Colour Display System SEMIGRAF 240 - The history of Ericsson

ERICSSON 

REVIEW 

3 

1978 

COLOUR DISPLAY SYSTEM SEMIGRAF 240 

OPERATIONAL EXPERIENCE OF ANA 30 IN ARHUS 

NEW GENERATION OF 120 AND 480-CHANNEL FDM SYSTEMS 

FOR TWO-WIRE CABLE OPERATION 

AXB 20 - OPERATION AND MAINTENANCE CHARACTERISTICS

ERICSSON REVIEW 

NUMBER 3 1978 VOLUME 55 

Copyright Telefonaktiebolaget LM Ericsson 

Printed in Sweden, Stockholm 1978 

RESPONSIBLE PUBLISHER DR. TECHN. CHRISTIAN JACOB/EUS 

EDITOR GUSTAF 0. DOUGLAS 

EDITORIAL STAFF FOLKE BERG 

EDITOR'S OFFICE S-12625 STOCKHOLM 

SUBSCRIPTION ONE YEAR $6.00 ONE COPY $1.70 

PUBLISHED IN SWEDISH, ENGLISH, FRENCH AND SPANISH 

Contents 

86 • Colour Display System SEMIGRAF 240 

92 • Operational Experience of ANA 30 in Arhus 

96 • New Generation of 120 and 480-Channel FDM Systems 

for Two-Wire Cable Operation 

106 AXB 20 - Operation and Maintenance Characteristics 

COVER 

The colour display system SEMIGRAF 240, developed 

by SRA Communications AB, a member of 

the Ericsson Group, replaces a conventional 

control panel. The cover shows a schematic picture 

of the operational state of a blast furnace.

Colour Display System 

SEMIGRAF 240 

Bjorn Karbeus 

This article presents the new computerized colour display system SEMIGRAF 240. 

which replaces conventional types of control panels. SEMIGRAF 240 has been 

developed by SRA Communications AB, a member of the Ericsson Group. 

UDC681 326: 

621.397 132 

Fig. 1 

Control room with display units that form the 

opera tor pane I for control of an ore dressing plant 

The transition from the earlier manual 

control and supervisory systems of various 

types to computerized systems 

makes new demands on the units that 

transfer orders and information between 

operator and system. 

For a long time various types of control 

panels with instruments, switches and 

controls provided the normal solution. 

In large systems such control panels can 

be very extensive, and can sometimes 

take up a whole wall. They are therefore 

expensive and difficult to change. An 

improvement was achieved by introducing 

various types of black/white graphic 

displays as operator units. The operator 

could then fetch information from the 

system, and also control it by feeding in 

various commands. However, in many 

cases it proved to be difficult for an 

operator to assimilate the displayed information 

quickly and correctly. The introduction 

of colour as an aid in the 

structurization of the displayed pictures 

made it very much easier to recognise 

and understand the information shown. 

Background 

SRA Communications AB have worked 

on different types of displays, both 

black/white and colour since 1969. 

SEMIGRAF is the registered trade mark 

for colour display systems manufactured 

by SRA. 

The first system, designed SEMIGRAF 

210, was delivered in 1974 and since 

then many systems have been supplied 

for a number of different applications, 

such as power supervision, ore dressing, 

railway control and supervision of 

coaxial cable networks.

BJORN KARBEUS 

SRA Communications AB 

To the 

computer 

Fig. 2 

A SEMIGRAF system consists primarily of a control 

unit, colour TV and keyboard. A light-pen can 

be added as an accessory for interactive work with 

the display. 

A picture is stored and generated in the control 

unit tor display on the colour monitor. Signals representing 

red, green and blue beams and for 

synchronization go from the control unit to the colour 

monitor. Input takes place via a keyboard 

Fig. 3 

The control unit is the central unit for picture generation. 

The picture to be displayed is stored in the 

picture store. The character generator interprets 

the content ot the picture store and generates the 

characters to be displayed on the screen. 

The video unit converts the digital signals to 

analog signals for operating the colour monitor. 

The time base generates timing and control signals 

for the various parts of the control unit. 

The 8-bit processor is the administrative unit, 

which via the I/O unit handles the communication 

with the keyboard and the main computer 

Display 

SEMIGRAF 240 is the newest member of 

the SEMIGRAF family. Utilization of the 

new integrated circuits, which have become 

available during the last few years 

as a result of the great advances in 

semiconductor technology, has made 

Keyboard 

87 

possible the design of an equipment 

with a performance which only a few 

years ago could hardly have been attained 

within a limited framework. 

A SEMIGRAF 240 system consists of a 

varying number of units depending on 

the application, fig. 2.

88 

Fig. 4 

The three beams red, green and blue sweep in a 

fixed pattern over the screen. The desired picture 

is obtained by means of intensity modulation 

Fig. 5 

The picture is built up ot characters, which are 

generated in matrix form. There are two types of 

characters, alphanumeric (letters, figures and 

punctuation marks) and graphic (lines, corners, 

squares etc.) 

The control unit is the central unit in 

which the displayed picture is generated. 

A block diagram is shown in fig. 3. 

The control unit has a modular structure 

and can thus be adapted to different 

display requirements. Starting with a 

basic unit extra functions can be added 

to give the desired overall function. 

The picture is displayed using the raster 

method, i.e. the picture is drawn by 

means of intensity modulation of three 

beams (Red, Green and Blue), which 

sweep in a fixed pattern over the surface 

of the colour monitor all the time, fig. 4. 

Inside the glass surface of the colour 

monitor there is a pattern of red, green 

and blue phosphorus dots. By means of 

intensity modulation the different 

phosphorus dots can be made to light in 

a desired pattern so that the picture 

stored in the picture store of the control 

unit appears on the screen. 

The beams sweep over the screen so 

that a complete scan takes 20 ms. Every 

picture is drawn in exactly the same 

tracks. In this respect it differs from a 

normal TV system, which works with 

odd and even fields. Since all fields are 

the same, a true 50 Hz picture frequency 

is obtained and the 25 Hz flicker 

obtained in an ordinary TV system is 

avoided. This gives a picture that is 

practically free from flicker. 

The screen can be imagined as being 

divided into a grid with squares in rows 

and columns. In each square - character 

position - one character can bewrit- 

ten. The characters are divided into two 

categories, alphanumeric characters 

(letters, figures and punctuation marks) 

and graphic characters (lines, corners, 

rectangles and other symbols) which 

are used to build up the graphic information, 

fig. 5. 

The displayed picture is stored in a 

picture store with capacity for one or 

four pictures. There is a place reserved 

in the picture store for each character 

position on the screen. Each place in the 

memory has a maximum length of 20 

bits. These bits give the character to be 

displayed and the colour and whether 

blinking is available or not. Thus each 

individual character that is displayed 

has its own colour information stored. 

Each character is allocated two colours, 

a foreground colour, which is the colour 

of the symbol itself, and a background 

colour, for the remainder of the character 

position when it is displayed, fig. 6. 

The content of the picture store is read 

out concurrently with the sweep of the 

beams (R, G, B) over the screen. The 

time base controls the various time 

sequences. The synchronization signal 

S makes the monitor work in synchronism 

with the control unit. The information 

read out from the picture store only 

indicates which character is to be displayed 

at a certain moment, not the 

actual shape of the character. The latter 

information is provided by the character 

generator, which contains descriptions 

of all the different characters that can be 

generated The character generator 

permits the display of two sizes of

Fig. 6 

Each character position is associated with two 

colours, the foreground colour, which is the colour 

of the character itself, and the background colour, 

which is displayed in the remainder of the character 

position 

Fig. 7 

Schematic picture of a digester for wood pulp 

characters. The two character sizes can 

be combined as desired. 

Storing a new picture 

So far the article has described briefly 

how a new picture, which lies ready in 

the picture store, is drawn on the 

monitor screen, but not how a new 

picture is generated and stored in the 

picture store. 

A picture in the picture store is generated 

either from the keyboard or from a 

main computer, or from a combination 

of the two. 

When a picture is built up from the 

keyboard the visible cursor is used, 

which is a white blinking symbol consisting 

of two horizontal lines. The size 

of the cursor is exactly that of a character 

position, and it indicates to the 

operator the spot on the screen where 

the next character to be written will be 

placed. The cursor can be moved about 

on the screen with special keys in the 

keyboard. 

The following parameters can be 

specified before a character is written 

on the screen: 

— Foreground colour 

— Background colour 

— Blinking or not 

— Character set (alphabet) 

89 

All characters that are then written will 

have the status specified in accordance 

with the above until another status is 

specified. 

When the voltage for the control unit is 

switched on, white foreground colour 

on a black background is automatically 

set up and the alphanumeric character 

set is selected. The operator can then 

specify the desired colour, blink etc. before 

writing any characters on the 

screen. 

The characters that are written on the 

screen are stored in character stores 

which can be of two types: PROMs and 

read/write memories (RAM). 

Characters stored in a PROM cannot be 

altered unless the memory elements are 

removed and replaced by new ones, 

programmed with a new set of 

characters. Characters stored in a 

PROM are preserved even when the 

voltage is switched off.

90 

Fig. 8 

Keyboard for SEMIGRAF 240 with individual power 

feeding. The communication with the control unit 

is carried outin series form via opto-insulated current 

sections. There are built-in circuits for acoustic 

alarm (bell). 

The read/write memory for character 

storage enables characters with 

arbitrary shapes, within the limits of the 

character matrix, to be programmed in 

from a main computer or from the 

keyboard. Characters stored in the 

read/write memory are lost when the 

voltage to the control unit is switched 

off, and must be programmed in again 

when starting up. 

The building up of new characters for a 

user-oriented character range is simplified 

by the built-in interactive routine for 

creating new characters with the aid of 

the keyboard. 

When a new character is to be built up 

this routine is started by depressing a 

key on the keyboard. A frame is then 

displayed on the screen, within which 

the character is shown magnified during 

the building-up process. A cursor can 

then be moved within the frame and 

each point in the character matrix can 

be specified as foreground or background. 

When the character matrix has 

been built up as desired, the character 

can be stored in the character store under 

the desired name. The programmed 

character can then be written on the 

screen and thereby checked that it is 

correct. If the operator is not satisfied 

with a certain character it can be returned 

to the programming frame, cor 

rected and then finally stored again. 

