Abstract: A tuning system for use in a receiver of an optical transmission system. The receiver includes a data channel transporting a data signal and a monitoring channel transporting a copy of the data signal. The tuning system includes a processing module for processing the copy of the data signal to generate a control signal conveying tuning information. This tuning information is used by the receiver to alter an operating point of the receiver on the data channel. The operating point of the receiver that is susceptible to be altered by the control signal is a decision threshold applied on the data signal to discriminate one binary value from another binary value on the data channel of the receiver. This approach allows, when required or desired, tuning of the system while the system is in service. This is possible since the tuning of the system is performed using the monitoring channel, and does not disturb nor corrupt the actual data being transported on the data channel.