the line similarly the receiver side of the slte shown in fig1 also includes dcf 212 this functions analogously to the dcf 112 in the transmitter side moreover further dcf not shown may be incorporated at other stages of the transmission reception of the signal for example dcf may be placed after the bmds 108 in order to compensate the entire signal or prior to the cmds 104 in order to compensate individual channels additional dcf may be incorporated in the receiver side of the slte in the same way although not shown in fig1 it is possible that one or more bands may be replaced by loading channels loading channels do not transmit data but provide light to balance the transmission system loading channels of this kind are not the subject of the present invention which relates to the optimisation of parameters for data channels produced by transponders of the type described above the system shown in fig1 is controlled centrally by a device such as a rack control processor rcp not shown the rcp is able to monitor and assess characteristics of the system and to instruct actions by system components other components in the system notably the transponders may also have a degree of independent logic and some control over their settings in particular the transponders acting as transmitters are able to receive measurements of optical signal quality such as bit error rate ber from far end receivers which receive the channel transmitted by the transponder this information is typically contained in the transmission overhead of a return optical signal transmitted by the receiver the present invention is able to manage and.