- Humidity
- Pressure differences
between
the indoor and
outdoor climate
User
The public,
24 hours per day
Protection against
vandalism
System and
function
Capacity
Installation through
a wall in an unsupervised
environment
Maintenance
- Operator
- Serviceman
Fig. 3
An ATM is subjected to many requirements; the
main one being that it must provide the public
with a 24-hour facility for obtaining money
might have wondered how this money is
kept. The notes, new and used, often of
several denominations, are kept securely
in the machine safe, which is approved
for the storage of very large
amounts.
It is not possible to manipulate the machine
by means of forged cash cards or
to trick the system in any other way. The
built-in security feature, encryption of
essential data in combination with verification
of the personal code in the central
bank computer, makes any such attempt
impossible.
However, the protection against different
types of attack must be improved
continually, and the manufacturers of
both hardware and software must always
be at least one step ahead of the
cleverest criminals.
In addition to unique security requirements
there are very stringent environmental
requirements made on automatic
teller machines. They can be subjected
to rather tough treatment from
some customers and they must also be
able to withstand large variations in the
weather.
E281 is designed for installation
through a wall, outdoors or in an entrance
hall. The machine is equipped
with Ericsson's terminal computer and
Fig. 4
The division of the E281 development work between
Ericsson and Omron. The safe is supplied
by a local manufacturer

66
Fig. 5
Network configuration
E281 can either be connected to the local computer
in System E2100 via a two-wire cable or be
remotely connected via the telecommunications
or data network to a host computer. Alternatively
E281 can be used completely off-line
Fig. 6
Automatic teller machine E281 is built up of four
main parts: a front, electronics cabinet, printer
cabinet and safe
thereby forms an integral part of terminal
system E2100. E281 has a modular
structure which simplifies operation
and maintenance.
The design of the units operated by customers
and their positions on the front
of E281 meet exacting ergonomic requirements.
The division of the development work
between Ericsson and Omron is outlined
in fig.4. Certain stages of the development
work required very close collaboration,
such as the actual construction
of the machine so that it satisfies
the stringent environmental and
ergonomic requirements, and the adaptation
of Omron's units to European security
requirements.
System connection
E281 can either be connected to the local
computer in system E2100 via a twowire
line or be remotely connected via
the telecommunications or data network
to a host computer. Alternatively
E281 can be used entirely off-line, fig. 5.
Structure
E281 comprises four basic parts: a front,
electronics cabinet, printer cabinet and
safe, fig. 6. When positioning the four
parts in relation to each other particular
attention was paid to:
- the need for safe and reliable transport
of notes from the note dispenser,
through the wall of the safe and out
through the slot in the front
- the need for a simple means of transporting
withdrawal statements from
the printer and out through the slot in
the front
- security and good ergonomic characteristics
in the positioning of units operated
by the customers
- easy handling when replenishing the
note store and changing paper and
ribbon in the printer
- simplicity in the replacement or repair
of faulty parts.
Front
Fig. 7 shows the positions of the various
units on the front. The opening of the
magnetic card reader is placed bottom
right and the slots for notes and withdrawal
statements are at bottom left.
The visual display unit is placed above
the keyboard on the right-hand side, and
the two units are so close together that
they can easily be seen in one glance.
The keyboard is placed at a convenient
height for the hand and in such a way
that the customer hides the keyboard
and VDU from persons queuing behind.

Fig. 7
The front of E281
Physical environment
The parts of E281 that are placed indoors, i.e.
the units in the electronics cabinet and safe,
satisfy the requirements of Ericsson's STD EIS/
T1025-315.
The parts placed on the front, e.g. the customer
keyboard, meet very stringent demands as regards
outdoor environment.
Ambient temperature
indoors
outdoors
Humidity
indoors
outdoors
Voltage
Frequency
Electrical safety in
accordance with
and
+ 10 to +40°C
-40 to +50°C
20 to 85%
20 to 100%
220V + 10%
50Hz± 2%
IEC 380/435
UL478
A mains failure will not damage the machine.
Battery backup is provided for memories and
automatic program loading.
The front is equipped with a combined
handbag rest and writing shelf at a convenient
writing height. The front also
has a handle, bottom left, as an aid for
elderly and handicapped customers.
The front is made of thick steel plate in
order to prevent vandalism and entry
into the bank premises through the machine.
It is equipped with a flange for
efficient sealing between the machine
and the wall. A lamp illuminates the
units operated by the customers.
Electronics cabinet
The electronics cabinet holds most of
the units in the machine. A fan that removes
surplus heat is placed at the top
of the cabinet. The fan also creates overpressure
in the machine, which prevents
dust from being sucked in through the
slots in the front.
The units are mounted on guide rails in
the cabinet in order to simplify maintenance.
One pair of rails holds the following
units:
- Magnetic card reader and writer, together
with return slot
- Visual display unit for the customer
- Control units
- Voice guidance unit
- Operator panel
- Visual display unit for the operator
- Battery
The other pair of rails holds the journal
printer and its control unit. Other units,
such as the computer, floppy disc unit
and power supply unit, are placed on
shelves in the cabinet.
Printer cabinet
The receipt printer is mounted on guide
rails and placed in a separate cabinet on
top of the safe.
Safe
E281 can be equipped with different
types of safes. The actual design and the
choice of material for the walls are governed
by local theft-protection regulations.
The note dispenser and its control unit
are mounted on guide rails in the safe.
Burglar alarm equipment can also be
installed in the safe.
Communications
E281 can be used on its own, off-line, or
on-line, either connected to a local computer
in a bank off ice or as a terminal in a
network. The following types of connection
are possible:
- Permanent or switched circuits in the
telephone network with signalling in
accordance with CCITT Recommendation
V.24/V.28.
- Public or private data networks with
signalling in accordance with CCITT
Recommendations X.21 and X.25.
- Standardized local two-wire bus
(SS3) having a maximum length of
1500 m, a tranfer rate of 300 kbit/s and
with up to 16 drop points per bus and
local computer.
Synchronous as well as asynchronous
and bit orientated (HDLC/SDLC) protocols
can be used.
External communications can also be
arranged by means of System Network
Architecture (SNA) communication,
which can be used towards permanent
lines or X.25 networks. E281 has sufficient
computer capacity to accommodate
the software for SNA.
Operating system
The E281 operating system offers the
usersawell-defined and secureenvironment
in which several different application
programs can be executed.
The application programs and the core
of the operating system are protected
from each other by a function which ensures
that the applications programs do
not carry out unauthorized operations,
e.g. overwrite other programs, and
provides a user-friendly interface for the
basic functions of the operating system.
The operating system has the following
subfunctions:
- A real-time executive system, RTX,
which handles the communications
between processors, allocation of
processor time, allocation of memory,
real-time clock, calendar etc. The

