Abstract: A method to transmit and receive significantly larger serial data stream to achieve conformance to the signal interface constraints of a pre-installed transmission system thus minimising bit error rate for both the large serial data streams and the pre-installed streams the method includes the steps of de-serialising an initial incoming signal into M data streams, wherein M>2, each M data stream having a data rate of D/M Gbps, partially serialising and encoding M data streams into K symbol groups where K is an integer greater than or equal to 1, each K symbol group characterized by N concurrent data bits of the N data streams, wherein each N data stream has a data rate of D/(N·K), processing each of the K symbol groups to provide one modulated output signal the K modulated output signals then being transmitted via K channels of an existing wavelength division multiplexing system, so as to enable transmission of significantly large data streams over pre-installed transmission networks.