TP-Link Omada Gigabit WDM Bi-Directional SFP Module 20 km, 1310 nm TX / 1550 nm RX

TP-Link Omada 1000Base-BX WDM Bi-Directional SFP Module (TL-SM321B) - 5 Years Local Warranty

The TL-SM321B is the "B" half of TP-Link's 20 km bi-directional Gigabit pair. It transmits on 1310 nm and receives on 1550 nm — the mirror image of the TL-SM321A — so that the two together carry a full-duplex Gigabit link over a single strand of single-mode fibre rather than the usual two.

A Full Gigabit Link on One Strand

Standard duplex optics consume two fibre strands per link. WDM bi-directional modules put both directions on one strand, separating them by wavelength at each end. Where strands are leased and billed individually, or where a riser bundle is already fully patched, that halving is often what makes a link viable at all. The TL-SM321B uses an LC simplex connector, which is what the single-strand arrangement requires.

Twenty Kilometres of Single-Mode Reach

TP-Link publishes a maximum cable length of 20 km over 9/125 µm single-mode fibre, at the full 1.25 Gbps data rate under IEEE 802.3z. That covers most Singapore inter-site distances in one hop. For shorter runs there is a separate 2 km family — the TL-SM321A-2 and TL-SM321B-2 — with the same wavelength arrangement but a different optical budget. The two families should not be mixed on one link.

Always Ordered With a TL-SM321A

The ends of a WDM link are not interchangeable. This module transmits 1310 nm and receives 1550 nm; the TL-SM321A does the reverse. A working link needs exactly one of each, so the quantity to plan against is the number of links, not the number of ports. Two B modules facing each other will never establish a link, and no amount of switch configuration will change that — the wavelengths simply do not meet.

DDM, MSA Compliance and Hot Swapping

Digital Diagnostic Monitoring lets the host switch read the module's live optical transmit and receive power, temperature and supply voltage, so a degrading long-haul strand is visible as a trend rather than a surprise. The module is SFP-MSA compliant and hot-swappable, seating in any standard Gigabit SFP cage and replaceable without powering the switch down. It draws 3.3 V from the host and measures 55.4 x 14.6 x 12.9 mm.

Ideal For

Singapore businesses running Gigabit links over leased or scarce single-mode fibre, and IT teams connecting remote sites, blocks or cabinets where only one strand is available. Supplied by SourceIT with local Singapore warranty, GST invoice and project pricing on request.