Facit AB joins the Ericsson Group Office Communication System DIAVOX 406 2Mbit/s Line Terminal Equipment in the BYB Construction Practice 24-Channel

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1 ERICSSON REVIEW Facit AB joins the Ericsson Group Office Communication System DIAVOX 406 2Mbit/s Line Terminal Equipment in the BYB Construction Practice 24-Channel PCM System Experience from the Introduction of ATC in Sweden RIFA Capacitors for Power Electronics Miniaturized Power Modules

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3 ERICSSON REVIEW Vol.60, 1983 Contents Components Page RIFA Capacitors for Power Electronics 34 Power Supply Systems Miniaturized Power Modules 42 Computer Controlled Power Supply Equipment for Telecommunication Plants 94 Optimizing the Power from a Wind Turbine 159 Ericsson Power Systems, a New Division within RIFA 207 Sealed Lead-acid Batteries for Small Telecommunication Plants 222 Railway Signalling Systems Experience from the Introduction of ATC in Sweden 29 Subscriber Equipment Office Communication System DIAVOX406 7 Coin-Box Telephones 73 MD110 in the Automated Office 88 Office Communication System DIAVOX ERICOM DIRECT 214 Telephone Exchanges and Systems Operator Position Subsystem in AXE Test System LPA Development of Line Circuits for AXE Line Circuit Component SLAC for AXE Line Circuit Component SLIC for AXE Ericsson's First Automatic Telephone Exchange 100 Years 233 Telex and Data Transmission ERIPAX, a Data Communication System 80 ERIMAIL Message Handling System 110 Alfaword, A Program for Word Processing using Alfaskop System Ericsson Series The New Oslo Telex Exchange - Operation and Operational Reliability 130 The New Oslo Telex Exchange - Operating Functions 136 Transmission Technology 2 Mbit/s Line Terminal Equipment in the BYB Construcion Practice Channel PCM System 22 Remote Subscriber Multiplexer, RSM 58 Optical Fibre Line System for 140 Mbit/s 144 Miscellaneous Facit AB joins the Ericsson Group 2 Radar PS-46/A for Aircraft JA37 46 ALARMCOM HAZ111 03, a Security and Supervision System 102 Mobile Radio System C Information System for Public Transport Services 164 Computer-controlled System for Road Traffic Control 226 Copyright Telefonaktiebolaget LM Ericsson Stockholm 1983

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5 ERICSSON REVIEW Number Volume 60 Responsible publisher Gosta Lindberg Editor Gosta Neovius Editorial staff Martti Viitaniemi Address S Stockholm, Sweden Subscription one year $ 12 one copy $ 3 Published in Swedish, English, French and Spanish with four issues per year Copyright Telefonaktiebolaget LM Ericsson Contents Facit AB joins the Ericsson Group Office Communication System DIAVOX Mbit/s Line Terminal Equipment in the BYB Construction Practice 24-Channel PCM System Experience from the Introduction of ATC in Sweden RIFA Capacitors for Power Electronics Miniaturized Power Modules Cover RIFA s miniaturized power modules-d.c./d.c. converters for W designed for mounting on printed board assemblies or on indivudual chassis

6 Facit AB joins the Ericsson Group Lars Ramqvist The Ericsson Group continues the restructuring of its extensive activities with the creation of eight business areas. One of these areas comprises information systems for private telecommunications and data communication, and office automation. The activities in this area were assembled into one unit on January 1st when Ericsson Information Systems AB was formed. This company has been described in a previous issue of Ericsson Review'. On January 1st Facit AB (not including its US and Canadian operations) joined the Ericsson Group as a member of this area. In this article the background to the acquisition is described, as well as the market requirements and strategies that make it desirable for Facit to join Ericsson Information Systems. A summary of the Facit products is also given. UDC 061.5: Table 1 The US market in billion US dollars (1980 level) for office work stations according to McKinsey Annual growth Personal computers Data terminals Word processing The basic business idea of Ericsson Information Systems AB, and thus for the whole Ericsson business area of information systems, isto utilizethetelecommunication and systems know-how of the Ericsson Group to provide customers in the international market with products and advanced, integrated information systems. The acquisition of Datasaab in 1981 gave Ericsson a considerable fund of know-how and experience in the field of terminals and minicomputers. Recent market trends have clearly shown a great increase in the sales of technically advanced but easily operated and fairly cheap personal computers and terminals, and that communication facilities are required for these terminals. This has emphasized the need for an extensive marketing campaign. Facit has been in the business of distribution via retailers for a very long time, and thus has the necessary experience and resources for such a campaign. Table 1 shows that the market for data terminals, equipment for word and text processing and personal computers is growing very fast in the US. A similar development is expected in Western Europe. By personal computers are meant computers intended for individual use, business-orientated and costing less than US dollars not including printers. As a result of this market development traditional manufacturers of typewriters and simple terminals have tried to extend their activities into the field of systems and communications. This development was also apparent in the case of Facit AB. The aim of Ericsson Information Systems is to supplement its product range with such terminals and personal computers, and to ensure that these can be integrated into information networks. Thus, relatively speaking, the product range of Ericsson Information Systems will develop towards simple terminals rather than towards the more complex systems. Fig. 1 Facit has marketed calculators throughout the world for more than 40 years. The design of each new Facit calculator is based on extensive knowhow regarding usage and technology