68
Technical data for units
Computer
- Central unit with connection of terminal bus
(SS3)
- Memory module for 256, 384 or 512 kbytes in
RAM. Battery backup during mains failures
- Input and output controller for one RS422
and three RS232 interfaces and a parallel
interface, e.g. for video camera and alarms
- Control unit for two floppy disc units
- Transmission line interface for V.24/V.28 and
X.24/X.27.
Note dispenser
- Two, three or four denominations
- Up to 25 notes per transaction
- A total capacity of more than 10000 notes.
Visual display unit
- 9" with green text on a dark background
- 31 characters per line and 14.5 lines with normal
character size
- The size of the characters can be varied and
combined in the same picture
- The characters can be displayed flashing or
reversed
- A part of the screen can show a moving picture,
which is achieved by shifting between
four patterns
- RAM of 40 kbytes for approximately 150 set
pictures
- Character generator for standard characters
in PROM of 16 kbytes, for customized text in
RAM of 8 kbytes and for moving pictures in
RAM of 8 kbytes
Customer keyboard unit
- For personal identification and selection of
function and amount
- Equipped with a security module for identification
of the customer's personal code.
Sensitive data in the security module can be
protected against access or manipulation by
means of built-in security devices. The security
module is programmable for easy adaptation
to verification systems that are
unique to the bank.
- The security module can be used for encryption
of sensitive information between the machine
and the host computer
- The keyboard has ten numerical keys, eight
function keys and keys for READY and FAULT
- The keyboard is designed to withstand vandalism
and outdoor environment
- In the numerical block the key for the figure 5
also has a dotted relief to aid people with
impaired vision.
RTX process communication is used
throughout the system, including
communication with a superior local
computer. RTX also manages restarts
after power failure without the user
having to be aware of it.
- Loaderfor loading E281, eitherfrom a
floppy disc unit connected to E281 or
Magnetic card reader and printer
- For standard magnetic cards in accordance
with ISO 2894 and ISO 3554
- Motor driven, with battery backup for the return
of cards in the case of a power failure
- Combined read and write head
- Magnetic tracks in accordance with ISO standards
o Reading and writing, track2, standard
o Reading, track 1, option
o Reading and writing, track 3, option
- Watermark test in accordance with the specification
of the manufacturer, EMI/MALCO,
option
Receipt printer
- Character generator for 256 characters in
PROM
- Matrix printing in both directions
- Printing rate 100 characters per second, corresponding
to 2.1 lines per second including
line feed
- Character size normally 7 x 9 or 8 x 9 dots and
for enlarged print 7x 18 or 8x18 dots
- Up to 40 characters per line with normal
characters and 20 characters per line with
enlarged characters
- Up to 16 lines per transaction
- Paper roll for 3000 transactions
- Indications for paper almost finished and paper
run out
- Equipped with inked ribbon cassette
- Semi-automatic loading of paper
- Function for retrieval of forgotten withdrawal
statements.
Journal printer
The technical data for the journal printer are
identical with the data for the receipt printer
with the following exceptions:
- Only normal character size
- Up to 36 characters per line
- Up to 13 lines per transaction
- Monitoring of the paper feed.
Floppy disc unit
- One or two units, controlled by the control
unit in the computer
- 51/4" disc
- A capacity of 0.65 Mbyte per unit.
Voice guidance
- Speech recorded on a magnetic drum
- Maximum message length 3.5 seconds per
track
- Up to 32 messages, which can be linked together.
Customer detector
- Senses when a customer is within approximately
1 m of the machine. Can be used to
start up the VDU or voice guidance.
from a rigid disc unit connected to a
superior local computer. During operation
there is only one loader in
E281. The loader carries out the initial
loading of the computer as well as the
reloading of applications programs,
and hence applications programs can
be changed during operation.
- A transport system, which handles internal
data transfers between the
computers in a system. Outside the
transport system the system is entirely
independent (except as regards
performance) of the type of link used
to interconnect the computers, e.g.
fast wire bus, permanent circuit or
switched circuit in a public data network
Remote terminals are thus fully
integrated in the system.
- Management functions for different
interfaces towards external units.
During operation each management
function is stored in the computer.
The following interfaces are available:
o RS422 towards Omron units
o Interface for RS232 units
o Floppy disc interface. This function
also starts file processing systems
at the lowest level
o Transmission adapter interface,
which is used by the communications
software
o Parallel interface for control of external
units such as video camera,
lights and alarms. The parallel interface
consists of two gates, each
for eight bits. Each eight-bit gate
can be defined as an input or output
gate.
- A maintenance module, MM, which
on request from an operator diagnoses
the units in E281. The module is
controlled from an operator panel at
the rear of E281.
- A system diagnostics module, SDM,
which handles the reporting of faults
to the operator, gathers fault and operating
statistics and on request presents
the gathered information.
Applications system
All functions offered by E281 are controlled
by the application program, written
in the program language DIL. DIL
has been specially developed for the
management of units connected via a
serial interface (RS) and of transactions.
These properties make the language
particularly suited for use in E281.

69
Fig. 8
E281 is the result of collaboration between Ericsson
Information Systems and Omron Tateisi Electronics
The application program is divided into
a basic part, which is unique to E281,
and a customizing part. In the basic part
the properties of the operating system
and the various units are optimized.
The basic application has well defined
interfaces for the customizing of texts
and layouts for the VDU, the keyboard,
printer, floppy disc unit, magnetic card
reader and printer, parallel interface and
transaction format. Customizing is done
by encoding unique program sections
and is controlled by means of parameters.
The basic application also contains
functions for the recording of alarms
and forwarding them to a central system
in the case of, for example:
- Hardware fault in a unit
- All notes gone
- Form for withdrawal statements
finished.
The basic application comprises three
types of functions:
- System functions
- Customer functions
- Service functions.
Access to the different functions is controlled
via the operator panel at the rear
of the machine and can be tied to an
authorization check using magnetic
cards or codes.
System functions
E281 normally contains the following
system functions:
Initiated from E281:
- Insertion and removal of note cassette
- Reading of cassette status
- Loading of encryption keys in the security
module
- Loading of date and time for off-line
operation.
Initiated from a central system:
- Opening and closing of E281
- Status enquiry
- Reading of cassette status
- Message to the VDU or statement
printer.
Automatic:
- Service supervision and status reports.
Customer functions
The customer functions include:
- Withdrawal of notes
- Account balance enquiry or enquiry
concerning recent transactions. The
answer is shown on the VDU or received
as a printout
- Blocking of accounts, for example
after loss of the cash card
- Choice of personal code
- Transfer to another account.
Service functions
Initiated from E281:
- Testing of the units, using a standard
module in the application program.
The unit status is displayed on the operator
panel or output on one of the
printers
- Unauthorized withdrawal from the
note dispenser is prevented by means
of a lock controlled by the basic application
program.
Initiated from a central system:
- Statusenquiry to the units forthe purpose
of checking their function.
Security
A cash dispenser must meet two types of
security requirements, physical and logical.
A combination of these is necessary
in order to reach a level of security
that is acceptable to banks.
In general it is also necessary to establish
administrative routines for the
handling of sensitive modules, program

70
Fig. 9
Automatic teller machine 281
media etc. These routines must then be
followed during the whole life of the design,
i.e. during development, production,
delivery, operation and maintenance.
Physical security
Physical security comprises protection
against burglary and vandalism.
It is essential to protect the large sums of
money kept in the safe. The safe has
been tested by the Swedish Association
for Protection Against Theft and was
given very high marks for the protection
of valuables against different types of
attack. The safe can also be equipped
with an alarm which can be connected
to the general alarm system of the bank.
The units placed in the front are protected
against vandalism in various
ways such as by unbreakable glass in
front of the VDU and shutters for the
slots for the magnetic card and notes.
Logic security
The logic security is built into E281 and
can be used for the following functions:
- Verification of the personal code
- Orders to the note dispenser
- Authorization check for operators.
Code verification
The identification of a customer is based
on the information stored on the magnetic
card and on a personal identification
number, PIN, chosen by the bank or
the customer. The identification can be
reinforced by a water mark number that
is permanently stored on the card.
Identification can be performed using a
common algorithm, such as Data Encryption
Standard, DES, which is key
controlled, oran algorithm uniquetothe
bank. The input parameters for the verification
process are any algorithm key,
card data, for example the card number,
and the PIN. If the watermark method is
used the WM number read from card
track 0 can also be used as an input
parameter. The result of the algorithm
calculation is compared with a check
sum computed when the card is activated
The electronic circuits for the PIN verification,
i.e. algorithm circuits, key register
and comparator circuits, belong to
the E281 customer keyboard unit. The
encapsulated circuits are effectively
protected against unauthorized monitoring
or tapping of confidential information.
Orders to the note dispenser
A PIN verification carried out by the keyboard
unit gives a positive or negative
result. The result is interpreted and
checked by the protected electronic circuits
in the note dispenser. A correct
positive result from the PIN verification
is a prerequisite for an order to dispense
notes.
Authorization check for operators
The authorization of an operator is
checked via the operator panel at the
rear of E281 and is used in connection
with changeover between the system,
customer and service modes. The identification
is similar to the customer identification
but a specially allocated personal
code is used.

