The optical mux/demux modules are passive devices that optically multiplex and demultiplex a specific band of ITU wavelengths. In the transmit direction, the optical mux/demux modules multiplex signals transmitted by the transponder modules over optical cross connections and provide the interfaces to connect the multiplexed signal to the DWDM trunk side. In the receive direction, the optical mux/demux modules demultiplex the signals from the trunk side before passing them over optical cross connections to the transponder modules.