7 LARS RAMQVIST Ericsson Information Systems AB Fig. 2 Facit Correct 8111, with line display and four different memories In view of this development it was logical that Facit and Ericsson Information Systems should combine and thus not only increase their competitiveness in the international market but also help to further strengthen the Swedish electronics industry. Facit AB, excluding its US and Canadian activities and the Addo factory in Malmo, Sweden, joined the Ericsson Group on January 1st, 1983 as one of the companies in the Ericsson business area Information Systems. Facit products, a summary Facit markets equipment for office work stations and peripheral computer equipment which is suitable for incorporating in data communication systems. The marketing is performed by the company's own subsidiaries in 13 countries with about 1400 employees, including 350 in Sweden. Approximately 85% of the sales by the subsidiaries is to about 1000 retailers. The development trends will gradually lead to separate units for calculation, writing, bookkeeping, telex, data recording etc. being combined into machines that can be used for all routines and form part of one and the same data communication system. The basic business idea of Facit is to be able to meet the need for such machines in the international market Office products The range of office products comprises calculators, typewriters, personal computers and office furniture. These products are mainly developed and manufactured in Sweden. Calculators are bought from Japan. Within the part of the market covered by Facit's range of personal computers the company today has approximately 5% of the world market, fig. 1. In this field Facit has retained its prominent position since the time when calculators were mechanical. Printout is an essential function in office work. Facit develops, manufactures and markets anything from simple manual typewriters, through electrical typewriters to sophisticated electronic machines with extensive text and word processing facilities. The modern electronic machines, such as Facit 8111, fig. 2, are microprocessor controlled and can be equipped with communication units. ERITEX 10 is another product in the same category. Developed jointly Fig. 3 The Facit personal computers in the DTC6500 series are intended for industrial use, for administrative routines and for graphical calculations

8 4 by Facit and Ericsson Information Systems it is a teletex terminal in accordance with CCITT recommendations, based on the Facit typewriter8110. Facit has approximately 10% of the world market for electronic typewriters and carries out extensive development work in this product field. The stored program control of electronic typewriters will gradually lead to integration with personal computers. For some years Facit has marketed a personal computer designated DTC (Desk Top Computer), fig. 3. A clear market trend can already be observed for typewriters and simple terminals built with separate units (modules) for keyboards, display screens, computers and stores The rapid development in the field of office machines means that furniture is again becoming a product of interest as regards the overall handling of information in the office. The greatest increase is expected in the sale of furniture specially designed for terminals and for writing tasks. The range of furniture marketed by Facit is of high quality throughout, with consideration paid to ergonomic properties, fig. 4. Data products This field comprises printers, display terminals, punch tape equipment and storage units with magnetic media, fig.5. These products are manufactured mainly in Facit's factories at Atvidaberg (Sweden) and are to a great extent sold to different manufacturers who use them as system components in their products. The market for printers and terminals is expected to expand rapidly. Facit has an extensive printer range. Current printers use daisy wheels or matrix printers. Printers using optical technology are also being developed. The printers are becoming increasingly sophisticated and will be able to handle different types of graphics. There is a constantly increasing demand for terminals. Facit supplies terminals for TTY and other types of asynchronous connection to computers. Considerable marketing successes have been achieved during recent years. Fig. 4 Facit has manufactured office furniture since Today the range comprises the furniture series Facit 80, Facit Data and Facit Ekonom

9 Fig. 6 The printer Zata Tryckerierna AB make continuous forms and form sets. Their product range also includes packaging printing, screen printing and advertising printing Facit has a very strong position in the market for paper tape punches. The Facit 4070 tape punch has been a bestseller for many years. The printerszatatryckenerna AB, fig. 6, is a subsidiary of Facit AB. It operates independently of other Facit activities. Coordinating Facit and Ericsson Information Systems The purpose of acquiring Facit AB and coordinating its activities with those of Ericsson Information Systems is to further extend and reinforce these activities in the field of office automation and integrated information systems. Facit provides Ericsson Information Systems and the Group's other companies in this field with a widespread distribution organization as well as several new products. The integrated activities include the development, manufacture, marketing, sales and maintenance of products, hardware, software and systems. The marketing will cover the Nordic countries and the rest of Western Europe, and also other areas through previously developed channels. Ericsson Information Systems has recently supplemented its product range with personal computers and ERITEX and teletex terminals. As the telecommunications monopoly is terminated in various countries it will be possible to sell different types of telephone sets, another product in the range of Ericsson Information Systems, to other customers than telephone administrations. For the whole of this category of simpler products Ericsson Information Systems urgently needs a more finely meshed distribution network than the present one of the Ericsson Group The strategy is therefore to market these products from Ericsson Information Systems together with the Facit products. This in its turn means that a more complete range is obtained, that recruiting of good retailers is made easier and that the distribution organization can be strengthened further. This strategy also includes increasing the sales volumes for the Facit products, since they can now be supplemented with system and communication products from Ericsson Information Systems. From a strategic point of view the Facit products thus complement the Ericsson products very well. In terms of fig 7 the Facit activities fall within the subsection Terminals in the functional diagram of the business area Information Systems. In the Information Systems area great importance is attached to the long-term development of an integrated information system based on a common system structure and a coordinated choice of microcomputers, operating systems, programming languages and support systems for program development. Within the field of integrated information systems the Facit products will Fig. 5 The different Facit peripheral equipment for data ion

