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TP-Link ISM321B-20 1000Base-BX WDM Bi-Directional Industrial SFP Module

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$ 38.56


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TP-Link ISM321B-20 1000Base-BX WDM Bi-Directional Industrial SFP Module

https://arcip.com.au/web/image/product.template/9303/image_1920?unique=4829781

The TP-Link ISM321B-20 is a 1000Base-BX WDM bi-directional industrial SFP module for extending transfer distance from TP-Link industrial switches over one fibre. It is a single-mode SFP LC transceiver with an LC simplex (LC/UPC) connector, 1.25 Gbps data rate and 20 km maximum cable length on 9/125 um single-mode fibre. It transmits at 1310 nm and receives at 1550 nm, so it is used together with the ISM321A-20 at the other end. It supports DDM, SFP-MSA and hot swap, runs at 3.3 V, is a Class 1 laser product and is rated -40 to 85 degrees C.

$ 38.56 38.56 AUD $ 49.59 incl. GST

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SKU
TL-ISM321B-20
Barcode
1210002602013

The TP-Link ISM321B-20 is a 1000BASE-BX WDM bi-directional industrial SFP module. It sends and receives on a single strand of 9/125 um single-mode fibre up to 20 km, transmitting at 1310 nm and receiving at 1550 nm through an LC simplex connector, at 1.25 Gbps. TP-Link says to use the ISM321A-20 and ISM321B-20 together. DDM, SFP-MSA compatibility, hot-swap and a -40 to 85 degrees C rating are listed.

ISM321B-20 overview

The ISM321B-20 is TP-Link's 1000BASE-BX WDM bi-directional industrial SFP module. TP-Link describes it as an industrial WDM SFP module introduced for extending transfer distance: attached to TP-Link's industrial switches, it can extend the distance to 20 km with one single fibre, and TP-Link notes that users can choose whether and which fibre modules to use according to demand in order to lower cost. It is a single-mode SFP LC transceiver built to IEEE 802.3z, with a 1.25 Gbps data rate over 9/125 um single-mode fibre and a maximum cable length of 20 km.

WDM bi-directional technology is the reason to choose it. Instead of a fibre pair, the ISM321B-20 transmits and receives on a single strand, which TP-Link highlights as cost saving. It transmits at 1310 nm and receives at 1550 nm through an LC simplex port with an LC/UPC connector. Because the wavelengths are reversed at each end, TP-Link's note is to use the ISM321A-20 and ISM321B-20 together: the ISM321A-20 transmits at 1550 nm and receives at 1310 nm. Fit an ISM321B-20 at one end of the fibre and an ISM321A-20 at the other. Two ISM321B-20 modules on the same fibre will not form a link.

Compared with TP-Link's ISM311LS, which is a 1000BASE-LX module using a duplex LC connector and two fibres at 1310 nm, the ISM321B-20 halves the fibre count for each link, which matters where spare cores in an existing cable are limited. Both modules share the same 20 km reach, 1.25 Gbps rate, 3.3 V supply, 0.794 mW (-1 dBm) maximum laser output power and Class 1 laser classification. The ISM321B-20 supports Digital Diagnostic Monitoring (DDM), is compatible with the Small Form Pluggable Multi-Source Agreement (SFP-MSA) and is hot-pluggable, so it can be inserted or replaced with the switch running. Certifications are FCC and CE.

TP-Link rates the ISM321B-20 for industrial operation from -40 to 85 degrees C, with storage across the same range and 5 to 85% RH operating and storage humidity, non-condensing. It measures 56.4 x 13.4 x 10.97 mm (2.22 x 0.53 x 0.43 in) on the datasheet, rounded to 56.4 x 13.4 x 11.0 mm on the product page. TP-Link's AU product page lists the package content as the module (printed there as ISM321LB-20) and an installation guide.

Key features

Single-fibre WDM

Bi-directional on one strand of single-mode fibre, cost saving.

Tx 1310 nm / Rx 1550 nm

Used together with the ISM321A-20 at the far end.

Up to 20 km

Extends transfer distance to 20 km from TP-Link industrial switches.

1000BASE-BX, 1.25 Gbps

IEEE 802.3z Gigabit with an LC simplex (LC/UPC) connector.

DDM

Digital Diagnostic Monitoring supported.

SFP-MSA and hot-swap

SFP-MSA compatible and hot-pluggable.

-40 to 85 degrees C

Industrial operating temperature range.

ISM321B-20 specifications

At a glance

1000BASE-BX
1.25 Gbps
Single fibre WDM
Tx 1310 / Rx 1550 nm
LC simplex
Up to 20 km
DDM
-40 to 85 degrees C
ISM321B-20 full specifications
Transceiver
Standards and ProtocolsIEEE 802.3z,TCP/IP
Wave LengthTx: 1310 nm Rx: 1550 nm
Power Supply3.3V
Fibre Type9/125 µm Single-mode
Max. Cable Length20 km
Data Rate1.25Gbps
ConnectorLC Simplex
Regulatory ComplianceFCC, CE
EnvironmentOperating Temperature: -40˚C~ 85˚C (-40˚C~ 185˚F); Storage Temperature: -40℃~85℃ (-40˚C~ 185˚F); Operating Humidity: 5%~85% non-condensing; Storage Humidity: 5%~85% non-condensing
Hardware Features
DDMYes
SFP-MSAYes
Hot SwappableYes
Dimensions ( W x D x H )2.2 0.5 0.4 in (56.4 13.4 11.0 mm)

Source: TP-Link's published specifications for this model (TP-Link Australia product page and datasheet). Some features run only in Standalone Mode or only under an Omada Controller; throughput figures are TP-Link's lab results. TP-Link may change specifications without notice.

