QSFP28

QSFP28 is the 100 Gb/s module (4 × 25G) that defined the 100GbE era. It keeps the QSFP+ outline and management model while raising each lane to 25G, and it is the most widely deployed 100G form factor in datacentres today.

Key facts

Specifications

• SFF-8665 — QSFP+ 28 Gb/s 4X Pluggable Transceiver Solution (QSFP28).
• SFF-8679 — QSFP+ 4X Hardware and Electrical Specification 1.8.
• SFF-8662 — 28 Gb/s Connector (Style A); SFF-8672 — 28 Gb/s Connector; SFF-8663 — 28 Gb/s Cage (Style A).
• SFF-8636 — Management Interface.
• SFF-TA-1004 — Tunable QSFP+/QSFP28 Memory Map for ITU Frequencies.

Management interface

Paged SFF-8636 exactly as for QSFP+, with 100G compliance codes from SFF-8024. Two details matter at 100G:

• FEC — many 100G PMDs require RS-FEC (CWDM4, SR4 at full reach); host and module FEC settings must agree or the link will not train.
• Power class — the module advertises its power class; a host may hold a module in low power until it confirms it can supply the class.

Compatibility notes

• Accepts QSFP+ modules (port drops to 40G).
• 4×25G breakout to four SFP28 links (SR4/PSM4).
• Mechanically fits QSFP56 and QSFP-DD ports; a QSFP-DD cage runs a QSFP28 on four of its eight lanes.

In CodingBox

Fully supported per SFF-8636: identity, per-lane DDM, thresholds and vendor pages as editor tabs, with checksums recalculated on write. QSFP28 is the second most-recoded form factor after SFP+ — see Vendor lock.