GB1448174A - Data transmission systems - Google Patents

Abstract

1448174 Data transmission SIEMENS AG 25 Feb 1974 [12 March 1973] 8427/74 Heading H4P In a transmission system in which clock pulses are transmitted from an originating station or exchange over a channel of different frequency and concurrently with data, which pulses are separated by means of filters, the amplitude of the pulses is monitored at each subscriber position and when this falls below a determined minimum level, continuous start polarity is issued by subscribers apparatus which clears the connection. A subscriber parallel/serial transmitter RS is clocked by pulses T2 through LP filter TP to a 2 wire line and through another LP filter TP passes to a receiving circuit EV in an exchange. Synchronizing pulses T1 of higher frequency than the cut-off frequency of LP filters pass via BP filters and 2 wire-line to an amplifier VE to a frequency divider FT producing pulses T2. If pulses T1 as received do not reach a determined level as detected by P, through ET a continuous start polarity is issued and similarly at the exchange in the event of line disconnection a continuous start polarity is issued through EV thus clearing the connection.