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
Editor Gosta
Llndberg
Neovius
Editorial staff Martti
Viitaniemi
Address S-126 25 S t o c k h o l m , Sweden
S u b s c r i p t i o n one year $ 16
Published in Swedish, English, French and Spanish with four issues per year
Copyright Telefonaktiebolaget LM Ericsson
Contents
42
49
52
58
63
71
80
•
•
•
•
•
•
•
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
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.
Greater need for heat
dissipation
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
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, en-
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
vironmental 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.
44
The actual product environment
Environmental factors and characteristic
environments during the life of the products
Fig. 3
Summary of the different concepts that affect the
environment and environmental endurance of the
products
Climatic
environment
Handling
environment
Chemical
environment
Storage
environment
Mechanical
environment
Transport
environment
Biological
environment
Operating
environment
Electrical
environment
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 c o n d i t i o n i n g
equipment. Administrations exploit this
feature for various purposes, for example to repair c o o l i n g equipment w i t h o u t
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).
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
The requirements of different countries
are often based on recommendations by
CISPR (Comite
International
Special
des
Perturbations
Radioelectrique).
This is the c o m m i t t e e that, under the
International Electrotechnical Commission, w o r k s on the standardization of
matters c o n c e r n i n g interference of
broadcasting
and television. Fig.4
shows an example of such requirements.
When designing the B Y B 2 0 2 cabinets
an electrically screened version was
also developed. Measurements show an
attenuation factor of 50 dB in the frequency range 3 0 - 5 0 0 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
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
The screened cabinet can be supplemented by special cable runs with similar attenuation properties.
stand discharges of 15kV against the
cabinet casing.
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
Functional units
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.
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.
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.
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
Input/Output Subsystem
CPS
Central Processor Subsystem
GSS
Group Switching Subsystem
TSS
Trunk and Switching Subsysten.
CCS
• I
Common Channel Signalling Subsystem
Subscriber Switching Subsystem
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
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
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.
Technical data
Cabinet
Height
Width
Depth
Required ceiling height
Aisle width
Load on the floor
2133 mm
1 200and 720 mm
400 mm
2650mm
800 mm
4 kN/m2
Magazine
1M
1 BM
Height
Width
N
Depth
Printed board spacing
0.1" (2.54mm)
1.6" (40.64 mm)
6 BM (234.8 mm)
Nx3BM
1-8
220 mm
6 M or 8 M
Printed board
Height
Depth
2 or 4 layers
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.
222 mm
178 mm
Wiring unit
Wrapped or printed board
2 or 6 layers
Pin spacing
1M
Operating conditions
Temperature
Normal range
Safe function
Relative humidity
Normal range
Safe function
5-40°C
0-45°C
20-80%
5-90%
References
1. Almquist, R.: A Cooling
System for
Electronic
Telephone
Exchanges.
Ericsson Rev. 58 (1981):4, pp. 1 8 8 195.
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.
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-
Active
Low
ERIK ALBERTSSON
Ericsson Power Systems
RIFA AB
sures low maintenance costs for the
ERICOOL cooling systems. Periodic
preventive maintenance is usually sufficient.
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-
ERICOOL
Local energy costs
Passive
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 fol-
lowing 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. 188195.
2. Alexandersson, R., Junborg, A. and
Vesterberg, H.-J.: Passive Cooling of
Premises for Electronic
Equipment.
Ericsson Rev. 61 (1984):3, pp. 128131.
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.
Brief system description
ERICOOL has been described in a previous issue of Ericsson Review1, 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.
cooling
telecommunication equipment
Since the introduction of electronictelephone systems, the thermal density has
increased from 100 to 500 W/m2 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.
Fig. 1
The telephony equipment is cooled by means of
self-convection. This method gives efficient cooling and a quiet and draught-free environment
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:
53
RAGNAR A L M Q U I S T
Ericsson Power Systems
RIFA AB
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.