A set of characters that has been built up 

in this way can be read into the main 

computer by means of a special command 

and stored there in a bulk store. 

When the system is started up, or when a 

new set of characters is required, the 

character store can then be loaded with 

the desired set. 

Keyboard 

The keyboard for SEMIGRAF 240 has 

been specially designed so that it can be 

placed a long way away from the control 

unit. 

The keyboard has its own power supply 

and when installed is connected to the 

nearest wall socket. Communication between 

the keyboard and the control unit 

takes place via a cable with four conductors. 

The character codes have a 

length of 8 bits and are sent from the 

keyboard in series form at a signalling 

speed of 300 Baud. The keyboard contains 

a locking key with which the 

operator can signal to the control unit 

when it is to be on-line. The keyboard 

also contains a bell which can be activated 

from the control unit. All communication 

to and from the keyboard 

takes place with current loops of 20 mA.

Fig. 9, left 

The control unit consists of a 19 printed board unit 

with built-in power supply 

Fig. 10 

The processor board, CPU, is a complete eight-bit 

computer with central processing unit, program 

store, data store, vectorial break logic and two interfaces 

in series 

Communication with 

a main computer 

The control unit can communicate with 

a main computer in parallel or series 

form. The standard version has a series 

channel in accordance with CCITT V24 

in full duplex and the transmission 

speed is switchable between 110 and 

9600 Baud. The transmission is carried 

out either with or without parity check. 

Transmission with parity check is carried 

out in blocks with a maximum 

length of 128 bytes, each block starting 

with STX and finishing with ETX. 

Any type of parallel connection may be 

used, the choice depending only on the 

type of computer to which the control 

unit is to be connected. 

Division into hardware 

and software 

The functions of the control unit can be 

divided into two groups: 

a. the control of the colour monitor, 

which is tied to the timing sequence 

b. other functions. 

The direct drawing of the picture on the 

colour monitor is a fast process that 

must be repeated regularly in order to 

maintain the picture on the screen. All 

the direct picture drawing on the screen 

is implemented in hardware. 

The 8-bit microprocessor included in 

the control unit is quite unable to operate 

at the speeds required to carry out 

the direct picture drawing, since each 

raster point in a picture has a time dimension 

of only about 100 nanoseconds. 

The tasks of the processor are: 

— to handle the communication with a 

main computer via the computer input 

and output devices 

— to handle the communication with 

the keyboard via the keyboard input 

and output devices 

— to interpret the character sequences 

received from keyboard and computer 

and to carry out the requested 

functions 

— to write in external information in the 

picture store 

— to write in the character store 

— to move information in the picture 

store (editing) 

— to fetch information from the picture 

store or character store and send it to 

the main computer (e.g. "read line"). 

Many functions are thus carried out or 

controlled by software, which gives a 

unit that can easily be adapted to special 

application requirements. 

It has also been possible to adapt the 

system to the users — human beings — 

and at the same timeto arrange efficient 

means of communication with a main 

computer.

Operational Experience 

of ANA 30 in Arhus 

Henning Kortsen and Christian Neergaard-Petersen 

An article in a previous issue of Ericsson Review described how the Jutland 

Telephone Company, Jydsk Telefon A/S or JTAS, Denmark, was modernizing its 

crossbar exchanges ARF 10 by converting them to ARE 11 exchanges with the aid 

of the control system ANA 30\ This applies for the whole of the Arhus exchange 

area. The new exchanges offer better traffic routing and operational supervision 

possibilities and also sa vings as regards personnel. It is also possible to improve the 

service to the subscribers in the form of new facilities and traffic possibilities. 

In this article the results of the operational experience from Arhus are described, 

and the associated questions regarding organisation, reduced personnel requirement 

and training are discussed. However, since the modernization is still in progress, 

with ANA 30 now being installed in the exchanges in the city suburbs, it is 

only possible to present the operational results of ARE 11 in Arhus Centrum, the 

main exchange with 25 000 lines which has been in operation during the whole of 

1977. This exchange also contains the operating centre for the whole zone. 

UDC 621.395.722 

Fig. 1 

The Arhus operating centre and the manned and 

unmanned exchanges in the Arhus exchange area 

O Manned exchange 

• Unmanned exchange 

Organisation 

The Arhus operating centre is a common 

unit of great importance to all exchanges 

in the area. From there it is 

possible to inform about operating conditions, 

assist in the clearing of serious 

faults, carry out changes of subscriber 

category and provide a number of other 

essential services. 

After the modernization five of the thirteen 

local exchanges in Arhus will be 

manned, fig. 1. (Whether an exchange is 

manned or not is determined on the 

basis of size and position.) The associated 

five maintenance areas are 

each managed by a chief engineer, who 

reports to a main-office manager. 

If assistance is needed for a complicated 

fault the area concerned turns direct to 

the operating centre. The reguired assistance 

can be given via a teleprinter or 

display unit, fig. 2. 

In the operating centre the category 

allocation of each subscriber in the 

whole area is written into the subscriber 

category memory with a teleprinter, fig. 

3. This is done for all categories except 

the interception service category, which 

is written in by the interception 

operators, who are placed in a special 

room (the switchboard room). 

All external applications, including fault 

reports, are routed to the operating 

centre. All alarms from the local exchanges 

and the 30 rural automatic exchanges 

in the area are also taken in to 

the centre. 

Any alarms outside working hours are 

connected to the switchboard room, 

where an operator calls a repairman 

when necessary. It is then advantageous 

that all exchanges in the area can be 

controlled from the operating centre. 

The operating centre is always kept in-

HENNING KORTSEN 

CHRISTIAN NEERGAARD-PETERSEN 

Jydsk Telefon A/S 

Arhus, Denmark 

Table 1 

Number of faults during 1 year in ANA 30, 

Arhus Centrum 

1 

Type of device ?o ?f 

' faults 

Traffic control processor, TCP 4 

Multiplexor. MUX") 2 

Translation store. TRS 3 

Code receiver for tone frequencies, 

KMK 4 

Code receiver, KM 3 

Signal transfer unit for SR, STU-L 3 

Signal transfer unit for FIR, STU-I 3 

Identification unit for GV, IDG 1 

Total 23 

*) Each processor is connected to a duplicated multiplexor 

in each rack that contains mterworking devices. 

MUX ensures that only one processor at a time is connected 

to any device in the rack in question 

Table 2 

The distribution of the faults among different 

groups of equipment 

Number of Per- 

Fault source faults per cent- 

10 000 lines age 

Control system ANA 30 9 2 0 2 

REG-L in the former 

ARF 100registerequipment (510) (1.1) 

Switching system (ARF100) 320 6 9 

Subscriber lines and 

telephone sets 4300 92.9 

Fig. 2 

The operating centre provides assistance with 

the analysis of a fault 

formed of the whereabouts of each repairman. 

It is of great value to be able to 

contact each individual repairman from 

the operating centre. 

A common spare part store for the five 

maintenance centres has been set up at 

the operating centre. Defective printed 

board assemblies are sent from the 

centre to LM Ericsson's workshop in 

Copenhagen for repair. 

For the time being all communication 

between the exchanges and the operating 

centre or the switchboard room 

takes place via telephone circuits, which 

are connected up through the public 

telephone network to modems connected 

in the exchanges in question. 

Operational statistics 

After a running-in period the operational 

statistics for exchanges with control 

system ANA 30 show that the number of 

faults and serious operational disturbances 

has been greatly reduced. 

The trunking diagram of fig. 4 shows an 

ARF 100 exchange in Arhus which has 

been modernized with control system 

ANA 30. 

93 

three processor groups, 23 faults occurred 

in the ANA 30 equipment during the 

whole of 1977. Table 1 shows the faults 

distributed among types of devices. 

21 of the faults were routine faults and 

did not disturb the traffic handling, but 

two caused serious operational disturbances, 

particularly as they occurred 

during the busy hour. One fault resulted 

in the breakdown of a traffic control 

processor TCP, and the other in the 

malfunctioning of a multiplexor, MUX. 

The operational disturbances occurred 

because faults occurred in the automatic 

changeover to the standby units at 

the same time. 

In order to illustrate the fault distribution 

table 2 has been prepared, showing the 

different categories of faults that occurred 

in the 25-year old local exchange in 

Arhus during one year. Values available 

for the earlier crossbar registers REG-L 

have been given in brackets to facilitate 

a comparison between ANA 30 and 

REG-L. 

When the above results are compared it 

should be remembered that ANA 30 has 

more sophisticated traffic characteristics 

than the old ARF 100 registers. 

In Arhus Centrum, with 25 000 lines and The operator is notified of faults in con-

94 

Fig. 3 

Changing subscriber categories from the 

operating centre 

trol system ANA 30 by means of alarms 

and printouts administered by the operation 

and maintenance processor, 

OMP. 

Faults in the switching system can also 

be found with the aid of ANA 30, since its 

printouts show the switching processes 

in the form of digits and control signals. 

Other printouts specify the device 

groups that exceed the permitted error 

level limits (STU, KS, KM). These printouts 

can indicate faults in the switching 

system and the network. 

After the introduction of ANA 30 it has 

also been possibleto keep the switching 

system in better condition than before, 

since the latter system has gradually 

been adjusted to the exacting signalling 

and time conditions that apply for 

ANA 30. 

In spite of the fact that ANA 30 gives detailed 

fault information, the supplementary 

fault reports from the subscribers 

are of importance, for example 

when there is a fault in the signal reception 

from the push-button sets. 

Experience from ANA 30 in Arhus 

Centrum shows that after a running-in 

period the system is very reliable. The 

operational statistics show that the duplication 

of most of the function units in 

ANA 30 ensures that large operational 

disturbances are to all intents and 

purposes eliminated. 

Saving in personnel 

By the middle of 1978 115 000 lines in 

the Arhus area were connected to 

ARE 11 exchanges with ANA 30. If these 

subscribers were to have been served by 

ARF 100 instead, 21 technicians would 

have been required for the operation 

and maintenance of the exchanges, not 

including the MDF staff. 

It is estimated that after the modernization 

with ANA 30 the number of technicians 

required will be reduced to 18, a 

saving of 3. Furthermore it is expected 

that the staff will be kept at this number 

during the coming years despite the fact 

that the number of subscribers is expected 

to increase by 8 % annually. 

