What wavelengths are used for transmitting and receiving with the TL-SM321A?

The TL-SM321A uses a transmission wavelength of 1550nm and a receiving wavelength of 1310nm.

What is the maximum transmission distance for the TP-Link TL-SM321A module?

The maximum transmission distance for the TP-Link TL-SM321A module is up to 20 km using 9/125 µm single-mode fiber.

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Single-mode SFP Module, WDM Bi-Directional communication on a single fiber
Work with TL-SM321B as a pair and create a full-duplex gigabit path between your switches, storage devices, and server
Wavelength: Tx 1550nm, Rx 1310nm. Data Rate: 1.25Gbps. Port Type: LC Simplex
Always keep the protective dust plug on the SFP's optical bores until you are ready to make a connection
Compatible with all SFP ports on TP-Link product including JetStream switches, and media converter MC220L
Developed in accordance with the Small Form Pluggable Multi-Source Agreement (SFP-MSA), TL-SM321A uses an integrated LC Bi-Directional optical interface connector, and the data link is up to 20 km for 9/125 µm SMF(Single-Mode Fiber)
TL-SM321A incorporates the Digital Diagnostic Monitoring (DDM) feature which is compatible with SFF-8472. DDM supports real-time monitoring of the transceiver and shows parameters including the transceiver current which transmits/receives optical power and operating temperature