Abstract: The transmission of digital message signals of a first and/or second type, for example in the form of data signals and/or digitally encoded voice signals, takes place in time channels of a transmission medium designed for time-division multiplex operation. Timeslots periodically repeatedly appearing in successive pulse frames are allocated to the time channels. The respective time channel is thereby divided into a defined plurality of time sub-channels. In a first embodiment, one of the time sub-channels of the respective time channel is defined as a control channel in which at least a part of the available transmission capacity is reserved for the transmission of control data. Details regarding the type of digital message signal provided for the respective time sub-channel is specified and are contained in these control data.