In addition there is a saving of 1/2 man 

year per year because such administrative 

tasks as category changes, route 

changes etc. are carried out by means of 

commands.

Fig. 4 

Tmnking diagram with ARF 100 in Arhus, 

modernized by the addition of control system 

ANA 30 to ARE 11 

SLM Subscriber stage marker 

GVM Group selector marker 

IDS Identification unit for A-subscriber 

STU-L Signal transfer unit for SR (SR - cord line relay 

set) 

STU-I Signal transfer unit for FIR (FIR - junction 

line relay set) 

SS Code sender finder 

KMK Code receiver tor tone frequencies 

KS-MFC Code sender lor MFC 

GV-KME Matching unit for group selectors 

IDG Identification unit 

KM-MFC Code receiver tor MFC 

TCP Traffic control processor 

OMP Operation and maintenance processor 

SCS Subscriber category store 

TRS Translation store 

ADS Abbreviated dialling store 

Just the disconnection and reconnection 

of bad payers by command saves 

1/3 man year per year among the MDF 

staff. 

Even though a saving in personnel is 

important this is not the main purpose of 

the modernization. The main objective 

is to obtain a system that offers many 

new facilities and services and which 

can later be equipped with still more, for 

example common channel signalling 2 . 

Training 

On the basis of the experience gained 

hitherto the training requirements can 

be described as follows. Technicians 

with electromechanical training should 

attend a basic course, after which they 

can handle the exchange and repair 

common faults. This basic course 

should include the following subjects: 

1. Binary and hexadecimal 

number systems 

2. Basic system knowledge 

3. System structure 

4. The traffic control processor, 

TCP 

5. The operation and maintenance 

processor, OMP 

IIGV 

KS-MFC IDG 

7 hrs 

4 ,, 

3 ,, 

14 ,, 

14 ,, 

95 

6. Commands 21 ,, 

7. Subscriber category store, 

SCS 7 ,, 

8. Translation store, TRS 10 ,, 

9. Signal transfer units, 

STU-L and STU-I 4 ,, 

10. Traffic recording and 

statistics 7 ,, 

11. Flow charts and program 

knowledge 14 ,, 

12. Operating a processor panel 7 ,, 

13. Fault tracing 14 ,, 

14. Exchange tester 14 ,, 

Total 140 hrs 

After a year's work with the system, exfended 

ANA 30 training can suitably be 

provided to give a more detailed insight 

into the problems. Such a course, which 

would enable the technician to handle 

difficult fault clearing problems, could 

include the following: 

1. Microcomputer course 24 hrs 

2. Processor APN 110, theory 24 ,, 

3. Program knowledge 48 ,, 

4. TRS, build-up 4 ,, 

5. TRS, data 28 ,, 

6. APN 110, build-up 24 ,, 

7. Multiplexor, MUX 8 ,, 

8. Identifier for GV, IDS 8 ,, 

9. TRS-SCS 16 ,, 

10. The operating manual 8 ,, 

11. Follow-up 8 ,, 

Total 200 hrs 

Together, these courses provide a 

sound syllabus. The personnel are free 

to attend the extended course or not. 

Even though it may not be actually 

necessary to train all personnel the 

costs involved are small and it helps to 

maintain the interest and sense of responsibility 

of the personnel. 

In 1978 an extended course for 6 technicians 

will be arranged in Arhus. 

References 

LMeland, F. and Rishoj, E.: Crossbar 

Exchanges in Arhus Become 

SPC Exchanges. Ericsson Rev. 54 

(1977):2, pp. 86-89. 

2. Andersen, H. and Pedersen, V.K.: 

Field Trial with Common Channel 

Signalling. Ericsson Rev. 55 (1978): 

1, pp. 20-27.

New Generation of 120 and 

480-Channel FDM Systems 

for Two-Wire Cable Operation 

Per-Erik Johansson 

Systems ZAX-ZAC 120 T and ZAX-ZAC 480 T utilize one cable pair jointly for both 

directions of transmission. The systems are intended for single-tube coaxial cables 

and for increasing the capacity of existing twin cable networks. There is also an 

extensive range of branching eguipment available for these systems, and they are 

thus well suited not only for public telecommunications networks but also for military 

networks and power, railway and pipeline projects. 

The earlier generation of this system was introduced at the end of the 1960s, and 

sincethen morethan 13 000 kilometres of the system have been installed on various 

types of cable in widely diverging climatic conditions. 

The article describes briefly the experience gained from the first generation of the 

line equipment for two-wire operation over small-core coaxial cable, ZAX 120 T\ 

and also the main technical features of the new systems. 

UDC 621 395.4 

621.315.212 

Fig. 1 

Installation testing of ZAC 120 T equipment for the 

Swedish State Railways 

Experience from the earlier 

system generation 

The experience from the first generation 

of 2-wire systems, ZAX 120 T, can in all 

essential respects be considered as very 

good. When ZAX 120T was introduced it 

was the aim to offer a system alternative, 

based on single-tube coaxial pairs for 

mounting on existing poles, which 

could be used instead of, for example, 

12-channel aerial line systems. 

The fears that an aerial coaxial cable 

would be subjected to cable breaks 

more often than a buried cable have 

proved to be unfounded. It has been 

established, however, that the cable 

must be robust in order to withstand 

rough handling during installation, and 

the stresses caused by strong winds, 

so-called galloping, which can occur in 

open terrain. Another important reguirement 

is that the cable has good 

screening against external interference 

from, for example, MW transmitters. 

This means that the coaxial tube should 

be provided with a magnetic screen and 

a surrounding conducting layer of 

aluminium or a similar material. 

LM Ericsson's single-tube coaxial cables 

were modified at an early stage 

when the area of the suspension wire 

was increased and an aluminium screen 

was introduced. 

The method originally chosen for fault 

location of cable breaks was found to be 

not wholly reliable in areas where 

thunderstorms occur frequently. A modification 

was therefore introduced 

whereby a shunt resistor was fitted in 

each amplifier in the power feeding 

path. If a cable break occurs the fault is 

located by reading off the summed feeding 

current on an instrument that is 

graduated direct in number of stations 

up to the fault. Since the modification 

the location of cable breaks has functioned 

quite satisfactorily. 

The check and test points etc., which as 

a precautionary measure had been 

specified for the buried equipment, 

proved to be unnecessarily extensive. 

The experience gained from ZAX 120 T 

is similar to that of conventional large 

coaxial cable systems. The most com-

PER-ERIK JOHANSSON 

Transmission Division 

Telefonaktiebolaget LM Ericsson 

Fig. 2 

Line repeater tor ZAX-2AC 480 T, seen trom two 

directions. The unit contains all electronic equipment 

for a dependent repeater station. The power 

separation filter and directional filters are shown 

on the left. On the right are the fault location oscillator, 

the amplifier and the pilot receiver 

mon cause of traffic disturbances is 

damage to the cable, not faults in the 

electronic equipment. 

During the last ten years the system has 

been put into operation in a number of 

different applications. The frequency 

allocation plan used, in accordance with 

CCITT G 356, 1A, has made possible direct 

through-connection to larger 

systems and has also been advantageous 

when arranging various forms of 

leak branching stations. The possibility 

of carrying out small leak branchings 

along a line on a group basis has also 

been of particular interest. 

Among the military applications can be 

mentioned a special arrangement for 

line networks, whereby automatic 

changeover to standby routes maintains 

full capacity between the leak branching 

stations included in the system, even if 

the cable on the first-choice route 

should be damaged. 

The line repeaters have pilot regulation, 

which is necessary because different 

sections of the cable may be run in different 

ways, for example in air, buried or 

laid in ducts, and are thus subjected to 

extremely varying temperature conditions. 

The regulation range of ±4 dB at 

the pilot frequency has proved to be suf 

ficient for all climatic regions. 

97 

In order to meet a growing need to be 

able to increase the traffic capacity of 

existing twin cables through the introduction 

of modern carrier systems with 

more than 12 channels, the equipment 

was also adapted for use with that type 

of cable. The transmission characteristics 

of paper insulated twin cables have 

been determined by means of extensive 

field measurements and theoretical 

studies 2 . The system has proved to be 

very suitable for use on such cables, and 

has made it possible to increase the 

capacity many times over without laying 

new cables, at only the relatively low 

cost for the electronic equipment. 

The system is designed so that a changeover 

from coaxial cables to twin cables 

is possible without termination or 

division into separate pilot sections. 

The equipment installed for the Swedish 

State Railways constitutes an example 

of a countrywide network for 120 channels 

on twin cables. Further extensions 

of this network are planned. The cables 

used, which were installed as long ago 

as the 1920s, consist of lead-sheathed 

paper insulated twin and quad cables 

with 0.9-1.3 mm conductors. The extensions 

will also include coaxial cables.

98 

Fig. 3 

Translation of basic supergroups to a 480-channel 

line group 

General principles for 

the new generation 

of systems 

The systems comprise two equipments 

designated ZAX-ZAC 120 T and ZAX- 

ZAC 480 T. The designation ZAX-T 

means equipment for two-wire transmission 

via a coaxial cable and ZAC-T 

the corresponding equipment for symmetrical 

twin cable. The transmission 

capacities are 120 and 480 telephone 

channels respectively. 

The guiding principles for the new development 

have been based partly on 

experience from the first generation of 

two-wire systems and partly on the 

technical innovations incorporated in 

the design of the latest versions of 

four-wire systems, ZAX 960-9 and ZAX 

2700-4 4 . 

The basic principles can be summarized 

as follows: 

- the line repeaters are constructed in 

accordance with the principle applied 

for submarine cable systems, 

with a common repeater for both directions 

of transmission 

— the line group is always obtained in 

its basic position at the interface between 

the multiplex equipment and 

the line group equipment 

— the line group modulation frequency 

is transmitted to the other terminal or 

branching station for regeneration 

and to provide full synchronization 

between the stations 

- the same frequency is used for the 

line pilot and the modulation of the 

line group 

- automatic level regulation of the line 

amplifiers is carried out using the line 

pilot 

- cable faults are located with the aid of 

the remote power feeding. 

