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Small metallic SFP transceiver module with LC simplex port and dust plug

TP-Link

TP-Link TL-SM321B 1000Base-BX BiDi SFP Transceiver 20km

SKU CH-ZKM9-MT5T4 MPN TL-SM321B

A single-mode SFP transceiver enables bidirectional gigabit links over one fiber strand up to 20 km

  • Port countLC
  • Product typeTransceiver
  • Supported standardsIEEE 802.3z
  • Optical wavelengthTX: 1310 nm / RX: 1550 nm
  • Fiber modeMulti-mode Optical Fiber
  • Maximum range20 KM
  • Bidirectional WDM link on a single fiber strand
  • Reaches 20 km over 9/125 µm single-mode fiber
  • Hot-swappable SFP module compliant with SFP-MSA standard
  • Real-time health data via Digital Diagnostic Monitoring
  • Paired with TL-SM321A for full-duplex gigabit connectivity

Target and purpose

The TP-Link TL-SM321B is a 1000Base-BX WDM bi-directional SFP transceiver built for network engineers who need to link switches, storage or servers over a single strand of single-mode fibre. It transmits at 1310 nm and receives at 1550 nm, delivering a 1.25 Gbps full-duplex path up to 20 km. The module complies with IEEE 802.3z and the SFP-MSA, and it is hot-pluggable into any compatible SFP port.

Capacity and headroom

The transceiver operates reliably from 0 °C to 70 °C and tolerates storage from -40 °C to 85 °C, with humidity rated up to 90 % non-condensing. Digital Diagnostic Monitoring to SFF-8472 gives real-time visibility of optical power, current and temperature. Maximum reach is 20 km on 9/125 µm single-mode fibre; beyond that distance the link budget is exhausted and a different module or intermediate amplification would be required.

Deciding specification

This module uses an LC simplex connector and the 1310 nm TX / 1550 nm RX wavelength pair, so it must be paired with the matching TL-SM321A unit (TX 1550 nm / RX 1310 nm) to complete a bi-directional link. If your patch panel or existing fibre plant uses duplex LC connectors or a different wavelength plan, this transceiver will not integrate without redesigning the cabling.

How it compares

Measured against everything we stock in SFP & SFP+ Transceiver Modules, at today’s prices. Recalculated every night.

Price $42.99
Cheaper than about 78% of the 1,471 comparable items (median $138.99).

Specifications

Product
Brand nameTP-Link
Model nameTL-SM321B
Product typeTransceiver
Performance
Transfer speed1.25 Gbit/s
Connectivity
Supported standardsIEEE 802.3z
Optical wavelengthTX: 1310 nm / RX: 1550 nm
Fiber modeMulti-mode Optical Fiber
Maximum range20 KM
Ports & slots
Port countLC
Size & build
Shipping weight0.23 kg
Package size229 × 152 × 51 mm
Environment & compliance
Temperature rangeOperating Temperature: 0–70 °C (32–158 °F)
Storage Temperature: -40–85 °C (-40–185 °F)
Humidity rangeOperating Humidity: 10–90% RH, Non-Condensing
Storage Humidity: 5–90% RH, Non-Condensing

Questions about this item

Will the TL-SM321B work in a legacy switch that only supports the original SFP MSA without DDM?

Yes, the module complies with SFP-MSA so it fits mechanically and electrically; DDM is optional and simply ignored by older hardware.

How can I verify the TL-SM321B is operating correctly once installed?

Check the switch port LED for link-up and use the management interface to read DDM values — optical TX/RX power, temperature and supply current — which are reported per SFF-8472.

Does the package include the matching TL-SM321A module and a single-mode patch cord?

No, only the TL-SM321B transceiver with its protective dust plug is supplied; the TL-SM321A counterpart and a 9/125 µm LC simplex patch cord must be purchased separately.

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