10 Distributing companies Common technologies Fig. 7 The functional structure of Ericsson Information Systems Production complement existing systems for office support functions in an excellent way, fig.8. The acquisition of Facit AB has further strengthened the position of the Ericsson Group as an international manufacturer and supplier of products for private telecommunications and data communications as well as office automation. Fig. 8 The structure of an integrated information system References 1. Ramqvist, L. and Thoren, T: Ericsson Information Systems - A New Company. Ericsson Rev. 58(1981 ):4. pp

11 Office Communication System DIAVOX 406 Greger Jismalm The DIAVOX family produced by the Ericsson Group has now been supplemented with DIAVOX 406. an electronic office communication system for four trunk lines and six extensions. The system is intended as an alternative to small PBXs for applications where line selector function and efficient traffic distribution are essential, for example for banks, travel agencies, lawyers' offices and health centres. The system is also intended as a secretarial or line selector system for a small group of extensions in an enterprise with a PABX. for example type ASB900, ASB 100 or ASB20. In the case of PABX type MD110 these functions are handled by the digital system telephone DIAVOX Courier 700 :. The author describes the system features and how they are utilized, and the programming of various functions. He also gives a brief description of the technical and mechanical structure of the system. UDC DIAVOX 406 is an office communication system for a maximum of four trunk lines and six extensions. It provides quick and efficient internal communication facilities and a flexible distribution of the external traffic. The system consists of a central unit, to which special telephones are connected in a starshaped network. The trunk lines can be connected to a local telephone exchange, or a PABX or both. DIAVOX 406 offers traffic facilities that can easily be adapted to suit the individual requirements of small offices. Buttons for direct access to extensions, lines and services make the system efficient and easy to operate. GREGER JISMALM Ericsson Information Systems AB Telephone sets The telephone set design and the speech circuits are the same as for the standard DIAVOX 100 telephone set. The set is equipped with a key-pad and a button and lamp (LED) for each extension and trunk line, the lamps giving yellow and red lights respectively, fig. 1. The lamps flash rapidly for incoming calls and slowly for parked calls, give a steady light with short breaks for busy extensions and steady lightfor "absent extensions and occupied lines. Calls are only indicated at the extension concerned. Parked calls are only indicated at the extension which put the call on hold. The sets also contain a button with a light-emitting diode for each of the functions diversion (D), transfer (T), conference (C) and recall (R). The last function is the same as the corresponding one in the standard set, i.e. it is used for inquiries to the superior system, such as a PABX. Traffic distribution DIAVOX 406 can be adapted to suit different traffic distribution requirements Fig. 1 Telephone set for DIAVOX L1-L4 D T C R Extensions Trunk lines Diversion Transfer Conference Recall

12 Fig. 2 Line selector system for small companies and offices. The adaptation is carried out by means of programming. The installer uses any of the extensions to input customer data, which give the desired traffic distribution. Any changes in the customer data at a later stage can easily be input by service personnel, or by the customer if preferred. Before such reprogramming can be carried out a special switch in the central unit must be set to the programming position. Line selector system Travel agencies and ticket booking offices usually require the traffic to be distributed directly to theextensions in parallel. This type of routing is also required for order registration and fault complaint reception in large enterprises. In this way the incoming, common calls can be dealt with without unnecessary delay. If at any time the system has more incoming calls than there are free extensions, the calls can easily be parked, so that they can then be handled by the first free extension, fig. 2. Combinations of a line selector system and an operatorassisted system can be arranged by excluding one or more extensions from incoming calls on the common route (broken line). Operator-assisted system In a small company it is often desirable to route all incoming traffic to an operator, who distributes the calls to the extensions. Any extension in DIAVOX 406 can be used as the operator's set, fig. 3. The set indicates the states of all extensions, i.e. the ones that are engaged and also the ones whose calls are being diverted (absent/do not disturb) The distribution of calls is carried out by means of the transfer button (T). and can be done before or after answer. In the case of distribution before answer the system calls the operator again if the called extension has not answered within a certain time. System with alternating operators One demand which is often encountered is for a system with alternating operators, i.e. where it is possible to change operator at different times during the day or on different days of the week without having to rearrange the extensions. Such a system can easily be obtained by programming for two operators in the customer data. The traffic is then transferred from one operator to the other by means of the diversion button (D) on the telephone set. A lightemitting diode indicates whether the traffic has been diverted or not. Double executive-secretary system DIAVOX 406 has several advantages as a secretarial system under a PABX. The most common method is then to divide the system between two groups, with an executive and a secretary in each group, fig. 4. The PABX lines of the four extensions are then connected to the system. Calls on the secretary's line go direct to the secretary, whereas calls on the executive's line either go straight to the executive or are filtered by the secretary (broken line). The line is switched over to the secretary either manually by means of the D button on the executive set, or automatically, when calls are not answered. The remaining two telephone sets can. if desired, be placed in conference rooms or arranged for the convenience of visitors etc. A useful feature of the double executivesecretary system is that the secretaries can answer each others' telephones on a temporary basis, for example during lunch or vacations. The executive line is then diverted in two stages, first to the usual assistant and then, with the aid of the diversion button on the secretary's set, to the other secretary (dotted line). Fig. 3,left Operator-assisted system Fig. 4, right Double executive-secretary system

