Abstract: An electro-optic interface structure for use in a multi-protocol OEO WDM network, the interface structure comprising a rate multiplying encoding unit for applying a rate multiplying line code to an electrical transmit data signal prior to conversion of the electrical transmit data signal into an optical WDM channel signal, and a rate dividing decoding unit for applying a corresponding rate dividing line code to an electrical receive data signal converted from a received optical WDM channel signal, wherein the encoding unit is arranged such that, in use, the same rate multiplying line code can be applied to electrical transmit data signals of different protocols, and wherein the decoding unit is arranged such that, in use, the application of the same corresponding rate dividing line code can create electrical signals of different protocols.