The TP-Link ISM321A-20 is an SFP module with industrial specifications, designed for single-mode optical connection (SMF) and WDM bi-directional technology — allowing transmission speeds of up to 1.25 Gbps and long-distance coverage of up to 20 km, through a single fiber optic cable. It features an LC/UPC port, compatibility with SFP-MSA standards, "hot-plug" operation for easy installation, and support for digital monitoring (DDM). It is suitable for use in harsh conditions (operating temperature from -40 °C to +85 °C) and provides a reliable solution for network environments with long distances and demanding requirements.