Bi-Directional SFP+ transceivers use a single strand of fiber to transmit and receive data. This is possible by using two different wavelengths. Different combinations of wavelengths are available for BiDirectional communications, most used being 1270/1330nm. The BiDi transceivers are also known as WDM (Wavelength Division Multiplexing). BiDi SFP+s are only available for single-mode 9/125um fiber.