Field Trial of Optical Fibre Cable-TV System Optical Fibre System for ...

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Reliability of Equipment Branko Tigerman Calculations of the reliability and availability performances of transmission systems and networks are based on data concerning the reliability of the equipment used. Ericsson s transmission equipment has high built-in reliability which affects system and network planning, for example by reducing the need for redundancy in the equipment. The author describes the prediction method used and its trustworthiness, together with the way of presenting reliability data for transmission equipment and systems. Ericsson's views on redundancy in connection with demands for duplication of multiplexing and line equipment are also given. Finally some typical MTBF values for some of the most frequent function blocks are shown in order to give an idea of the reliability of Ericsson's transmission equipment. UDC 621.395.45 telecommunication reliability transmission lines redundancy Reliability, which originated in the fields of defence and space research, is today an important parameter also for transmission equipment. It should therefore be specified together with other technical data of the system. Quantitative reliability data are required, together with other transmission engineering and economic factors, BRANKO TIGERMAN Public Telecommunications Division Telefonaktiebolaget LM Ericsson in order to be able to assess the efficiency of equipments and systems. Such quantitative data consist of reliability and availability values, which have therefore become important basic parameters for transmission equipment. In order to be able to calculate the real value of different reliability parameters the equipment must have been in operation for a certain length of time and a number of failures must have occurred. The more reliable the equipment, the longer the time required for a relevant number of failures and the smaller the practical possibilities of making an assessment based on observations. Predictions are therefore used during the development and design of new equipment; they are based either on experimental values or observations of other, similar units. Fig. 1 All integrated circuits are fully tested before assembly
204 Fig. 2 Automatic testing of multiplexing equipment after manufacture Reliability predictions of failure occurrence as a function of time provide information regarding the future behaviour of the equipment and the system. The result is also used as a basis for the planning of maintenance and for calculating the operating costs during the life of the equipment, life cycle costs (LCC). The reliability of complex systems and networks depends on their design and construction. The calculations are based on the predicted reliability of the equipment used. The purpose of the telecommunication network is to offer the customer good services. The service quality in the network is a function of such factors as the availability of the network. In order to meet technically and economically feasible availability requirements and to increase the probability of transmission paths surviving catastrophes it is sometimes necessary to introduce redundancy at relevant points in the network. The views on the use of redundancy expressed here are based on Ericsson's experience of the operation of equipment with high built-in reliability. They may be of assistance when deciding on the requirements and design of redundancy in systems, links or networks. Reliability is one of the basic design parameters in Ericsson's transmission equipments. High built-in reliability has been achieved by - using selected components of high quality 1 - limiting the stress by reducing the power (derating) - reducing the power consumption in order to keep the temperature low - careful checking of components and manufacture - improving the design on the basis of operational experience (follow-up). It is certainly economically justifiable to have high reliability built into the equipment right from the start. Loss of income and the cost of maintenance work and spares in connection with failures can warrant the expenditure of up to 40% more for equipment with higher built-in reliability 6 . If a decision-maker is to be able to assess and trust the data supplied by the manufacturer the prediction method must be known and its trustworthiness verified. Prediction results must be presented in a suitable form and a clear manner and should be easily understandable even by non-specialists, i.e. anybody with a normal technical training. The panel "Terminology and Definitions" explains concepts and termsina somewhat simplified form. It is a difficult task, and one of considerable responsibility, to express oneself in a simple and easily understandable way in a discipline that uses such complicated mathematical tools as those used for reliability calculations. The price that has to be paid for simplicity is reduced mathematical accuracy, limited terminology, simplified models and last but not least, some loss of the author's technical prestige. Reliability prediction and its trustworthiness Prediction method The prediction is carried out by mean of special computer programs, using the parts count method, i.e. the fa""
Page 1 and 2: ERICSSON REVIEW 4 1985 Field Trial
Page 3 and 4: Trial of Optical Fibre Cable-TV Sys
Page 5 and 6: Head end (HC] 280 Mbit/s Farsta aut
Page 7 and 8: 158 Switching equipment Fig. 7 Futu
Page 9 and 10: 160 Fig. 10 The teleconference room
Page 11 and 12: GERHARD GOBL Public Telecommunicati
Page 13 and 14: Fig. 5, above left Two-channel A/D
Page 15 and 16: Digital input signals Digital outpu
Page 17 and 18: Power ZAV 280/4 has individual powe
Page 19 and 20: Wavelength Division Multiplexing fo
Page 21 and 22: 172 Subscriber side BP-890 Controll
Page 23 and 24: Fig. 8 Transmission characteristics
Page 25 and 26: Most computer cabinets are 19" wide
Page 27 and 28: 178 Fig. 5 Modems in Series 7 Modem
Page 29 and 30: Computer Aided Production of Plasti
Page 31 and 32: Fig. 4 Product geometry displayed o
Page 33 and 34: Rectifier for Mobile Telephone Syst
Page 35 and 36: I OR | OFU OS I CMUP HlsHi W±±±h
Page 37 and 38: 188 Fig. 6 The rectifier with the o
Page 39 and 40: Fig. 9 Rectifier BMJ A01 001 with t
Page 41 and 42: The Renewal of the London Undergrou
Page 43 and 44: 194 Rickmansworth, and the Loughton
Page 45 and 46: 196 Fig. 5 Optical fibre cable rout
Page 47 and 48: 198 In planning the optical fibre n
Page 49 and 50: Fig. 9 The digital telephone DIAVOX
Page 51: 202 Fig. 11 Transmission equipment
Page 55 and 56: 206 Relative occurrence for F Fig.
Page 57 and 58: Fig. 5 Field testing of a 140 Mbit/
Page 59 and 60: 210 Fig. 7 The system down time as
Page 61 and 62: MTBF (years) Equipment 2-5 Transmul

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