In a motor vehicle, messages from control units arrive at input ports of a switch apparatus with each message indicating a destination address and a priority level. Each input port of the switch apparatus receives at most messages with a predetermined maximum data volume overall, for one priority level or for some or all of the priority levels, during each predetermined unit of time. The received messages are assigned to output port(s) based on their destination address and the messages assigned to each output port are sent onward. This guarantees time limits for the respective transmission period.