What Is the Difference Between 100G QSFP28 and 100G SFP112?

1. 100G QSFP28 vs SFP112: Key Differences

The QSFP28 and SFP112 form factors address different host interface architectures. QSFP28 commonly uses four electrical lanes operating at approximately 25 Gbps each for a 100G aggregate interface. SFP112 uses one electrical lane operating at approximately 112 Gbps to support 100G-class networking.

The table describes common design characteristics. Exact optical features, power consumption, diagnostic capabilities, reach, and interoperability must be verified using the particular module's datasheet and the host platform documentation.

2. QSFP28: Established 100G Optical Connectivity

QSFP28 is widely used for 100G Ethernet because it combines four high-speed electrical lanes in a compact pluggable module. Depending on the optical standard, those lanes can be implemented as parallel optical channels, wavelength-multiplexed channels, or a single-wavelength optical interface with internal signal conversion.

100G QSFP28 SR4

100GBASE-SR4 is a short-reach multimode interface operating at approximately 850 nm. It uses four transmit and four receive optical lanes, with each lane operating at approximately 25 Gbps. A common implementation uses an MPO-12 connector with eight active fibers.

SR4 is appropriate for supported short-reach data center links. The supported distance depends on the installed multimode fiber grade, the complete channel, and the applicable interface specification.

100G QSFP28 LR4

100GBASE-LR4 uses four optical wavelength channels multiplexed over a duplex single-mode fiber connection. It supports transmission up to 10 km under the applicable Ethernet specification. This architecture allows 100G connectivity over two optical fibers instead of the eight active fibers commonly used by SR4.

100G QSFP28 Single-Lambda Optics

Some QSFP28 variants support single-lambda 100G transmission. These modules transmit a 100G optical signal on one wavelength using an appropriate high-speed modulation architecture, rather than using four separate 25G optical wavelengths or four parallel optical lanes.

A single-lambda QSFP28 module still uses a QSFP28 physical and host interface. Its internal electrical-to-optical conversion allows a four-lane electrical host interface to work with a single-wavelength optical transmission design. This architecture differs from SFP112, which is designed around a single high-speed electrical lane at the host interface.

C-LIGHT provides 100G QSFP28 optical transceivers and 100G QSFP28 single-lambda modules for supported Ethernet and optical transport applications. Selection should follow the host interface, required reach, and optical standard.

3. SFP112: Single-Lane Electrical Connectivity for 100G

SFP112 is a compact form factor designed for 100G-class optical transmission using one high-speed electrical lane. The number 112 refers to the approximately 112 Gbps electrical lane rate used to carry a 100G Ethernet-class signal, not a requirement that the Ethernet service itself operate at exactly 112 Gbps.

By using a single high-speed host lane, SFP112 can simplify the electrical lane architecture between the switch ASIC and the module. When supported by the host platform, its smaller form factor can also enable greater front-panel port density than larger modules.

Single-Wavelength Optical Transmission

SFP112 optical implementations are designed around a single-lane electrical interface and can support single-wavelength optical transmission. Examples of published product implementations include 100GBASE-LR1-class and ER1-class modules, with reach determined by the applicable optical specification and product design.

SFP112 is a form factor and electrical-interface design, not a universal optical reach designation. A 100G SFP112 module should be identified by its exact optical standard, wavelength, fiber type, connector, and supported distance. Do not assume all SFP112 modules provide the same reach or optical performance.

4. 100G QSFP28 vs SFP112: Electrical and Optical Lane Architecture

The most important technical distinction is how each form factor connects to the host system. In common QSFP28 designs, the switch provides four electrical lanes at approximately 25 Gbps each. An SFP112 port instead supplies one electrical lane at approximately 112 Gbps.

These distinctions matter when planning switch ASICs, front-panel port layouts, breakout configurations, and optical module upgrades. The form factor determines the mechanical and electrical interface, while the optical standard determines the fiber, wavelength, reach, and transmission characteristics.

A single-lambda QSFP28 module and an SFP112 module may both transmit 100G on one optical wavelength, yet their host electrical interfaces can be different. Their optical similarities do not make the modules physically interchangeable.

