Selection and Testing of Electronic Components for LM

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LARS G ERICSSON AKE PERSSON Telephone Exchange Division Telefonaktiebolaget LM Ericsson Fig 1 Block diagram of the hardware. An AKE 13 exchange can be equipped with up to 8 data processing blocks (DPB) Each DPB is synchronously duplicated, i.e. consists of two sides, each with a complete processor with stores and a transfer unit. Both sides normally work In synchronism, which Is continuously monitored. However, only one side Is executive. When there Is a discrepancy between the sides the faulty unit Is disconnected. The duplication can be utilized, for example, when changing programs and a further 18 exchanges are on order. Thus the further development of the system that is continuously being carried out is founded on long and extensive experience. System characteristics The telecommunications administrations' need of transit exchanges with high capacity increases with the expansion of the long-distance traffic. Previously it has not always been possible to satisfy the need for such large exchanges, and hitherto it has been a fairly common practice to combine a number of exchange units, each with a relatively low maximum capacity, to form what is, from the point of view of the network, one common switching point. A way of solving these problems that is often more economical for the telecommunications administrations and also technically more suitable, not least from the point of view of operation and maintenance, is to install a single exchange having the required capacity. AKE 13, with the following inherent properties, is able to satisfy all reasonable demands as regards lines and traffic: — maximum number of incoming lines, 30000 — maximum number of outgoing lines, 30 000 — maximum number of switched calls per hour for the control system APZ 150, 750 000 — maximum traffic capacity of the switching network with an internal congestion of 0.2 %, 25 000 erlangs The switching capacity is among the largest in the world. The system also meets very stringent demands as regards reliability and operating characteristics. Synchronously duplicated multi-processor system The AKE 13 control system is built up of a suitable number of synchronously duplicated data processing blocks (DPB), with a maximum of eight blocks. The
Table 2 Extended AKE 13 exchanges Exchange Fig.2 Helsinki Copenhagen Mexico City Mexico City Rotterdam DC Rotterdam DC Rotterdam INT Turku Turku Ålborg Ålborg Time Jan -77 Nov -75 Sept -75 Sept -76 Mar -73 July-74 May -76 Feb -75 April -77 Aug -74 Feb -77 Size of the extension 4 processors 9 600 multiple pos. 2 „ 7 200 2 „ 7 200 1 „ 3 600 1 200 1 ,, 3 600 1 „ 1 200 800 1 600 3 000 1 200 data processing capacity of the system can thus be extended in step with the increase in the number of lines, fig. 1. This means that the central, most complex and, for the operation most important part of the system need never be larger than what is required for handling the traffic on the lines connected at the time. The factor that is most important for the reliability is the synchronous duplication of the control system. It provides — the fastest possible fault detection through continuous comparison of the function of the duplicated units — the possibility of easily separating software faults and hardware faults — simple and reliable fault localization — the minimum loss of traffic handling capacity when a fault occurs — the possibility of introducing new functions without disturbing the traffic Thanks to the duplication it is possible to reload the whole system without disturbing the traffic. The two sides in the system, A and B, which normally work in synchronism, are separated by means of a command, fig. 2. Side A is then loaded with exchange programs and data from a tape unit. Side B continues the traffic handling without interruption. When the loading is completed, the newly loaded side A takes over the traf Size of the exchange after the extension 6 processors 15 000 multiple pos. 6 ,, 20 400 4 „ 15 000 5 .. 18 600 2 „ 6 000 3 „ 9 600 2 ,, 3 600 2 „ 6 400 2 „ 8 000 4 „ 8 400 4 „ 9 600 fic handling and side B is put in the standby state. If any operational disturbance should then occur because of faults in the newly loaded software, there will be an automatic changeover to side B and the traffic handling will again be carried out by the original software. When it has been proved that the newly loaded side A works satisfactorily, updating of side B is ordered and also a return to synchronously duplicated operation. The updating is carried out by copying the contents of the A-side stores. This facility, which through separation of the system sides enables programsto be loaded and verified without interruption of the traffic handling, can also be used when making major changes in the software. The possibilities offered by the synchronous duplication and multi-processor arrangement have been utilized in the methods for installation and testing of extensions that have been used successfully in AKE exchanges already in operation, table 2. The system can be extended by the addition of new data processing blocks without it being necessary to change the contents of the program stores already in service. If the extension does not include any new functions it is sufficient to make certain minor adjust-
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Selection and Testing of Electronic Components for LM

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