The experimental space-division electronic exchange `test¿

An experimental electronic exchange known as Test 1 is being developed in Sweden. The high operating speeds of electronic solid-state components enable the control functions of an electronic exchange, which are digital by nature, to be centralized. As a result, the data handling may be accomplished by a special-purpose computer. In the Test 1 programme, temporary data and traffic-routing information are stored in three types of memory. The data handling is concentrated a logic unit which performs transfers, comparisons and elementary arithmetical operations. The speech path is a space-division network arranged as a link system with p-n-p-n triodes as cross-points. The marking of the different cross-points is performed stage by stage and the wanted action is tested between stages, making it possible to detect faulty cross-points. The grouping arrangement of the cross-points constitutes eight successive switching stages between the incoming and the outgoing side of the exchange. This seems to be economical in a capacity range about 1000¿10000 subscribers and a corresponding total traffic range of about 60¿1000 erlangs. The required number of cross-points per subscriber is between 8 and 12 when the total traffic per subscriber 0.06 erlang and the overall grade of service of the exchange is 0.01. The organization of the logic unit and memories has been developed study of typical automatic-telephone-exchange routines. The programming facilities of Test 1 and the general organization of the station programmes are described, and an example of call progress is given.