SFP28 Transceivers
What Is an SFP28 Transceiver?
An SFP28 transceiver is a compact pluggable network interface commonly used for 25 Gigabit Ethernet. SFP28 modules install into compatible ports on network switches, server network adapters, storage systems and other high-speed enterprise networking equipment.
SFP28 retains a compact form factor similar to SFP and SFP+ while supporting a substantially higher single-lane signaling rate. This allows enterprise networks to increase server and switch bandwidth without moving to a physically much larger transceiver for each individual 25GbE link.
Depending on the network design, an SFP28 port may use an optical transceiver with fiber, a direct-attach copper cable or an active optical cable.
SFP28 at a Glance
Why Is SFP28 Used for 25GbE?
SFP28 provides a single-lane interface for 25GbE, making it particularly useful for increasing bandwidth between servers and access or leaf switches while retaining the familiar compact SFP-style form factor.
For organizations moving beyond 10GbE, a 25GbE connection provides 2.5 times the nominal Ethernet line rate of a 10GbE connection without requiring multiple physical 10GbE links for the same amount of raw bandwidth.
This makes SFP28 particularly relevant for virtualization hosts, hyperconverged infrastructure, storage traffic, high-performance computing and other workloads that can exceed the practical capacity of 10GbE server connections.
How Does an SFP28 Module Work?
The network device provides the SFP28 cage and high-speed electrical interface. The installed transceiver or cable assembly connects that electrical interface to the selected physical transmission medium.
With an optical SFP28 transceiver, electrical data from the host is converted into optical signals for transmission through fiber. Incoming optical signals are converted back into electrical data for the network device.
For short copper connections, an SFP28 DAC assembly provides an electrical link directly between compatible ports without separate optical modules.
Common SFP28 Transceiver Types
The correct SFP28 module depends on the required distance, fiber infrastructure, optical specification and capabilities of the network equipment.
25GBASE-SR
A short-reach 25 Gigabit Ethernet optical interface designed for multimode fiber and commonly used for data-center connections.
25GBASE-LR
A long-reach 25 Gigabit Ethernet optical interface designed for longer connections over single-mode fiber.
SFP28 DAC
A fixed Twinax cable assembly used for short 25GbE links between compatible SFP28 interfaces.
SFP28 AOC
An active optical cable integrates the optical interfaces and fiber into a complete factory-assembled cable.
SFP28 SR vs. LR
Passive vs. Active SFP28 DAC
Passive SFP28 DAC
Passive DAC assemblies do not contain active signal-conditioning electronics. They are typically selected for shorter 25GbE connections when supported by both endpoints.
Active SFP28 DAC
Active DAC assemblies include signal-conditioning electronics and can support applications requiring additional electrical reach. Compatibility must still be confirmed for the connected equipment.
What Is an SFP28 AOC?
An SFP28 Active Optical Cable, or AOC, integrates optical conversion hardware and fiber into a complete cable assembly with SFP28 interfaces at both ends.
AOCs provide an alternative to short copper DAC assemblies when a lighter optical cable or greater supported reach is desirable, while avoiding the need to select separate optical transceivers and fiber patch cords.
SFP28 DAC vs. AOC vs. Fiber Transceivers
DAC
A fixed copper assembly commonly selected for short, high-speed connections between nearby equipment.
AOC
A fixed optical assembly that combines the interfaces and fiber into one factory-terminated cable.
Optical Transceivers
Separate SFP28 modules and fiber cabling provide modularity and multiple optical reach options.
SFP28 DOM and DDM
Many SFP28 optical transceivers provide digital diagnostic monitoring capabilities. When supported by both the module and network platform, DOM or DDM information can help administrators monitor transceiver operating conditions and optical signal levels.
SFP+ vs. SFP28
SFP+
- Commonly associated with 10GbE
- Single-lane high-speed interface
- Optical, DAC and AOC options
- Widely deployed in enterprise data centers
SFP28
- Commonly associated with 25GbE
- Higher single-lane signaling rate
- Optical, DAC and AOC options
- Common for modern server access networking
SFP28 vs. QSFP28
SFP28
SFP28 is commonly used as a single-lane 25GbE interface for server, storage and switch connectivity.
QSFP28
QSFP28 combines multiple high-speed lanes in a quad small-form-factor interface and is commonly associated with 100 Gigabit Ethernet connectivity.
How SFP28 Fits into 100GbE Networks
One important reason 25GbE became attractive for data-center server connectivity is its relationship to higher-speed network architectures. Certain compatible 100GbE QSFP28 interfaces can be configured for breakout connectivity into multiple 25GbE links.
A supported breakout configuration can allow a higher-speed switch interface to connect to multiple 25GbE server or network interfaces. Whether breakout is available depends on the specific switch, port, cable or optical configuration and firmware.
What Should You Check Before Buying an SFP28?
Physical Fit Does Not Guarantee SFP28 Compatibility
SFP28 uses an industry-standardized form factor, but network equipment vendors can impose additional requirements for supported transceivers and cables. A module that physically fits the port may still be rejected or operate incorrectly if the host platform does not support its coding, speed or optical configuration.
For enterprise deployments, verify the exact switch or network-adapter model, port capabilities, firmware version, supported transceiver type and cable configuration before purchasing components.
Why Is My SFP28 Link Not Working?
The switch or NIC may reject a transceiver that is not recognized or supported by its firmware.
The port may be configured for a different operating speed or mode than the connected interface.
The installed fiber must match the optical requirements of the selected SFP28 transceiver.
Duplex optical links require the transmit path at one endpoint to connect to the receive path at the other.
Contamination on fiber end faces can increase optical loss and prevent a reliable 25GbE link.
The connected equipment may require a particular passive or active DAC configuration or vendor coding.
SFP28 Transceiver FAQ
What is SFP28?
What speed is SFP28?
What is the difference between SFP+ and SFP28?
Can I use an SFP+ module in an SFP28 port?
Can I use an SFP28 module in an SFP+ port?
What is the difference between 25GBASE-SR and 25GBASE-LR?
What is an SFP28 DAC cable?
What is the difference between SFP28 and QSFP28?
Are all SFP28 transceivers compatible?
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