Frequency Planning of
Digital Radio-Relay
Networks
Heinz Karl
The performance characteristics of digital radio-relay systems differ significantly
from those of analog systems. This also includes the influence of interfering
signals from other radio-relay transmitters. The planning of radio frequencies for
a digital radio-relay network must therefore be based on other criteria than for
analog systems.
The author discusses new criteria of interference predictions for a digital radiorelay
network. The paper has been presented as Ericsson's contribution at Bell
National Radio Engineers' Conference in Denver. USA, September 1985.
HEINZ KARL
Ericsson Telecom
Telefonaktiebolaget LM Ericsson
the margins of the planning objectives
for the overall performance of the radio
circuit. The performance is expressed in
terms of bit-error ratio, BER.
digital systems
radio links
interference
network topology
Fig. 1
BER versus receiver input level, L R,, for various
values of CIR and co-channel interference
(4FSK - 6/8 Mbit/S)
i
CIR = 12dB
CIR = 15dB
• CIR = 20 dB
CIR = *
BER
The mechanism of
interference
In radio-relay networks the various radio
paths are isolated from each other either
by different radio frequencies or, when
using the same radio frequency, by appropriate
antenna discrimination and/or
topographical isolation. Despite that, a
certain amount of undesirable energy
from surrounding transmitters will always
interfere with the wanted signal at
a radio-receiver input.
The task of the network-planning engineer
is to select radio frequencies and
antenna types in such a way that the
influence of interfering signals is within
The influence of interfering radio signals
depends mainly on the following
parameters:
- The radio signal-(=carrier)-to-interference
ratio, CIR, that is the level of
the wanted signal with respect to the
combined levels of disturbing signals.
- The radio-channel spacing between
disturbing and disturbed signals. The
larger the separation between the two
signals, the higher the attenuation of
the disturbing signal in the radio frequency
(r.f.) and intermediate frequency
(i.f.) bandpass filters in the receiver
assembly.
- The type of modulation applied to the
disturbed and disturbing signals.
In order to economize on the frequencies
allocated to a particular service, it is
desirable to use the same radio frequency
as often as possible. This will also be
of benefit for the management of spare
parts. This paper will therefore mainly
be devoted to interference caused by
transmitters operating at the same radio
frequency as the disturbed path: cochannel
interference, particularly at
high radio frequencies.
The influence of interfering
signals
When conveying TDM (Time Division
Multiplex) signals, the influence of interfering
radio signals on the performance
is not detectable during fading-free
time, as long as the carrier-to-interference
ratio, CIR, is at least 20dB. It is
only during fading, when the receiver
input level, L Rx , comes close to its
threshold level, L Te , that the bit-error
ratio will be degraded. An example may
explain this:
Fig. 1 shows the BER versus L Ri , for various
values of CIR. The curves in this

72
Fig 2
Simplified RL network, with the paths
a
b
in a triangular configuration
in a quadrangular configuration
interference path
figure are typical of a radio-relay link
(RL) with a capacity of 6 or 8 Mbit/s applying
4FSK-modulation (Frequency
Shift Keying between four frequencies).
If we assume a fading-free input level
L Rx = -60dBm, the bit-error ratio, BER,
will be better than 10~ 8 , as long as CIR
>15dB. A resulting level L,= -82dBm
from all interfering signals at that receiver
input meets this requirement with
a good margin. If L Rx drops to -67dBm,
which gives a CIR of 15dB, the BER decreases
to 6-10 6 (instead of

73
Table 1
Logical chart for uncorrelated events between
wanted and Interfering signals for various fading
events
yes
no
interfering signal considered
interfering signal not considered
correlated with those for the wanted signals
A2—»C or A1 —. B respectively. They
can therefore be excluded from the interference
considerations.
The rain fading for the interfering signals
B-^A2, C —A1, D^G and F*->-E is
basically uncorrelated with the corresponding
wanted signals. For short interference
paths, however, a certain degree
of correlation cannot be excluded:
If, as an example, the distances A-B,
A-C and also B-C are about 5km, or
less, the probability that a rain cell
covers both the wanted path (e.g.
B^>A1) and the interference path
(C^A1), or parts of them, has to be
taken into account. The shorter the
length of the interference path, the higher
the degree of correlation.
One possible way of taking this into consideration
in the interference calculation
would be to decrease gradually the
influence of the interfering signal with
decreasing length of the effective interference
path; the effective interference
path being defined as:
diet, = d, sin(a|>/2)
d, actual length of the interference path
in km
ip angle between interference and
wanted path
Fading correlation summary
The uncorrelated events for fading of
interfering and wanted signals are summarized
in table 1.
Interference calculation
Path Multipath Rain
Effective interfering
Wanted/ path length path length
interfering «10 km >10km s=5km >5km
A-»B/A2-»B no yes no no
AA1 no yes partly yes
A-*C/A1-»C no yes no no
AG no yes partly yes
F«_G/E-»F no yes partly yes
The principal work in drawing up a frequency
plan is the prediction of the influence
of interference on the overall
performance.
Two different approaches to such a prediction
are discussed here:
- Starting from a given receiver input
level, L Rx , and calculating the influence
on the performance
- Starting from an allowed interference
level, L h at the input of the disturbed
receiver, and selecting the proper antennas
and/or radio frequencies.
Starting from a given input level
This approach is illustrated by fig. 1 and
fig.2a. Path A-B is assumed to be the
disturbed path, and A-C the disturbing
path. The length of both is assumed to
be 4.5 km. The input level during fadingfree
time at A1 (and at B) is L R „
Using an RL equipment of the type
Ericsson MINILINK18 (ML18), with a
built-in antenna of 0.6 m diameter, a value
of
L Rx = -43.0dBm
is obtained.
The receiver threshold level for
BER = 10 -3 and an undisturbed path
(CIR = °°) is L Te . This can be taken from
the equipment's data sheet. For ML18,
the corresponding value is:
L Te = -80.0 dBm
See also fig. 1.
The flat-fading margin is then:
The interfering signal C^A1 reaches
the receiver A1 via antenna A1 with a
level, L,, which, as an example, could be:
L,= -92.0dBm
If more than one interfering signal has to
be considered, L, is the resultant level of
n combined individual levels, L,,, namely:
n
L, = 10lg 210 L||/1 °
i=i
Starting from the interfering level, L h of
-92dBm in the diagram in fig. 1, a CIR

74
value of 15dB can be found at a threshold
level, L Tel , of -77dBm. The CIR value
for 15dB corresponds to the difference
between these two levels:
The threshold level has thus decreased
by:
L Te , is now the new threshold level in the
presence of interfering signals:
This gives a new flat-fading margin, M R ,
of:
see fig.3 for ML18. A, = 0dB for cochannel
operation.
t_pi has its previous significance.
Formula (1) can be used for interfering
sources with a transmitted spectrum
similar to that of ML18, see fig.4. The
formula applies to the range between
BER = 10~ 3 and 10 7 , and to degradation
figures, D, of not more than 10dB, corresponding
to CIR = 12dB.
For the above example, i.e. for:
n = 1
A, = 0 (co-channel interference)
L,= -92.0 dBm
To allow for a more handy estimation of
the performance degradation, a computer-adapted
formula has been introduced:
D degradation of the threshold level,
L Te , in dB
n number of interfering paths
K equipment parameter: K = 92dBm
for ML18
A, attenuation of the interfering signal
in dB in the receiver, dependent on
the r.f. spacing between disturbed
and disturbing path, and the r.f. and
i.f. filters in the receiver assembly,
i.e. the same degradation as from the
diagram. Differences between the diagram
and the formula are within the
margins of accuracy for the formula.
The same procedure has to be repeated
to obtain the influence of interfering signals
at receiver A2, and, in case of path
lengths >10km, also for the receivers B
and C, see table 1.
It should be noted that there is no such
symmetry between the interfering levels
at the two ends of a path as there is for
the wanted signal:
L, A1 =£ L IB whereas L RxA1 = L RxB
This gives us two different fading margins,
M R , for the two directions of transmission
on the same path. The smaller
of these two fading margins must be
used for the prediction of the performance.
From the above we can conclude that
the degradation of the fading margin by
interfering signals must be known before
the performance prediction can be
completed.
Fig. 3
Attenuation, A,, of an interfering signal in the
receiver vs frequency spacing
Another question is how to consider a
partial correlation of the rain fading. In
table 1 it was stated that a partial correlation
could be applied for interference
paths

