Abstract: A communication system includes a plurality of communication stations communicating with each other over a communication channel, wherein each station is provided with a station number which is transmitted as part of a data signal. Transmission control circuitry in each station detects the presence of a carrier wave on the communication channel indicating that another station is transmitting data. The station number is read from the transmitted data and is used to determine the length of a waiting period during which no carrier wave is detected, and after which the station can transmit data. Data collision circuitry is provided which causes data retransmission in the event of a data collision on said channel, after a waiting period determined by the station number of the transmitting station.

Abstract: In a data transmission system wherein data are transferred between a control station and a plurality of tributary stations under the control of the control station, the tributary stations are sequentially selected and during the selection of each tributary station, data is transmitted first from the control station to the selected tributary station, and then from the tributary station to the control station; the control station and tributary station performing collection and processing of data during the transmission times to overcome delays and wait periods.