TP-LINK SM321B-VER4 | 1000Base-BX WDM Bi-Directional SFP Module (1310nm TX / 1550nm RX) - 20KM
SKU: SM321B-VER4Networking › Network Accessories
฿467
Price includes 7% VATPrice updated November 2, 2026
In stock6 units1 year manufacturer's warranty
For orders placed before 12:00 on a business day; weekends excluded
GenuineFree delivery from ฿5,000Tax invoice
Dual-fiber WDM SFP module for Single-Mode fiber optic networks, supporting up to 20 km transmission distance using a single fiber in both directions, with DDM and Hot Swappable features
Key features
- Supports up to 20 km transmission distance over Single-Mode fiber
- Uses a single fiber in both directions via WDM Bi-Directional technology
- Supports DDM (Digital Diagnostic Monitoring) for real-time status monitoring
- Designed for Hot Swappable operation without powering down the device
- Compliant with SFP-MSA and IEEE 802.3z standards
Product description
The TP-LINK SM321B-VER4 is a WDM Bi-Directional network interface module compliant with the 1000Base-BX standard, enabling bidirectional data transmission over a single Single-Mode fiber optic cable by using different wavelengths for transmission (TX: 1310 nm) and reception (RX: 1550 nm). This effectively reduces fiber cable usage and lowers installation costs for long-distance networks. It supports signal transmission up to 20 km and is compatible with TP-Link switches, routers, and media converters. To operate fully, it must be used in pair with the TL-SM321A module. The module supports SFP-MSA and Hot Swappable functionality, along with DDM (Digital Diagnostic Monitoring) for real-time monitoring of operational status such as transmit/receive power, optical signal strength, and internal module temperature, enabling precise network health tracking by system administrators.
More features
- Uses TX:1310 nm / RX:1550 nm wavelengths for bidirectional data transmission
- Compatible with TP-Link switches/routers and media converters
- Compact size: 55.4 x 13.7 x 12.9 mm
- Operates at 0–70 °C and can be stored at -40–85 °C
- Supports operation in environments with 10–90% RH humidity (non-condensing)
Pros and limitations
Pros
- Transmits signals up to 20 kilometers over a single fiber.
- Significantly reduces fiber cabling costs.
- Supports DDM for real-time status monitoring.
- Hot-swappable module replacement without system shutdown.
- Complies with SFP-MSA standards and works immediately with TP-Link devices.
Limitations
- Must be used with TL-SM321A module to ensure full system functionality.
- Not supported in environments with humidity exceeding 90% or condensation.
Who it is for
Ideal for network administrators who need to extend Gigabit network connectivity over single-mode fiber, especially in large-scale projects such as multi-floor office buildings, factories, or inter-station networks.
Connectivity
SFP
Specifications (24)
- Standard
- IEEE 802.3z, TCP/IP
- Data Rate
- 1.25 Gbps
- Port Type
- LC Simplex
- Cable Type
- Single-Mode Fiber
- Fiber Type
- 9/125 μm Single-Mode
- Application
- Gigabit Ethernet Media Converter, Switch, Router, Server
- DDM Support
- Yes
- Form Factor
- SFP
- Power Supply
- 3.3 V
- Compatibility
- Works with TL-SM321A as a pair
- Hot Swappable
- Yes
- Wave Length RX
- 1550 nm
- Wave Length TX
- 1310 nm
- Max Cable Length
- 20 KM
- Storage Humidity
- 5–90% RH, Non-Condensing
- Safety & Emission
- FCC, CE
- Operating Humidity
- 10–90% RH, Non-Condensing
- SFP-MSA Compliance
- Yes
- Storage Temperature
- -40–85 °C (-40–185 °F)
- Operating Temperature
- 0–70 °C (32–158 °F)
- Transmission Distance
- Up to 20 KM
- Dimensions (W x D x H)
- 2.1×0.5×0.5 in (55.4×13.7×12.9 mm)
- Digital Diagnostic Monitoring
- Yes (DDM)
- Wavelength Division Multiplexing
- Bi-Directional WDM
Datasheets and manuals straight from the manufacturer — select a document to open or download it.
13 questions
Frequently asked questions about this product
Compiled from manufacturer information
Which module must be used with the SM321B-VER4 for it to work?
This module must be used in pair with the TL-SM321A module to enable full WDM Bi-Directional functionality, as both modules transmit and receive signals over the same fiber using different wavelengths
Can this module be used with non-TP-Link switches?
Yes, it can be used with non-TP-Link switches, provided the switch supports SFP and has a dedicated port for WDM Bi-Directional modules. However, compatibility with other manufacturers should be verified for assurance
Can the module's operational status be monitored?
Yes, this module supports DDM (Digital Diagnostic Monitoring), which allows real-time monitoring of values such as transmit/receive power, optical signal level, internal module temperature, and usage statistics
What is the maximum transmission distance?
This module supports a maximum transmission distance of 20 kilometers using 9/125 μm Single-Mode fiber optic cable
Can this module be replaced while the system is running?
Yes, this module supports Hot Swappable operation, meaning it can be removed and installed without powering down the device or interrupting system operation
What types of fiber optic cables can it be used with?
It is compatible only with 9/125 μm Single-Mode fiber optic cables and does not support Multi-Mode cables
What is the operating temperature range?
This module operates within a temperature range of 0–70 °C and can be stored at -40–85 °C, making it suitable for general environments and some areas with high or low temperatures.
Is there a warranty?
Yes, this module comes with a 1-year warranty covering defects in materials and parts.
Is it in stock?
The TP-LINK SM321B-VER4 | 1000Base-BX WDM Bi-Directional SFP Module (1310nm TX / 1550nm RX) - 20KM is in stock and ready to ship. Orders placed before 12:00 on a business day are delivered within 1–3 business days (Bangkok and vicinity) or 2–5 business days (other provinces). Order online at store.gist.co.th or contact our sales team at 092-251-4017.
How much does it cost?
The price is ฿467 (including 7% VAT). It is in stock and ready to ship. Business customers can request a quotation at sales@gist.co.th.
How long is the warranty?
Warranty period: 1 year (manufacturer's terms). To make a warranty claim, call 092-251-4017 or 065-523-5262, or email sales@gist.co.th (Mon–Fri 9:00–18:00), then send the product with your order number to our head office, or bring it to the head office in person.
How long does delivery take?
Orders placed before 12:00 on a business day are delivered within 1–3 business days (Bangkok and vicinity) or 2–5 business days (other provinces). Free delivery on orders of ฿5,000 or more (a ฿150 delivery fee applies below this amount).
Is it genuine?
Genuine products sourced from distributors in Thailand, covered by the manufacturer's warranty. Full tax invoices are available.
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Genuine products
Sourced from distributors in Thailand and covered by the manufacturer's warranty
Warranty period
1 year
Covered by the manufacturer's warranty; you can make claims through GIST
Claims through GIST
Ship the product to our head office or bring it in person
Warranty conditions
- A receipt or other proof of purchase is required
- The product must not have been modified or altered
- Damage caused by misuse is not covered by the warranty
- To make a warranty claim, call 092-251-4017 or 065-523-5262, or email sales@gist.co.th (Mon–Fri 9:00–18:00), then send the product with your order number to our head office, or bring it to the head office in person.Head office: 554 Sky Nine Center, Floor 12A, Room 554/62, Asok-Din Daeng Road, Din Daeng Subdistrict, Din Daeng District, Bangkok 10400
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Price
฿467