Tp Link TP-LINK TL-SM321B - 1000Base-BX WDM Bi-Directional Gigabit Single-Mode SFP Module - Plug and Play - LC Simplex Interface - Hot Pluggable - Up to 20km Distance - Support SFP-MSA & DDM

What This Product DoesTP-Links TL-SM321B adopts the latest standard 1000Base-BX, transmitting over one single-mode fiber with one different wavelength going in each direction. Paired with TL-SM321A, You can extend the network distance up to 20Km with TP-Links routers, switches and media converters for reliable high-speed long-distance communication.