75
Fig. 4
Transmitted spectrum from an 8 Mbit/s, 4FSKmodulated
radio-relay link
to take the same percentage for the degradation
of the threshold level and fading
margin:
If, in the example, the interference path
C to A1 has a length of 4.5 km and an
angle ip = 90 degrees to the wanted path
B-A1, the effective interference path
would be:
This would be 64% of 5 km and decrease
the degradation D from 3.0 to 2.0dB.
The fading margin, M R , could then be
increased to 35.0dB.
The approach discussed above has the
following disadvantages:
- If radio links already exist in that particular
r.f. band and within the geographical
area concerned, performance
predictions can be carried out
only when all data concerning the
links involved are known.
- Each new RL has an impact on the
performance of the existing ones. A
check of their performance is necessary.
To avoid the new RL degrading
the performance of the existing ones
to below the planning objectives,
stringent requirements for discrimination
of the new antennas may be
necessary. For each additional link,
the requirements will be more stringent
or new radio frequencies will
have to be used.
- An interference level higher than the
threshold level, L Te , (CIR = «>) may
lock the receiver onto that interference
signal in case its "own" transmitter
at the opposite end breaks
down. This connects a subscriber
onto a non-authorized conversation
or data stream, and in the case of frequency
diversity it prevents the link
from switching over to the diversity
channel.
The first two disadvantages can be overcome
by allowing for ample fading margin
for the first links in a network, to give
"space" in their performance for a future
degradation.
The locking of a receiver onto an interfering
signal can be avoided by planning
for interference levels:
Another method would be to provide the
links either with pilot supervision, each
link with its own pilot frequency, or to
use different scrambling sequences for
the various links.
Starting from an allowed interference
level
This approach starts from the assumption
of a maximum number of paths
which can interfere mutually. In this
case, the above formula (1) can be used
to determine the maximum interference
level contribution, L h from each interfering
path:
D, K, A, and n have their previous significance.
Assuming 12 interfering paths and an
allowed degradation of the threshold
level by 10dB for the planned path, we
obtain a maximum level for each interfering
signal of:
for co-channel interference. The value
for L N can be increased by A, in the case
of adjacent-channel interference.

76
The critical parameter in this approach
is the parameter n, i.e. the number of
paths interfering with the wanted signal.
The definition interfering path can also
be interpreted in the following way:
n paths of all interfering paths can be
allowed to interfere with a level of l_ h . All
other paths can be disregarded,
provided that they contribute with an interference
level of:
The planning procedure is as follows:
Calculate the planning threshold level
for the receiver:
and the flat-fading margin:
The minimum CIR for each individual
interference contribution is:
Calculate the attenuation, A,, or the
level, Li,, of each interfering signal and
compare them with the requirements:
- For configurations in accordance
with fig. 2a, where A, is determined
only by the antenna discrimination,
A GA , in the nodal point A, i.e.
This applies to the case where nodal
point (A) disturbs outstations (B and
C). It also applies in the opposite direction,
provided that the fading-free
input levels at A1 and A2 are equal.
Otherwise see below.
To keep the costs for the antenna
down, it is essential not to use higher
fading margins, M FI , than the BER
planning objectives require.
- For configurations according to
fig. 2b:
output level of the disturbing
transmitter in dBm
A 0 free-space attenuation in dB between
the disturbing transmitter
and disturbed receiver
A GTx antenna discrimination in dB
for the transmitting antenna
A GRx do. for the receiving antenna
The parameters which can be chosen
freely are A GTx , A GRx and L Tx . Low L Tx
requires less A GTx and/or A GRx , but it
also decreases the fading margin for
its own path. Hence, the fading margin,
M F |, should not beset higherthan
required by the BER performance objectives.
When applying this approach, performance
calculation and interference calculation
(frequency planning) can be
performed more independently of each
other. However, during the first stage of
a network implementation the performance
of the radio links will be a great
deal betterthan predicted, as the prediction
considers a completely implemented
network.
The problem is here to estimate the final
extension of the network. If the estimation
is too optimistic, and the network
stays at e.g. 5 links instead of the planned
12 links, the 5 links will have too
ample fading margins, and money may
have been spent unnecessarily.
Planning practice
Both approaches to interference calculations
have their benefits. The first
approach is appropriate (and may give
more economical solutions) for lowdensity
networks, with only a few radio
paths. Possible future extension could
be provided for by using other frequency
channels within the same r.f. band.
In dense networks, e.g. metropolitan
areas, where a continuous extension
can be expected, the second approach
will be the best one.
In order to optimize the utilization of radio
frequencies, i.e. to use as few different
frequencies as possible, the following
should be taken into consideration:
For all those paths which operate with
the same radio frequency, the path
which at a repeater station or a nodal

77
Fig. 5
The radio-relay link tower at Ericsson's head
office is the nodal point in Ericsson's radio relay
network for data communications (station HF in
fig. 6)
point requires the largest fading margin,
M Fh (normally the longest path) sets the
reference receiver input level (fadingfree
time) at that station. For all the other
incoming paths,
- the receiver input levels at that station
should have the same value as the
reference level. This can be achieved
by decreasing the transmitter output
level at the opposite station. (To
achieve symmetry between the two
directions of transmission, both the
transmitting and receiving signal at
the opposite end have to be attenuated
equally)
- the antennas at that nodal station
should have the same gain as for the
reference path.
A trade-off between antenna gain and
receiver input level is possible
If the above conditions are met, only the
discrimination of the antenna in the
nodal point (including polarization discrimination)
determines how soon (in
terms of the angle between two paths)
the same frequency can be used again.
With a CIR mm of about 24dB (ace. to the
example above) and a fading margin
M F |=12dB the necessary antenna discrimination
would be 36dB. Applying
the 0.6m built-in antenna in an ML18
radio link would allow for a reuse of the
same r.f. beyond 12 degrees for the
same polarization plane, and beyond 5
degrees for orthogonal polarization
planes.
Fig. 6 and fig. 7 show two networks, one
star and one serial network, both implemented
with Ericsson's MINILINK. In
both cases the same frequencies have
been used throughout. The transmitter
output levels have been adjusted with
attenuators in the outstations.
Conclusions
When summarizing the various aspects
discussed above, some conclusions can
be drawn:
Correlation between performance
prediction and frequency planning
The correlation between performance
prediction and frequency planning is
much closer for digital RL than for analog
RL, especially if paths are planned
using the first method. Feedback of information
between the two planning
steps is essential, as the results from
one step have an impact on those of the
other, even if the latter has been performed
some time ago. This may cause
some administrative problems, not least
if the frequency planning is the responsibility
of a centralized, governmental

