The TL-SM321A from TP-LINK utilizes the latest 1000Base-BX standard for transmission over a single strand of fiber optic cable with different wavelengths for each direction. You can extend the network range by 10 km using TP-LINK routers, switches, and media converters to achieve high speed and stability. It is a bidirectional WDM SFP module that uses a single fiber, thus saving costs.