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

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193 ROGER LINTON Communications Engineer (Signalling) London Underground Limited Transport area of operation, fig. 2. To provide the desired degree of security against route and central exchange failure two transit switching centres (TSC) were planned, interconnected by high capacity links and each having its own independent junction route to each of the 18 exchanges. A project team of 10 people was established and specifications were prepared and issued in 1978 for replacement exchanges and transmission systems, all to be of solid state equipment. After detailed assessment of competing combinations of exchange and transmission networks, an integrated digital exchange and PCM transmission system was selected which complied with the specification and gave the best value for money. A contract was placed with Thorn Ericsson Telecommunications in September 1979 to supply, install and commission a 10000-line digital PABX (later known as MD110) configured to London Transport network requirements, with a Ready for Service date of September 1984. 2 " 4 This project involved the work of a number of London Transport internal departments, as well as contractors. Sites had to be found for new exchange buildings and it was imperative that critical path analysis techniques were applied to this project. This was done by the projectteam and it proved invaluable for the coordination of work and in making certain changes as the project progressed. Exchange buildings and equipment Eleven of the new exchanges are flatroofed single-storey brick buildings, fig. 3, and of three standard sizes, the remaining eight exchanges are accommodated in existing office buildings or stations. Buildings are divided into separate rooms for switching equipment, battery and rectifier, MDF and Technicians store, fig. 4. The equipment room has a computer type floor and is air conditioned. The battery room has a solid floor, and an extraction unit is provided for the two batteries. The old network consisted of 15 exchanges, and as some exchange areas had been stretched beyond normal line limits the opportunity was taken to correct this situation by providing three additional exchanges. Harrow-on-the-Hill has been replaced by the three exchanges Neasden, Ruislip and Loughton Rickmansworth nault Fig. 2 The new MD110 exchange network with transit exchanges at Baker Street and Embankment has an initial capacity for 10000 extension lines A MD 110 transit exchange, TSC MD110 Hounslc West Acton Lillie Br 'dge Head office Stockwell Becontree stepney breen
194 Rickmansworth, and the Loughton area has been cut in half by the provision of an exchange at Hainauit. Also Leicester Square area has been divided between Baker Street and a new exchange at Embankment. The switching equipment consists of circuit boards which plug in a shelf called a magazine; the magazines are housed in a lockable cabinet. Each equipped cabinet is known as a Line Interface Module (LIM) and contains control equipment, digital switching equipment, processor and telephone line interface boards. If an exchange has more than two LIMs (i.e. approx. 400 analogue telephones) then a Group Switch Module (GSM) is provided to route calls between LIMs. The common equipment, such as Group Junction Units (GJUs), Tone Receivers, Tone Senders and Multi-Party Conference Units have assigned positions in the magazines due to the large number of time slots that these boards require. All remaining board positions are interchangeable as each of these units only requires a maximum of eight time slots. Extra GJUs may be added to cope with high levels of LIM-to-LIM traffic. The control equipment in a LIM has the capacity to handle all traffic originating and terminating within the LIM. In the event of a fault on a PCM link, the LIM will recognise the problem and continue to process internal callsand routeexternal calls via Baker Street/Embankmeni TSC as appropriate. A main distribution frame (MDF) is provided with fused connections and test jacks on the line side for the termination of trackside cables, and with gas discharge tubes for high voltage protection on the exchange side. All cable terminations are wire wrapped. Flexiblecables with connectors are run from the exchange side of the MDF to the LIM and plug directly into telephone line interface boards. Two lead acid batteries to give a six busy hour reserve capacity are provided in each exchange and are arranged in a divided floating system. Normally one battery is charged from a Transformer/ Rectifier set connected to the local authority supply and the other is connected to the London Transport generated supply. This power supply and battery arrangement provides maximum flexibility so that either battery can be easily isolated from the exchange for maintenance and, under mains failure, either rectifier is available to charge both batteries. Transmission system Each exchange has a number of PCM routes to both Baker Street and Embankment TSCs. 2Mbit/s primary PCM multiplexers are not required as a Fig. 3 One of the eleven brick buildings that were erected for the new exchanges
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: The Renewal of the London Undergrou
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 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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