The TP-Link ISM321B-20 is a SFP module of the BX WDM Bi-Directional type, designed for reliable long-distance optical connections. It supports transmission speeds of up to 1.25 Gbps over single-mode fiber (SMF), with a coverage distance of up to 20 km. It features an LC port, operates within a temperature range from -40°C to +85°C, and is hot-pluggable for easy installation. Ideal for use in industrial networks or applications requiring stable and efficient optical communication.