TP-LINK´s TL-SM321B adopts the latest standard 1000Base-BX, transmission over a single strand of fiber, with one different wavelength going in each direction. You can extend the network distance up to 10Km with TP-LINK´s Routers, Switches, Media Converters to provide high speed and stability. - WDM Bi-Directional SFP Module - Supports WDM Bi-Directional technology, using a single strand of fiber, cost saving