By Andee | 06 November 2025 | 0 Comments
What is 25G SFP28 module? How does 25G SFP28 module work in Data Center?
What is 25G SFP28 module?
25G SFP28 is a compact, hot-pluggable transceiver used primarily in data centers for network connectivity. It transmits and receives data at a rate of 25 Gigabits per second (Gbps). The "SFP28" stands for "Small Form-factor Pluggable 28," where the "28" signifies a single-lane data rate of up to 28 Gbps, making it perfectly suited for 25G transmission.
1. The Role: What It Does
Think of an SFP28 module as a "translator" for a network switch or network interface card (NIC). Its job is to:
Convert electrical signals from the device's port into optical light signals (for fiber optic cables) or electrical signals (for DAC cables).
Transmit these signals over a cable.
Receive incoming signals and convert them back into electrical signals for the device to process.
2. The Key Feature: Speed - 25 Gigabits per second (25G)
The 25G standard emerged as a "sweet spot" for data centers, offering a significant performance boost over 10G without the immediate cost and complexity jump to 40G or 100G.
Efficiency: It provides 2.5 times the bandwidth of 10G using a single lane, making it simpler and more efficient than 40G, which often uses four 10G lanes bundled together.
ToR (Top-of-Rack) Standard: 25G has become the dominant standard for the link between servers and the Top-of-Rack (ToR) switch in modern data centers.
3. The Form Factor: SFP28
The SFP28 form factor is the same physical size as the older SFP (1G) and SFP+ (10G) modules. This is a critical advantage because it allows for backward compatibility.
You can plug an SFP28 module into an SFP+ port (and it will typically operate at 10G speeds).
You can plug an SFP+ module into an SFP28 port (and it will operate at 10G speeds).
This provides flexibility and a smooth upgrade path for network operators.
4. Common Types and Cabling
25G SFP28 modules come in several varieties to suit different distances and cable types:
SR (Short Range):
Use Case: Very short distances within a data center rack or between adjacent racks.
Media: Multi-mode fiber (MMF - usually OM3 or OM4).
Distance: Up to 70m on OM3, 100m on OM4.
Wavelength: 850nm.
LR (Long Range):
Use Case: Connecting across a campus or between data center buildings.
Media: Single-mode fiber (SMF).
Distance: Up to 10 kilometers (km).
Wavelength: 1310nm.
ER (Extended Range):
Use Case: For even longer distances.
Media: Single-mode fiber (SMF).
Distance: Up to 40 km.
Wavelength: 1310nm.
DAC (Direct Attach Copper):
What it is: A fixed-length copper cable with SFP28 connectors permanently attached on both ends.
Use Case: Extremely short connections (typically ≤ 5m), such as within a single rack between a switch and a server. It's the lowest cost and power option for these short runs.
Not a true "module": It's a passive or active cable assembly, not an optical transceiver.
AOC (Active Optical Cable):
What it is: Similar to a DAC, but the cable is fiber optic, and the "modules" on the ends are permanently attached. It's a single, integrated unit.
Use Case: Short to medium distances (up to 100m) where the flexibility and lighter weight of fiber are beneficial over copper. More expensive than DAC but less than separate modules and patch cables.
Why is 25G SFP28 So Important?
Server Connectivity: It is the perfect upgrade from 10G for server network cards, providing more bandwidth for modern applications without a massive cost increase.
Cost-Effectiveness: Delivering 25G over a single lane (SFP28) is more efficient and often cheaper per gigabit than the older 40G standard (which used QSFP+ form factor).
Path to 100G: A common way to build a 100G network is to use a switch with QSFP28 ports (100G). Each 100G port can be "broken out" into four independent 25G SFP28 connections using a special cable. This allows one 100G switch port to connect to four different 25G servers.
Comparison Table
25G SFP28 module is a fundamental building block of modern high-speed data centers. It strikes an optimal balance between performance, cost, power consumption, and density, making it the de facto standard for connecting servers to the network edge. Its backward compatibility with the widespread SFP+ ecosystem makes network upgrades straightforward and cost-effective.
Of course. Let's dive into how the 25G SFP28 module actually works within a data center environment.
At a high level, the 25G SFP28 module acts as the critical interface between the electronic world of the network device (switch, server, router) and the optical world of the fiber cabling that interconnects everything.
Its job is to transmit and receive data at 25 Gbps, enabling high-speed communication between devices.
The Core Function: How it Works Technically
Inside every optical SFP28 module, there are two key data paths:
The Transmit Path (Electrical -> Optical):
The switch/server generates digital electrical signals (ones and zeros).