Fig. 2
The modular structure makes for simple installation and enables the equipment to be extended in
step with the telephone system
W
Circulation during normal operation
v'
Circulation during a mains failure
CC
PU
MV
WT
CU
Cooling coil
Pump unit
Mixer valve
Water tank
Cooling unit
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 w o r l d . Some of the administrations that have installed the system
have made their o w n 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 w o u l d 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
c o n s u m p t i o n 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
Singapore6
"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 t e l e c o m m u n i c a t i o n s 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
PU
MV1
MV2
WT1
WT2
CU1
CU2
DC
Cooling coil
Pump
Mixer valve 1
Mixer valve 2
Operating tank
Standby tank
Operating cooling unit
Standby cooling unit
Cooler (heat exchanger)
are now forming the basis of the second
generation of ERICOOL.
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%.
The most important features, the high
reliability and energy saving, have been
extended further through different system designs, fig. 5.
Alternative system designs
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.
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.
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
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/m2.
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. 188195.
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.
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-
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.
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
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
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. 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 20foot 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
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
Fig. 9
Cooling module for Container 3500
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
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,
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 compo-
nent 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. A l e x a n d e r s s o n , R., J u n b o r g , A. and
Vesterberg, H.-J.: Passive Cooling of
Premises
for Electronic
Equipment
Ericsson Rev. 61 (1984):3, pp. 1 2 8 131.
2. Wolpert, T.: The Reliability of Auxiliary
Systems - Power and Cooling;
Further
Insights.
Intelec
Proceedings
(1983), pp. 1 0 9 - 1 1 6 .
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.
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.
Fig. 1
Automatic teller machine E281 as seen by the
customer
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.
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
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.
Fig. 2
The growth rate of automatic teller machines,
ATM, in the US and Europe
the US
Europe
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
Maintenance
- Operator
System and
function
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
Capacity
Installation through
a wall in an unsupervised environment
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
Fig. 4
The division of the E281 development work between Ericsson and Omron. The safe is supplied
by a local manufacturer
- Serviceman
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
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
thereby forms an integral part of terminal system E2100. E281 has a modular
structure w h i c h simplifies operation
and maintenance.
The design of the units operated by customers and their positions on the front
of E281 meet exacting e r g o n o m i c requirements.
Fig. 6
Automatic teller machine E281 is built up of four
main parts: a front, electronics cabinet, printer
cabinet and safe
The division of the development work
between Ericsson and Omron is outlined in f i g . 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 c o m p u t e r in system E2100 via a twowire line or be remotely connected via
the t e l e c o m m u n i c a t i o n s 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 t h r o u g h the slot in
the front
- security and g o o d e r g o n o m i c characteristics in the positioning of units operated by the customers
- easy handling when replenishing the
note store and c h a n g i n g 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 o p e n i n g 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 q u e u i n g behind.
Fig. 7
The front of E281
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
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
- 4 0 to +50°C
20 to 85%
20 to 100%
220V + 10%
5 0 H z ± 2%
IEC 380/435
UL478
A mains failure will not damage the machine.
Battery backup is provided for memories and
automatic program loading.
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
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
-
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.
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
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:
Fig. 8
E281 is the result of collaboration between Ericsson Information Systems and Omron Tateisi Electronics
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.
digital systems
radio links
interference
network topology
Fig. 1
BER versus receiver input level, LR,, for various
values of CIR and co-channel interference
(4FSK - 6/8 Mbit/S)
CIR = 12dB
CIR = 15dB
i • 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
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.
