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

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Table 1 Comparison of predicted and observed MTBF for some function blocks Equipment Channel/SG SG/MG MG/SMG SMG/LG (2700) 30-channel PCM 2 Mbit/s line system (2 terminals + 2 rep.) 8 Mbit/s line system (2 terminals + 4 rep.) Older Predicted 5.2 27 30 36 10 - - Mean time between f; tilures, IV TBI- (years des gn (M4) New desig Observed Predicted 11 7.1 27 33 31 31 27 36 11 18 - - 26 19 i (MS) Observed 10 71 28 31 18 39 29 Fig. 4 The correlation between predicted and observed failure rate for function blocks (magazine = shelf) x Different function blocks Observed value = Predicted value prediction and the use of the data in future calculations. Telecommunications administrations and manufacturers represent different viewpoints in practical applications. Telecommunications administrations and users of telecommunication services are mainly interested in the availability of the service and equipment. However, the availability is dependent on external application and maintenance factors as well as the built-in reliability of the equipment. The calculation model becomes complex because of factors that vary with time and space and also from one case to another. The manufacturer of transmission equipment, on the other hand, is only responsible for the built-in reliability. Application factors are beyond his control. Under given operating conditions the built-in reliability is only dependent on components and design parameters, and the calculation model is therefore relatively simple. It is also easy to compare equipment from different manufacturers. The reliability parameters of the equipment, i.e. the failure rate or mean time between failures, constitute the basic data for calculations concerning systems, links and networks. The following parameters have proved suitable for use in most practical cases: the failure rate z, the mean time between failures MTBF, reliability R, availability A, and down time DT. See the panel "Terminology and Definitions". Of the many possible ways of presenting reliability data two extreme cases may be mentioned. In the first case the whole equipment is regarded as a single item and all failures are counted without their effects being considered. In the other case a failure effect analysis is made, i.e. the effect the failure has on the transmission capacity of the equipment is considered and the failures are structured. The presentation method using structured failures is considered most suitable for transmission equipment 4 . A brief description is given below. Observed failure rate (failures/10 9 h) 10 5 Structured presentation Different types of failures in equipment can affect the transmission capacity in different ways. With respect to its transmission capacity the equipment can be in different (but well defined) states depending on which and how many functions are being affected by the failure. 10 4 10 3 - 102 102 Worse than predicted: 38% x X X * / / X X X X/ / / TT1— 103 w / * / / X X X
Fig. 5 Field testing of a 140 Mbit/s coaxial cable system taken into account by presenting the corresponding reliability parameter "cumulatively upwards", i.e. for equipment "at or above" the given capacity level. In practice, information is sometimes required regarding the reliability of a certain channel, a frequency band or at bit stream. This is also provided by cumulatively upwards structured presentation. However, it is often sufficient to present just the values for "complete failure" and for "failures preventing transmission". A simplified presentation can, for example, take the following form: Complete failure: MTBF (45) = 61 years Failures preventing transmission: MTBF,, 5+) = 8.5 years The indices in brackets give the number of affected Mbit/s, and a plus means that it is cumulative upwards. MTBF n 5+, thus means that everything is considered that affects "1.5 and more Mbit/s", i.e. all equipment for 1.5, 6 and 45 Mbit/s. IfevenMTBF, 7.6 years is given, the value includes failures that affect "Oand more Mbit/s", i.e. all equipment failures. The information is used in the planning of the life cycle costs (LCC). This presentation method has been applied for more than ten years in the tendering for transmission equipment. The extra work involved in obtaining the data and the slightly lengthy presentation are more than compensated by the detailed information it provides regarding the reliability of the equipment with respect to its transmission capacity. Failure effect analysis and structured presentation also show the advantages of a well planned design with high maintainability. These advantages would otherwise remain hidden or even be interpreted as disadvantages. For example, sophisticated control and supervisory equipment, which does not have a direct effect on the transmission, can reduce repair times and increase the availability. However, in an unstructured presentation the supervisory equipment would give rise to a higher failure rate for the equipment as a whole than for similar equipment without these supervision facilities. Optical fibre equipment, for example, can have the following failure rates: 2(565) = 11^3 FIT MTBF l565l =103år Z (0 , = 992 FIT MTBF (01 = 115 år Z (0+) = 2105 FIT MTBF |0+l = 54 år Without structuring the MTBF would be given as MTBF = MTBF (0 ,, = 54 years. The value that is relevant to the transmission capacity is MTBF (565) = 103 years, however. The fault detector and alarm unit contribute with 992 FITbutdo not affect the transmission capacity of the equipment. An unstructured presentation would show a higher MTBF for equipment without these units, and this equipment would then be seen as more reliable. Reliability data in tenders When tendering, reliability data can be presented asgeneral information forth customer or in response to certain points in the specification. At the same time a list is supplied of units (print board assemblies) recommended a: spares for the equipment.
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 and 52: 202 Fig. 11 Transmission equipment
Page 53 and 54: 204 Fig. 2 Automatic testing of mul
Page 55: 206 Relative occurrence for F Fig.
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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