These signals enter the SFP28 module via its electrical connector.
A laser driver chip powers a precise laser (e.g., a VCSEL for multi-mode fiber, or a DFB laser for single-mode).
This laser rapidly turns on and off, modulating the light to encode the electrical data onto an optical signal.
The light is emitted into the attached fiber optic cable.
The Receive Path (Optical -> Electrical):
A faint light signal arrives from the fiber cable.
A photodiode inside the SFP28 module detects this light.
The photodiode converts the modulated light pulses back into a weak electrical signal.
A transimpedance amplifier (TIA) boosts and cleans up this electrical signal.
The restored, clean digital electrical signal is then passed to the switch/server for processing.
In short: It's a high-speed translator: Electrical <=> Optical.
How it Works in the Data Center Ecosystem: Key Applications
Here’s how this "translation" function is applied in specific, critical roles within a data center.
1. Server to Top-of-Rack (ToR) Switch Connectivity (The Primary Role)
This is the most common and important use case for 25G SFP28.
The Setup: A rack of servers, each with a 25G Network Interface Card (NIC), is connected to a Top-of-Rack (ToR) switch.
Server Side: A 25G SFP28 transceiver is plugged into the server's NIC.
Switch Side: A 25G SFP28 transceiver is plugged into the switch's port.
Connection: A duplex fiber optic cable (or an AOC) connects the two modules.
The Data Flow: When a server needs to send data to another server (or out of the rack), its SFP28 module converts the data to light, sends it to the ToR switch, which then routes it to the correct destination port.
Why 25G here? It's the perfect upgrade from 10G. It provides 2.5x the bandwidth to handle the demands of modern applications, virtualization, and storage without the cost and complexity of a full 40G/100G upgrade to every server.
2. Uplink from ToR Switch to Spine Switches (Using Breakout Cables)
This is where 25G's efficiency truly shines and enables a smooth path to 100G.
The Setup: A ToR switch needs a high-speed uplink to a core (Spine) switch to handle traffic from all its connected servers.
Spine Switch: Has a 100G QSFP28 port. Instead of using a single 100G transceiver, you use a 100G to 4x25G Breakout Cable.
ToR Switch: Has four 25G SFP28 ports.
The Data Flow: The breakout cable effectively "splits" the single 100G link from the spine into four independent 25G lanes. Each of these 25G lanes connects to a 25G SFP28 port on the ToR switch, providing an aggregate of 100G of uplink bandwidth.
Why this is brilliant: It allows data center operators to build high-performance 100G spine networks while using cost-effective and ubiquitous 25G SFP28 technology for the leaf (ToR) tier. This creates a 25G ToR -> 100G Spine architecture, which is the gold standard for modern leaf-spine data centers.
3. Direct Server-to-Server Interconnects
For applications requiring low-latency and high-throughput between specific servers (e.g., high-performance computing clusters, database replication), SFP28 modules can be used to connect two servers directly via their NICs, often using a simple DAC (Direct Attach Copper) cable if they are in the same rack.
Real-World Data Center Workflow Example
Let's trace a data packet through a system using 25G SFP28s:
Request: A user requests data from a web application.
Server Processing: The request reaches a web server (e.g., in Server 1). The application server needs to query a database server (in Server 2) in the same rack.
Conversion to Light (Tx):
Server 1's CPU prepares the database query.
The 25G NIC on Server 1 sends the electrical data to its SFP28 module.
The SFP28 module converts the data to a 25G optical signal and transmits it over the fiber cable to the ToR Switch.
The ToR Switch receives the optical signal on its SFP28 port, converts it back to electrical data, and processes it.
The switch identifies that the destination is Server 2, connected to another one of its 25G SFP28 ports.
Conversion to Light Again (Tx):
The switch forwards the electrical data to the SFP28 module connected to Server 2.
This SFP28 module again converts the electrical signal to light and sends it down the fiber to Server 2.
Back to Electronics (Rx):
Server 2's SFP28 module receives the optical signal, converts it back to an electrical signal, and passes it to its NIC and then CPU.
Response: The database server processes the query, and the entire reverse path is taken to send the response back to the original web server and out to the user.
Performance: 25G provides a significant bandwidth boost over 10G for server access.
Efficiency: It's more efficient and cost-effective than 40G for single-lane traffic.
Scalability: It is the fundamental building block for 100G/400G networks using breakout cabling.
Density & Power: The SFP28 form factor allows for high port density on switches and has relatively low power consumption.
25G SFP28 module is the workhorse of the modern data center, forming the critical 25G edge that connects every server to the network fabric.