On the basis of these principles systems 

ZAX-ZAC 120 T and ZAX-ZAC 480 T have 

been developed to meet the varying demands 

of a diverse market. Some such 

demands are: long power feeding sections, 

the possibility of selective 

monitoring of line repeaters, several 

variants of leak branching and adaption 

to longer regulation sections on symmetrical 

twin cables. Some of these improvements 

are based on solutions 

already applied in corresponding 4-wire 

cable systems. 

The two new systems are very similar 

and therefore only the system 

characteristics of ZAX-ZAC 480 T will be 

described here. 

Frequency plan for 

two-wire transmission 

A 480-channel line group lies in the frequency 

position 60-2044 kHz and is 

formed by translating eight basic 

supergroups 312-552 kHz, fig. 3. When 

this line group is to be transmitted in two 

directions over the same pair of conductors 

it is necessary to use different 

frequency ranges for the two directions 

of transmission. Thus the 480-channel 

line group is transmitted in the basic 

position in one direction, and in the 

other direction the line group is modulated 

with 4588 kHz to 2544-4528 kHz 

on the send side. On the receive side this

Fig. 4 

Frequency allocation for ZAX-ZAC 480 T 

Fig. 5 

The transmission principle for two-wire system 

ZAX-ZAC 480 T. One repeater, common for both 

directions, is used in accordance with the method 

for submarine cable systems 

Kn - 7044 2544-4588 

group is demodulated to its original frequency 

position using the same carrier, 

fig. 4. The line frequency range will 

therefore be 60-2044 kHz in the transmission 

direction "low send" (LS), 

whereas in the other direction, "high 

send" (HS), the frequency range will be 

2544-4528 kHz. In the HS direction the 

carrier 4588 kHz is also used as the line 

pilot, fig. 5. 

The frequency 4588 kHz is the 37th 

harmonic of the master frequency 124 

kHz. At the receiving station for the high 

transmission band 2544^1588 kHz the 

line pilot is received in a phase-locked 

oscillator for use as the carrier for demodulation. 

In the same oscillator the 

frequency 4588 kHz can also be divided 

down to 124 kHz for use as the master 

frequency in the receiving terminal. 

Since the transmitted frequency 4588 

kHz is in synchronism with the transmitting 

terminal the whole transmission is 

synchronous and thus there is no need 

for any frequency comparison equipment. 

A common amplifier is used for both directions 

of transmission. The wellknown 

method from submarine cable 

systems is applied for this purpose, 

where an amplifier is connected in as a 

common component between four directional 

filters, connected in a ring. The 

directional filters separate the frequency 

bands of the two directions of transmission. 

The same type of repeater is 

used in both the terminal and the intermediate 

repeater stations. 

Line repeaters for 

coaxial or twin cables 

The fundamental design of the line 

equipment is adapted for use on both 

normal and small-core coaxial cables 

and symmetrical twin cables with different 

conductor areas and insulation. This 

provides complete flexibility in a line 

network, for example for transition from 

an existing twin cable in a built-up area 

to a new coaxial cable. The cables can 

be mounted on poles or buried. 

The differences in transmission 

characteristics between coaxial and 

twin cables that affect the design of the 

line repeater consist mainly of difference 

in impedance, attenuation 

characteristics and temperature dependence. 

Whereas coaxial cables that meet the 

requirements of CCITT Rec. G 622 are 

alike, different twin cables can have different 

transmission data depending on 

conductor area and insulation. In view 

of this a basic version of the line repeater 

has been designed which is suitable 

for the coaxial cable impedance of 75 

ohms and uniform attenuation, whereas 

paper-insulated twin cables require impedance 

matching and a different regulation 

function. 

The line repeater, fig. 2, which comprises 

a complete intermediate repeater 

equipment for both directions of transmission, 

is available in two versions, 

regulated and unregulated. 

The regulated line repeater, which contains 

a pilot receiverand thermistor, can 

regulate the gain by slightly more than 

±4 dB at the pilot frequency 4588 kHz. 

The unregulated repeater has adjustable 

gain, in six steps of 1.5 dB/step. 

Both variants can be equipped with line 

building-out networks in which a maximum 

of 37 dB cable attenuation can be 

simulated. The nominal gain of 44 dB at

100 

Fig. 6 

Line terminating shelf stack for ZAX-ZAC 480 T. 

The top shelf contains equipment for sending and 

receiving line groups and the bottom shelf contains 

the multiplex equipment for eight 

supergroups with level regulation 

Fig. 7 

The temperature coefficient TK for the attenuation 

in a coaxial cable (1.2/4.4 mm), left, and paper-insulated 

twin cable (0.9 mm, 29 nF/km), right 

the pilot frequency corresponds to the 

attenuation of 3.9 km of small-core 

coaxial cable at a temperature of +10° 

C. When this repeater is used on twin 

cables an adapter is provided which 

contains transformers for matching the 

impedance of the twin cable, 150-130 

ohms bal., to the unbalanced 75 ohms of 

the repeater. 

Adaptation to the attenuation characteristics 

of different twin cables is arranged 

by equipping the repeater with a special 

correction network. Line building out 

can also be included with the same 

network and thus make it easier to install 

thesystem on existing cable routes. 

The temperature coefficient (TK) of 

coaxial cables and plastic-insulated 

twin cables is approximately 2 %> per °C 

over the whole of the relevant frequency 

range, fig. 7. In the case of paper-insulated 

cables, however, this factor rises 

with frequency and is approximately 4.7 

%o per °C at the pilot frequency. The difference 

in TK between coaxial cables 

and paper-insulated twin cables means 

that different regulation networks must 

be used. 

The relationship between the number of 

regulated repeaters and the number of 

unregulated repeaters in a line section is 

dependent on the anticipated temperature 

variation in the cable. In the case of 

a buried coaxial cable approximately 

one repeater out of every four should be 

regulated, whereas for buried paper-insulated 

cables one out of every two or 

three should be regulated. In the case of 

aerial cable every repeater should be 

regulated. 

Terminal equipment 

The terminal equipment, fig. 6, which is 

accommodated in a shelf stack of two 

shelves in the M5 construction practice, 

is used in both terminal stations and 

power-feeding intermediate repeater 

stations and also where through-connection, 

branching or frequency changeover 

is to be arranged. 

In addition to the above-mentioned 

modulation equipment for high transmitting/low 

receiving (HS) or low 

transmitting/high receiving (LS) of the 

line band, the shelf stack also contains 

pre-emphasis and de-emphasis 

networks and fixed and/or variable 

equalizers. 

The use of the M5 construction practice 

has meant a reduction in the space required 

for the equipment, and consequently 

it has been of practical 

advantage to accommodate the complete 

multiplex equipment in the same 

shelf, including level regulation equipment 

for the supergroups and all the 

necessary equipment for generating the 

required frequencies from the input 

basic frequency of 124 kHz. 

There is a well defined interface between 

supergroups and the line group, 

which gives complete freedom of choice 

between through-connection of line 

groups or supergroups. It is also possible 

to connect in a mastergroup (812- 

2044 kHz) together with supergroups 

1-3. 

The send and receive directions of the 

line group are connected to the line 

through a two-wire hybrid and via a

Fig. 8 

Location of a cable fault 

Fig. 9 

Power feeding on coaxial cable (1.2/4.4 mm) for 

ZAX 480 T. The distance between power feeding 

stations is a maximum of 280 km at a feeding voltage 

of 800 V 

power separation filter. This filter constitutes 

both the input point for the remote 

power feeding to the line repeaters 

and the earth separation between line 

and terminal equipment. 

Power feeding and 

fault location 

All line repeaters are series fed with direct 

current. The system works with 

"floating earth", i.e. the outer conductor 

of the coaxial cable is not earthed and 

the power is fed between the inner and 

outer conductor. On twin cables the 

power is fed between the phantom 

circuit in the transmission pair and a 

separate return pair. This return pair 

contains an access point for a two-wire 

physical service telephone. The remote 

power feeding unit provides a constant 

current of 100 mA while the output voltage 

is dependent on the prevailing 

load, i.e. the number of repeaters and 

the type of cable. The maximum output 

voltage is 1000 V for coaxial cable and 

300 V for paper-insulated twin cables. 

The front of the unit contains separate 

instruments that show the output current 

and voltage. In order to prevent injuries 

to personnel the remote power 

feeding unit has been designed so that 

its output voltage falls to zero if there is 

an interruption of the feeding current, 

and so that restarts must be carried out 

manually. However, this safety function 

can be disconnected if desired, and the 

unit will then give a no-load voltage of 

1160 V. 

101 

As an extra protective measure all live 

parts that are within reach are automatically 

earthed immediately the terminal 

cover is removed or the lid of the repeater 

housing of the buried intermediate 

repeater stations is opened. 

The voltage to the line repeaters is taken 

out over zener diodes with a voltage 

drop of 20 V per regulated repeater and 

10 V per unregulated. The length of the 

power feeding section, fig. 9, is dependent 

on the type of cable and the number 

of regulated and unregulated repeaters. 

Loop connection of the power is easily 

arranged by means of a simple strapping 

direct in the repeater. 

Cable faults are located with the aid of 

the power feeding unit. If the cable is 

short-circuited the constant current will 

still be fed out. The output voltage is 

then read off on the instrument on the 

unit. It is easy to calculate the distance 

to the short circuit since the voltage 

drop per repeater section is known. 

In the case of a cable fault where the 

inner and outer conductor do not make 

contact with each other, a constant voltage 

with the same polarity as the ordinary 

voltage is fed out. Each repeater 

contains a high-ohmic resistor connected 

between the inner and outer 

conductor. The fault is located by reading 

off the summed output current on 

the power feeding unit instrument, 

which is graduated in number of stations 

uptothe position of thefault, fig. 8.

Fig. 10 

Branching for direct termination 

Fig. 11 

Branching for remote termination 

Telephony 

channels 

Fig. 12 

Remotely fed branching terminal 

Main traffic 

Branched traffic 

Fig. 13 

Remote power feeding unit with instruments for 

output voltage and current. The press buttons on 

the right are used when locating a cable break 

A fault in a repeater is located with the 

aid of an oscillator built into the repeater. 

Each oscillator is tuned to a fault 

location frequency which is individual 

for each repeater station. The fault location 

frequencies lie in the band 4800- 

5000 kHz at intervals of 2 kHz , and they 

can be measured in the receiving terminal 

using an ordinary selective instrument. 

