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Fig. 4X8011Aarhus is a central point in the Danishtrunk network with direct junctions tomost main exchanges in the countryMaintenance of Aarhus Trunk ExchangeThe Aarhus trunk exchange, as already mentioned, is run jointly by theDanish P.T.T. and J.T.A.S. Maintenance and fault clearing are the responsibilityof J.T.A.S.When the Aarhus trunk exchange opened, a large proportion of manualoperation was considered necessary. Later, automatic operation was used moreand more, the Aarhus subscribers and manual exchange operators themselvesdialling the distant subscriber's number or manual exchange, as the casemight be. This necessitated extensive changes in the trunk exchange, whichhave naturally affected the maintenance situation.The trunk circuits to and from Aarhus consist of two-wire and four-wirelines. For the two-wire toll lines there are two switching stages with 400outlets each and a load of roughly 100 erlangs per stage. The trunk circuitsalso have two switching stages with 400 outlets each, the load being about240 erlangs per stage. The numbers of circuits terminating at the trunkexchange as at July 1, 1956. are tabulated below.Table 5Type of circuitInc.Orig.BothwayTotalInternational circuitsP.T.T. circuitsJ.T.A.S. trunk circuitsToll circuits . .8 31918889189592827629292006563853622836051,250The holding time of connections on trunk circuits is about 250 seconds andon toll circuits about 205 seconds. The busy hour calling rate is 12.3 % forboth types of circuit.
The same practice is adopted at the trunk exchange as at the local exchange,that traffic tests are performed in order to check the quality of service andfor fault tracing purposes. But routine tests—of tariffs, registers, lines, andthe like—are also retained to a much greater extent at the trunk exchange.The tests are at present done at fairly frequent intervals, but it has not yetbeen decided whether this will continue in future. The centralograph, whichis connected into the circuit every time a fault condition arises, is a greathelp in tracing. The intention had been to record the faults indicated by thecentralograph on punch cards, and so obtain an overall picture of the faultsand their frequency in different parts of the equipment. However, the faultshave proved too few to justify the use of this method.In traffic tests during the first six months of 1956 there were 23,080 callsto trunk exchanges. The faults numbered 480 or 2.08 %. They are classifiedin table 6, from which it is seen that the fault percentage at the trunk exchangeand local exchange is only 0.60 %.Table 6Total number of test calls 23,080Number of faults on line, repeater station ordistant exchange 342 <strong>1.</strong>48 %Number of faults at local or trunk exchange .... 138 0.60 %480 2.08 %Altogether 279 fault cards were handled during the first six months of 1956,of which 263 were cleared and 16 remained untraced. The faults are specifiedin table 7.Table 7Out-of-adjustment faults 121Dirty contacts 9Burnt contacts 2Sticking armatures 1Opens 13Shorts 34Leakage 1Soldering faults 36Installation faults 5Parts out of position 7Burnt-out coils or resistors 12Wear 9Defective <strong>com</strong>ponents 13Other faults 0Total 263In addition, 147 faults occurred in the switchboard operators' equipmentand a few out-of-adjustment faults on keys.The time, including supervisor's time, spent on clearing faults at the trunkexchange during the period was 6,026 hours. Assuming the same conditionsduring the second six months, the time spent on maintenance per line andyear would be 9.7 hours.The number of connections established through the trunk exchange isabout 24.6 millions a year. Thus the maintenance time per 10,000 connectionsis 4.9 hours.7
Page 3 and 4: ERICSSON REVIEWVol. XXXIV 1957RESPO
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