25G SFP28 is a compact, hot-pluggable transceiver used primarily in data centers for network connectivity. It transmits and receives data at a rate of 25 Gigabits per second (Gbps). The "SFP28" stands for "Small Form-factor Pluggable 28," where the "28" signifies a single-lane data rate of up to 28 Gbps, making it perfectly suited for 25G transmission.
1. The Role: What It Does
Think of an SFP28 module as a "translator" for a network switch or network interface card (NIC). Its job is to:
Convert electrical signals from the device's port into optical light signals (for fiber optic cables) or electrical signals (for DAC cables).
Transmit these signals over a cable.
Receive incoming signals and convert them back into electrical signals for the device to process.
2. The Key Feature: Speed - 25 Gigabits per second (25G)
The 25G standard emerged as a "sweet spot" for data centers, offering a significant performance boost over 10G without the immediate cost and complexity jump to 40G or 100G.
Efficiency: It provides 2.5 times the bandwidth of 10G using a single lane, making it simpler and more efficient than 40G, which often uses four 10G lanes bundled together.
ToR (Top-of-Rack) Standard: 25G has become the dominant standard for the link between servers and the Top-of-Rack (ToR) switch in modern data centers.
3. The Form Factor: SFP28
The SFP28 form factor is the same physical size as the older SFP (1G) and SFP+ (10G) modules. This is a critical advantage because it allows for backward compatibility.
You can plug an SFP28 module into an SFP+ port (and it will typically operate at 10G speeds).
You can plug an SFP+ module into an SFP28 port (and it will operate at 10G speeds).
This provides flexibility and a smooth upgrade path for network operators.
4. Common Types and Cabling
25G SFP28 modules come in several varieties to suit different distances and cable types:
SR (Short Range):
Use Case: Very short distances within a data center rack or between adjacent racks.
Media: Multi-mode fiber (MMF - usually OM3 or OM4).
Distance: Up to 70m on OM3, 100m on OM4.
Wavelength: 850nm.
LR (Long Range):
Use Case: Connecting across a campus or between data center buildings.
Media: Single-mode fiber (SMF).
Distance: Up to 10 kilometers (km).
Wavelength: 1310nm.
ER (Extended Range):
Use Case: For even longer distances.
Media: Single-mode fiber (SMF).
Distance: Up to 40 km.
Wavelength: 1310nm.
DAC (Direct Attach Copper):
What it is: A fixed-length copper cable with SFP28 connectors permanently attached on both ends.
Use Case: Extremely short connections (typically ≤ 5m), such as within a single rack between a switch and a server. It's the lowest cost and power option for these short runs.
Not a true "module": It's a passive or active cable assembly, not an optical transceiver.
AOC (Active Optical Cable):
What it is: Similar to a DAC, but the cable is fiber optic, and the "modules" on the ends are permanently attached. It's a single, integrated unit.
Use Case: Short to medium distances (up to 100m) where the flexibility and lighter weight of fiber are beneficial over copper. More expensive than DAC but less than separate modules and patch cables.
Why is 25G SFP28 So Important?
Server Connectivity: It is the perfect upgrade from 10G for server network cards, providing more bandwidth for modern applications without a massive cost increase.
Cost-Effectiveness: Delivering 25G over a single lane (SFP28) is more efficient and often cheaper per gigabit than the older 40G standard (which used QSFP+ form factor).
Path to 100G: A common way to build a 100G network is to use a switch with QSFP28 ports (100G). Each 100G port can be "broken out" into four independent 25G SFP28 connections using a special cable. This allows one 100G switch port to connect to four different 25G servers.
Comparison Table
| Feature | SFP+ (10G) | SFP28 (25G) | QSFP28 (100G) |
| Data Rate | 10 Gbps | 25 Gbps | 100 Gbps |
| Form Factor | SFP+ | SFP28 | QSFP28 |
| Common Use | 10G Server Access | 25G Server Access, 5G Mobile Fronthaul | Data Center Spine/Leaf, Aggregation |
| Physical Size | Small | Same size as SFP+ | Larger |
| Lanes | 1 x 10G | 1 x 25G | 4 x 25G (or 1 x 100G) |
Of course. Let's dive into how the 25G SFP28 module actually works within a data center environment.
At a high level, the 25G SFP28 module acts as the critical interface between the electronic world of the network device (switch, server, router) and the optical world of the fiber cabling that interconnects everything.
Its job is to transmit and receive data at 25 Gbps, enabling high-speed communication between devices.
The Core Function: How it Works Technically
Inside every optical SFP28 module, there are two key data paths:
The Transmit Path (Electrical -> Optical):
The switch/server generates digital electrical signals (ones and zeros).