The influence of interfering radio signals depends mainly on the f o l l o w i n g
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 d u r i n g fading-free
time, as long as the carrier-to-interference ratio, CIR, is at least 2 0 d B . It is
only during f a d i n g , w h e n the receiver
input level, LRx, comes close to its
threshold level, LTe, that the bit-error
ratio will be degraded. An example may
explain this:
Fig. 1 shows the BER versus LRi, for various values of CIR. The curves in this
72
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 = - 6 0 d B m , the bit-error ratio, BER,
Fig 2
Simplified RL network, with the paths
a
b
in a triangular configuration
in a quadrangular configuration
interference path
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 LRx drops to -67dBm,
which gives a CIR of 15dB, the BER decreases to 6 - 1 0 6 (instead of <10~e for
CIR = oo). If LRx drops just 3dB more, to
- 7 0 d B m , CIR decreases to 12dB, and
the limit for the planning objective of
BER = 1CT3 is reached
The influence of interfering signals is
thus not noticeable until fading occurs
and then as a deterioration of the receiver threshold level, LTe. This is the
same as a drecrease of the path's fading
margin, M. It is therefore of interest to
discuss the correlation between fading
of the wanted and the interfering signal
Fading correlation between
wanted and interfering signal
a)
When studying mutual interference
within an RL network it is easiest always
to consider two paths at a time, the disturbed and the disturbing path. These
two paths are either part of a triangular
configu rat ion, fig. 2a, or of a quadrangular one, fig.2b.
Multipath fading
Concerning multipath fading, the fading
events for the wanted and the interfering
signals are uncorrelated for all disturbing connections, whether the paths
A - B and A - C or D-E and F-G resp.
use the same radio frequency or not.
Even in the case of co-channel operation, the fading of the interfering signal
travelling from antenna A1 to antenna C,
fig. 2a, is uncorrelated with that of the
wanted signal A 2 ^ C, provided that the
distance between antennas A1 and A2 is
at least 150 wavelengths.
For short paths, however, i.e. paths having a length of about 10 km and less,
multipath fading may be disregarded.
This is especially applicable to high radio frequencies (r.f. == 13GHz), as at these frequencies and short path lengths,
fading caused by rain will always be the
dominating planning parameter.
Rain fading
In the case of rain fading, the fading
events for interfering signals from A1 to
C, and from A2 to B, fig. 2a, are always
73
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 - ^ A 2 , C — A 1 , 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 e x c l u d e d :
If, as an example, the distances A - B ,
A - C and also B - C are about 5 k m , or
less, the probability that a rain cell
covers both the wanted path (e.g.
B^>A1) and the interference path
( C ^ A 1 ) , 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 w o u l d 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.
fluence of interference on the overall
performance.
Two different approaches to such a prediction are discussed here:
- Starting from a given receiver input
level, LRx, 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 d u r i n g fadingfree time at A1 (and at B) is LR„
Using an RL equipment of the type
Ericsson MINILINK18 (ML18), with a
built-in antenna of 0.6 m diameter, a value of
LRx = - 4 3 . 0 d B m
is obtained.
The
receiver
threshold
level
for
BER = 1 0 - 3 and an undisturbed path
(CIR = °°) is LTe. This can be taken from
the equipment's data sheet. For ML18,
the corresponding value is:
LTe= - 8 0 . 0 dBm
See also fig. 1.
The flat-fading margin is t h e n :
Interference calculation
Table 1
Logical chart for uncorrelated events between
wanted and Interfering signals for various fading
events
yes
interfering signal considered
no
interfering signal not considered
The principal work in drawing up a frequency plan is the prediction of the in-
The interfering signal C ^ A 1 reaches
the receiver A1 via antenna A1 with a
level, L,, w h i c h , as an example, c o u l d be:
L,= - 9 2 . 0 d B m
Path
Multipath
Wanted/
interfering
path length
« 1 0 km
A-»B/A2-»B
A<~B/C->A1
A-*C/A1-»C
A<-C/B-*A2
D-»E/F-*E
D«-E/G^D
F_»G/D->G
F«_G/E-»F
no
no
no
no
no
no
no
no
>10km
Rain
Effective interfering
path length
s=5km
>5km
yes
yes
yes
yes
yes
yes
yes
yes
no
partly
no
partly
partly
partly
partly
partly
no
yes
no
yes
yes
yes
yes
yes
If more than one interfering signal has to
be considered, L, is the resultant level of
n c o m b i n e d individual levels, L,,, namely:
n
L, = 10lg 2 1 0 L | | / 1 °
i=i
Starting from the interfering level, L h of
- 9 2 d B m in the diagram in fig. 1, a CIR
74
value of 1 5 d B can be f o u n d at a threshold level, LTel, of - 7 7 d B m . The CIR value
for 1 5 d B corresponds t o the difference
between these t w o levels:
The threshold level has thus decreased
by:
LTe, is now the new threshold level in the
presence of interfering signals:
see f i g . 3 for ML18. A, = 0 d B 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, corres p o n d i n g to CIR = 1 2 d B .