Fig- 6
Example of a star network with optimized receiver
input levels at the nodal point
Computer centre
Remote computer terminals
Radio-relay link repeater
5V
RF channel number and polarization
Station Transmitter output power
in dBm
HF 15.0
Kl 13.0
KK 6.0
AL -1.0
VH -6.0
TN -11.0
Repeater 11.5
Input levels of the receivers in nodal point HF:
L Bx=-49.0...-51.2dBm
agency, and the performance prediction
that of the operating company.
Nevertheless, at Ericsson we have taken
the consequences and combined our
hitherto independent computer programs
for performance and interference
calculation into one program, with feedback
and loops between the various
subprograms.
Economical considerations
Whether we use planning method 1 or 2,
we can plan for either one of the following
alternaves:
- If we plan for a high degradation by
interfering signals, e.g. 10dB, the
necessary CIR will be low, and the requirements
for the antenna discrimination
will also be low. This gives
small antennas. The high threshold
degradation, however, moves the
threshold level towards higher values,
and thus also the value of the
receiver input level during fading-free
time. This necessitates a higher transmitter
output level.
- If we plan for a low degradation, e.g.
only 1 dB, the necessary CIR will be
high, requiring antennas with high
discrimination. The transmitter output
level can then be low.
The question is where to spend the
money: high transmitter output level
(and the equivalent cost increase for a
solar power device, for example) or
large and highly discriminating antennas,
which require more expensive
masts.
Frequency economy
Frequency economy means utilizing an
RL network with as few frequencies as
possible. To achieve this all receivers in
an RL station should operate at about
the same input level, identical antennas
being implied.
Controlled transmitter output level
When harmful interfering signals are
present, the performance of a digital RL
during fading is limited by the interfering
signal. On the other hand, the Derfor-

Fig. 7
An example of a serial network with optimized
receiver Input levels In the repeater stations
Local exchange
Radio relay link repeater
1H
RF channel number and polarization
Station Transmitter Receiver
output power input level
in dBm in dBm
A 15.0 -43.8
B 15.0 -43.8/-46.0
NC 12.0 -46.0/-47.3
D 0.0 -47.3
mance of the path is always better than
BER = 10~ 8 , as long as the receiver input
level is just a few dB above the threshold
level.
If the output level for each transmitter is
decreased so that the receiver input
level is 4 or 5dB above its threshold
level, the level of the interfering signals
at that receiver input will also be decreased
Fading will be compensated by
increasing the transmitter output level.
In the conventional way, fading decreases
the level of the wanted signal,
while that of the combined interfering
signals remains constant. If we operate
with fading compensation by increased
transmitter output level, fading will instead
increase the level of interfering
signals generated by that transmitter.
That results in an increase of only one
(or a few) interfering signal(s) at a time at
the disturbed receivers. Since the necessary
CIR will be the same for the combined
level in the first case as for the
individual level in the second case, the
value of the individual interference level
may now reach higher values. This can
be used either to decrease the requirements
for the antennas, or to increase
the number of radio links in a particular
area, or a combination of both.
This approach seems to be the most
promising way to improve the economy
of radio links, both in terms of costs and
frequency utilization. Today's technology
should make it possible to design
level-controlled transmitters without
eating up its benefits.
This paper is the result of discussions
over a longer period between Mr. P-0
Gustavsson, Ericsson Radio Systems
AB, and the author. Mr. Gustavsson has
also contributed the degradation formula.

Modulation and Switching Using Optical
Components in Lithium
Bo Lagerstrom and Bjorn Stoltz
Collaboration between Ericsson Telecom and RIFAAB as regards integrated
optics has led to the manufacture of advanced optical components in lithium
niobate (LiNb0 3 ). Their applications include optical modulators for Gbit systems
and switch arrays for directional coupling of optical signals.
The authors describe these and other components and also the relationships
between design and application.
optical modulation
integrated optics
manufacture
Fig. 1
Waveguide channels, electrodes and polarization
directions in a crystal with a)Z-cut and b) Y-cut
Electrode
Optical waveguide
Electrical field lines
Optic communication systems using
single-mode fibres as the transmission
medium permit extremely high transmission
rates. Optical switches with
modulation rates of several GHz are now
practicable using electro-optic crystal
materials such as lithium niobate
(LiNb0 3 ). During the last three years
Ericsson has built up design knowhow
and measuring equipment. CAD systems
adapted for optical circuit design
are used. The manufacturing engineering
has been developed by RIFAAB, and
the manufacture produces optical components
with a very high performance
level.
Two applications are of particular interest
to optic communications systems:
high-speed modulators and switch arrays.
Phase modulators constitute a
special variant. They are used in coherent
systems with the light frequency
as the carrier at 300 THz. Such a system
permits the transmission capacity of the
optical fibre to be exploited to the full.
The switch array is used for directional
coupling of optical signals. Its operation
is not dependent on the frequency and
encoding of the signal that carries the
information.
Properties of the material
Lithium niobate is a negatively uniaxial
crystal with high double refraction. By
double refraction is meant different refractive
indices in different directions.
The ordinary refractive index is
n 0 = 2.221 and the extraordinary
n e = 2.145 for a light wavelength of
1.3u.m. The crystal has the interesting
property of combining good transmission
over a large wavelength range with
large electro-optic coefficients. This
means that the refractive index is effectively
changed by an applied electrical
field.
It is also possible to manufacture optical
single-mode waveguides having low
losses by doping the crystal with titanium.
Lithium niobate is therefore
widely used in the field of integrated optics
for the manufacture of opto-components
for light wavelengths of between
0.6 and 1.5|im.
The change in refractive index with an
applied electrical field can be expressed
as
where n is the refractive index, r the
electro-optic coefficient and E the applied
electrical field. The largest coefficient,
r 33 , of 30-10~ 12 m/V, is normally
used in order to ensure low operating
voltages for the components. In this
case both the optical and the electrical
fields must be orientated along the optical
axis (zaxis) of the crystal. Two different
cuts of the crystal can thus be
used, fig. 1.
In one case the crystal is cut with the
surface perpendicular to the z axis and
the light waveguides along the y axis
(Zcut). The light is then TM polarized
and the electrodes must be placed on
top of the waveguides. In the other case
the crystal is cut with the surface parallel
to the z axis and the light propagation
along the x axis (Y cut). The light is then
TE polarized and the electrodes are
placed bv the side of the wavenuides.

81
Bo Lagerstrom
Ericsson Telecom
Telefonaktiebolaget LM Ericsson
Bjorn Stoltz
RIFAAB
Fig. 3
An 8x8 array with 64 switch points in a busbar
structure. Each switch point is a directional
coupler controlled by an operating voltage of
approximately 30 V
Both crystal orientations are used, but
Z-cut crystals usually give simpler electrode
structures and better coupling to
the optical fibres. The components described
in this article are manufactured
on Z-cut lithium niobate and are polarization-dependent.
Design and application
An optical switch is usually based on a
directional coupler. Fig. 2 shows how
the beam is switched between the two
adjacent light waveguides. The switching
is controlled by electrodes along the
interactive area. The design of the electrodes
controls the frequency characteristics
and efficiency of the component.
The two inputs are independent of
each other. If the switch is in the cross
state with respect to one input, the same
state applies to the other input.
The optical waveguides are designed for
single-mode transmission, low propagation
loss and a light distribution that
suits a single-mode fibre. Both the coupling
length in the interactive area and
the coupling efficiency to the fibre can
be optimized by varying the width and
depth of the waveguide channel along
the direction of propagation. A typical
waveguide channel for a wavelength of
1.3 urn is approximately 5^m wide and
3-5 urn deep.
A theoretical simulation of the circuit
function can be performed using a numerical
method, the beam propagation
method, BPM, which calculates the
propagation of the beam in the crystal.
The input data for the program consists
of production parameters and information
concerning the geometry of the circuit.
The BPM results include the coupling
length in a directional coupler,
crosstalk between light channels, bend
losses and coupling losses. The optical
attenuation is dependent on the length
and complexity (curved structures) of
the component.
The major part of the design work is the
designing of the electrodes. Two essential
parameters are the products of frequency
and length and of operating voltage
and length. Both the operating voltage
and the frequency are inversely proportional
to the length of the component.
Typical values:
- Frequency times length
- Operating voltage times
length
"lOGHzcm
8Vcm
One of the consequences of this type of
component is the element of trade-off
that exists between operating voltage
and bandwidth. A shorter component
permits higher frequencies but also re-
Fig. 2
An optical switch is usually based on a directional
coupler. Theoretical simulation of the circuit
function is done by means of the beam
propagation method (BPM) and shows how the
light is switched between the adjacent waveguides