These signals enter the SFP28 module via its electrical connector.
A laser driver chip powers a precise laser (e.g., a VCSEL for multi-mode fiber, or a DFB laser for single-mode).
This laser rapidly turns on and off, modulating the light to encode the electrical data onto an optical signal.
The light is emitted into the attached fiber optic cable.
The Receive Path (Optical -> Electrical):
A faint light signal arrives from the fiber cable.
A photodiode inside the SFP28 module detects this light.
The photodiode converts the modulated light pulses back into a weak electrical signal.
A transimpedance amplifier (TIA) boosts and cleans up this electrical signal.
The restored, clean digital electrical signal is then passed to the switch/server for processing.
In short: It's a high-speed translator: Electrical <=> Optical.
How it Works in the Data Center Ecosystem: Key Applications
Here’s how this "translation" function is applied in specific, critical roles within a data center.
1. Server to Top-of-Rack (ToR) Switch Connectivity (The Primary Role)
This is the most common and important use case for 25G SFP28.
The Setup: A rack of servers, each with a 25G Network Interface Card (NIC), is connected to a Top-of-Rack (ToR) switch.
Server Side: A 25G SFP28 transceiver is plugged into the server's NIC.
Switch Side: A 25G SFP28 transceiver is plugged into the switch's port.
Connection: A duplex fiber optic cable (or an AOC) connects the two modules.
The Data Flow: When a server needs to send data to another server (or out of the rack), its SFP28 module converts the data to light, sends it to the ToR switch, which then routes it to the correct destination port.
Why 25G here? It's the perfect upgrade from 10G. It provides 2.5x the bandwidth to handle the demands of modern applications, virtualization, and storage without the cost and complexity of a full 40G/100G upgrade to every server.
2. Uplink from ToR Switch to Spine Switches (Using Breakout Cables)
This is where 25G's efficiency truly shines and enables a smooth path to 100G.
The Setup: A ToR switch needs a high-speed uplink to a core (Spine) switch to handle traffic from all its connected servers.
Spine Switch: Has a 100G QSFP28 port. Instead of using a single 100G transceiver, you use a 100G to 4x25G Breakout Cable.
ToR Switch: Has four 25G SFP28 ports.
The Data Flow: The breakout cable effectively "splits" the single 100G link from the spine into four independent 25G lanes. Each of these 25G lanes connects to a 25G SFP28 port on the ToR switch, providing an aggregate of 100G of uplink bandwidth.
Why this is brilliant: It allows data center operators to build high-performance 100G spine networks while using cost-effective and ubiquitous 25G SFP28 technology for the leaf (ToR) tier. This creates a 25G ToR -> 100G Spine architecture, which is the gold standard for modern leaf-spine data centers.
3. Direct Server-to-Server Interconnects
For applications requiring low-latency and high-throughput between specific servers (e.g., high-performance computing clusters, database replication), SFP28 modules can be used to connect two servers directly via their NICs, often using a simple DAC (Direct Attach Copper) cable if they are in the same rack.
Real-World Data Center Workflow Example
Let's trace a data packet through a system using 25G SFP28s:
Request: A user requests data from a web application.
Server Processing: The request reaches a web server (e.g., in Server 1). The application server needs to query a database server (in Server 2) in the same rack.
Conversion to Light (Tx):
Server 1's CPU prepares the database query.
The 25G NIC on Server 1 sends the electrical data to its SFP28 module.
The SFP28 module converts the data to a 25G optical signal and transmits it over the fiber cable to the ToR Switch.
The ToR Switch receives the optical signal on its SFP28 port, converts it back to electrical data, and processes it.
The switch identifies that the destination is Server 2, connected to another one of its 25G SFP28 ports.
Conversion to Light Again (Tx):
The switch forwards the electrical data to the SFP28 module connected to Server 2.
This SFP28 module again converts the electrical signal to light and sends it down the fiber to Server 2.
Back to Electronics (Rx):
Server 2's SFP28 module receives the optical signal, converts it back to an electrical signal, and passes it to its NIC and then CPU.
Response: The database server processes the query, and the entire reverse path is taken to send the response back to the original web server and out to the user.
Performance: 25G provides a significant bandwidth boost over 10G for server access.
Efficiency: It's more efficient and cost-effective than 40G for single-lane traffic.
Scalability: It is the fundamental building block for 100G/400G networks using breakout cabling.
Density & Power: The SFP28 form factor allows for high port density on switches and has relatively low power consumption.
25G SFP28 module is the workhorse of the modern data center, forming the critical 25G edge that connects every server to the network fabric.
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