100G QSFP28 to 25G SFP28 Adapter Transceiver Module

  A 100G QSFP28 to 25G SFP28 Adapter Transceiver Module is a networking device that converts a single 100 Gigabit Ethernet (GbE) port into four separate 25 GbE connections. It enables you to connect four 25G devices to one 100G switch port, effectively "splitting" the bandwidth into four smaller channels.

These modules are the core components that enable the technology described previously. Let's break down the specific types of modules and how they work.

What is a 100G to 25G Adapter Module?

It's a device that takes a single 100Gbps signal (typically using a 4x25Gbps electrical lane structure inside the switch) and "adapts" or "breaks it out" into four separate 25Gbps signals. This can be done in two primary ways:
1.Inside the Switch: Using a QSFP28 Breakout Transceiver.
2.Outside the Switch: Using a Media Converter or Gearbox Module.

Type 1: QSFP28 Breakout Transceivers (Most Common "Module")

This is the standard and most widely used type of module. It's a QSFP28 form-factor transceiver that you plug directly into the 100G switch port. Its key feature is that it is designed to connect to four separate 25G devices via fiber optic cables.
How it works:
The switch sends four electrical 25G lanes to the QSFP28 module.
The module converts these to four optical signals.
It has a multi-fiber connector (MPO/MTP-12) on its end.
You use an MPO-to-4xLC Breakout Harness (a special fan-out cable) to connect the single MPO port to four duplex LC fiber pairs, which then plug into four SFP28 transceivers on the 25G devices.
Common Standards:
100G SR4 QSFP28: Uses multi-mode fiber (OM3/OM4). Reaches up to 100 meters.
Example: You plug a 100G SR4 module into your switch. You connect it via an MPO-12 to 4xLC duplex breakout harness to four 25G SR SFP28 modules in your servers.
100G PSM4 QSFP28: Uses single-mode fiber. Reaches up to 500 meters.
100G DR/FR QSFP28: Uses single-mode fiber for longer reaches (500m to 2km).
Use Case: Ideal for structured cabling in data centers where you want to run a single MPO trunk cable from a central patch panel to a top-of-rack switch, then break out to individual servers.

Type 2: Standalone Media Converter / Gearbox Modules

This is a more literal interpretation of an "adapter module." It's an external, standalone device (often in a 1RU chassis) that acts as a converter between form factors.
How it works:
You plug a standard 100G QSFP28 transceiver (e.g., for long-haul 100G links) into one side of the module.
On the other side, it has four SFP28 slots.
You plug four standard 25G SFP28 transceivers into these slots.
The module internally "gearboxes" or converts the signal, taking the 100G input and splitting it into four 25G outputs.
Use Case:
Legacy Integration: Connecting a new 100G core switch to an older distribution switch that only has 25G SFP28 ports.
Protocol Conversion: In some cases, these devices can also convert between different Ethernet protocols or extend distances.
Test Labs: For flexibility in connecting equipment with different port types.

Key Advantages of Using Modules over Breakout Cables

1.Flexibility: You can choose the exact fiber type (multi-mode/single-mode) and distance (SR/LR/ER) for your environment by selecting different SFP28 transceivers for the server ends.

2.Repairability: If a cable is damaged, you only need to replace the MPO harness or a single LC patch cable, not an entire expensive active assembly.
3.Standardization: Uses standard, interchangeable transceivers on both ends, which can be spares for other parts of your network.
4.Longer Distances: Enables breakout over much longer distances than what is possible with AOCs or DACs.

Critical Configuration Requirement

Just like with breakout cables, the 100G switch port must be configured in "breakout mode" (e.g., breakout mode 4x25g) for the QSFP28 transceiver method to work. The standalone media converter method does not require this, as the switch just sees a standard 100G link.

Summary: Module vs. Cable

Feature	QSFP28 Breakout Transceiver (Module)	Breakout Cable (AOC/DAC)
Form	QSFP28 Module + MPO-to-LC Harness	Integrated QSFP28 to 4xSFP28 cable
Flexibility	High - Choose fiber type & optics	Low - Fixed type and length
Cost	Medium (module + harness + 4x SFP28s)	Lower for short reaches
Best for	Structured cabling, longer reaches, data centers	Direct server-to-switch, short reaches, simplicity

In conclusion, when you search for a "100G to 25G adapter module," you are most likely looking for a QSFP28 breakout transceiver (like a 100G SR4) and its corresponding MPO-to-LC breakout harness. Always confirm compatibility with your switch vendor and ensure the switch port is configured for breakout mode.