Fig. 4
A non-blocking 8x8 switch array contains 64
switches. Each directional coupler is 2 mm long
and controlled by an operating voltage of approximately
30 V
Electrode
Optical waveguide
Table 1
Number of Inputs Number of LiNb0 3 8x8
or outputs
chips
32 3
64 10
128 25
256 65
Fig. 6
The electrode structure for a directional coupler
modulator, in the form of a decoupled transmission
line, gives an impendance of 50 ohms
Transmission line
Electrode
Optical waveguide
quires a higher operating voltage, which
is difficult to generate. On the other
hand the voltage does not set limits for a
switch array that works at low switching
rates (MHz).
Present-day LiNb0 3 materials make it
possible to manufacture components
having a length of 60mm. An 8x8 array
with an optical through-connection loss
of 5-7dB has been manufactured. It
contains an array of 64 switch points,
fig.4. Each switch point is a directional
coupler controlled by a voltage of approximately
30 V. The array is such that a
free input can always be connected to a
free output without traffic between
other inputs and outputs having to be
rerouted, so the array offers full accessibility.
Several arrays can be used to build up
large networks in such a way that full
accessibility is retained. The arrays are
best arranged in multi-link systems, a
structure which is also called a Clos network.
2 Table 1 gives the number of
LiNb0 3 chips needed to build up large
Clos networks.
Other structures than arrays and Clos
networks may be more suitable in cases
where short interruptions in the traffic
over established circuits are permissible.
The directional coupler can also be used
as a modulator. The electrode is then
designed as a transmission line for microwaves,
a travelling wave electrode, in
order to achieve high modulation frequencies.
The electrodes must be wide
and thick so that electrical losses are
minimized, which leads to a design with
decoupled electrodes in order to ensure
low impedance (50ohms) and operating
voltages, fig. 6. Using this decoupled
electrode design, a component has
been manufactured which has a bandwidth
of 3.0GHz and a switching voltage
of approximately 8V. The bandwidth is
limited by the electrical losses in the
transmission line and the theoretical
limit is approximately 5.5GHz for a decoupled
transmission line.
An alternative to the described modulator
is provided by the Mach-Zehnder
modulator. In this the beam is split between
two waveguides, and an optical
path length difference is introduced by
means of an electrical field. This gives
rise to constructive and destructive interference
- on and off state respectively
in the modulator - at the point
where the beam waveguides are re-
Fig. 5, right
The directional coupler can also be used as a
modulator. In order to achieve high modulation
frequencies the electrode is designed as a transmission
line for microwaves, a travelling wave
electrode
Fig. 7, far right
An optical Mach-Zehnder modulator. The electrode
is constructed as a coplanar transmission
line, which gives a bandwidth that is limited to
approximately 7 GHz by phase disparity between
the electrical and optical wave propagation

Fig. 8
A push-pull design for the electrode in a Mach-
Zehnder modulator ensures a low operating voltage
(lower picture). Phase modulation in an
interferometric structure (Nlach-Zehnder) gives
constructive/destructive interference, i.e. in/off
states of the modulator (top picture)
Electrode
Optical waveguide
Fig. 9
The diagram shows how switches S1 and S2
switch the data bit stream and how the highspeed
modulator (XM) modulates the beam from
the laser. In the passive state the beam passes
straight through S1 and S2, the bypass function
F
Wideband amplifier
Optical waveguide
Operating voltage
Electrode
joined, fig.8. A push-pull construction
results in a low operating voltage,
3-5V. In this case the optical geometry
permits a coplanar transmission line,
which gives an even greater bandwidth.
For an electrode of 1 cm the bandwidth
is limited to approximately 7GHz by
phase displacement between the electrical
and optical wave propagation.
An optical fibre data bus has been
designed using opto components in
LiNb0 3 . An optical bypass function prevents
system cutoff if individual terminals
are switched off. It also permits expansion
of the data bus without interruptions
to the traffic. This bypass function
is provided by directional couplers
arranged in accordance with fig. 9, giving
an overall loss (fibre-chip-fibre) of
less than 5dB. Low-frequency directional
couplers (S1 and S2) and a highspeed
modulator (XM) for 2.4Gbit/s are
integrated on one and the same chip.
When the component is active the data
bit stream is connected via S1 toadetector
for demultiplexing and signal processing.
The terminal unit (optical chip,
detector and laser) repeats the data bit
stream continuously and feeds out data
generated by the terminal. In the passive
state, the bypass function, data passes
straight through S1 and S2. A modified
version can be used for bit processing
and works as a MUX/DMUX or an interface
between high and low data rates.
Manufacture
Lithium niobate, LiNb0 3 , is available
commercially in the form of polished
wafers, 3" in diameter and 1 mm thick.
Optical components are so large that
the chips are usually handled individually.
The first step in the process is therefore
to cut the wafer into a number of
suitable chips, usually 2-10 per wafer.

6
84
Fig. 10
Manufacture of LiNbO, waveguides
a resist deposited
b exposure through a chrome mask
c development
d evaporation of titanium
e resist lifted off
f diffusion
Waveguides are created by diffusing titanium
strips into the crystal. 60-90nm
titanium is evaporated on to a photolithographic
resist pattern on the chip,
fig. 10. When the resist is lifted off, only
the titanium that is to form the desired
optical waveguide channels remains.
The chip is heated in oxygen for five to
seven hours in a temperature of 1030-
1050°C, whereby the titanium is diffused
into the crystal. The increase in refractive
index and the depth of diffusion are
controlled by means of the titanium
thickness and diffusion parameters. The
process is optimized primarily for low
bending losses and a high fibre coupling
efficiency. After the diffusion the
crystal ends are polished to optic quality
in order to make possible the coupling
to optical fibres.
The metal electrodes must be insulated
from the optical waveguides in order to
minimize the optical losses caused by
absorption in the electrodes. This is
done by evaporating a 180-260 nm buffer
layer of silicon dioxide (Si0 2 ) on to the
chip surface. This is particularly important
for Z-cut crystals, with the electrodes
placed directly above the waveguides,
and TM polarized light. Theelectrodes
are usually made of gold and
manufactured through a technique similar
to that of the waveguides.
High-frequency components require
thick electrodes in order to minimize
electrical losses. High-frequency electrodes
are also made of gold but by
means of electroplating. The chip is covered
by a thin layer of gold which serves
as the cathode for the plating. This is
covered by a resist mask in a three-layer
process, fig. 11. First a thick (ca. 4um)
resist layer is placed on the chip. On top
of this a silicon nitride layer of approximately
100 nm is deposited using chemical
vapour deposition, CVD. The last
layer is a thin (ca. 1 um) photoresist,
which is exposed and developed. Next
the silicon nitride layer is etched with a
freon plasma, with the top resist layer as
the mask. Finally the lower, thick resist
layer is etched by means of oxygen, with
the silicon nitride as the mask.
This is a strongly anisotropic method
and gives the resists straight and welldefined
edges. Electrodes with thicknesses
of up to 3-4 nm can be manufactured
with a separation of a few um.
The coupling to optical fibres consists
of aligning and optimizing each fibre to
the optical waveguide, after which they
are bonded.
Conclusion
This article describes the current state
of the research and development in integrated
optics at RIFAAB and Ericsson
Telecom. The number of applications in
optical fibre systems is expected to increase
in future.
Components that are not polarizationdependent
will make LiNb0 3 chips compatible
with the technique for presentday
single-mode fibres.