Branching 

An important requirement for the category 

of line systems to which ZAX-ZAC 

120 T and 480 T belong is that it must be 

possible to branch off the wanted 

number of channels at arbitrary places 

along the line, in an easy and economical 

way. This facility has already been 

exploited in many cases where the first 

generation of ZAX 120 T has been installed. 

The frequency plans that apply for the 

120 and 480-channel systems, where the 

modulation frequency for the high line 

band is always accessible on the line, 

makes it easy to arrange both stop and 

leak branching. 

Stop branching in two-wire systems can 

only be arranged at a four-wire point, 

which means that the line group bands 

in both directions are terminated in the 

ordinary way by translation to the basic 

frequency band. In such a station it is 

also possible to arrange equalization 

and remote power feeding and it is also 

easy to carry out frequency frogging, 

which is advantageous as regards noise 

in the case of very long lines. 

Stop branching 5 , which is also utilized 

on large line systems, is well known and 

will not be discussed in detail here. 

Leak branching can be arranged on 

two-wire systems without the necessity 

of terminating the line group band in the 

main through path. The main advantages 

of this method are that it requires 

very little extra equipment and that local 

arrangements and power losses do not 

affect the main through-going traffic. 

The disadvantage of leak branching is 

that the frequency band that has been 

branched off cannot be used for new 

traffic after the branching point, which 

would be possible in the case of stop 

branching. 

Three types of leak branching are possible 

in the LM Ericsson 120 and 480channel 

systems: 

— branching for direct termination, fig. 

10 

— branching for remote termination, 

fig. 11 

— remotely fed branching terminal, fig. 

12.

Fig. 14 

Interiorview of a repeater station with a branching 

hybrid for re mote termination 

Fig. 15 

Portable carrier frequency service telephone 

Branching for direct termination implies 

that a desired frequency range in the 

line group band is terminated in a station 

with local power, which is in direct 

connection with the main line. This station 

can be arranged for traffic in one 

direction or both directions. The equipment 

that needs to be added to the main 

lineconsistsof a passive branching unit. 

The advantage of a passive unit is that a 

power failure in the local station does 

not affect the main line traffic. 

The frequency range of the line group 

band that is used for branching varies 

depending on whether the connected 

terminating equipment is equipped with 

subgroups, groups or supergroups. 

The carriers required can be generated 

from a basic frequency of 124 kHz, 

which is regenerated from the line pilot 

of the system. The station will thus be 

fully synchronized with its main station. 

Branching for remote termination 

means that the station for the branched 

traffic is situated so far from the main 

line that line repeaters are required in 

the branched line. The equipment that is 

required in the main line is a passive 

branching unit in this case also, and it is 

placed in the same housing as the line 

103 

repeater of the main line, fig. 14. The remote 

power in the main line is not affected 

by the branching and the line repeaters 

in the branched line are power 

fed from the terminating station. 

Remotely fed branching terminal means 

that the station for the branched traffic 

is powered from the power feeding on 

the main line. 

The station is installed in a sealed housing 

designed for burying in the ground, 

and can be equipped for up to 12 telephony 

channels with 4-wire or 2-wire 

termination with E and M signalling. 

Three channels can be provided with 

subscriber signalling units. In this case 

also, the carrier generation is based on 

regeneration from the line pilot. 

In this case the terminating group is 

placed in supergroup No. 2. The station 

is powered through a special DC/DC 

converter, which from the constant current 

of the remote powerfeeding gives a 

constant voltage of 12 V. 

A fault in the terminating equipment will 

not affect the traffic in the main line in 

this branching case either. The number 

of remotely fed branching terminalsthat 

can be arranged along a line is of course

Fig. 16 

Housing for one line repeater, right. On the left is 

shown a cut-away view of a housing for a remotely 

fed branching terminal with the multiplex equipment 

at the top and the line repeater and DC/DC 

converter below 

Fig. 17 

The line repeater shelf for rack mounting accommodates 

three repeaters. The connection to the 

power input adapter and the termination box for 

coaxial cable can be seen above the various repeaters 

dependent on the type of cable and input 

points for the power feeding. 

The application possibilities described 

above are of great economical importance 

when the systems are used in 

public telecommunication networks, 

and they are often an essential condition 

for their use in military networks, railway 

systems and pipeline projects. 

Service channels 

Systems ZAX 120-480 T also contain two 

extra carrier channels for service 

purposes and the transmission of special 

functions. These connections constitute 

a complement to the systems 

when the systems are installed for railways, 

power lines or pipelines and can, 

for example, also be used for an alarm 

telephone when the system is run along 

a motorway. 

These channels, with a bandwidth of 

approximately 4 kHz each, are placed in 

the frequency range between the edge 

of the frequency band of the directional 

filter and the regular line band for the 

transmission direction in question, fig. 

4. One of the channels is only intended 

for speech connections when servicing 

and maintaining the system. A portable 

loudspeaking telephone containing 

equipment for sending and receiving in 

both directions of transmission is provided 

for use on this channel. 

The telephone, fig. 15, which is fed from 

a dry battery, is of the "handy-talkie" 

type and can be connected direct to the 

system line repeaters. The other channel 

can be used for, for example, an 

omnibus speech connection or for voice-frequency 

telegraphy, data transmission 

etc. as required. 

The additional equipment for this channel 

is permanently housed in the system 

line repeater housing, and is powered 

from the line. 

Mechanical construction 

The equipment in a terminal or powerfeeding 

intermediate repeater station is 

mounted in racks, whereas the dependent 

intermediate repeaters are 

mounted in sealed steel housings, 

which are designed for burying in the 

ground. 

The terminal rack, which can be the LM 

Ericsson M4 or M5 rack, accommodates 

three completely separate line systems 

for ZAX-ZAC 480 T. Each system has its 

own power feeding in the form of a converter 

from battery voltage to 12 V, 

which is the operating voltage of the 

equipment. Test outlets, alarm indicator 

and a switch for changeover from Aalarm 

to B-alarm are provided on the 

front of each unit. 

The line equipment in a terminal comprises 

line matching, line repeater, remote 

power feeding unit, central frequency 

generation and power supply 

unit. 

These various functions are combined 

to form shelves or shelf stacks, which in 

principle makes possible arbitrary placing 

in the rack or combination with other 

equipment, figs. 6, 13 and 17. 

The intermediate repeater station for 

outdoor installation consists of a line 

repeater mounted in a sealed housing 

made of steel. The housing is available

Technical data for two-wire coaxial and twin cable systems 

ZAX-2AC120T ZAX-ZAC 480 T 

Supergroup translating equipment 

Frequency range 

Basic supergroup 312-552 kHz 312-552 kHz 

Line group 60-552 kHz 60-2044 kHz 

Nominal levels 

Basic supergroup 

Sending -36 or -35 dBr -36 or -35 dBr 

Receiving -23 or-30 dBr -23 or-30 dBr 

Line group 

Sending -36 dBr -33 dBr 

Receiving -23 dBr -33 dBr 

Impedance, in/out 75Qunbal. 75 L> unbal. 

Regulation and supervision of supergroups 

Regulation range, aut. > 4 dB +4dB 

Manual adjustment range ! 4 dB ' 4 dB 

Line equipment 

Frequency range 60-1304 kHz 60-1528 kHz 

Gain at pilot frequency 48.1 dB (1364 kHz) 44 dB (4588 kHz) 

Repeater spacing' (nom.) 

Coaxial cable 1.2/4.4 mm 7.8 km 3 9 km 

Coaxial cable 2.6/9.5 mm 17.8 km 8.9 km 

Twin cable, paper insulated 1.2 mm, 38 nF/km 3.6 km (ca)' 1.4km(ca)* 

Twin cable, plastic insulated 0.9 km, 33 nF/km 5.3 km (ca)' 2.6 km (ca)* 

Line regulating pilot and carrier 1364 kHz 4588 kHz 

Pilot level -10dBmO -10dBm0 

Regulation range per repeater at pilot frequency ±4dB +4 dB 

Remote power feeding 

Series feeding with constant direct current (nom.) 100 mA 100 mA 

Max. distance between power-feeding stations 

Coaxial cable 1.2/4.4 mm (Max. 800 V) 410 km 280 km 

Twin cable, paper insulated 0 9 mm (Max 250 V) 90 km* 45 km* 

No general repeater distance can be given for symmetrical 

cable, particularly if it is paper insulated. The maximum 

possible gain may be limited by near-end crosstalk 

Fig. 18 

Interior of an intermediate station for twin cable 

systems. The connection between the line pairs 

and the repeater is made via the adapter for impedance 

matching, which is placed on top of the 

line repeater 

in two sizes. The smaller, with a height of 

approximately 60 cm and an outer 

diameter of approx. 40 cm, has room for 

one line repeater and a branching 

hybrid when required, figs. 14 and 16. 

The larger housing, which is ca 124 cm 

high and has an outer diameter of 

approx. 64 cm, is used when a remotely 

fed branching terminal is to be installed. 

The housings are connected to the line 

cable by means of stub cables which are 

made up in the factory, and which are 

available in two different versions. The 

stub cable for coaxial cable working 

consists of the same type of cable as that 

used for the line cable, and is jointed by 

means of an ordinary straight joint, but 

in the case of balanced twin cables a 

branch joint is made to the main cable 

using a special stub cable that contains 

a number of screened, balanced pairs. 

This stub cable, which has a lead sheath, 

is also equipped with a valve for connection 

to the pressurization system of the 

main cable. Up to three individual stub 

cables can be connected to the housing, 

so that branching can be arranged on 

the line. The housing and the outer 

sheath or armouring of the cable are always 

earthed. 

105 

References 

1. Johansson, P.-E.: H.F. Line Equipment 

ZAX120 TforTwo-Wire Operation 

on Small-Diameter Coaxial 

Cable. Ericsson Rev. 47 (1970):4, 

pp. 122-136. 

2. Fredricsson, S.: Transmission Properties 

of Paper-Insulated Twin 

Cables at High Frequencies. Ericsson 

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

3. Salerius, K.: Independent Telecommunications 

Network on Cable 

Systems. Progressive Railroading 

Sept. (1976), pp. 103-104. 

4. Kaltgren, O.: A New Generation of 

Line Systems for Small-Core and 

Normal Coaxial Cables. Ericsson 

Rev. 57 (1974):2, pp. 48-53. 

