In a third generation (UMTS) mobile radiotelephone system, data are transmitted between a base station and a mobile station in packet form via the air interface. A connection control protocol with the task of, inter alia, establishing whether and which of the data packets have been lost during the transmission, using control data, functions in both stations. These control data are added to each packet that is sent by the connection control protocol. Several packets can be transmitted within the transmission interval and the number of packets can vary from interval to interval. This allows different data transmission rates. The inventive method enables the number of packets that are sent via the air interface to be reduced, by transmitting larger, rather than more, packets within a predetermined interval, while not affecting the possibility of varying the data transmission rate.