GB1177186A - Improvements in or relating to Telecommunications Exchange Systems - Google Patents

Abstract

1,177,186. Digital transmission systems. SIEMENS A.G. 26 April, 1968 [28 April. 1967], No. 19813/68. Heading H4P. In a data communication exchange system, signals lasting more than a certain time, e.g. clearing signals, are detected. Each incoming line is associated with a respective detector, the detectors being sampled sequentially by clock pulses. In a first embodiment of a detector the time of occurrence and the direction of a change in level of a received signal are stored, and the time stored is subtracted from the time of occurrence of the next clock pulse fed to the detector. The result indicates the duration of the signal. The clock pulses recur at 120 m.sec. intervals. If no change in level occurs in the next 120 m.sec., the time stored is subtracted from the time of the next clock pulse. When there has been no change in level for at least 210 m.sec. the line is cleared. In a second embodiment, each clock pulse causes a store to be read out and then a counter, which feeds the store, to be incremented. The contents of the counter and store are erased when a change in level occurs on the associated line. When the number read from the store reaches a given number, the line is cleared.