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136 ] Do not allow more staff in the exchange premises than is absolutely necessary, and keep the premises closed and free from dust to the greatest possible extent. • Give the maintenance staff the necessary supervisory equipment, with the possibility of supervising the service quality outside the exchange premises. • Take no action before the supervisory equipment indicates that the service quality has fallen below a certain permissible value. • Train the staff so that they are able to quickly localize and correct faults on the basis of the information obtained. Successive introduction of CCM in various countries CCM is applied nowadays to a greater or lesser extent by all the LM Ericsson customers. Some examples are given below. In order to further develop the ideas that were put forward at the 1956 Maintenance Conference, during autumn of the same year the design of control rooms for the ARF exchanges in Alborg and Odense were discussed with the respective Danish Telecommunications Administrations, FKT and JTAS. As a result a control room was taken into service in Alborg the following year, and in Odense at the beginning of 1959. That the right solution was chosen from the very beginning is borne out by the fact that the supervisory equipment in the Odense exchange still functions in accordance with the principles that were laid down 20 years ago. In Australia the first crossbar switch exchange from LM Ericsson was installed during 1962. In connection with this the Administration then introduced CCM, under the name Qualitative Maintenance 2 . Since then the Australian Administration has gone even further than what is included in normal CCM, and have developed their own supervisory equipment 3 . As an example may be mentioned ADR (Automatic Disturbance Recording equipment). With this equipment it is possible, among other things, to transmit to a supervising centre, information concerning faults detected by the register control <strong>set</strong> RKR and the state of important marker relays. In this way experts stationed at the supervisory centres can help the local maintenance staff to analyze the causes of faults. CCM was introduced in Holland in April 1966 in the Dordrecht and Zwijndrecht areas with very good results. The separate article mentioned in the introduction makes clear how, since then, CCM has so successfully spread over the whole of Holland. Results achieved Experience has shown that the administrations that have applied the above- Example of some different combinations of test connections — Control circuit for routing the test connections —— Connection on test, connected to TRTM either direct or via TRTS
137 Table 1 Budgeted maintenance contributions for the AR system of JTAS in Denmark System Hours/subscriber line or trunk line 1970 1971 1972 1973 Local exchange system with crossbar exchange type ARF Rural exchange system with crossbar exchange type ARK Transit exchange system with crossbar exchange type ARM 0.35 0.33 5.0 0.30 0.26 0.28 0.28 0.25 0.22 4.20 3.20 2.80 mentioned principles for their crossbar exchanges or similar types of exchanges, have been able to successively improve the service quality and to reduce their maintenance staff. As early as 1956, at the first Maintenance Conference, LM Ericsson expressed the opinion that the maintenance work for a normally maintained ARF exchange should not exceed 0.3 hours per subscriber line and year, with an operational reliability such that the fault rate does not exceed 0.1 % 4 . Certain administrations have achieved very much better results and others are on the way to doing this. An example of this is presented in the article from Holland. It may also be mentioned that an article by B. J. Carrol, Australia, contains a statement to the effect that: "It is the opinion of the author that terminal exchanges equipped for 10,000 lines can be maintained satisfactorily by one man" 3 , which corresponds to a maintenance contribution per line and year that is only one half of the standardized value of 0.3. JTAS in Denmark have reported figures for the maintenance of AR type of exchanges. It is interesting to note the reduction from year to year for the different systems, table 1. The crossbar exchanges of type AR have been in operation, with good results, for over 25 years. In no case has it been shown that the maintenance required has increased as the equipment becomes older. However, in certain cases there may be good reason for thoroughly investigating common relay equipment, such as markers, after 10 to 15 years in service, since these are so few in numbers yet of such vital importance for the correct operation of the whole exchange. This does not in any way detract from the substantial advantages that are gained with CCM. References 1. Broby, S.-B.: Electronic Traffic Route Tester TRT m 70. Ericsson Rev. 51 (1974): 3, pp. 80—87. 2. Moot, G.: The Effect of Human Factors on some Aspects of Australian Post Office Maintenance Operations. Maintenance Conference 1974. 3. Carrol, B. J.: Maintenance and Performance of LM Ericsson Crossbar Switching Equipment in Australia. Part 1 and 2. The Telecommunication Journal of Australia 1973, pp. 72—77, 143—149. 4. Hansson, K. G.: Maintenance Conferences at LM Ericson. Ericsson Rev. 52 (1975): 1, pp. 2—13.
Page 1: ERICSSON REVIEW 3 1976 GEOSTATIONAR
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Page 22 and 23: 128 ed by about 100 kohms. In order
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