13 9 Larger secretarial group Another common configuration consists of a secretary attending the telephones of two or three people, fig. 5. If there is a spare line in DIAVOX406 it can, for example, be used as a private direct line to the public telephone network (red). Systems without secretary attendance, where the extensions answer each others' calls, are also possible. Combination systems In small companies it can sometimes be desirable to combine two of the traffic cases described above, for example a group with operator assistance and an executive-secretary system, fig. 6, or an operator-assisted group and a line selector for order registration. Other combinations and intermediary types are also possible. Call functions and handling The handling routines have been made simple and quick, and also so flexible that they can be adapted to suit different customer requirements. Incoming external calls Incoming external calls are indicated by rapidly flashing red lamps and a ringing signal, which is usually programmed to have the same timing as the incoming ringing signal. A call is answered by lifting the handset. An external call is terminated by replacing the handset, which results in disconnection of the call. If the handset is not replaced, but a new line or another extension is chosen, the external call in progress is automatically put on hold, parked. A parked call is indicated by slow flashing of the red lamp above the button for the line in question. The call is resumed by depressing the line button. Outgoing external calls An outgoing external call is initiated by depressing the button for a free line. The extension then receives the dialling tone from the PABX or the local exchange and can dial the desired number. Incoming internal calls An incoming internal call is indicated by a rapidly flashing yellow LED above the button forthe called extension, together with a ringing signal which is usually programmed to coincide with the pressing of the button in the calling extension. Such programming makes it possible to develop simple codes that could, for example, indicate the purpose of the call before it has been answered. The call is answered by lifting the handset. The internal call is terminated by replacing the handset, and the call is then disconnected. Outgoing internal calls An internal call is initiated by depressing the button for the wanted extension. The LED for the extension indicates that the extension is engaged on another call, and also if the person sought is out, i.e. calls to the extension are being diverted (button D has been depressed). This feature means that all internal call attempts normally result in completed calls. The system contains no internal busy tone. Inquiry In order to make an inquiry call during an external call it is only necessary to press the button of the required extension, as for an ordinary internal call. The external line is then automatically put on hold. Fig. 5,left Larger secretarial group Fig. 6, right Combination system

14 10 Fig. 7 DIAVOX 406 is an office communication system for a maximum of four trunk lines and six extensions Alternating inquiries, transfer and conference During an inquiry call the caller can choose between returning to the external call by depressing the appropriate line button (L), transferring the parked call to the called internal extension (T) or setting up a conference (C) between himself, the external caller and the called internal extension. There is no need to make this choice before the inquiry call is made. Moreover, the need for transfer or conference is often only realized during the course of the inquiry call. Transfer before reply An extension which is used as an operator's set can make use of the facility Transfer before reply. In this case the operator initiates an inquiry call by depressing an extension button, but does not wait for an answer and immediately depresses the transfer button instead. The called extension then receives the internal ringing signal and parking indication for the external line concerned. The call is connected up when the handset is lifted. Such transfers can also be made to busy extensions. If a call that has been transferred before reply is not answered within 50 seconds, the call is transferred back to the operator. Waiting calls An extension which is used as an operator's or secretary's set is often called from outside or internally while it is engaged. These other calls are indicated as waiting calls. The ringing signal is then muted in order not to disturb the call in progress. Waiting calls are answered by finishing the call in progress, replacing the handset and lifting it again. Waiting calls can also be answered by depressing the button adjacent to the flashing LED. The call in progress is then automatically parked. Priority calls Internal calls are normally made to free extensions without diversion indications. In emergencies it is also possible to call an extension which is already engaged, a so-called priority call. Such a call is indicated as an internal waiting call at the called extension. Selective parking The automatic parking mentioned above is always selective. This means that the line is indicated as parked only at the extension where the parking was arranged. Confusion as to who has parked which line is thereby avoided. An external call can also be put on hold by depressing one's own extension button. This feature would enable a person to talk to a visitor during a telephone call without having to hold a hand over the microphone. General parking In booking offices, ticket offices and order reception groups it is often an advantage if a parked call can betaken bya person otherthan theone whooriginally answered and parked the call. During busy periods calls can then be answered by asking the customer to wait. The general parking facility is then used. An external line is put on general hold when the transfer button is depressed without any inquiry call being made first. The LED will then flash slowly at all extensions, and the call can be taken by the first free extension. Recall from a parked call An extension will be called by the system if the handset is replaced while any line is still on hold, in order to avoid the risk of parked calls being forgotten. The call is connected up when the handset is

