The present invention relates to a communications system (1) with at least one node (101, 102, 110), a control instance (10) and a shared communications medium (11). The at least one node is designed to receive messages that are or were transmitted in a first transmission mode. This first transmission mode has a lower data transmission rate and/or transmission complexity than a second transmission mode. The control instance (10) determines a first of the nodes in order to transmit data thereto in the second transmission mode or in order to release the shared communications medium (11) for the first node to transmit data in the second transmission mode. The control instance communicates this to the first node by means of a message (501, 502, 503, 504). This message is transmitted in the first transmission mode.