5. Echarti, P.: Branching Equipment 

for FDM Systems. Ericsson Rev. 54 

(1977):4, pp. 180-184.

AXB 20 - Operation and Maintenance 

Characteristics 

Lars-Erik Logdberg, Arne Persson and Eric Strindlund 

AXB 20 - LM Ericsson's new all-electronic stored program controlled system for 

telex and asynchronous data traffic - has previously been described in detail in 

Ericsson Review No. 1/77\ 2 . The present article deals with certain of the system 

characteristics, which in some respects are unique and which concern its operation, 

maintenance and general handling. The article is limited to the parts of system AXB 

20 that are considered of particular interest in this connection. 

UDC 621.394.3 

681.327.8 

Fig. 1 

The main telephone exchange building in Malmo, 

which houses the telex exchange 

Fig. 2 

The AXB 20 exchange in Malmo comprises 2010 

lines but has data store capacity for 3900 subscribers, 

i.e. also the subscribers connected to the 

seven subordinate exchanges. In this way all telex 

subscribers in southern Sweden can be offered 

such facilities as: 

— keyboard selection 

— abbreviated address 

— call with no selection (hot line) 

— call interception service 

— printed service signals 

— automatic broadcast calls 

— call duration advice 

— collective numbers 

The asynchronous data system AXB 20 

belongs to the system family AX, which 

also includes telephone exchange 

system AXE 10 and synchronous data 

system AXB 30. In the AX family the control 

computers with operating system, 

input output devices and maintenance 

system, and also the program language 

and programming system are the same. 

This also applies as regards the 

mechanical construction, power supply, 

handling and documentation. 

The first AXB 20 exchange was put into 

operation in Malmo in October 1977. By 

modifying the subordinate exchanges 

which are connected to Malmo telex exchange, 

fig. 1, it has been possible to 

introduce the new facilities offered by 

the system throughout the whole of 

southern Sweden, i.e. for approximately 

3900 subscribers. Fig. 2 shows where 

the seven subordinate exchanges are 

situated and also the national and direct 

international routes primarily concerned. 

In the initial stage Malmo telex exchange 

is equipped for 2010 subscriber/trunk 

lines, but space has been 

reserved in the exchange for a further 

6000 lines. Fig. 3 shows the layout of the 

telex exchange. 

The control room contains input and 

output devices for the man-machine 

communication and for charging (IOS 

unit in a separate room) as well as 

equipment for the operation and 

maintenance of the exchange. Among 

the most important items in the control 

room is the Engineering Control Board 

(ECB) with the associated display terminal 

(DLD) and teleprinter (TPR). 

Engineering 

control board, ECB 

Since the line maintenance costs constitute 

a large part of the total maintenance 

costs it is important to have good

LARS-ERIK LOGDBERG 

ARNE PERSSON 

ELLEMTEL 

ERICSTRINDLUND 

Data Communication Department 

Telefonaktiebolaget LM Ericsson 

Fig. 3 

Layout for the AXB 20 exchange in Malmo 

AL Alarm panel 

CPS Central processor subsystem 

ECB Engineering control board 

DLD Display device 

IOS Input/output subsystem 

LE Line equipment section 

ME Maintenance equipment section 

MPR Monitoring printer 

PRO Printer device 

TPR Teleprinter 

TWO Typewriter device 

XE Switching equipment section 

facilities for testing the lines. System 

AXB 20 is equipped with an engineering 

control board (ECB) for metallic connection 

of any line in the exchange. A 

line is connected to the control board by 

means of a command from the display 

terminal (DLD) associated with the 

board, fig. 4, and measurements are carried 

out with the instruments included in 

the control board. As all testing takes 

place from the control room there is no 

need for staff in the switchroom. 

The engineering control board contains 

instruments for measuring current, 

voltage, insulation and leakage resistance 

and also character distortion. 

For test purposes it is also possible, by 

means of commands, to send text with a 

certain amount of distortion and also to 

initiate monitoring, which means that all 

text that is written on a certain subscriber's 

teleprinter is also written on a 

monitoring teleprinter (MPR) in the control 

room. 

Facilities are also provided for connecting 

a subscriber teleprinter via its subscriber 

line to the ECB teleprinter (TPR) 

for tracing faults. Other test instruments, 

such as the ink jet recorder 

shown in fig. 5, can easily be connected 

to the ECB when required. 

The engineering control board has 

proved to be very useful because it is so 

easy to handle. The wanted line can be 

accessed in quite simply by means of a 

command, the necessary instruments 

are easily connected or changed with 

push-buttons and disconnection is carried 

out by simply depressing a button. 

(Hence no jack panels with test cords 

etc.). 

The above examples are functions that 

contribute to fast fault localization and 

thus to simpler maintenance of the line 

networks. More such functions will be 

described later in this article, but first a 

few words on how system AXB 20 facilitates 

the work of the operating staff in a 

telex exchange. 

Operation 

One of the basic aims when designing 

AXB 20 was that it should be possible for 

personnel who has worked with the 

old mechanical telecommunication 

systems to handle the operation of this 

system. The fact that AXB 20 is processor 

controlled does not mean that the 

system operators have to be computer 

experts. This aim has meant very stringent 

requirements on the design of the 

man-machine communication in the 

system. 

Commands 

In system AXB 20 the man-machine 

communication is handled by a subsystem, 

the Input/Output Subsystem, 

lOS. The hardware in lOS consists of I/O

Fig. 4 

Display terminal connected to the engineering 

control board. 

The text displayed on the screen shows that subscriber 

number 33329 with multiple position 145 in row section 3 

has been connected in by means of a command. Alter that 

the subscriber line in question has been connected to the 

control board with another command. 

The text on the screen that has a white background has 

been initiated by the system, and the remainder has been 

written by the operator 

Fig. 5 

It is easy to connect external test instruments to 

the engineering control board, for example the ink 

jet recorder shown here 

devices with connection units and the 

software administers commands and 

printouts. 

A set of approximately 300 commands 

have been developed based on the 

CCITT recommendation concerning 

man-machine language, MML. Each 

command consists of a command code 

and a parameter part. 

The command code, which determines 

the function to be carried out by the 

command, consists of five alphanumeric 

characters and is built up in the following 

way: 

The commands are functional, i.e. each 

command belongs to a certain function 

group, given by the first two characters 

in the command code. A function group 

may consists of, for example, the various 

IOS functions. 

The parameter part contains the values 

that are required to carry out the function 

specified in the command code. If a 

parameter value is given that is not accepted 

by the system, a printout is 

obtained which states why the system 

has not accepted it. 

All I/O devices with keyboards, like all 

commands, are assigned to different 

categories. When a command is input 

on an I/O device a check is made in the 

data store as to whether the combination 

of I/O device category and command 

category is permitted. In this way 

the utilization of commands is facilitated, 

and at the same time disturbances 

and complications are avoided. 

Operational manual 

The operating staff is provided with an 

operational manual, which consists of 

the following seven main parts: 

— general operational instructions 

— operation 

— maintenance 

— testing 

— command descriptions 

— command record descriptions 

— printout descriptions 

The last three parts serve as a reference 

library for the others. 

A short example of how to use the operational 

manual: 

A new subscriber is to be connected. 

The operator looks in the manual, part 

"Operation", headline "Subscriberdata 

changes" and finds there the operational 

instruction "Connection of a subscriber". 

This instruction contains a reference 

to the headline "Command description 

for SUSNO" (the command 

code SUSNO = Subscriber Number 

Open). 

The contents of the operational instruction 

and command description aregiven 

in fig. 6.

Fig. 6 

Excerpts from the operational manual concerning 

the connection of a subscriber 

The operator usually goes direct to Item 4, I.e. to the ECB, 

since items 1-3 have usually been carried out beforehand 

and it is only necessary to check this 

Connection of a subscriber 

connection 

Extent 

Connection of a subscriber- both as regards 

hardware and software. 

References 

- Operational instructions for work in the MDF 

(Main Distribution Frame) 

- Command description for SUSNO 

— Operational instructions for testing a line 

— Operational instructions for reporting 

Execution 

Action Comments 

1. Run the MDF wires See the operational instructions 

for work in 

the MDF 

2. Insert a line adaption 

board if required 

3. Install the teleprinter 

4. Connect in the line See the command dewith 

a command scription for SUSNO 

(ECB) 

5. Test the line (ECB) See the operational instructions 

for testing a 

line 

6. Report See the operational instructions 

for reporting 

Command description for 

SUSNO 

Example of a command for activating a subscriber 

line 

1. SUSNO: SNB=33329, DEV=LIC-3-145; 

EXECUTED 

SUSNO=Subscriber Number Open 

SNB=33329 gives the subscriber number 

DEV=LIC-3-145 gives the multiple position 

The command specifies that subscriber line 

number 33329 with multiple position 145 in 

row section 3 is to be activated. 

EXECUTED is written as an acknowledgement 

that the command has been carried out. 

2. SUSNO: SNB = 33329, 0EV=LIC-1-172; 

NOT ACCEPTED 

FAULT CODE 3 

This command cannot be carried out. Fault 

code 3 indicates that the subscriber line is already 

activated. 

The list below gives some of the checks that 

are carried out by the system when the command 

is executed: 

- Check that the command exists 

- Check that the records (SNB, DEV) exist 

- Check that the punctuation marks in the 

command have been used as specified 

- Check that the subscriber number belongs 

to a number series that is connected in the 

exchange 

- Check that the subscriber number is vacant 

- Check that the stated multiple number belongs 

to a row section that has been installed 

- Check that the stated multiple number is 

vacant 

Maintenance 

The stringent operational requirements 

for the telex network and the high labour 

costs for maintenance emphasize the 

need for reducing the manual operation 

and maintenance measures by increasing 

the efficiency and by automatization. 

This applies not only for the exchange 

equipment but also for other 

parts of the telex network, such as subscriber 

equipment, trunk and local lines 

etc. 

In system AXB20 the maintenance functions 

are to a great extent automatized 

and integrated in the normal operation 

of the system. The basic principle is that 

the system should be self-monitoring as 

far as possible, so that the need for 

preventive maintenance and manual 

supervision is reduced to a minimum. 

