Selection and Testing of Electronic Components for LM

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Table 3 Number of component faults per rack and operating year in the Rotterdam DC Fig. 8 Connection of the ITMC test desk to the switching network Type of equipment Central data processing equipment Test and control equipment I/O equipment Code switches Other switching devices No. of racks 30 17 2 64 90 change is small compared with one in a conventional exchange because the logic functions are carried out by the software.) Route supervision panel with lamps for indicating route congestion and various types of blocking. A typewriter that provides access to all supervisory functions in the system. The design of ITMC can vary depending on the size of the exchange and the number of international lines. The equipment is normally placed in a separate room. It is then often most convenient to put the U-link racks in the same room. For small international exchanges, the ITMC equipment can be placed in the maintenance desk in the control room. Operational experience The SPC technique has made it possible to rationalize the operation and maintenance work to a very great extent. The administrations have pointed out many advantages, for example: - that changes of traffic routing data, route information and also charging and accounting data require considerably less resources and can be carried out in very much shorter time in AKE 13 than in conventional systems. A comparison is made on the last page of this article — that it is easier to introduce functional changes since the majority of the 1972 No. of faults per rack 04 1 82 2.0 0.047 0.28 No. of racks 47 32 4 128 158 1975 No. of faults per rack 0.28 1.53 0.25 0056 0082 functions are realized in software — that the efficient supervision and fault localization functions have meant that in AKE 13, more often than in previous systems, faults are detected and cleared before the subscribers complain — that the connection and testing of lines is greatly facilitated by the maintenance panel and typewriter provided. Extension of exchanges in operation It has already been mentioned that several AKE 13 exchanges in operation have been extended, table 2. The great flexibility of the system offers an almost unlimited variety of extension configurations, but experience from the extensions that have been carried out shows that it is possible to limit and standardize the number of extension configurations and still meet all requirements that the administrations may have. This standardization has the following advantages: — it admits the development of standardized methods and aids — it gives short installation and testing times — extensions can be carried out without specialist aid — it reduces the amount of resources required in all handling stages — it gives high reliability Component reliability In a previous article on the first AKE 13 exchange, Rotterdam DC 1 , the number
Fig. 9 System restart frequency in the AKE 13 exchange in the Rotterdam DC with 3 DPBs and 9 600 multiple positions 1. The switching stages and data store were extended at the beginning of 1973 2 The exchange was extended by the inclusion ot a new data processing block and new switching stages at the beginning ot 1974 3. An inverter fault occurred in June 1975 — Mean value tor 4 months of component faults per rack was given for the various parts of the system during the first year of operation, 1972. These figures are given in table 3, supplemented by the corresponding figures for 1975. It should be noted that the exchange has been extended in the meantime. The table verifies the high component reliability, which has proved to be very stable and has even improved during the time the exchange has been in operation. System restart The system restart is such a basic function in the fault clearing operations that it deserves a special description. A software or handling fault can manifest itself in several ways, for example through — the normal program handling ceasing wholly or partly — an unauthorized attempt to write data in a specially protected area — a jump in the software being addressed to an unequipped part of the store. Number of automatic restarts per month 133 Restart takes place when any of the above fault situations occur. A hardware fault in a processor side is detected by the system maintenance unit and can usually be located and isolated without affecting the operation. In the exceptional cases when this is unsuccessful, for example if a double fault occurs, restart also takes place. Such a restart means that temporary data are cleared, whereby any faulty data are removed. The system is then set to an initial state where it can start handling traffic again. In the first place a normal system restart takes place, in which calls in the register state (i.e. connections in the process of being set up) are disconnected. This takes approximately 30 seconds and during this time no new calls can be accepted. Calls that have already been established are not affected. If repeated normal restarts do not have the desired effect, or if the number of restarts during a short period of time exceeds a preset value, a major system restart takes place. This means that established calls are also disconnected. Such restarts are relatively few and are carried out in approximately 15 seconds. The exchange staff may sometimes want to "clean up" the exchange and they then carry out a manual restart, normal or major. A manual system restart is also carried out in connection with function changes and when a data processing block is put into operation or taken out. These manual restarts are usually carried out during periods of low traffic. Subscribers who happen to call the exchange during a system restart experi-
Page 1: ERICSSON REVIEW 3 1977 SELECTION AN
Page 4 and 5: Selection and Testing of Electronic
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Page 8 and 9: Fig. 6 Humidity test High air humid
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Selection and Testing of Electronic Components for LM

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