QSFP+ & QSFP28 Transceivers

QSFP is the high-density form factor that carries 40G and 100G links. The two generations are physically similar and functionally quite different, and confusing them is the most expensive mistake in this category.

How the two generations are built

• QSFP+ (40G) — four lanes of 10 Gbps
• QSFP28 (100G) — four lanes of 25 Gbps

That lane structure is why breakout works: a 40G port can commonly be split into four 10G links, and a 100G port into four 25G links, given platform support and the right cable.

Reach types and the connectors they use

• SR4 — multimode, short reach, uses an MPO/MTP-12 ribbon connector
• LR4 — single-mode, typically to 10 km, uses duplex LC and multiplexes four wavelengths onto one fibre pair

The connector difference is critical and catches people out constantly: SR4 needs MPO trunk cabling, LR4 needs ordinary LC duplex. They are not interchangeable, and no adapter bridges them sensibly.

Direction of compatibility

A QSFP+ module will often work in a QSFP28 port at 40G. The reverse is generally not true — a QSFP+ port cannot drive a QSFP28 module at 100G, because the electrical lanes only run at 10 Gbps. Treat backward compatibility as one-directional and verify per platform.

We stock QSFP coded for Cisco, HPE, Aruba, Dell, Juniper, Mellanox and IBM platforms. Give us the switch model at each end and the fibre already installed and we will match optics and cabling as one set.