SFP vs SFP+ vs QSFP28: Transceiver Module Comparison Guide

Quick Answer

SFP runs at 1 Gbps, SFP+ at 10 Gbps, and QSFP28 at 100 Gbps (4×25G). SFP+ modules fit in SFP+ and SFP28 cages (backward compatible). QSFP28 modules fit in QSFP28 and QSFP-DD cages. Choose based on required port speed, fiber reach, and switch compatibility. See the full comparison table below.

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Selecting the right transceiver module is one of the most consequential decisions in network design. The form factor you choose determines port density, bandwidth capacity, power consumption, and cabling infrastructure for years to come.

This guide compares the three most widely deployed transceiver form factors — SFP, SFP+, and QSFP28 — and helps you decide which is right for your application. For a broader introduction to how transceivers work, see our Optical Transceiver Guide.

Quick Comparison

What Is an SFP Module?

The Small Form-factor Pluggable (SFP) transceiver is the original hot-swappable module that replaced the larger GBIC form factor in the early 2000s. SFP modules support data rates up to 1 Gbps and use an LC duplex fiber interface.

Key characteristics:

• Data rate: 100 Mbps to 1 Gbps (Fast Ethernet and Gigabit Ethernet)
• Form factor: Compact, approximately 8.5mm × 13.4mm × 56.5mm
• Hot-swappable: Insert or remove without powering down the host device
• Digital diagnostics: DOM/DDM support for real-time monitoring of TX power, RX power, temperature, voltage, and bias current
• Electrical interface: Single-lane serial, defined by SFF-8472

SFP modules are still widely deployed in access layer switches, enterprise edge routers, and legacy infrastructure. They are available in copper (RJ45) variants for short-reach applications where fiber is not needed.

What Is an SFP+ Module?

SFP+ is the enhanced version of SFP, supporting data rates up to 10 Gbps. It uses the same physical form factor as SFP, which means SFP+ modules fit into SFP cages (though at reduced speed). This backward compatibility was a deliberate design choice that protected existing infrastructure investments.

Key characteristics:

• Data rate: 10 Gbps (10 Gigabit Ethernet, 8G/16G Fibre Channel)
• Form factor: Identical to SFP (same cage)
• Signal handling: Moved the CDR (Clock and Data Recovery) and signal conditioning from the module to the host device, reducing module complexity and cost
• Power consumption: Slightly higher than SFP (< 1.5W typical)
• Electrical interface: SFF-8431

SFP+ became the dominant 10G interconnect for data centers and enterprise networks. Its combination of small size, low power, and high port density made it the preferred choice over the larger XFP form factor.

What Is an SFP28 Module?

SFP28 is a 25 Gbps single-lane transceiver that uses NRZ (Non-Return-to-Zero) signaling at 25.78 Gbaud. Despite the higher data rate, SFP28 shares the exact same MSA mechanical form factor as SFP and SFP+ — the modules are physically identical in size and connector layout.

Key characteristics:

• Data rate: 25 Gbps (25 Gigabit Ethernet, 32G Fibre Channel)
• Form factor: Identical to SFP/SFP+ (same dimensions, same LC duplex interface)
• Signaling: Single-lane NRZ at 25.78 Gbaud
• Backward compatibility: SFP and SFP+ modules work in SFP28 cages at their native speeds. However, SFP28 modules do not work in SFP+ cages — the host-side electrical signaling operates at 25G rates that SFP+ SerDes cannot handle.
• Power consumption: < 1.5W typical
• Electrical interface: SFF-8402

SFP28 is the standard transceiver for 25GbE server NIC uplinks and Top-of-Rack (ToR) switch ports in modern spine-leaf data center architectures. It is also the building block for QSFP28 breakout connections — a single QSFP28 port can fan out to four SFP28 ports via a breakout cable.

Common reach variants include SR (100m on OM4 multimode fiber) and LR (10 km on OS2 single-mode fiber). Pricing ranges from $30–120 per module depending on reach, vendor, and whether the optic is OEM-branded or third-party compatible.

What Is a QSFP28 Module?

QSFP28 (Quad Small Form-factor Pluggable 28) is the standard form factor for 100 Gbps networking. The "28" refers to the 28 Gbps per-lane signaling rate, with four lanes providing 4 × 25G = 100G aggregate bandwidth.

