Abstract: The invention relates to a method for medium access control by transmission units (2) for data transmission over a network (1), wherein data from a transmission unit (2) can be transmitted over the network within cyclical time slots. The method is particularly suited as a control protocol in a local powerline network within a building. It is proposed that access to a non-occupied time slot (8) by a plurality of transmission units (2) is controlled in that one of said transmission units (2) wins the corresponding time slot (9) of the next cycle based on comparing priority values. Each priority value is determined by the type, the amount and/or a time delay of the data to be transmitted, and the corresponding time slot of the following cycle is reserved for data transmission by said winning transmission unit (2).