15 11 Fig. 8 DIAVOX 406 offers traffic facilities which can easily be adapted to suit the individual requirements of small offices lilted again. If a call has been parked for 50 seconds while another call is in progress, the extension will also be called again by the system, with a "waiting call" indication. Loudspeaking intercom The telephone sets can be equipped with the loudspeaking unit DIAVOX 250 as an optional extra. It is placed under the telephone set. If the loudspeaking unit is switched on and the extension is free, all internal calls come in on the loudspeaker after a short preliminary tone. The call can then be answered hands-free. Manual diversion All calls on a private trunk line are diverted to an attendant position when the diversion button (D) is depressed. The red LED above the button is then lit. The diversion is cancelled by depressing the button again. Incoming calls are indicated by flashing lights, but no ringing signals are obtained in an extension where the calls have been diverted. Automatic diversion In an executive-secretary system unanswered calls on the executive line are automatically diverted after a certain time. The time can be set to 8 or 20 seconds, and the function can also be inhibited. Once a call has been automatically diverted in this way the system will divert all subsequent calls without any delay until the executive has returned and used the telephone again. Two-stage diversion In the case of two parallel executive-secretary groups it is possible for a secretary to divert both direct calls, and calls that have already been diverted from the executive's line, to the other secretary by depressing the diversion button. Programmable functions The following functions are programmed for each extension: - Belongstogroup 1 orgroup2, orboth - Receives calls from common lines in the group (operator) - Receives calls from a private line (executive, secretary) - Receives diverted calls within the group (secretary) - Is barred for outgoing calls - Will answer calls by depressing the line button. Barring of outgoing calls can be useful in booking systems where the lines should not be occupied unnecessarily. A group manager etc. could be exempt from the barring. He could then help the other extensions to make outgoing calls when necessary by selecting a trunk line, parking it and letting another extension take it. A facility for manual answering of calls by pressing the line-buttons is sometimes requested by secretaries who have to answer calls on several lines, and who want to be able to choose between external calls on different lines or internal calls from different extensions. The normal procedure with automatic answer means that the system connects up an incoming call as soon as the handset is lifted. It is then the system that makes the choice if there is more than one incoming call. The following functions are programmed for each line: - Belongs to group 1 or 2 - Common or private line. If private, the extension is specified. The following functions are programmed for each system: - Internal ringing signal manual, double or single cadence

16 Fig. 9 Structure of the DIAVOX 406 system - Automatic diversion after 8 or 20 seconds or only manual diversion - Two-stage diversion - Register calling by means of earth closure or break, and other matching of line signals to a superior system. The following functions are chosen when ordering a system: - Telephone sets for tone or pulse dialling - Pulse/pause ratio, speed etc. with pulse dialling - Adaptation of transmission and current feeding conditions in the telephone sets and central unittoexisting standards. System structure Fig.9 shows a block diagram of the DIAVOX 406 system structure and fig. 10 a block diagram of the telephone sets. Each extension is connected to the central unit via three wire pairs. One pair is used for analog speech and two for digital signalling. The central unit consists of the following subunits: - switch matrix - trunk line circuits - internal link circuits - through-connection relays released during power failure - control system with a microprocessor, input and output parts, digital signalling circuits and a battery unit. Signalling system The digital signal ling channel is used for all signalling between the extensions and the central unit. The buttons for internal calling and the hook-switch function also use this channel, so that the central unit requires no signal detection on the speech pair The digital line signal is biphase modulated with a timing frequency of 1.3kHz. This frequency is chosen so that the microprocessor in the central unit can scan all six extensions during each bit interval. The central unit sends its information bits continuously to each extension. Each bit controls a light-emitting diode or the tone ringer. The transmission timing is extracted from the continuously received signal. The state of all push-buttons and the hook-switch is continuously transmitted from the extensions. The microprocessor compares two consecutive signal words for each extension. The signal is accepted only if the two words are identical. In this way sporadic line interference is prevented from causing faulty connections. Control system The control system consists of a microprocessor with a 4 k eight-bit word program store (ROM) and a 0.5k word data store (RAM). In the case of a mains failure the part of the data store that contains programmed customer data is protected by a battery for at least 24 hours. The battery is charged continuously during normal operation. If the battery is not connected, or if it is not charged and a mains failure occcurs. the system reverts to a basic programming in the line selector mode. During the mains failure the trunk lines are through-connected to one extension each. These extensions are thus each connected directly to a different line and can be used for calls. The pushbutton set can be used for dialling in the normal way. The microprocessor is connected direct to modulators and demodulators for the digital signalling. The other functions, such as ringing signal detection, relay closure etc.. are detected and controlled via special inputs and outputs. Each circuit comprises 16 inputs or outputs.

