A powerful aspect of fibre communication systems is that signals of many different wavelengths can be sent along a single optical fibre cable simultaneously, without signal interference. The technology that combines a number of wavelengths into the same fibre cable is known as wavelength-division multiplexing (WDM). Similarly, separating and distributing the signals is known as de-multiplexing. Multiplexing and de-multiplexing techniques are used in fibre communication systems to increase link capacity, flexibility, and speed, and to reduce cost.