DATAKOMMUNIKATIONSSYSTEM

In a data communication system a plurality of remote stations and a central station are arranged in a series loop. The central station transmits a succession of time slots to the loop and information is transferred between the central station and the remote stations with character interleaving under control of the central station. Each remote station includes one or more terminals. A terminal wishing to transmit a message sends a request-for-service signal to the central station in the first free time slot received by its remote station. The terminal cannot transmit a message or a further request-for-service signal until it receives a proceed signal from the central station. After receiving a proceed signal the terminal can transmit a message. At the end of the message the terminal is again locked out (i.e. it cannot transmit message data) but remains free to transmit a request-for-service signal by which means it may again obtain a line position.