Fig. 11
Plating of high-frequency electrodes
a resist and silicon nitride deposited
b exposure
c development
d vapour etching
e plating
f resist lift-off and etching of gold contact
The growing interest in coherent systems
will mean new applications on
both the send and receive side in which
integrated optics is an essential factor.
Further markets are to be found in sensor
technology and military applications.
The use of integrated optics will
also grow as optical amplifiers are developed.
In the long run semiconductors are likely
to replace certain LiNb0 3 circuits in
applications that require a very high degree
of integration. However, lithium
niobate components provide better
matching for single-mode fibres and will
probably be predominant in a large
number of applications for many years.
Fig. 12
An optical data bus chip assembled with an
electrical and optical interface. Low-frequency
directional couplers and a high-speed modulator
for 2.4 Gbit/s are integrated on the optical chip
References
1. Thylen, L: Integrated Optics. Ericsson
Rev. 61 (1984):F, pp. 49-52.
2. Clos, C: A Study of Non-Blocking
Switching Networks. Bell-System
Technical Journal, March 1953 pp
406-424.

New Hardware in AXE 10
Urban Hagg and Kjell Persson
System AXE 10 was designed with a structure based strictly on function modules.
It was anticipated that it would be necessary to add. remove or replace parts of
the system in order to adapt it to different applications and different markets, and
to modernize its hardware in step with the technical development. The structure
is a significant reason for the international success of the system.
The authors give brief descriptions of a number of new and modernized units,
which are now being introduced in AXE 10. Integrated circuits developed within
the Ericsson Group are largely used in these units.
telecommunication equipment
modules
integrated circuits
computer architecture
Fig. 2
Some of the circuits developed within the Group.
From the left:
A
B
C
Gate arraty circuits in an arithmetic and logic unit
(ALU) in central processor APZ212
Standard cell ICs In an exchange terminal circuit
Full custom circuits tor line circuit tunctions
The development of AXE 10 has been
directed towards providing digital alternatives
for all telephony applications.
Starting with local exchanges 2 , AXE 10
now includes tandem and transit exchanges,
international exchanges,
mobile telephony 3 , operator facility 4 ,
rural network applications, common
channel signalling 5 and, before long,
digital subscriber lines and nodes in the
ISDN (Integrated Services Digital Network)
6 .
Since the introduction of AXE 10 a number
of functions have been added in
order to meet demands from administrations
in over sixty countries. For example,
extensive adaptation work has been
carried out in order to meet specific requirements
as regards signalling Most
of this work was implemented in software.
Large hardware changes have also been
made in the system. At an early stage it
became clear that digital switching systems
would have great advantages. Digital
group switches 7 were soon introduced.
The next step was to digitalize
the subscriber switch. 8 This made it possible
to arrange remote subscriber
switches, connected via digital line systems.
A small subscriber multiplexer 9
for 30 subscribers extends the economical
application range to include very
small subscriber groups. Modern components
and new manufacturing engineering
have resulted in the development
of two new central processors 10 for
AXE10: APZ211, which replaces the
earlier APZ 210, and APZ 212 for applications
which require very high capacity.
These two processors represent highly
developed real time processor engineering
for telecommunications applications
both as regards hardwareand
operating systems.
The successful introduction of these
new units is a tribute to the modular
structure of AXE 10.
Parts of the system have remained unchanged
in spite of the continual hardware
improvements.
Fig. 1 shows what parts have now been
renewed.
New components
Development in the field of electronic
components has been very rapid during
the 20 years or so of its existence, and
everything points to this trend con-

87
URBAN HAGG
KJELL PERSSON
Ericsson Telecom
Telefonaktiebolaget LM Ericsson
Fig. 1
Block diagram of the hardware structure in
AXE 10
CP
MAU
RP
SP
ST-C
ST-R
ETC
CSR
DAM
GS
LSM
RPBC
Central processor
Maintenance unit
Regional processor
Support processor
Central signal terminal
Regional signal terminal
Exchange terminal circuit
Code sender and receiver
Digital announcement machine
Group switch
Line switch module
Bus interface
New products
Existing products
tinuing. Recent years have above all
meant greater development of components
for special applications.
Since its introduction in the world market
AXE 10 has continually been rationalized
in step with component development.
Integrated circuits developed
within the Group have now
reached such a degree of sophistication
that the time has come for their introduction
on a broad scale in most of the
units in AXE 10.
Three different types of internally developed
integrated circuits are used in
AXE 10: gate array, standard cell and full
custom circuits, fig. 2.
The choice of type of IC for a certain
application is determined by the development
time, development and manufacturing
costs and production volume.
Gate array circuits are primarily
used in low-volume products (e.g. central
processors), whereas optimized full
custom circuits are used in large-scale
manufacture, for exam pie for line circuit
functions. Standard cell circuits are
used in the intermediate range.
Results
The objectives of the new units include a
reduction of the number of printed
board assemblies to about half in a normal
local exchange (for approximately
8000 subscribers) and to approximately
a third in transit exchange applications
(for approximately 6000 junction lines).
The comparisons referto fully digital exchanges.
Fig.3 illustrates the changes
resulting from the new engineering applied
to a local exchange.
Fig. 3 also shows that the power requirement
is not reduced to the same extent
as the space requirement. This makes
new demands on the construction practice.

88
Relative scale
Fig. 3
Comparison of some characteristics of the new
and the previously used hardware in AXE 10
Earlier hardware
New hardware
Number of
printed boards
Number of types
of printed board
assemblies
Power
consumption
Floor space
requirement
24 BM
Fig. 5
Equipment for 128 subscribers in new and previous
hardware respectively
PSM
SDM
LSM
Processor and switch magazine
Subscriber device magazine
Line switch module
The advantages of the hardware rationalization
can be summarized as follows:
- Reduced space requirement
- Lower power consumption
- Increased reliability
- Fewer faults
- Fewer operator interventions
- Fewer types of printed board assemblies
- Simplified handling
- Fewer spare parts required
- Lower handling costs.
Cabinet construction
practice
The new hardware units make greater
demands on the ability of the construction
practice to dissipate heat. A
new cabinet construction practice has
been developed in order to meet these
demands without having to use fan cooling
and also to obtain efficient screening
against electromagnetic radiation.
The cabinet has six shelves for magazines
and space for cabling along one
side, fig. 4.
The new cabinet construction practice
has a standard width of 24 BM for
magazines (BM = building module =
40.64 mm) and 3 BM for cabling. A similar
cabinet of half the width (12BM) is
used for I/O units.
The cabinet construction practice is
used for all new units in AXE 10, and the
units are assembled into magazines designed
to fit into a total shelf width of
24BM.
The changeover to a cabinet construction
practice makes it possible to
deliver cabinets fully equipped and tested.
The cabinet is described in greater detail
in another article in this issue of
Ericsson Review. 1
Fig. 4
Cabinet construction practice for AXE 10
Subscriber switch
In AXE 10 the subscriber switching subsystem,
8 SSS, constitutes the majorityof
the hardware in a local exchange. If the
total amount of hardware is to be cut
down to any noticeable extent, SSS
must therefore be reduced considerably.
Previously the equipment for 128
subscribers consisted of two magazines,
a processor and switch magazine,
PSM, and a subscriber device magazine,
SDM. After the introduction of new
printed board assemblies one 24BM
magazine was sufficient for 128 subscribers.
A group of 128 subscribers is
called a line switch module, LSM, figs.5
and 6.