What's in the box

  • ISM321LB-20
  • Installation Guide

Source: TP-Link's published package contents.

Who the ISM321B-20 is for

Single-core fibre links

  • One strand per link
  • Up to 20 km single-mode
  • Pairs with ISM321A-20

Harsh environments

  • -40 to 85 degrees C operation
  • 5 to 85% RH humidity
  • Industrial SFP design

Monitored links

  • DDM diagnostics
  • Hot-swappable
  • SFP-MSA compatible

ISM321B-20 compared

The ISM321B-20 is one half of TP-Link's single-fibre industrial SFP pair; the ISM311LS is the two-fibre 1000BASE-LX alternative. All three figures below are from TP-Link's industrial SFP datasheets.

SpecificationISM321B-20ISM321A-20ISM311LS
Type1000BASE-BX WDM1000BASE-BX WDM1000BASE-LX
WavelengthTx 1310 nm, Rx 1550 nmTx 1550 nm, Rx 1310 nm1310 nm
ConnectorLC simplexLC simplexLC duplex
Fibres per linkOneOneTwo
Max cable length20 km20 km20 km
Data rate1.25 Gbps1.25 Gbps1.25 Gbps
Operating temperature-40 to 85 degrees C-40 to 85 degrees C-40 to 85 degrees C

Source: TP-Link Australia product pages for each model.

Buy the ISM321B-20 from ARC IP Networks

ARC IP Networks supplies TP-Link Omada products from Australian stock at competitive prices, with the full manufacturer's warranty, Australia-wide delivery and trade pricing for installers and MSPs.

  • New TP-Link Omada product from Australian stock.
  • Manufacturer warranty: the full TP-Link manufacturer's warranty for this model.
  • Australia-wide delivery to every state and territory.
  • Trade and project pricing: call 1300 100 440 or email info@arcip.com.au.

Frequently asked questions

Straight answers about the ISM321B-20 from the ARC IP Networks team.

Last reviewed October 2026.

A 1000BASE-BX WDM bi-directional industrial SFP module from TP-Link that carries Gigabit over a single strand of single-mode fibre.

An ISM321A-20. TP-Link says to use the ISM321A-20 and ISM321B-20 together, because their transmit and receive wavelengths are reversed.

No. Both would transmit at 1310 nm and receive at 1550 nm. Pair it with an ISM321A-20.

Up to 20 km over 9/125 um single-mode fibre.

An LC simplex port with an LC/UPC connector.

The ISM311LS is 1000BASE-LX on a duplex LC connector using two fibres at 1310 nm. The ISM321B-20 uses one fibre with WDM (Tx 1310 nm, Rx 1550 nm).

Yes. DDM, SFP-MSA compatibility and hot swap are listed.

-40 to 85 degrees C operating and storage.

The module and an installation guide.

Need more than one ISM321B-20 for a single-fibre industrial link?

Ask ARC IP Networks for volume and project pricing on TP-Link Omada products.

Brand TP-Link

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ARC IP Networks Pickup Address: 6 George Street, Blackburn, VIC 3130


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ARC IP Networks ships to New Zealand. Please note:


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Please note: Refunds for lost, missing, or delayed orders cannot be processed until shipping partner investigations are complete. This does not affect your rights under the Australian Consumer Law, and refunds or replacements will be provided where required once loss or damage is confirmed.

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ARC IP Networks complies with the Australian Consumer Law (ACL).

If a product is faulty, damaged, not of acceptable quality, or does not perform as advertised, you are entitled to a repair, replacement, or refund in accordance with ACL.

Manufacturer Warranty Returns

For faults developing after 14 days within the warranty period:

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  • Where required, a manufacturer RMA may be arranged
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Dead on Arrival (DOA)

Products that arrive faulty or damaged must be reported within 14 days of delivery.

ARC IP Networks will arrange assessment, replacement, or refund as appropriate.

Change of Mind & Non-Faulty Returns

Change-of-mind returns must be requested within 14 days of delivery. For change-of-mind returns, the product must be unused, unopened, in its original packaging, and returned with all accessories and documentation. These conditions apply only to change-of-mind returns and do not limit or exclude your rights under the Australian Consumer Law. Some products are not eligible for change-of-mind returns, including:

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Important

This does not affect your rights under Australian Consumer Law.

If a product is faulty, not of acceptable quality, or does not meet advertised specifications, it remains eligible for return regardless of category.

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  • Approved refunds are processed within 7 business days of receiving returned goods
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  • Store credit may be offered only with customer consent

Handling fees and non-returnable service charges may not be refundable where permitted by law.


Restocking Fees

For approved change-of-mind or non-faulty returns, a 15% restocking fee applies.

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  • Restocking fees do not apply to returns made under the Australian Consumer Law, including faulty, damaged, or misrepresented goods.

Return Shipping Costs

  • Change-of-mind returns: The customer is responsible for return shipping costs.
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Non-Warranty Repairs

For issues not covered by warranty:

  • ARC IP Networks will provide a quote before proceeding
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Return Methods

Returns may be made:

  • In-store at ARC IP Networks – 6 George Street, Blackburn VIC 3130
  • Or by shipment as instructed by our support team

Proof of purchase is required for all returns.

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