Key characteristics:

• Data rate: 100 Gbps (4 × 25 Gbps lanes)
• Form factor: Approximately 18.4mm × 13.5mm × 72.4mm (roughly 2× the width of SFP+)
• Fiber interface: MPO/MTP-12 for SR4 (multimode), LC duplex for LR4/ER4 (single-mode with WDM)
• Power consumption: < 3.5W typical
• Breakout capability: Can split into 4 × 25G SFP28 connections using breakout cables
• Electrical interface: SFF-8665

QSFP28 is the workhorse of modern data center spine-leaf architectures. It delivers 10× the bandwidth of SFP+ in roughly 2× the physical space, making it far more port-density efficient.

What Is a QSFP+ Module?

QSFP+ (Quad Small Form-factor Pluggable Plus) is a 40 Gbps transceiver that aggregates four 10G lanes into a single module. It uses the same physical cage form factor as QSFP28, making the two mechanically interchangeable — QSFP+ modules work in QSFP28 cages at 40G speed, and many switches auto-detect the module type.

Key characteristics:

• Data rate: 40 Gbps (4 × 10 Gbps lanes)
• Form factor: Identical to QSFP28 (same cage, same edge connector)
• Fiber interface: MPO/MTP-12 for SR4 (multimode), LC duplex for LR4 (single-mode with CWDM)
• Power consumption: < 3.5W typical
• Breakout capability: Can split into 4 × 10G SFP+ connections using breakout cables

QSFP+ remains widely deployed in 40GbE spine-leaf uplinks and is still the workhorse interconnect in many enterprise and campus networks. Common variants include SR4 (100m on OM4), LR4 (10 km on OS2), and PSM4 (500m on OS2 using parallel single-mode fibers). While QSFP28 (100G) is gradually replacing QSFP+ in new deployments, the installed base of 40G infrastructure remains massive, and QSFP+ modules will continue shipping in volume for years.

SFP Module Types

Not all SFP modules are the same. The SFP module type you need depends on distance, fiber type, and wavelength requirements. Here are the main categories of SFP optical modules:

SFP SX and SFP LX are by far the most common. SX is the default choice for multimode fiber runs within a building, while LX covers single-mode links up to 10 km. For longer distances, EX and ZX modules use higher-power lasers and more sensitive receivers — but cost significantly more.

SFP BX (bidirectional) modules are worth special attention. They use wavelength-division multiplexing to transmit and receive on different wavelengths over a single fiber strand instead of the usual two. BX modules always ship in matched pairs — one transmits at 1310nm and receives at 1490nm, while its partner does the reverse. This cuts fiber usage in half, which can save substantial costs in fiber-scarce or long-distance deployments.

SFP-T (copper) modules accept a standard RJ45 Ethernet cable instead of fiber. They are used for short-reach connections (up to 100m) where fiber is unnecessary — for example, connecting a nearby server, management port, or out-of-band monitoring device.

SFP+ Module Types

SFP+ module types mirror the SFP family but operate at 10 Gbps. In addition to fiber optics, SFP+ introduced two important copper interconnect types — DAC and AOC — that dominate short-reach data center links.

DAC (Direct Attach Copper) cables are pre-terminated SFP+ assemblies with integrated copper twinaxial cable. They are the cheapest and lowest-latency option for links under 7 meters — the standard connection from a ToR switch to server NICs. DAC cables draw less power than optical transceivers because there is no laser or photodiode.

AOC (Active Optical Cable) assemblies embed the transmitter and receiver optics directly into the cable ends. They combine the plug-and-play convenience of DAC with the longer reach of fiber (up to 100m). AOCs are lighter and thinner than DAC, which improves airflow in dense rack environments.

For infrastructure components, CZT manufactures the SFP+ cage assemblies that house these modules on switches and NICs.

SFP Fiber Connector Interfaces

The SFP fiber connector type determines how a transceiver module interfaces with the fiber optic patch cable. Understanding this interface is critical for ordering the correct cables and patch panels.

SFP and SFP+ LC Connector

All standard SFP and SFP+ optical modules use the LC (Lucent Connector) duplex interface. The LC connector features:

• 1.25mm ceramic ferrule (half the size of SC's 2.5mm ferrule)
• Push-pull latching mechanism for secure mating
• Duplex clip holds two LC connectors (TX and RX) in a single assembly
• Insertion loss: ≤ 0.2 dB typical
• Return loss: ≥ 50 dB (UPC), ≥ 65 dB (APC)

The LC duplex interface is the reason SFP transceivers are often called "SFP transceiver LC connector" modules — the LC fiber connector is inseparable from the SFP form factor. When specifying patch cables for SFP or SFP+ ports, you will always need an LC connector on the switch/transceiver end. The other end depends on your patch panel — typically LC-LC, LC-SC, or LC-MPO.

