Abstract: A process is disclosed for the transmission of data between subscribers of a public dial telephone system in which at least a telephone, a data modem having a tone transmitter and a tone receiver, and a data device are connected to the dial telephone system. The data modem is equipped with a circuit for ringing voltage detection with bridging of ringing pauses. For transmission of a data answering tone and, if applicable, for selection of a channel position, in the case of manual operation, after operation of a data key, a distinction between the `called` state and `calling` state is made according to whether, at the start of loop current, a ringing voltage was detected by the data modem or not.