SFP fiber optic transceiver TP-LINK ISM321A-20 WDM Bi-Directional 20 km single-mode LC 1.25Gbps

TP-LINK ISM321A-20 is an SFP fiber optic transceiver module for single-mode LC (UPC) connections. It supports bi-directional WDM transmission over a single fiber at 1.25 Gbps (IEEE 802.3z) and is hot-swappable, designed for 9/125 µm fiber with a reach up to 20 km. The module operates from a 3.3 V input and is specified for wide temperature and humidity ranges suited to network equipment such as switches and routers.

Advantages

The module offers hot-swap capability for easy field replacement without powering down equipment, compatibility with single-mode 9/125 µm fiber, and an LC (UPC) fiber connector for common enterprise cabling. It supports a maximum link distance of 20 km at a data rate of 1.25 Gbps and meets IEEE 802.3z standards. Compact dimensions and low-profile design allow installation in standard SFP ports.

Suitable for

• Extending optical links between switches and routers over single-mode fiber
• Point-to-point fiber connections up to 20 km
• Upgrading network uplinks to 1.25 Gbps using SFP slots

Key specifications

• Form factor: SFP fiber optic transceiver
• Data rate: 1.25 Gbps (1250 Mbit/s)
• Transmission type: Bi-directional WDM over single-mode fiber
• Supported fiber: Single-mode, 9/125 µm
• Connector: LC (UPC)
• Maximum transfer distance: 20,000 m
• Interface: 1.25 Gigabit Ethernet (IEEE 802.3z)
• Input voltage: 3.3 V
• Operating temperature range: -40 to 85 °C
• Operating relative humidity: 5–85%
• Dimensions (W×D×H): 56.4 × 13.4 × 11 mm

How to use

Insert the SFP transceiver into a compatible SFP port on a switch or router until it latches. Connect the LC fiber patch cord to the LC (UPC) connector on the module, ensuring correct alignment for bi-directional WDM pairs. The module is hot-swappable, so replacement or installation can be performed without powering down the host device. Verify link status in the network device management interface and confirm transceiver compatibility with the host equipment.

Recommendations

Use single-mode 9/125 µm fiber with LC (UPC) connectors and maintain proper fiber cleanliness. Avoid exceeding the specified temperature and humidity ranges and follow manufacturer guidelines for optical budget and link planning to ensure reliable 20 km links.