For a detailed comparison of LC vs SC connectors, see our LC vs SC Fiber Connector Guide.

QSFP Connector Interfaces

QSFP+ and QSFP28 modules use two different fiber connector interfaces depending on the optic type:

• MPO/MTP-12 — used by SR4 (short-reach multimode) modules. The MPO connector carries 12 fibers in a single ferrule, of which 8 are active (4 TX + 4 RX). This enables parallel 4-lane transmission over multimode fiber. See our MPO/MTP Connector Guide for details.
• LC duplex — used by LR4, ER4, and CWDM4 (single-mode WDM) modules. These use wavelength-division multiplexing to carry 4 lanes over just 2 fibers, so the standard LC duplex connector is sufficient.

SFP vs SFP+: Key Differences

While SFP and SFP+ share the same physical form factor, they differ in several important ways:

The most important practical difference is backward compatibility. An SFP module will work in an SFP+ cage at 1G speed. An SFP+ module inserted into an SFP-only cage will typically negotiate down to 1G. This flexibility simplifies migration from 1G to 10G infrastructure.

SFP+ vs QSFP28: Key Differences

Moving from 10G to 100G involves a more significant architectural shift:

QSFP28's breakout capability is a major advantage. A single QSFP28 port can connect to four separate 25G SFP28 ports using a breakout cable, providing flexible connectivity between spine and leaf switches.

SFP+ vs SFP28: The 10G to 25G Transition

SFP+ and SFP28 share the same physical form factor but represent different generations of server connectivity. The transition from SFP+ (10G) to SFP28 (25G) is one of the most common upgrade paths in data center networking.

The key upgrade driver is bandwidth per server port. A 25G SFP28 NIC provides 2.5× the bandwidth of a 10G SFP+ NIC at roughly similar power and port density. In a spine-leaf architecture, upgrading from 10G SFP+ to 25G SFP28 at the server edge — combined with 100G QSFP28 at the spine — delivers a balanced, non-blocking fabric.

Migration path: If your switches have SFP28 cages, you can insert existing SFP+ modules and they will operate at 10G. This lets you upgrade infrastructure incrementally — install SFP28-capable switches now, then swap individual SFP+ modules for SFP28 as servers are refreshed.

SFP+ vs QSFP+: When to Upgrade from 10G to 40G

The choice between SFP+ and QSFP+ typically arises at the aggregation or spine layer. SFP+ delivers 10G per port, while QSFP+ delivers 40G (4× 10G lanes) in a slightly wider module.

When to stay with SFP+: You have many 10G endpoints (servers, access switches) and do not need more than 10G per link. SFP+ cabling is simpler (2-fiber LC patch cords) and the installed base of 10G switches is enormous.

When to upgrade to QSFP+: Your spine-leaf uplinks are saturated at 10G, or you need 40G inter-switch trunks. QSFP+ breakout cables let you connect one QSFP+ port to four SFP+ ports, providing a flexible upgrade path without replacing leaf switches.

SFP vs QSFP: Architecture Comparison

At the highest level, SFP and QSFP represent two fundamentally different transceiver architectures: single-lane versus quad-lane.

The SFP family excels where you need many individual ports at lower speeds — server NICs, access switches, and edge routers. The QSFP family excels where you need maximum bandwidth density — spine switches, core routers, and data center interconnects.

In a modern spine-leaf architecture, both families work together: SFP28 (25G) at the server edge, QSFP28 (100G) at the spine, with breakout cables bridging the two. This is the dominant design pattern in hyperscale and enterprise data centers as of 2026.

Other Transceiver Form Factors

The SFP family is not the only game in town. Here is a brief overview of other form factors you may encounter:

The industry is rapidly moving toward 400G with QSFP-DD and OSFP, and 800G is already in development. However, QSFP28 at 100G remains the volume leader for data center deployments.

Transceiver Compatibility Matrix

One of the most common questions in network design is whether a given module will physically and electrically work in a given cage. The table below provides a comprehensive cross-reference.

Note: Backward-compatible modules run at the speed of the module, not the cage. An SFP (1G) in an SFP+ cage still operates at 1 Gbps. Always verify electrical compatibility with your switch vendor's hardware compatibility list — physical fit does not guarantee full operational support on every platform.

