Frequently Asked Questions About 100GbE QSFP28 Transceivers

01, Sep. 2025

 

Frequently Asked Questions About 100GbE QSFP28 Transceivers

1.What is QSFP28 transceiver?

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A: The QSFP28 transceiver is a high-rate optical module for 100G Ethernet. It employs QSFP form factor. The QSFP28 transceiver has four signal channels, each with a maximum transmission rate of 28 Gbps. It is available in a variety of fiber link distances. The QSFP28 transceiver is used in the InfiniBand system, called EDR. EDR QSFP28 transceiver has stricter performance requirements.

2.What are the main applications of the QSFP28 transceiver?

A: The QSFP28 transceiver is mainly employed in the data center for 100G connections of core switches and core routers.

3.What are the main types of 100G transceiver?

A: There are QSFP28 transceivers, CFP4 transceivers, CFP2 transceivers, CFP transceivers.
Currently, the main 100G transceiver is the QSFP28 transceiver.

4.Is it possible to insert QSFP+ transceivers to QSFP28 fiber ports for use?

A: No. Different communication protocols were complied for different data rates.

5.What are the differences between SFP28 and QSFP28 transceivers?

A: They are different on data rate, form factor and working principle.
The transmission data rate of SFP28 transceiver is 25 Gbps, that of QSFP28 is 100 Gbps;
The form factor of SFP28 is SFP, that of QSFP28 is QSFP;
The SFP28 transceiver uses single-channel transmission and has a transmission rate of 25 Gbps;
The QSFP28 transceiver uses four channels of transmission with a transmission rate of 25 Gbps per channel.

Transceiver Type

SFP28

QSFP28

Form Factor

SFP

QSFP

Data Rate

25Gbps

100Gbps

Working Principle

Single channel

Quad channel

6.What are the specifications of the QSFP28 transceiver?

A: Check the chart below:

QSFP28 transceivers

SR4

LR4

PSM4

 CWDM4

Fiber Type

MMF (multi mode)

SMF (single mode)

SMF (single mode)

SMF (single mode)

Wavelength

850nm

nm, nm,
nm, nm

nm

nm, nm,
nm, nm

Link Distance

70 meters (OM3);
100 meters (OM4)

10 km

500 meters

2 km

Fiber Cores

8 core

2 core

8 core

2 core

Interface

MTP/MPO

LC

MTP/MPO

LC

7.Can the QSFP28 transceiver work with CFP transceiver?

A: Yes! Both are products of the Ethernet protocol and can interoperate with each other.

8.What is the operating temperature range of QSFP28 transceiver?

A: The standard operating temperature range of QSFP28 transceiver commercial version is 0°C to 70°C; that of industrial version is -45°C to +85°C;
Commercial version products are generally applied. There are also some data centers that use products with operating temperatures ranging from 20°C to 50°C to reduce costs.

9.What are the differences between transceivers QSFP28 CWDM4 and QSFP28 LR4?

A: The wavelength is different.
The operating wavelength of the QSFP28 LR4 transceiver is nm, nm, nm, nm, and the wavelength interval is 5nm;
The operating wavelength of the QSFP28 CWDM4 transceiver is nm, nm, nm, nm, wavelength interval 20nm;
The QSFP28 LR4 transceiver and the QSFP28 CWDM4 transceiver have different working wavelengths and cannot communicate with each other.

10.What are the differences between transceivers QSFP28 SR4 and QSFP28 LR4?

A: They are different in transmission distance, fiber core, interface type and price.

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The QSFP28 SR4 transceiver supports link lengths of up to 70m over OM3 and up to 100m over OM4 multimode fiber with MPO connectors.
The QSFP28 LR4 transceiver supports link lengths of up to 10km over a standard pair of G.652 single-mode fiber with duplex LC connectors.

The QSFP28 SR4 transceiver requires 8-core fiber, while the QSFP28 LR4 optical module requires a 2-core fiber.

The interface of the QSFP28 SR4 transceiver is MTP/MPO interface, while that of the QSFP28 LR4 transceiver is the LC interface.

Check the chart below for specifications:

QSFP28 transceiver

SR4

LR4

Fiber Type

MMF (multi mode)

SMF (single mode)

Wavelength

850nm

nm, nm,
nm, nm

Link Distance

70 meters(OM3)
100 meters (OM4)

10 km

Fiber Cores

8 cores

2 cores

Interface

MTP/MPO

LC

11.What is FEC (Forward Error Correction)? Does the QSFP+ module need to use the FEC function?

A: QSFP+ transceiver does not require FEC function.

