Transceivers Since communication over a single wavelength is one-way (simplex communication), and most practical communication systems require two-way (duplex communication) communication, two wavelengths will be required if on the same fiber; if separate fibers are used in a so-called fiber pair, then the same wavelength is normally used and it is not WDM. As a result, at each end both a transmitter and a receiver will be required. A combination of a transmitter and a receiver is called a transceiver; it conv.