17 13 Fig. 11 Printed board assembly for DIAVOX 406 Telephone devices The trunk line circuit detects a ringing signal, connects the line to the switch matrix and puts the line on hold. Digit transmission out on the trunk lines takes place direct from the telephone set via the path through the switch matrix. The switch matrix is a congestion-free reed switch with 2-pole cross points. Internal call connections are power fed from an internal link. The internal link attenuates the speech level by approximately 8dB in order to provide a level similar to that of an average external call. Central unit The central unit is installed in a cabinet made of moulded plastic and intended for wall mounting. The front of the central unit conists of a lockable lacquered metal plate. All electronic equipment in the central unit is mounted on one printed board, fig. 11. The printed board assembley is equipped with a multipoint plug for connection to a jack on the power unit. The cables from the trunk lines and extensions are connected in a separate main distribution frame. Slot connectors are used, where the insulated wires are pressed in between cutting edges without any previous stripping. The connector strip also contains lightning protectors for the trunk lines. The MDF is connected via a cable with a multipoint plug to a jack on the printed board assembly in the central unit. DIAVOX 406 can be connected to 110 or 220V, 45-65HZ. References 1. Jismalm, G, and Magnusson, S.: Office Communication System DIAVOX 824. Ericsson Rev. 56 (1979):3. pp Reinius, J. and Sandstrom, O.: DIAVOX Courier 700. Digital System Telephone formd 110. Ericsson Rev. 59(1982):2. pp

18 2 Mbit/s Line Terminal Equipment in the BYB Construction Practice Dagfinn Danielsen and Kjartan Tafjord Ericsson has developed 2Mbit/s line terminal equipment for pair cable and fibre cable. The use of construction practice BYB for the equipment facilitates integration with telephone exchange equipment and other transmission equipment. The article illustrates the use of this type of equipment and describes its design and function. UDC : Digital telephone exchanges and digital transmission systems are being installed to an ever increasing extent. In urban networks 2Mbit/s line systems with 30 PCM channels are now predominant on routes between the exchanges. The average route length is 5-7km, with 3-4 intermediate repeaters. The transmission medium is existing pair cable or new PCM cable, optimized for 2Mbit/s line systems. In future, 2 Mbit/s line systems will be used to an even greater extent in the local networks between parent exchanges and remote subscriber stages, RSS, and then on to remote subscriber multiplexers, RSM, fig.1. 2 Mbit/s line systems will also be used in large private telephone and data networks, for example for connecting remote line interface modules, LIM, to the central group selector stage in PABX system MD110 fig.2. In local networks and private networks the distances between a parent exchange and the above-mentioned remote units are usually short, requiring only one or a few intermediate repeaters. PCM and fibre cables will be used to a great extent. Fibre cables permit larger repeater spacing and give galvanic insulation and immunity to electromagnetic disturbances. Ericsson has developed a new generation of 2 Mbit/s line terminal equipment for pair cable and fibre cable, intended for the applications mentioned above. The equipment meets all relevant CEPT and CCITT recommendations. The basic requirements for the equipment are that it should - be suitable for integration with other equipment - be easy to operate - have high reliability - have good transmission characteristics. Fig, 1 The position of the line terminal, LT, in an AXE 10 network with remote subscriber stages, RSS, and remote subscriber multiplexers, RSM. Fig. 2 The position of the line terminal. LT, between the centrally placed group selector stage, GSS, and the line interface module, LIM, in the PABX system MD110 Fig. 3 The structure and interfaces of a line system for optical fibre. The maximum distance between two LTs is approximately 9 km for a wavelength of 890 nm LT Line terminal DL Digital line link DLS Digital line section D1 2048kbits interface. CCITT G.703 F1 Optical fibre interface kbaud ^ Interface cable, coaxial, 75ohms unbalanced, or pair cable, 120ohms unbalanced. _ Fibre cable

19 15 Fig. 4 Block diagram for the line terminating unit. LTU, in ZAD2-6. LTU contains: - all transmission functions - alarm and bit error detection - AIS switch - power feeding for its own transmission functions and a small number of intermediate repeaters LTU PFU SU CU PGU D1 S1 FLP Ub AIS FD SA DAGFINN DANIELSEN KJARTAN TAFJORD Fibre optics and line transmission Telefonaktiebolaget LM Ericsson 2 Mb it's 75 or 120Q T Line terminating unit Remote power feeding unit Supervisory unit Connection unit Pattern generator unit 2048 kbit s interlace Pair cable interface Fault location pair Battery voltage Alarm Indication signal Fault detector System alarm System design The main functions of the line terminal are - signal matching between the digital interface, D1, standardized by CCITT, and the line interface, S1 for pair cable or F1 for fibre cable - power feeding of the terminal equipment and intermediate repeaters - monitoring and indication of alarm conditions - fault location for its own regenerators. Printed board assemblies can be combined in different ways to form line terminals for the following types of 2 Mbit/s line systems - ZAD2-6, pair cable system with fault location in accordance with the fault detector method, FD, for one or twocable operation 2. - ZAD2-7, pair cable system with fault location in accordance with the loop connection method, SL, for singlecable working 1. - ZAM2-2, fibre cable system with fault location in accordance with the fault detector or loop method. In addition to the line terminals, line systems ZAD2-6 and ZAD2-7 include intermediate repeaters, which consist of regenerative repeaters in housings. These intermediate repeaters were developed for line systems ZAD2-4 and ZAD2-5. Line system ZAM2-2 for optical fibre comprises only two line terminals, since the low attenuation of the fibre permits long repeater spacing. However, if a repeater is required, two line terminals can be mounted back-to-back indoors and used as an intermediate repeater with local power supply, fig. 3. All three systems are identical as regards system structure and the division into printed board assemblies. Thus the same types of magazines and certain printed board assemblies are used in all the systems. Moreover it is possible to place different types of LT units (LTU) in one and the same magazine. An LT, figs. 4 and 6, consists of a systemspecific printed board assembly, LTU. and the following common printed board assemblies: - Remote power feeding unit, PFU, one per LT for pair cable systems - Supervisory unit, SU, one per magazine - Connection unit, CU, one per magazine - Pattern generator unit, PGU, which is an optional extra. LTU is a complete line terminal and contains all transmission functions as well as alarm detection and power supply of its own transmission functions, and a small number of intermediate repeaters. In certain cases it can work autonomously in a remote subscriber stage. PFU is used in ZAD2-6 and ZAD2-7 for routes with a large number of dependent repeater stations. SU contains all functions which are common for a magazine and which do not affect the transmission. There are two versions of the printed board assembly, one for the FD and one for the SL fault location method. CU is a passive printed board assembly for the input of battery voltage to the magazine, and isequipped with an inter-