For the above example, i.e. for:
n=1
A, = 0 (co-channel interference)
L,= - 9 2 . 0 d B m
This gives a new flat-fading margin, MR,
of:
To allow for a more handy estimation of
the performance degradation, a computer-adapted formula has been introduced:
D degradation of the threshold level,
LTe, in dB
n number of interfering paths
K equipment parameter: K = 9 2 d B m
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 f o r m u l a 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 > 1 0 k m , 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 t w o ends of a path as there is for
the wanted signal:
L,A1 =£ LIB whereas
LRxA1 = LRxB
This gives us t w o different fading margins, M R , f o r the t w o directions of transmission on the same path. The smaller
of these t w o fading margins must be
used for the p r e d i c t i o n 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 < 5 k m . One possibility
could be to set the degree of correlation
proportional to the effective length of
the interfering path, related to 5 km, and
75
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 - A 1 , 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.
Fig. 4
Transmitted spectrum from an 8 Mbit/s, 4FSKmodulated radio-relay link
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, LTe, (CIR = «>) may
lock the receiver onto that interference signal in case its " o w n " 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, Lh from each interfering path:
D, K, A, and n have their previous significance.
Assuming 12 interfering paths and an
allowed degradation of the t h r e s h o l d
level by 1 0 d B for the planned path, we
obtain a m a x i m u m level for each interfering signal of:
for co-channel interference. The value
for LN 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,
AGA, 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, MFI, than the BER
planning objectives require.
- For configurations
fig. 2b:
according
to
output level of the disturbing
transmitter in dBm
A0
AGTx
AGRx
free-space attenuation in dB between the disturbing transmitter and disturbed receiver
antenna discrimination in dB
for the transmitting antenna
do. for the receiving antenna
The parameters which can be chosen
freely are AGTx, AGRx and LTx. Low LTx
requires less AGTx and/or AGRx, but it
also decreases the fading margin for
its own path. Hence, the fading margin, MF|, 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,
MFh (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 CIRmm 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 B x =-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
A
B
NC
D
Transmitter
output power
in dBm
15.0
15.0
12.0
0.0
Receiver
input level
in dBm
-43.8
-43.8/-46.0
-46.0/-47.3
-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 nec-
essary 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 (LiNb03). 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
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
(LiNb03). 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
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
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
n0 = 2.221
and
the
extraordinary
ne = 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, r33, of 30-10~12m/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
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.
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
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
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. 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
or outputs
32
Number of LiNb0 3 8 x 8
chips
3
64
128
256
10
25
65
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).
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
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 - 7 d B 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
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
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. 8
A push-pull design for the electrode in a MachZehnder 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
joined, fig.8. A push-pull construction
results in a low operating voltage,
3 - 5 V . 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.
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
An optical fibre data bus has been
designed using opto c o m p o n e n t s 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 5 d B . 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 c o m p o n e n t is active the data
bit stream is connected via S1 t o a d e t e c tor 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 f u n c t i o n , data passes
straight t h r o u g h 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 c o m p o n e n t s 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 - 1 0 per wafer.
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 10301050°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 (Si02) 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 cov-
ered 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.
6
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 L i N b 0 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
The development of AXE 10 has been
directed towards providing digital alternatives for all telephony applications.
Starting with local exchanges2, AXE 10
now includes tandem and transit exchanges,
international
exchanges,
mobile telephony3, operator facility4,
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.
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
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 switches7 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 multiplexer9
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 processors10for
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. cen-
tral 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.
