A data transmission method for transmitting a digital optical signal over an optical transmission link includes creating a digital optical signal defining at least two service levels, each service level transporting information via a modulation scheme comprising at least three different modulation symbols. The data transmission method also includes transmitting the digital optical signal over the transmission link and receiving the transmitted digital optical signal at a remote end of the transmission link by demodulating the received signal and extracting the information of the at least two service levels. In case that the transmission performance is below a given threshold due to increased constraints of the transmission link a compensating action is taken to drop at least one of the service levels from the optical signal or to determine parameters associated with the transmission so as to increase one of the service levels to a predetermined quality level.