20 16 Fig. 5 LTU for ZAD 2-6 with a transformer in the send direction face for the connection of system alarms, SA, to external equipment. CU is used only in magazines having a width of 488 mm. PGU contains a pattern generator with ten outputs. Transmission characteristics The impedance of the D1 interface is normally 75ohms unbalanced, but can be strapped on the printed board assembly to 120ohms balanced. Version 1 of LTU, forzad2-6, figs.4 and 5, contains only a transformer in the send direction. The maximum cable attenuation up to the D1 interface is 6dB. The maximum permissible cable attenuation between the S1 interfaces is then 34dB. Version 2 of LTU, fig.4, is used if the cable attenuation is between 34 and 40dB or if AIS (Alarm Indication Signal) is required in the send direction. Version 2 contains a regenerator with simplified equalization in the send direction. The regenerator in the receive direction is of the same type as is used in the previously described intermediate repeaters 1. LTU for ZAD 2-7 contains the same types of regenerators in the send and receive directions as LTU for ZAD 2-6, version 2. In addition it is equipped with a special address decoder and a loop connection switch which is controlled by the decoder. The regenerator equalizer is optimized to give the lowest possible error rate over the whole equalization range for all relevant cable types. The equalization range is divided into two sections, corresponding to a cable attenuation of 0-20dB and 15-40dB respectively. In LTU for ZAM 2-2, figs. 6-7, both directions of transmission include the regenerator with simplified equalization. After regeneration in the send direction, the electrical signal in HDB3 code is converted in an LED transmitter to an optical signal in HDB3 code. The receiver input stage consists of a PIN diode and a preamplifier in the form of a hybrid circuit in thick film technique. The transmission medium is a graded index fibre cable. At a wavelength of 890nm the maximum transmission distance is approximately 9 km if 3 db cable Fig. 6 Block diagram for the line terminal in ZAM 2-2. LTU contains: - all transmission functions - alarm detection - circuits for fault location in accordance with the FD or SL method - power feeding F1 LED PIN a Optical fibre interface Light-emitting diode Receiver diode Power feeding

21 17 Fig. 7 LTU for ZAM 2-2. It is connected to the F1 interface by means of a plug-in optical connector which does not require readjustment Fig. 8 Line terminals, LT, for pair cable and fibre cable can be placed in the same magazines and work as intermediate repeaters. The optical fibre systems have unique properties, particularly galvanic insulation and insensitivity to disturbances, which make them especially suitable for certain applications is used. The fibre attenuation is considerably less at 890 nm than at 850 nm, which is the wavelength at which the fibre attenuation is defined. The difference is about 4 db over a 10 km route. The wavelength can be changed to 1300nm simply by replacing the send and receive diodes. The maximum transmission distance is much longer at the higher wavelength. Ability to withstand overvoltages The D1 interface has been dimensioned to withstand voltage spikes of 100 V with a duration of 2 us. The S1 interface has been dimensioned to withstand voltage and current surges from lightning strikes of up to 5kV and 200A with a pulse shape 10/700 us (rise time and time to half value respectively). The S1 interface has also been dimensioned to withstand 10A/50HZ for 0.5s. The interface for the fault location pair has been dimensioned for the same values as the S1 interface. The dimensioning described above gives overvoltage protection that is well in excess of the requirements of the relevant CCITT Recommendation, K.17. The nature of the transmission medium is such that the optical fibre line terminal does not need any protective circuits towards the line. Optical fibre systems, fig. 8, are thus particularly suitable for environments where the level of disturbance is extremely high, and where pair cable systems do not give satisfactory transmission quality. Power feeding For reasons of reliability all transmission functions in an LTU are powered by a d.c./d.c. converter which is integrated in the LTU. The intermediate repeaters in ZAD2-6 and ZAD 2-7 are fed either from the d.c./ d.c. converter, which in pair cable systems gives 55V/48mA, or from a separate power feeding unit. PFU, which gives 250V/48mA. The maximum number of dependent repeater stations which can be powered is approximately 4 and 20 respectively, depending on repeater spacing and cable type, figs. 9 and 10. PFU will only be required in exceptional cases, since, on average, routes contain only 3-4 dependent repeater stations. The output voltage from PFU, fig. 11, Fig. 9 Power feeding of intermediate repeaters from the d.c./d.c. converter in the LTU. The low output voltage, 55 V, facilitates cable work, particularly in the local networks where different personnel categories are employed. A maximum of seven dependent repeaters can be powered Fig. 10 Power feeding of intermediate repeaters from PFU

