A data transmission facility comprises a central station and a plurality of substations connected thereto via a data bus, the substations outputting a control signal dependent on the transmission or reception condition thereof. A plurality of substations are therefore capable of being connected to a serial point-to-point interface of the central station by way of a coupling device which is reversible with respect to the direction of transmission by optional activation or deactivation of level converters on the basis of control signals transmitted by the central station or by the substations. The data transmission facility is particularly suited for the transmission of operating state signals from intermediate locations of a communications transmission facility to a central evaluation facility.