GB1420078A - Digital transmission systems - Google Patents

Abstract

1420078 Digital data transmission; fault detecting GENERAL ELECTRIC CO Ltd 7 March 1973 [27 April 1972] 19660/72 Heading H4P A data transmission system comprises a series of error monitoring circuits positioned along a transmission path, each monitor being operable to detect errors in the transmitted signal and to send information regarding the errors to a control terminal which selects each monitor in turn by a command signal which causes the monitor currently selected to send a second command signal to the next adjacent monitor. The system utilizes a code in which three signal levels + 1, 0, - 1 are used, each group of four binary digits being coded into a group of three level digits. In addition, the codes are so constructed that strings of zeros and signals of like polarity are limited in length, and monitoring equipment associated with each regenerator in the transmission path indicates if a string greater than the permitted length occurs. Each monitor comprises a pair of trigger circuits, responsive to the + 1 and - 1 signals respectively and an integrator which is reset by these signals. The outputs from the two triggers are arranged to step a forward/backward counter, which produces an output if more than a predetermined number of consecutive pulses of one polarity occur. The integrator similarly produces an output if too many zeros occur. The integrator and counter outputs are fed to a monostable circuit which produces an output signal having a mark/space ratio dependent on the rate of fault occurrence. In order to set the first monitor into operation, the transmitting station transmits a continuous tone B and a short burst of a different tone A. When tone A ceases the monitor sends a " monitor held" tone C back to the transmitting station and, after a delay, transmits the output from the monostable. When it is desired the tone B is interrupted to cause the first monitor to turn off, and to transmit an A tone to the next monitor. Reinstatement of the B tone then turns on the next monitor in a similar manner. Selection of a particular monitor may be achieved by stepping on as soon as a C tone is received. This is done by counting the number of C tones received and comparing the count with a predetermined count.