A method of operating a transmission system (1) having a first network (2) and at least one second network (3), data being exchanged between these at least two networks (2, 3) in that data of the first network (2) is fed to duplication means (4), the inputted data being transmitted wirelessly to separator means (5) via at least two transmission paths (6, 7) using PRP and forwarded from the separator means (5) to the connected second network (3), characterized in that the data is transmitted in the form of data packets, and it is ascertained whether or not a data packet was transmitted, and it is determined based thereon whether or not the transmission system (1) is operating in a fault-free manner.