Fig. 6
An LSM magazine
AXE 10 subscriber switch
- Digital T-structure
- 128 subscribers per module
- 16 modules per group of 2048 subscribers
- Up to 32 digital links per group
- Not sensitive to asymmetrical load
The line circuit board in LSM contains
functions for eight subscribers and is
called LIC8, fig. 7. Different types of LIC8
are available for different types of subscriber
line current feeding.
Two full custom circuits have been developed
for line circuit funcions: the
subscriber line interface circuit, SLIC,
with line circuit functions for high voltages,
and the subscriber line audio processing
circuit, SLAC, for digital line circuit
functions. 11 ~ 13
The special regional processor in the
subscriber switch, EMRP, has been reduced
to two printed board assemblies,
partly through the use of memory components
with higher capacity.
In addition to the hardware changes already
mentioned the following improvements
are being introduced in SSS:
- As an alternative the LSM magazine
can be equipped for only 64 or32 subscribers.
- An SSS working as a remote unit is
equipped with an internal traffic function.
This means that a call between
two subscribers within the remote
unit will occupy neither speech channels
to the parent exchange nor multiple
positions in the group switch.
- Each LSM (128-group) can be equipped
with two PCM systems (for 2 or
1.5Mbit/s) instead of one. This increases
the traffic capacity so that the
maximum traffic per subscriber also
meets the requirements of some city
exchanges with a good margin.
See also the box "AXE 10 subscriber
switch".
Fig. 7
Line circuit board for eight subscribers
Group switch
Thegroupswitching subsystem, GSS, in
AXE 10 uses time-space-time (T-S-T)
switching, i.e. three-stage through-connection.
Minor hardware changes in
both the time and space switch magazines
have led to a considerable reduction
in the amount of floor space required
for GSS. Compared with pre-

Fig. 9
The equipment required for 480 digital circuits
using new (green) and earlier (yellow) hardware
respectively. The magazine module concept replaces
the earlier magazine group
ETC
RP
POU
DM
Exchange terminal circuit for 30 digital circuits
Regional processor
Power converter
Distribution module
AXE 10 group switch
- T-S-T structure
- Full redundancy
- 512 multiple positions per module
- Up to 128 modules (64 k)
- 25000 erlangs (congestion

91
Fig. 10
Magazine module for 32 code senders/receivers
Fig. 11
The announcement machine connected to the
rest of the hardware
DAM
RP-A
RP-B
GS
Digital announcement machine
Regional processor A
Regional processor B
Group switch
Fig. 12
Regional processor
The new code sender/receiver is controlled
by the new regional processor. It
forms a magazine module in a way similar
to ETC, i.e. two CSR magazines together
with two RP magazines. The
magazine module for CSR can be extended
by one or two CSR magazines,
fig. 10.
Announcement machine
The new digital announcement machine,
DAM, in AXE 10 has PCM samples
stored in electronic memories. The
choice of message and speech channel
is dynamically controlled by a microprocessor
on the basis of the traffic situation.
The announcement machine is controlled
by the new regional processor, and
the speech channels are connected to
the group switch via one to four 2 Mbit/s
circuits, fig. 11.
The announcement machine occupies a
12 BM magazine and has a capacity of
four messages and 128 speech channels.
It can store fixed or programmable
messages having a length of 32 and 64
seconds respectively.
A special variant of the machine can
store eight shorter messages.
A memory board for one message can
be replaced by a printed board assembly
for analog/digital conversion whereby
an external, analog source (e.g. a tape
recorder) can be used to give a message.
The announcement machine used hitherto
is analog, contains moving parts
and is not built up on printed boards.
Central processor
In systems with low to medium capacity
requirements APZ211 is used as the
central processor, CP. APZ212 10 is used
for high capacity requirements.
lnbothAPZ211 och APZ212the capacity
of the memory components has been
changed from 64 kbit to 256kbit, which
has resulted in smaller CP dimensions
and fewer printed board assemblies for
a given application.
Regional processor
The new regional processor, RP, in
AXE 10 includes gate array circuits and
new memory components.
Previously it was not possible to change
a program in RP without replacing hardware.
Dynamic RAMs (Random Access
Memory) are now being introduced for
the RP programs. At the same time software
is being developed for the central
processor that will aid the loading, functional
modification and fault handling in
the processs. The new RP is fully compatible
with the previous version.
The new regional processor occupies
only 3BM (5 printed board assemblies,
including the power board) and has up
to twice the capacity of its predecessor.
The memory capacity has been increased
considerably. Fig. 12 shows the
RP magazine.
System for input and output
of data
The previous input/output subsystem,
IOS, is being replaced by four new subsystems:
support subsystem, SPS, file
management subsystem, FMS, data
communation subsystem, DCS, and
man-machine communication subsystem,
MCS, fig. 13.
Unlike its predecessor the new I/O system
is not controlled by a regional processor.
A new type of processor, the
support processor, SP, is being introduced
for this purpose. It gives greater
flexibility and makes a number of previously
developed units available to
AXE10.
In the new I/O system, discs are the medium
used for mass storage. High-capacity
disc stores of the Winchester type
are used for the system standby copy,
logging, buffer storage of charging data
etc. Floppy discs are used as a transportable
medium for the input and output of
programs and data. The disc stores normally
hold approximately 50 Mbyte of
data each. The floppy discs use industrial
standard format and hold approximately
1.2 Mbyte each. Data links for up

92
Fig. 13
New subsystem structure for input and output
functions
IOS
SPS
DCS
FMS
MCS
Input Output Subsystem
Support Processor Subsystem
Data Communication Subsystem
File Management Subsystem
Man-Machine Communication Subsystem
to 64kbit/s can be included in the I/O
system, fig. 14.
In addition to the changes described
here the hardware used for terminal and
alarm interfaces is being rationalized.
A normal I/O system with full redundancy
is mounted in two special cabinets,
each with a width of only 12 BM.
In addition to VDUs and printers the terminal
interfaces in MCS can also connected
to a man-machine system, MMS,
which includes a personal computer.' 4
Summary
A large proportion of the hardware in
AXE 10 has been renewed, to a great extent
by integrated circuits developed
within the Group. This has resulted in
improved performance and simplified
handling. The modular structure of the
system facilitates introduction of new
units. The system software is largely unaffected
by the new hardware. This
means that the software remains the reliable
version that is now in operation in
more than 800 exchanges, a fact which
ensures high system quality in the new
exchanges.
Fig. 14
The hardware structure of the I/O system and its
connection to the central processor
CP
MAU
SP
Central processor
Maintenance unit
Support processor
References
I.Hellstrom, B. and Ernmark, D.: Cabinet
Construction Practice for Electronic
Systems. Ericsson Rev. 63
(1986):2, pp. 42-48.
2. Eklund, M. et al.: AXE 10 - System
Description. Ericsson Rev. 53
(1976):2, pp. 70-89.
3. Billstrom, 0. and Troili, B.: A Public
Automatic Mobile Telephone System.
Ericsson Rev. 57 (1980):1, pp. 26-36.
4. Morell, L.-E.: Operator Position Subsystem
in AXE 10. Ericsson Rev. 60
(1983):2, pp. 66-72.
5. Du Rietz, J. and Giertz, H.: CCITTSignalling
Subsystem in AXE 10. Ericsson
Rev. 59(1982): 2 pp. 100-105.
6. Ericsson Rev. 61 (1984): ISDN.
7. Ericsson, B. and Roos, S,: Digital
Group Selector in the AXE 10 System.
Ericsson Rev. 55 (1978): 4, pp. 140-
149.
8. Persson, K. and Sundstrom, S.: Digital
Local Exchanges AXE 10. Ericsson
Rev. 58 (1981): 3, pp. 102-110.
9. Larsson, C. and Ohlsson, E.: Remote
Subscriber Multiplexer, RSM. Ericsson
Rev. 60(1983): 2, pp. 58-65.
10. Jonsson, I: Control System for AXE 10.
Ericsson Rev. 61 (1984):4, pp. 146-
155.
11. Bjurel, G., Dudnik, A. and Hjortendal,
R.: Development of Line Circuits for
AXE 10. Ericsson Rev. 60(1983): 4, pp.
181-185.
12. Eriksson, G. and Svensson, T.: Line
Circuit Component SLAC for AXE 10.
Ericsson Rev. 60 (1983):4, pp. 186-
191.
13. Rydin, A. and Sundvall, J.: Line Circuit
Component SLIC for AXE 10. Ericsson
Rev. 60 (1983):4, pp. 192-200.
14. Backstrom, T. and Lambert, J. : Man-
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Ericsson Rev. 62(1985):2, pp. 82-92.

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