The function-oriented command language, 

in combination with rational 

training along the lines recommended 

by the manufacturer etc., enable the 

personnel to learn quickly how to handle 

an AXB 20 exchange correctly and 

efficiently. 

When a break or disturbance occurs it is 

normally the system itself that detects it, 

carries out automatic fault localization, 

isolates the fault (blocks the faulty unit) 

and informs the operator (gives an alarm 

printout). When the fault disappears the 

unit is deblocked and the operator is informed. 

Regeneration 

The system is regenerative, which 

means that the exchange sends out the 

characters completely undistorted even 

if they are received severely (up to 46 %) 

distorted. This is of great importance in 

the case of the international and intercontinental 

traffic with its long lines 

of varying quality, but above all it means 

that the requirements for the characteristics 

of the subscriber lines and the 

transmission qualities of the subscriber 

sets can be made far less stringent than 

in non-regenerative systems. 

Distortion supervision 

AXB 20 is equipped with automatic distortion 

supervision which checks the 

degree of distortion on the handled traffic. 

This means that all the lines con- 

109 

Fig. 7 

This example shows a disturbance supervision 

alarm, the initiation of disturbance recording and 

the resultant printout 

Alarm printout 

ALARM B/APT 

DISTURBANCE SUPERVISION ROT = 8 

END 

A disturbance supervision alarm is obtained 

from route 8. 

Command 

SVDRI:ROT = 8, OUT=SIN; 

EXECUTED 

The command SVDRI initiates disturbance recording 

on route 8, with immediate printout of 

every disturbance. 

Printout from the disturbance recording 

DISTURBANCE ROT=8 DEV=LIC-000-013 

TIME=1116 RCODE = 4 

On route 8 there was a disturbance on the line 

in position 13 in row section 0 at 1116 hours. A 

clear-confirmation signal had not been received 

(RCODE=4). 

The different disturbance codes are explained 

in a printout description, from which the following 

has been taken: 

RCODE Cause 

0 No call acknowledgement 

1 No proceed-to-select signal 

2 No through-connection signal 

3 No answer back 

4 No clear-confirmation signal 

nected to the exchange are supervised 

entirely automatically. 

If the distortion becomes too high on a 

line an alarm printout, specifying the 

line, is given on a typewriter. The 

typewriter need not be placed in the exchange 

control room, it can for example 

be installed in a separate operation and 

maintenance centre. The distortion limit 

that gives rise to an alarm printout can 

easily be changed by means of a command. 

Disturbance supervision 

Disturbance supervision means that 

circuits are supervised as regards various 

types of disturbances, for example 

missing signals in the signalling sequences. 

This function gives rise to an 

alarm when the ratio between the 

number of disturbances and the number 

of calls exceeds a certain preset value. 

The alarm printout specifies the number 

of the route. The alarm limit can be varied 

from route to route and can easily be 

changed by means of a command, 

whereby the exact degree of supervision 

required can be obtained.

110 

Fig. 8 

Procedure for changing digit analysis 

The example shows the procedure for changing the length 

ol the numbers In the 83 series from four to five digits. The 

red colour Indicates that the table is active and serving as 

the operative table. 

4 

4 

1 Copy the operative 

table into the 

standby table. 

. Load new data in 

the standby 

table. 

The standby table 

is loaded with 

the information 

that the number 

length must be 5 

digits if the 

number starts 

with 83 

3. Test the standby 

table 

A command and 

a special test 

connection are 

used to check 

the correct function 

of the standby 

table 

4 Activate the 

standby table. 

The standby table 

becomes the 

operative table 

and the former 

operative table 

becomes the 

standby, with the 

possibility of being 

activated 

again if necessary. 

The example above applies for the Swedish telecommunication 

network, which contains number 

series with four as well as five digits In this way it is 

also possible to change information concerning the 

length of international number series very easily 

Fig. 9 

A magazine with the duplicated central processing 

unit CPU 

If a disturbance supervision alarm is 

obtained for a route, further information 

regarding the cause of the disturbances 

can be obtained by ordering, by means 

of a command, disturbance recording 

on the route in question. This results in a 

printout that specifies which lines in the 

route are affected by the disturbances. 

Printouts for the recorded disturbances 

can beobtained in either of two ways. All 

disturbances recorded during a certain 

time can be given on one and the same 

printout or a printout can be obtained 

for each disturbance as it occurs. In the 

latter case the printout also contains a 

code that specifies the disturbance, for 

example no clear-confirmation signal 

from the other exchange. Fig. 7 shows 

an example of this. 

Disturbance supervision together with 

disturbance recording makes it possible 

to ascertain very quickly and easily 

which lines have an inferior signalling 

quality and what the causes of this can 

be. 

Flexibility 

The demand for flexibility has greatly influenced 

the basic structure of the AX 

systems and this has resulted in a modular 

structure for both the software and 

the hardware 1 . Some examples are given 

below to demonstrate the 

advantages of this flexibility. 

Analysis changes 

The analysis carried out by the system, 

i.e. determining outgoing route, tariff 

etc. on the basis of the identity of the 

calling subscriber and the dialled information, 

are based on the principle of 

successive table look-up operations. All 

analysis tables are built up with commands, 

even the initial loading, when 

the commands are stored on tape. The 

possibilities provided by this method are 

extremely extensive. Procedures have 

been developed for analysis changes 

which include standby tables, tests of 

the changed analysis and the possibility 

of returning to the original analysis if the

Fig. 10 

Function changes when installing a new program 

block 

1. Loading the 

block 

Command 

LASUL: 

BLOCK = TMSU, 

IO = CT-2, 

ThebiockTMSU, 

which is an optional 

program 

block, is loaded 

from cassette no 

2 

. Activating the 

block 

Command 

FCSUI: BLOCK 

= TMSU; 

The block is 

started and then 

establishes contact 

with the 

blocks with 

which it is to interwork. 

The 

block is thereby 

put into operation 

without any 

traffic disturbances 

new one should prove to be faulty when 

taken into service, in spite of the tests. 

This means that even extensive and 

complex analysis changes can be carried 

out without disturbing the traffic. 

Fig. 8 shows an example of an analysis 

change. 

Change of size and extensions 

Both the control system and the switching 

network in AXB 20 are synchronously 

duplicated. There are several reasons 

for this. In addition to the reliability 

advantages, such as rapid fault detection, 

there are great advantages as regards 

system changes and extensions. 

A change of size usually means an increase 

in the number of subscriber and 

trunk lines. Before such an extension is 

carried out the control system and the 

switching network are separated into 

two sides, fig. 9. The traffic can then be 

handled by one side while the new 

hardware concerned is connected in to 

the other side, after which the actual extension 

is initiated with a command. The 

traffic is then switched over to the extended 

side and the extension procedure 

is repeated for the first side. Finally 

the two sides are connected together so 

that they work in the parallel synchronous 

mode once more. 

Exchange extensions are also facilitated 

by the modular structure of the 

switching network, with module sizes of 

24, 256, 2048 and 6144 lines. 

Enlarging the data areas in the data 

store is another form of extension. It can 

concern, for example, data for routes, 

data for calls being set up or abbreviated 

number lists for subscribers with 

abbreviated addresses. These data 

areas are usually dimensioned so that a 

certain amount of extension, e.g. with 

new abbreviated numbers, is possible, 

but if the allocated data area is full it 

must be enlarged. In older SPC systems 

such an extension meant a reloading 

with subsequent restart. 

In system AXB 20 all changes in the size 

of data areas are carried out without any 

traffic disturbances, thanks to the 

method of command-controlled indirect 

addressing via a reference store internal 

in the system. In the case of commands 

that lead to the use of more data 

111 

area, for example to give a subscriber 

more addresses, a code can be output 

that indicates that the allocated data 

area is already full. The operator then 

gives a command that gives an increase 

in data area, after which the original 

command can again be given and can 

be accepted by the system. 

Function changes 

Function changes constitute a test of 

the flexibility of a system. 

In the case of the functions designed for 

system AXB 20 as optional blocks, a 

change only means a command-initiated 

loading of a new program block, 

followed by a local start, also indicated 

with a command, to establish the necessary 

contacts with interworking blocks. 

The traffic handling is not disturbed. 

Fig. 10 shows an example of the commands 

concerned. 

Aids and procedures have also been developed 

for large function changes that 

were not expected when specifying the 

exchange. This makes it possible to carry 

out changes with the minimum 

amount of manual work and with very 

little traffic disturbance, even when the 

changes are extensive and mean an alteration 

of the data structure. 

Summary 

The characteristics of system AXB 20 

which have been described above are 

some that are considered to be of 

particular interest because of the 

advantages they give the users compared 

with what earlier systems were 

able to offer. Many of these characteristics 

are the result of some general basic 

aims for the system design, which have 

thus resulted in practical advantages for 

the users of system AXB 20. 

Among the most positive results of the 

experience gained from the operation of 

the AXB 20 exchange in Malmo is the 

great usefulness of the engineering control 

board (ECB) with the associated 

equipment. One of its greatest advantages 

is that the switchroom can be kept 

free from operating staff since all testing 

is carried out from a separate control 

room. 

System data and references are given 

on the next page.

System data for AXB 20 

Application 

All electronic, stored program controlled system 

intended as a combined local and transit exchange 

for both national and international telex 

and asynchronous data traffic. 

Since the system is used predominantly for telex 

traffic, the data given below have been limited to 

the telex application. 

Multiple capacity 

30 480 subscriber lines and/or trunk lines. 

Call capacity 

Approximately 60 calls per second. 

TDM switching matrix 

Regenerating, bit-oriented time division multiplex 

matrix which is free from congestion The reception 

margin is better than 46 %. 

Data transmission speed 

50 bauds (up to 300 bauds for asynchronous data 

traffic). 

Line connection modes 

Single current, double current, frequency shift 

signalling. 

TB voltages 

±12 V, +30 V. +50 V, +60 V, ±80 V, start polarity 

+ or -. 

Signalling variants 

CCITTRec. U.1 type A and B, U 11 type C, U.12 

typeD, U,20 and X.70. 

Selection method 

Keyboard or keyboard/dial selection. 

Service signals 

OCC, DER, NC, GA, MOM, NCH, ABS, NP etc. and 

time information as the proceed-to-select signal. 

