28 Optical Splitter Ports

A single QSFP28 port can be split into four lower-speed optical channels, typically 25G each, using breakout cables or transceivers.

Overview of QSFP28 Splitter Functionality

QSFP28 (Quad Small Form-factor Pluggable 28) ports support four independent lanes, each capable of 25–28 Gbps, allowing a single 100G port to be split into four discrete 25G connections . This is commonly referred to as breakout or splitter functionality. The physical interface uses CAUI-4, which defines how the switch ASIC communicates with the module, and the module converts these electrical lanes into optical signals for CWDM4, LR4, ER4, or parallel fiber SR4/PSM4 connections .

Types of Splitter Implementations

1. Breakout DACs (Direct Attach Cables): Copper cables that split a single QSFP28 port into multiple SFP28 ports for short-distance connections .
2. Breakout AOCs (Active Optical Cables): Optical cables that provide longer reach while splitting a 100G port into four 25G links .
3. Breakout Transceivers: QSFP28 modules that connect to MPO-12 or parallel fiber and split into four SFP28 ports via patch panels or breakout cables .

Practical Use Cases

• Data Center Flexibility: One 100G port can serve multiple 25G devices, improving port utilization without adding extra 100G ports .
• Server Connectivity: QSFP28-to-4xSFP28 splitter cables allow a single 100G switch port to connect to four 25G server NICs .
• Network Upgrades: Breakout ports simplify transitions from 25G to 100G networks while maintaining compatibility with existing infrastructure .

Configuration Notes

On switches supporting AOS-CX, a QSFP28 port can be split using a CLI command (split), which disables the port, clears its configuration, and creates multiple interfaces. The split interfaces may require a reboot depending on the software version . Not all QSFP28 ports can be split into 25G or 10G channels; the switch must have MACs and PHYs that support the desired speeds .

Summary

28 optical splitter ports generally refer to the ability of a QSFP28 100G port to break out into four 25G optical channels. This is achieved using breakout cables, AOCs, or transceivers, enabling flexible, cost-effective, and high-density network deployments in data centers and enterprise networks .