A communications network including: an optical transmitter (12; 112) operable to generate a plurality of N available optical signals (S 1... S N) each optical signal having a different wavelength (λ 1 -λ N), wherein said optical transmitter is further operable to wavelength-division-multiplex the optical signals and to transmit the resultant wavelength-division-multiplexed signal; and a plurality of optical receivers (14; 114) connected to the optical transmitter (12; 112) by way of a passive optical network, each optical receiver being operable to receive the wavelength-division-multiplexed optical signals transmitted by said optical transmitter and having wavelength selection means (46, 42) and detection means for processing an optical signal selected from the said plurality by the wavelength selection means, to derive therefrom data carried thereby; the optical transmitter further including transmission control means connected for receiving data to be transmitted to the said optical receivers and operable to distribute, in a given time frame, the received data between said plurality of N available optical signals dynamically in dependence upon the respective amounts of data which it is desired to transmit to the different optical receivers in said time frame, and wherein the wavelength selection means is operable, in dependence upon control information sent from the transmitter to the receiver concerned and designating the optical signals allocated by the transmission control means, to select one (Ssel) of the optical signals of the said plurality of N available optical signals wherein: the control information is sent from the transmitter (12; 112) to the receiver (14; 114) concerned by way of the said passive optical network; the control information relevant to a given optical receiver is carried as overhead information by all of the optical signals; and the control information is divided into fields corresponding respectively to the said plurality of N available optical signals, each field specifying at least one optical receiver that is to select the corresponding optical signal, wherein the fields are ordered differently in the overhead information carried by the different optical signals wherein, for each optical signal, the last field in the overhead information is the field that corresponds to the optical signal concerned. an optical transmitter (12; 112) operable to generate a plurality of N available optical signals (S 1... S N) each optical signal having a different wavelength (λ 1 -λ N), wherein said optical transmitter is further operable to wavelength-division-multiplex the optical signals and to transmit the resultant wavelength-division-multiplexed signal; and a plurality of optical receivers (14; 114) connected to the optical transmitter (12; 112) by way of a passive optical network, each optical receiver being operable to receive the wavelength-division-multiplexed optical signals transmitted by said optical transmitter and having wavelength selection means (46, 42) and detection means for processing an optical signal selected from the said plurality by the wavelength selection means, to derive therefrom data carried thereby; the optical transmitter further including transmission control means connected for receiving data to be transmitted to the said optical receivers and operable to distribute, in a given time frame, the received data between said plurality of N available optical signals dynamically in dependence upon the respective amounts of data which it is desired to transmit to the different optical receivers in said time frame, and wherein the wavelength selection means is operable, in dependence upon control information sent from the transmitter to the receiver concerned and designating the optical signals allocated by the transmission control means, to select one (Ssel) of the optical signals of the said plurality of N available optical signals wherein: the control information is sent from the transmitter (12; 112) to the receiver (14; 114) concerned by way of the said passive optical network; the control information relevant to a given optical receiver is carried as overhead information by all of the optical signals; and the control information is divided into fields corresponding respectively to the said plurality of N available optical signals, each field specifying at least one optical receiver that is to select the corresponding optical signal, wherein the fields are ordered differently in the overhead information carried by the different optical signals wherein, for each optical signal, the last field in the overhead information is the field that corresponds to the optical signal concerned.