What Is QSFP28?

QSFP28 is the pluggable format for 100G optical links. The name breaks down plainly: QSFP stands for quad small form-factor pluggable, meaning four lanes in one module, and 28 is the generation number that distinguishes it from the earlier QSFP format, which delivered 40G. A QSFP28 module delivers 100G through four lanes of 25G each, running in parallel over a multi-fiber connector. That construction is the whole idea of the format, and everything else about it follows from it.

The four-lane construction is what makes 100G practical at density. A single QSFP28 port delivers 100G in roughly the space that once delivered 10G, which is what allows a modern switch to carry many 100G ports in one rack unit. The same construction makes breakout possible: because the four lanes are independent, a QSFP28 port can be broken out into four 25G connections, each serving a separate device, where a mixed-speed design is needed. The breakout guide on this site explains that option in detail.

The connector for a QSFP28 module depends on the variant. Parallel-optics variants use a multi-fiber connector, which carries all four lanes in one plug. Other variants use a duplex connector with wavelength multiplexing, carrying all four lanes on different wavelengths over a pair of fibers. The variant determines the connector, and the connector determines the fiber plant and the patch panels the link needs. A buyer should confirm the variant and the connector together during the inquiry, because they are not independent choices.

QSFP28 sits at the top of the speed range on this site, above the 40G QSFP+ family and the 10G SFP+ and XFP families. The fully specified 100G model here is the QSFP28 LR4, whose detail page states a 100G rate, a 1310nm wavelength, 10km and 20km reach options over single-mode fiber, 103.1Gb/s aggregate bandwidth, power consumption below 3.5W and a 0 to 70 degree Celsius operating range. Those figures belong to that model alone. The remaining QSFP28 titles on the series page are listed at series level, with no figures invented for them.

A buyer new to 100G should start from the link rather than the module: the distance, the fiber type already installed, and the equipment at each end. Those three answers narrow the family quickly, and the series page then narrows it to a title. Before ordering, confirm quantity, price and delivery time during the inquiry. Certificates are available upon request.