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

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199 Telstar House new exchanges. Twenty lines were connected at each exchange. Then between 10.30 hours and 12.30 hours the twenty users at each exchange had a schedule of numbers they were required to call on other exchanges. The results indicated that exchanges performed reasonably satisfactorily under load, and the excellent speech quality was noted for the first time. The cut-over night A control centre was established in the Communications Design office at Paddington from where the cut-over was coordinated. The network was split into three areas, each consisting of approximately five old and five new exchanges, and each area was allocated a telephone number to report to when the cut-over of exchanges were completed. The cut-over took place during the night of Friday/Saturday 8/9 February 1985. Work commenced at 21.30 hours to transfer telephones at four large office buildings with the exception of certain operational lines such as the Police and Head Controller which could not be changed until 02.30 hours the following morning. The main cut-over was successfully completed between 02.30 hours and 02.45 hours on Saturday 9 February 1985. After lines were transferred, an exchange co-ordinator first reported completion to the control centre and then rang the Communications Maintenance Centre to officially hand the new exchange over to the maintenance staff at Baker Street. Between the hours 03.00 and 07.00, telephones were tested until the second shift reported for duty to continue the process alongside contractor's staff. During the rest of the weekend installation staff commenced replacing rotary dial telephones with new multifrequency instruments. The weather during the cut-over night was terrible as heavy snow fell throughout the night. At the start of traffic on the Saturday morning trains were found frozen to the depot rails. The new telephone system was quickly put through its paces as Railway Operating staff telephoned throughout the railway in order to get a train service running. The only minor error with the cut-over was that three police lines were found to be left connected to the old telephone system. This was noticed by staff in an old exchange who heard equipment functioning. The matter was then quickly rectified. Post cut-over problems Below are some of the problems that have been experienced with the new system: - At Ruislip the exchange was repeatedly failing and then restarted itself automatically; the failures were due to some telephone lines indicating lost signalling. These lines were subsequently blocked on the terminal and manuallywedgedoutonthemain distribution frame, but no significant line fault appeared to exist. Stepney Green exchange also experienced troubles similar to those at Ruislip. Upon investigation it was found that only one line was indicating lost signalling due to an earth fault. - Lost signalling was also causing other exchange LIMs to crash, and the offending line faults ranged from unbalanced cable pairs to disturbances through small induced voltages. The MD110 system was highly sensitive to line characteristics; lost signalling indications were stored in a counter file (maximum 100) and, when an unacceptable level was reached, the respective LIM crashed. Once the LIM failed, the counter file was wiped clean, the LIM restarted and the whole sequence was repeated. The London Underground system was the first ti me the MD110 had been subjected to the majority of telephone lines being routed in external cabling running alongside an electrified railway. These cables obviously have other characteristics than the normal short internal cabling of a PABX in an office building. It was interesting to
Fig. 9 The digital telephone DIAVOX Courier 700 with 36 or 12 burtons note that these lines had worked fairly satisfactorily on the old electromechanical exchanges. To eradicate this problem, the contractor's engineers produced a successful software system patch, to only log lost signalling and not to crash the LIM. - Attheend of July acompletefailureof Embankment transit and local exchanges was experienced. Due to a defective cooling unit in the apparatus room, the temperature rose to over 45°C for a prolonged period. A temporary cooling unit was installed and both exchanges were reloaded, but only the local exchange came back successfully. The transit exchange was isolated from the rest of the system, so all inter-exchange calls were routed via Baker Street transit exchange without any loss of service. On investigation it was found that most of the controlling boards on LIMs 1 and 10, the Group Switch, Transmission Bay and both tapes from the tape unit were defective due to thermal breakdown. These boards were replaced and the transit exchange was finally tested and put back into service; all this took place over a weekend, and it was reassuring that it was not necessary to call out contractors for assistance asourown maintenance staff managed adequately. - Every week many lines are initiated or facilities changed in the customer data; this information is inserted directly to the memory boards from the exchange terminal and is stored "soft". If a data reload takes place, then soft information is lost; therefore the "soft" information is regularly dumped onto the tapes to provide a "hard" copy. For security reasons each exchange has three copies of the tape: one copy remains on site for backup purposes, and an identical copy and a reference copy of the previous issue are retained at Baker Street Maintenance Centre. Overall the new system has settled down very well, with only minor problems, which the maintenance staff are becoming competent to handle. Telephone instruments As the MD110 supports either rotary dial, Dual Tone Multi Frequency (DTMF) key phones or digital instruments this enabled the cut-over to be carried out without the need to change the existing loop disconnect telephones. Standard telephones with DTMF signalling and the digital telephone DIAVOX Courier/00 have been selected to cover the needs of London Transport telephone users. Digital telephone The digital telephone known as the DIAVOX Courier700, fig.8, is currently being installed as a replacement for existing Manager/Secretary arrangements, which were dial type instruments, and required multiple wiring between the manager's and secretary s instruments. A mains power supply was required to run this arrangement. In addition a further unit was needed to provide facilities like "stored numbers and "loudspeaker".
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: 198 In planning the optical fibre n
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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