Transceiver Reach Options

Each form factor is available in multiple reach variants, defined by standardized codes:

Rule of thumb: Use SR/SR4 for intra-building connections (data center rows), LR/LR4 for campus or metro links, and ER/ZR for long-haul or WAN connections.

For more on fiber types, see our guide on Single-Mode vs Multi-Mode Fiber.

How to Choose the Right Transceiver

Use this decision framework:

1. What bandwidth do you need?

• 1G access/edge → SFP
• 10G server/aggregation → SFP+
• 25G server NIC → SFP28
• 100G spine/core → QSFP28
• 400G next-gen core → QSFP-DD

2. What distance must you cover?

• < 300m within data center → SR (multi-mode)
• 300m - 10 km campus → LR (single-mode)
• 10 - 40 km metro → ER (single-mode)
• 40+ km WAN → ZR (single-mode with amplification)

3. What fiber is already installed?

• Multi-mode (OM3/OM4) → SR variants only
• Single-mode (OS2) → LR, ER, ZR variants

4. What does your switch support?

• Check the switch/router hardware compatibility list (HCL)
• Verify cage type (SFP, SFP+, QSFP28, QSFP-DD)
• Confirm software support for the specific transceiver

5. What is your budget?

• SR modules are cheapest ($30-100 for 100G SR4)
• LR modules cost 2-5× more than SR
• ER/ZR modules are premium ($500-2,000+)

SFP Cage Design and Compatibility

The SFP cage is the metal housing on the switch or NIC that receives the transceiver module. Cage quality directly affects signal integrity, EMI shielding, and module retention.

Key cage design considerations:

• Contact alignment: Precision-machined guide rails ensure proper electrical contact between the module's edge connector and the host PCB
• EMI shielding: The cage acts as a Faraday cage, containing electromagnetic emissions from the high-speed signals
• Heat dissipation: Metal cage construction helps conduct heat away from the transceiver module
• Retention mechanism: Spring clips or bail latches secure the module and prevent accidental ejection
• Stacking: Multi-port cages (1×1, 1×2, 1×4, 2×1, 2×2, 2×4) maximize port density on the faceplate

CZT manufactures precision SFP and SFP+ cages with tight tolerances for reliable module insertion and optimal signal performance. Our cages are designed to meet MSA specifications and are compatible with modules from all major transceiver vendors.

FAQ

Q: Can I use an SFP module in an SFP+ port? A: Yes. SFP modules are backward compatible with SFP+ cages. The port will operate at 1G speed. This is useful during migration from 1G to 10G infrastructure.

Q: Is QSFP28 backward compatible with QSFP+? A: QSFP28 modules fit in QSFP+ cages physically, but electrical compatibility depends on the host device. Many modern switches support both QSFP+ (40G) and QSFP28 (100G) in the same cage. Check your switch documentation.

Q: What is a breakout cable? A: A breakout cable splits a single QSFP28 port into four SFP28 (25G) connections, or a QSFP+ port into four SFP+ (10G) connections. This provides flexible connectivity between switches with different port types.

Q: How do I know which transceiver is compatible with my switch? A: Check the switch manufacturer's transceiver compatibility matrix (also called HCL or validated optics list). Using non-validated transceivers may trigger warning messages or be blocked entirely on some platforms.

Q: What is DOM/DDM? A: Digital Optical Monitoring (DOM) or Digital Diagnostic Monitoring (DDM) provides real-time telemetry from the transceiver: TX power, RX power, temperature, supply voltage, and laser bias current. This data is essential for troubleshooting link issues and proactive maintenance.

Q: What are the main SFP module types? A: The main SFP module types are SX (short-reach multimode), LX (long-reach single-mode), EX (extended reach 40 km), ZX (very long reach 80+ km), BX (bidirectional single-fiber), CWDM/DWDM (wavelength multiplexing), and SFP-T (copper RJ45). Each type is optimized for a specific distance range and fiber infrastructure.

Q: What fiber connector does an SFP transceiver use? A: SFP and SFP+ transceivers use an LC duplex fiber connector. The LC connector has a 1.25mm ceramic ferrule and push-pull latching mechanism. QSFP modules use either MPO/MTP-12 (for SR4 multimode) or LC duplex (for LR4/CWDM4 single-mode WDM).

Q: What is the difference between SFP+ and SFP28? A: SFP+ runs at 10 Gbps and SFP28 runs at 25 Gbps. They share the same physical form factor and LC duplex connector. SFP+ modules work in SFP28 cages at 10G speed (backward compatible), but SFP28 modules cannot operate in SFP+ cages because the host electrical interface runs at 25G.

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