5. Port Density, Power Consumption and Cooling

SFP112's smaller form factor can increase the number of 100G ports that fit on a front panel when the platform is designed around SFP112 cages. However, the overall benefit depends on the switch architecture, electrical signal integrity, heat dissipation, power delivery, and port layout.

It is not accurate to claim that every SFP112 module consumes less power than every QSFP28 module. Power depends on the optical reach, transmitter and receiver design, digital signal processing, and host implementation. A fair comparison should use the actual modules under comparable operating conditions.

6. Can SFP112 Replace QSFP28 in an Existing Switch?

Not directly. QSFP28 and SFP112 have different physical form factors and host electrical interfaces. A QSFP28 port cannot be assumed to accept an SFP112 module, and an SFP112 port cannot be assumed to support a QSFP28 module.

Even when the two modules support the same 100G Ethernet service or similar single-wavelength optical specifications, the host hardware must be designed for the relevant form factor and electrical signaling.

Existing fiber can often be retained if it meets the new optical interface's requirements. Nevertheless, upgrading the module form factor normally requires a compatible host port, and any change to the optical standard must be checked against the remote transceiver and installed cabling.

7. Choosing Between 100G QSFP28 and SFP112

The two form factors serve different infrastructure strategies. QSFP28 is a practical option for networks already designed around established 100G ports and supported modules. SFP112 is appropriate when the host platform is designed to use its single-lane electrical interface and compact physical format.

For existing infrastructure, the switch's supported module list should guide the choice. For a new hardware design, port density, electrical SerDes availability, module selection, power, cooling, and intended optical reach should be evaluated together.

8. Common 100G QSFP28 and SFP112 Selection Mistakes

Assuming Both Form Factors Are Physically Interchangeable

QSFP28 and SFP112 use different cages and mechanical interfaces. Equal nominal data rates do not make the modules interchangeable. The switch must have the correct port and electrical interface.

Confusing Electrical Lane Rate with Ethernet Service Rate

SFP112 uses a 112G-class electrical lane to carry a 100G Ethernet service. The electrical signaling rate is not the same as the nominal Ethernet data rate. The host, module, and optical interface must be designed for the correct signaling scheme.

Assuming All QSFP28 Modules Use Four Optical Lanes

QSFP28 is a physical and electrical form factor, not a complete description of the optical architecture. SR4 uses parallel optical lanes, LR4 uses wavelength multiplexing, and single-lambda variants use a different optical transmission design.

Assuming SFP112 Always Consumes Less Power

Smaller size may improve port density, but power consumption depends on the optical design, reach, signal processing, and host implementation. Compare actual module datasheets and thermal limits.

Choosing by Reach Without Checking the Optical Standard

Two modules rated for the same distance may use different wavelengths, fiber types, connectors, or modulation formats. Verify both ends of the link and the installed optical path.

Ignoring Host and Software Qualification

High-speed electrical interface requirements can restrict which switch platforms support SFP112. Verify hardware support, software release, electrical lane capability, FEC behavior, and optical interoperability before ordering.

9. 100G QSFP28 vs SFP112 Verification Checklist

10. Conclusion

100G QSFP28 and 100G SFP112 deliver the same nominal Ethernet rate through different form factors and host electrical interfaces. QSFP28 commonly uses four approximately 25 Gbps electrical lanes and supports a wide range of optical architectures. SFP112 uses a single 112G-class electrical lane and offers a smaller format for 100G-class optical connectivity where the host platform supports it.

QSFP28 remains a practical option for established 100G switch infrastructure, while SFP112 can support higher front-panel port density in appropriately designed systems. However, a QSFP28 module and an SFP112 module are not mechanically interchangeable, and equal optical service rates do not guarantee host compatibility.

For deployment planning, C-LIGHT offers 100G QSFP28 optical transceivers, including single-lambda 100G QSFP28 modules. The appropriate module should be chosen according to the switch interface, optical standard, reach, fiber type, and required link architecture.