Relative scale
88
Fig. 3
Comparison of some characteristics of the new
and the previously used hardware in AXE 10
Earlier hardware
N u m b e r of
printed boards
New hardware
24 BM
N u m b e r of types
of p r i n t e d b o a r d
assemblies
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.
Fig. 5
Equipment for 128 subscribers in new and previous hardware respectively
Cabinet construction
practice
PSM
SDM
LSM
The new hardware units make greater
demands on the ability of the construction practice to dissipate heat. A
Processor and switch magazine
Subscriber device magazine
Line switch module
Power
consumption
Floor space
requirement
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
Subscriber switch
Fig. 4
Cabinet construction practice for AXE 10
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
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.
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
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".
Group switch
Fig. 7
Line circuit board for eight subscribers
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
vious magazine groups in the low-level
construction practice (six shelves) the
floor area required has been reduced by
about a third.
The maximum number of multiple positions in the group switch is 65536
(64x1024).
The new group switch units are controlled by the new regional processor.
See also the box "AXE 10 group switch".
AXE 10 group switch
-
T-S-T structure
Full redundancy
512 multiple positions per module
Up to 128 modules (64 k)
25000 erlangs (congestion < 1 0 6 )
All types of network synchronization
Fig. 8
Exchange terminal circuit for 30 circuits
Exchange terminal for 30
channels
Exchange terminal for 24
channels
A new exchange terminal circuit,
ETC24, for 1.5Mbit/s has been developed for markets that use u-law PCM
In order to avoid wastage in the group
switch, which handles units of 32 channels (2Mbit/s), four bit streams at
1.5Mbit/s are combined into three bit
streams at 2 Mbit/s. This results in a unit
for 96 channels. Two such 96-channel
systems are installed in a magazine of
9BM, and magazine modules are formed in a way similar to that of ETC30.
The exchange terminal circuit ETC30
constitutes the digital interface for
2Mbit/s PCM line systems towards the
group switch.
Code sender and receiver for
MF signalling
The ETC for 30 channels now comprises
a single printed board assembly as
against five previously. The reduction
has been achieved by means of standard
cell circuits and a special power module
for mounting on printed boards, fig. 8.
Signalling between exchanges will to an
increasing extent consist of common
channel signalling, preferably CCITT
No. 7. However, it will take long for this
system to come into general use. In the
meantime a large part of the signalling
will require MF equipment for VF signalling.
Eight ETC 30 boards occupy a magazine
having a width of 9 BM. Two such maga- The new unit for MF signalling, code
zines, together with new regional pro- sender and receiver, CSR, is digital and
cessors, constitute a magazine module. can thus be connected directly to the
The magazine module replaces the pre- digital group switch.
viously used concept of magazine group
in AXE 10, fig. 9. A magazine module can The use of microprocessor and gate arconsist of anything from a part of one ray circuits has resulted in a unit whose
shelf up to several fully equipped cabi- performance is a considerable improvenets.
ment on earlier equipment. A9BM magazine holds 16 devices, which can all be
The new ETC30 is used for junction used as either transmitter or receiver.
lines and remote subscriber switches. Previous equipment comprised four
Fig. 9 shows that the space require- transmitters or four receivers and ocments for equipment for digital circuits cupied 18 BM. An eightfold reduction in
space has thus been achieved.
have been drastically reduced.
91
Fig. 10
Magazine module for 32 code senders/receivers
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
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
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.
Fig. 12
Regional processor
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. APZ21210 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
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.
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
A normal I/O system with full redundancy is m o u n t e d in t w o special cabinets,
each with a width of only 12 BM.
In addition to VDUs and printers the terminal interfaces in MCS can also c o n nected to a man-machine system, MMS,
which includes a personal computer.' 4
Summary
A large p r o p o r t i o n 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.
References
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
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. 140149.
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. 146155.
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. 186191.
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. : ManMachine Communication in AXE 10.
Ericsson Rev. 62(1985):2, pp. 82-92.
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