QSFP

The original Quad Small Form-factor Pluggable (QSFP) introduced the idea of four lanes in one pluggable module. Its early rates were modest by today's standards, but the mechanical outline it defined is still the basis of QSFP+, QSFP28, QSFP56 and QSFP112.

Key facts

Specifications

• INF-8438 — QSFP Transceiver 1.0: the original QSFP MSA (mechanical, electrical,

management basics).

• SFF-8436 — QSFP+ 4X 10 Gb/s Pluggable Transceiver: the successor document that

carried the QSFP family forward and defined its management memory until SFF-8636 took over.

Management interface

QSFP established the single-address, paged management model later formalised in SFF-8636: one two-wire address (A0h), a lower page always available, and upper pages selected by a page-select byte at address 127. Early modules follow INF-8438/SFF-8436 layouts; the fields are compatible in spirit with SFF-8636 but not always byte-for-byte.

Compatibility notes

• QSFP modules fit QSFP+ and later cages, but hosts may not support the old low rates.
• The four-lane layout is why every later QSFP generation supports 4× breakout into

single-lane SFP-class links.

In CodingBox

CodingBox reads original QSFP modules with the QSFP/SFF-8436 layout and treats them as the first member of the four-lane family alongside QSFP+.