Operator service 

The switching system permits the connection of 

operators' positions, equipped with display units, 

for manual assistance in the setting up of calls. 

Numbering 

Free choice of subscriber numbers for each line 

connection circuit, and also free choice of line 

and route number for each connection circuit. 

Redundancy 

All traffic handling units in the exchange are duplicated 

and work in a parallel synchronous 

mode. 

Processors 

Synchronously duplicated central processor. 

Regional processors for simple tasks. 

Memory capacity (with maximum capacity) 

Program store 1024 k words (16 bits) 

Data store 1024 k words (16 bits) 

Reference store 64 k words (32 bits) 

Rack dimensions 

Height 2250 mm (6 shelves) or 

2900 mm (8 shelves) 

Depth 620 mm (mounted back to back) 

References 

1. Strindlund, E. et al.: AXB 20 - All 

Electronic, Stored-Program Controlled 

System for Telex and Asynchronous 

Data Traffic. Ericsson 

Rev. 54 (1977):1, pp. 32^10. 

2. Strindlund, E. et al.: AXB 20 - Description 

of System. Ericsson Rev 

54 (1977):1, pp. 41-51.

The Ericsson Group 

With associated companies and representatives 

EUROPE 

SWEDEN 

Stockholm 

1. Telefonaktiebolaget LM Ericsson 

2. LM Ericsson Telematenel AB 

1. AB Rifa 

1. Sieverts Kabelverk AB 

1. SRA Communications AB 

5. ELLEMTEL Utveckhngs AB 

1. AB Transvertex 

4. Svenska Elgrossist AB SELGA 

1. Kabmatik AB 

4. Holm & Ericsons Elektnska AB 

4. Mellansvenska Elektnska AB 

4. SELGA Mellansverige AB 

Allngsas 

3. Kabeldon AB 

Gavle 

2. Vanadis Entreprenad AB 

Gothenburg 

4. SELGA Vastsvenge AB 

Kungsbacka 

3. BofaKabel AB 

Malmo 

3. Bjurhagens Fabrikers AB 

4. SELGA SydsverigeAB 

Norrkoping 

3. AB Norrkbpings Kabelfabrik 

4. SELGA Ostsvenge AB 

Nykoping 

1. Thorsman & Co AB 

Sundsvall 

4. SELGA Norrland AB 

Vaxjo 

1. Widells Metallprodukter AB 

EUROPE (excluding 

Sweden) 

Brussels 

2. Ericsson Belgium sa/nv 

DENMARK 

Copenhagen 

2. LM Ericsson A/S 

1. Dansk Signal Industri A/S 

3. GNT AUTOMATIC A/S 

1. I. Bager & Co A/S 

2. Thorsman & Co ApS 

Tastrup 

2. LM Ericsson Radio ApS 

FINLAND 

Helsinki 

2. Oy Thorsman & Co Ab 

Jorvas 

1. Oy LM Ericsson Ab 

FRANCE 

Boulogne sur Mer 

1. RIFA S.A 

Colombes 

3. Societe Francarse des 

Telephones Ericsson 

Marseille 

4. Etablissements Ferrer-Auran S.A. 

IRELAND 

Athlone 

1. LM Ericsson Ltd. 

Drogheda 

2. Thorsman Ireland Ltd. 

ITALY 

Rome 

1. FATME Soc per Az. 

1. Scarfini Soc. per Az 

5. SETEMER Soc per Az. 

2. SIELTESoc. per Az. 

The NETHERLANDS 

Rljen 

1. Ericsson Telefoonmaatschappij B.V. 

NORWAY 

Nesbru 

3. A/S Elektrlsk Bureau 

4. United Marine Electronics A/S 

Oslo 

2. SRA Radio A/S 

2. Thorsman & Co A/S 

4. A/S Telesystemer 

4. A/S Installator 

Drammen 

3. A/S Norsk Kabelfabrik 

POLAND 

Warszaw 


PORTUGAL 

Lisbon 

2. Sociedade Ericsson de Portugal Lda 

SPAIN 

Madrid 

1. industnas de Telecomumcaci6n S.A. 

(Intelsa) 

1. LM Ericsson S.A 

SWITZERLAND 

Zurich 

2. Ericsson AG 

UNITED KINGDOM 

Chorley 

2. Thorsman & Co. (UK) Ltd. 

Horsham 

4. Thorn-Ericsson Telecommunications 

(Sales) Ltd. 

3. Thorn-Encsson Telecommunications 

(Rentals) Ltd 

5. Swedish Ericsson Company Ltd. 

3. Thorn-Ericsson Telecommunications 

(Mfg) Ltd. 

6 Thorn-Encsson Telecommunications 

Ltd 

London 

4. United Marine Leasing Ltd. 

4. United Marine Electronics (UK) Ltd. 

WEST GERMANY 

Frankfurt-am-Main 

2. Rifa GmbH 

Hamburg 

4. UME Marine Nachnchtentechnik, GmbH 

Hanover 

2. Ericsson Centrum GmbH 

Ludenscheid 

2. Thorsman & Co GmbH 

Representatives in: 

Austria. Greece, Iceland, Luxembourg, 

Yugoslavia. 

LATIN AMERICA 

ARGENTINA 

Buenos Aires 

1. Cia Ericsson SAC I 

1. Industrias Electricas de Ouilmes S.A. 

5. Cia Argentina de Telefonos S.A. 

5. Cia Entremana de Telefonos S.A. 

BOLIVIA 

La Paz 


BRAZIL 

Sao Paulo 

1. Ericsson do Brasil Comercio e 

Industria S.A 

4. Sielte S.A. Instalacoes Eletricas e 

Telefonicas 

4. TELEPLAN, Projetos e Planejamentos 

de Telecommunicates S.A 

Rio de Janeiro 

3. Fios e Cabos Plasticos do 

Brasil S.A. 

Sao Jose dos Campos 

1. Telecomponentes Comercio e 

Industria S.A. 

Santiago 

2. Cia Ericsson de Chile S.A 

COLOMBIA 

Bogota 

1. Ericsson de Colombia S A. 

1. Fabricas Colombianas de Materiales 

Electricos Facomec S.A. 

COSTA RICA 

San Jose 


ECUADOR 

Quito 

2. Telefonos Ericsson C A 

GUATEMALA 

Guatemala City 


Port-au-Prince 

7. LM Ericsson 

MEXICO 

Mexico D.F. 

1. Teleindustria Ericsson, S.A. 

1. Latinoamericana de Cables S.A. 

deC V 

2. Telefonos Ericsson S.A. 

2. Telemontaie. S.A de C V 

PANAMA 

Panama City 

2. Telequipos S.A. 


PERU 

Lima 

2. Cia Ericsson S.A 

EL SALVADOR 

San Salvador 


URUGUAY 

Montevideo 

2. Cfa Ericsson S.A. 

VENEZUELA 

Caracas 

1. Cia Andnirrta Ericsson 


Bolivia, Costa Rica, Dominican Republic, 

French Guiana, Guadeloupe. Guatemala, 

Guyana, Honduras, Martinique, Netherlands 

Antilles, Nicaragua, Panama. Paraguay, El 

Salvador, Surinam, Trinidad, Tobago. 

AFRICA 

Algiers 


EGYPT 

Cairo 

7. Telelonaktiebolaget LM Ericsson 

LIBYA 

Tripoli 


NIGERIA 

Lagos 

1. LM Ericsson (Nigeria) Ltd. 

TUNISIA 

Tunis 


ZAMBIA 

Lusaka 

2. Ericsson (Zambia) Limited 


Installation Branch 


Angola, Benin, Botswana, Cameroon, Central 

African Empire, Chad, Congo, Egypt, 

Ethiopia, Gabon, Ivory Coast, Kenya, Lesotho, 

Liberia. Libyan Arab Republic, Madagaskar, 

Malawi, Mali, Malta, Mauretania, 

Morocco, Mozambique, Namibia, Niger, Nigeria, 

Reunion South Africa, Senegal, Sudan, 

Swaziland, United Republic of Tanzania, 

Togo, Tunisia, Uganda. Upper Volta, 

Zaire. 

ASIA 

INDIA 

New Delhi 

1. Ericsson India Limited 

INDONESIA 

Jakarta 

4. Ericsson Telephone Sales 

Corporation AB 

IRAQ 

Baghdad 


IRAN 

Teheran 

4. Ericsson Telephone Sales 

Corporation AB 

3. Simco Ericsson Ltd 

4. Aktiebolaget Enfon 

KUWAIT 

Kuwait 


LEBANON 

Beirut 

2. Societe Libanaise des Telephones 

Ericsson 

MALAYSIA 

Shah Alam 

1. Ericsson Telecommunications 

Sdn Bhd 

OMAN 

Muscat 


SAUDI ARABIA 

Riyadh 


Bangkok 

4. Ericsson Telephone Corporation 

Far East AB 

Ankara 

2. Ericsson Turk Ticaret Ltd. Sirketi 


Bahrein, Bangladesh. Burma, Cyprus. Hong 

Kong, Indonesia, Iran, Iraq, Jordan, Kuwait, 

Lebanon, Macao, Nepal, Oman, Pakistan, 

Philippines. Qatar, Saudi Arabia. Singapore, 

Sri Lanka, Syrian Arab Republic, United 

Arab Emirates. 

UNITED STATES and 

CANADA 

UNITED STATES 

Woodbury N.Y. 

2. LM Ericsson Telecommunications Inc 

New York, N.Y. 

5. The Ericsson Corporation 

CANADA 

Montreal 

2. LM Ericsson Limitee/Limited 

AUSTRALIA and 

OCEANIA 

Melbourne 

1. LM Ericsson Pty. Ltd 

1. Rifa Pty. Ltd 

5. Teleric Pty. Ltd. 

5. LM Ericsson Finance Pty. Ltd 

Sydney 

3. Conqueror Cables Ltd 


New Caledonia, New Zealand, Tahiti 

1. Sales company with manufacturing 

2. Sales and installation company 

3. Associated sales company with manufacturing 

4. Associated company with sales and 

installation 

5. Other company 

6. Other associated company 

7. Technical office

TELEFONAKTIEBOLAGETLM ERICSSON 

ISSN 0014-0171 m Sweden Ljungforetagen Orebro 1978

Colour Display System SEMIGRAF 240 - The history of Ericsson

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