FEC (Forward Error Correction) is a method to increase the credibility of data communication.
In a one-way transmission channel, once an error is found, the receiver will not have the right to request a transmission. FEC corrects errors during signal transmission. When an error occurs in the transmission, the receiver is allowed to reconstruct the data.
In the design of transceivers, the cost of FEC function is relatively high and is generally rarely used.

12.What is QSFP BIDI transceiver?

A: The QSFP Bidi transceiver refers to the QSFP+ single-fiber bidirectional (Bidi) optical module applied to 40G Ethernet. The QSFP Bidi transceiver is mainly used by Cisco, and there are fewer suppliers currently acquiring the technology.

The interface of the QSFP Bidi transceiver is a dual LC interface.
The transmission rate of the QSFP Bidi transceiver is 40 Gbps.
The operating wavelength of the QSFP Bidi transceiver is 850nm/890nm.
The QSFP Bidi transceiver is used on multimode fiber, supporting link distance is up to 100 meters over OM3 and up to 150 meters over OM4.
The QSFP Bidi transceiver has two signal channels, each with a transmission rate of 20 Gbps. Each channel can perform both transmit and receive operations on two wavelengths simultaneously. In this way, the access layer can be accelerated from 10 Gbps to 40 Gbps through two multimode LC fibers.

Specifications are as follows:

QSFP28 100G: Interoperability with 40G, 25G, & 10G - ProLabs

A 100G QSFP28 optic fiber module is a hot-pluggable transceiver module with a data rate of 100G. Each lane can carry up to 28Gbps of data, as indicated by the "28." The QSFP28 has four electrical lanes that can be configured as 4x10GbE or 4x25GbE depending on the transceivers used. The main types of QSFP28 optics consist of 100G QSFP28 SR4, QSFP28 PSM4, 100G QSFP28 LR4, and QSFP28 CWDM4, as seen below.

Optical Module Type

Interface

Fiber Type

Transmission Distance

100GBASE-SR4 QSFP28

MTP/MPO 12

Multimode OM4

100m

100GBASE-PSM4 QSFP28

MTP/MPO 12

Banded single mode

500m

100GBASE-LR4 QSFP28

LC Duplex

Single mode

10km

100GBASE-CWDM4 QSFP28

LC Duplex

Single mode

2km

How to Run 40Gbps on QSFP28 100G Port

100G QSFP28 interface should accelerate to the comparable 40G and function with 40G QSFP+ optics if the opposing equipment uses 40G service speed.

Hardware Support

  • QSFP+ 40G transceiver with MTP/MPO connector; MTP/MPO 12 fibers trunk cable
  • 40G QSFP+ to QSFP+ DAC Cable
  • 40G QSFP+ to QSFP+ AOC Cable

When using QSFP transceivers in QSFP28 ports, keep in mind that you have both single-mode and multimode (SR/LR) optical transceivers and twinax/AOC options that are available.

How to Realize 4x 10GbE Mode on QSFP28 100G Port

When the new switch only has 100G ports on one side and the existing devices only have SFP+ 10G ports on the other, it is probable to use the QSFP28 port in 4x 10GbE mode using a QSFP+ 40G optical transceiver.

Hardware Support

  • QSFP+ 40G transceiver with MTP/MPO connector; SFP+ 10G transceivers with LC connector; MTP/MPO-LC harness cable
  • 40G QSFP+ to 4x10G SFP+ Passive DAC Breakout Cable
  • 40G QSFP+ to 4x10G SFP+ Breakout AOC Cable

How to Realize 4x 25GbE Mode on QSFP28 100G Port

To achieve 100G transmission, four SFP28 can fully utilize the electrical lanes of the QSFP28.

Hardware Support

  • QSFP28 100G transceiver with MTP/MPO connector; SFP28 25G transceivers with LC connector; MTP/MPO-LC harness cable
  • 100G QSFP28 to 4x 25G SFP28 Passive DAC Breakout Cable
  • 100G QSFP28 to 4x 25G SFP28 Breakout AOC Cable

How to Restore QSFP28 100G Ports to Default Configuration

The following commands allow you to return the QSFP28 100G port to its default mode.

Configure the port to default mode

  • (config)# interface Ethernet1/1-4
  • (config-if-Et1/1)# no speed

Restore factory settings

  • Switch// delete Startup-config

With the necessary hardware, the switch's QSFP28 100G port can operate in 40GbE, 4x 25GbE, and 4x 10GbE modes in addition to 100G mode. Moreover, it is equally important to understand how to return the switch port to its default mode.

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Disclaimer: The information available may differ from device to device. For any further help, feel free to reach out to our support team.

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