22 Fig. 13 Fault location in accordance with the fault detection method, FD ED FD DRS FLP HDB3 error detector, incorporated in LTU Fault detector, included in SU Dependent repeater station Fault location pair Fig. 11 PFU for ZAD 2-6 and ZAD 2-7. The printed board assembly contains circuits for automatic shutdown, with manual or automatic restart in the case of a break in the power feeding loop, e.g. a cable break can be limited to 150 V, 200 V or 250 V by means of straps on the printed board assembly. Automatic limiting takes place if the specified current and voltage values are exceeded. PFU can also be strapped so that it is automatically switched off if a cable break occurs. The restart can be manual or automatic. In the latter case the output voltage falls to approximately 50V below the strapped value while the cable break remains, A d.c./d.c. converter on SU provides + 5V and -12V for all common functions which do not concern transmission. The d.c./d.c. converters and PFU operate with a battery voltage, U b, from -30V to -72V without any readjustment of the operating range. Fault supervision and maintenance All alarm functions are in accordance with CCITT recommendations, and Ericsson's general alarm principles for transmission equipment in the BYB construction practice 3. The primary alarms generate visual alarm indications, bay alarms (A and B alarm) and a system alarm, SA, which can be connected to external equipment, e.g. in a control room. The primary alarms for each LT are brought out to the front of the LTU. These alarm outputs can be connected to central supervisory equipment in the network, for example the transmission maintenance system ZAN 101. In the case of loss of signal or high error rate an alarm indication signal, AIS, is sent towards the D1 interface. In version 2 of LTU for ZAD 2-6, AIS is also sent towards the S1 interface, fig. 4. AIS can be inhibited by means of a switch on the front on LTU, which simplifies installation and testing as well as fault location. Fig. 12 Specially designed LSI circuit for supervision and fault detection. The circuit detects all primary alarms except power alarms, and gives error pulses to FD in SU when the FD method of fault location is used LST Loss of signal in the send direction LSR Loss of signal in the receive direction BER-3 Bit error rate a10 3 BER-5 Bit error rate ^10" 5

23 Fig. 15 Fault location in accordance with the loop connection method Fig. 14 Supervisory unit, SU, for the FD method. The printed board assembly contains the following functions, which are common for the whole magazine: - fault detector, FD - d.c./d.c. converter - AIS generator - bay alarm outputs Fig. 16 Instrument for locating cable breaks Aspecial LSI circuit in CMOS technique has been designed for the detection and indication of primary alarms excluding power alarms. The circuit contains both analog and digital functions for alarm and fault detection, fig. 12. Fault location Faulty regenerators are located with the aid of the fault detector method 2, FD, in ZAD 2-6, and the loop connection method 1, SL, in ZAD2-7. Either FD or SL can be used in ZAM2-2. The fault detector method The characteristic feature of the fault detector method, FD, fig. 13, is that bit errors in the line signal can be detected during traffic. The alarm circuit, fig. 12, included in each LTU contains two HDB3 error detectors, ED, one for each direction of transmission, which check the running digital sum. Error pulses are passed via the bit error bus from the repeater that is being addressed to the magazine fault detector, FD, which is incorporated in SU, fig. 14. FD in its turn is connected to the fault detector shelf via a separate wire pair, FLP. Any repeater can then be addressed from the fault detector shelf in the fault locating station, and information regarding bit errors can be transmitted to and analyzed in the shelf. The FD system is also used in all Ericsson's higherorder line systems. The method allows connection to the transmission maintenance system ZAN 101. Loop connection method The loop connection method, SL, fig. 15, was developed in connection with the development of line systems ZADO.7-1 and ZAD2-5. The method is based on remotely controlled loop connection. A portable fault location instrument is connected to the D1 interface. It feeds out address sequences which set up a time-limited loop connection betwen the input and output of each addressed LTU or intermediate repeater. The address sequences are chosen so that a normal transmission signal cannot cause loop connection during traffic. When the loop has been established, HDB3 encoded pseudo-random sequences having a length of bits are automatically fed out from the fault location instrument through the loop and back again. Any code errors are detected and indicated in the form of bit error rate. The main advantage of the SL method is that it does not req uire a separate supervisory pair, and is thus particularly suitable for cables with only a few wire pairs or fibre cables without any metal pairs at all. Locating a cable break Breaks in a pair cable are located by connecting a constant voltage of 100 V to the transmission pairs and measuring the sum current through shunt resistors in the dependent repeaters. A portable instrument has been designed for this purpose, fig. 16. The instrument, which is connected to the S1 interface, converts the measured current and displays the number of the faulty cable section on a digit indicator, fig. 17. The instrument can also be used for measuring output current and voltage, for example during installation testing.