Description
Single-Fibre Gigabit Connectivity — Cut Your Fibre Infrastructure in Half
The TP-Link TL-SM321B-2 is a 1000Base-BX WDM BiDi (Bi-Directional) SFP module that transmits and receives over a single strand of single-mode fibre using an LC simplex connector. By using separate wavelengths for TX (1310nm) and RX (1550nm), it eliminates the need for a second fibre strand per link — halving cabling costs and conduit usage compared to standard dual-fibre SFP modules. Ideal for inter-building links, IP surveillance backbones, and any installation where fibre runs are limited or expensive.
Important: The TL-SM321B-2 (TX 1310nm / RX 1550nm) must be paired with a TL-SM321A-2 module (TX 1550nm / RX 1310nm) at the opposite end of the fibre link. Two TL-SM321B-2 modules on the same link will not establish a connection.
Key Features
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Single-Strand BiDi Operation: Transmits and receives over one fibre strand using WDM technology — TX at 1310nm, RX at 1550nm — reducing fibre infrastructure by 50% per link.
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LC Simplex Connector: Standard LC simplex interface compatible with widely available single-mode fibre patch leads and infrastructure.
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1.25Gbps Gigabit Data Rate: Full 1000Base-BX Gigabit throughput for switch-to-switch and switch-to-media-converter fibre uplinks.
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10km Maximum Range: Supports single-mode fibre runs up to 10km — suitable for inter-building and campus network links.
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Digital Diagnostic Monitoring (DDM): Real-time monitoring of temperature, voltage, TX power, and RX power via the host switch management interface for proactive fault detection.
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Hot-Swappable: Insert or remove the module without powering down the host switch — minimising downtime during installation or replacement.
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SFP-MSA Compliant: Broad compatibility with TP-Link managed switches and media converters that accept standard SFP modules.
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Low Power: 3.3V powered directly from the host device — no external power required.
Common Use Cases
- Inter-building Gigabit fibre links using a single fibre strand per connection
- IP surveillance switch-to-switch fibre uplinks in large CCTV installations
- Conduit-constrained environments where maximising links per fibre count is critical
- Campus and multi-building networks requiring cost-effective single-mode fibre connectivity
- Adding Gigabit fibre uplinks to existing TP-Link managed switches without running additional fibre
Technical Specifications
| Model |
TL-SM321B-2 |
| Module Type |
1000Base-BX WDM BiDi SFP |
| Connector |
LC Simplex |
| TX Wavelength |
1310nm |
| RX Wavelength |
1550nm |
| Data Rate |
1.25Gbps (1000Base-BX) |
| Fibre Type |
9/125μm Single-Mode (SMF) |
| Max Cable Length |
10km |
| DDM Support |
Yes |
| Hot-Swappable |
Yes |
| SFP-MSA Compliant |
Yes |
| Required Pair Module |
TL-SM321A-2 (TX 1550nm / RX 1310nm) |
| Power Supply |
3.3V (from host device) |
| Standard |
IEEE 802.3z, TCP/IP |
| Operating Temperature |
0°C to 70°C |
| Storage Temperature |
-40°C to 85°C |
| Operating Humidity |
10–90% RH (non-condensing) |
| Weight |
60g |
| Certifications |
FCC, CE |
Frequently Asked Questions
What module do I need at the other end of the fibre link?
The TL-SM321B-2 (TX 1310nm / RX 1550nm) must be paired with a TL-SM321A-2 module (TX 1550nm / RX 1310nm) at the opposite end. Using two TL-SM321B-2 modules on the same link will not establish a connection — the wavelengths must be complementary.
Why use a BiDi SFP instead of a standard dual-fibre SFP?
Standard SFP modules use two fibre strands per link (one for TX, one for RX). A BiDi module uses a single strand by splitting TX and RX onto different wavelengths. This halves the fibre count required per link, reducing cabling costs and conduit usage — particularly valuable in installations where fibre runs are expensive or conduit space is limited.
What fibre cable is required?
The TL-SM321B-2 requires 9/125μm single-mode fibre with an LC simplex connector on each end. It is not compatible with multi-mode fibre (OM1, OM2, OM3, OM4) or LC duplex patch leads.
What does Digital Diagnostic Monitoring (DDM) do?
DDM allows the host switch to read real-time performance data from the SFP module — including optical TX and RX power levels, temperature, and supply voltage. This helps network administrators detect degraded modules or fibre links before they cause outages. DDM data is viewable via the switch's management interface.
Is it compatible with third-party switches?
The TL-SM321B-2 is SFP-MSA compliant, providing broad compatibility. TP-Link validates it specifically for use with TP-Link managed switches and media converters. Compatibility with third-party equipment is not guaranteed — some vendors restrict modules to vendor-coded units only.
Can I hot-swap it without rebooting the switch?
Yes. The TL-SM321B-2 is hot-swappable and can be inserted or removed while the host switch is powered on and running, minimising disruption during installation or replacement.
