CodingBox Documentation

QSFP+

QSFP+ is the 40 Gb/s four-lane module (4 × 10G) that made 40GbE practical and became the workhorse of datacentre spines in the 2010s. Its documents are the most extensive of any form factor, because the SFF Committee split mechanical, electrical, connector, cage and management into separate specifications.

Key facts

Lanes × rate4 × 10.3125 Gb/s (NRZ)
Total40G (also 4×14G for InfiniBand FDR, ~56G)
ConnectorMPO-12 (SR4/PSM4), LC duplex (LR4/ER4 via 4-λ CWDM), DAC/AOC
Supply3.3 V, up to 3.5 W typical
Applications40GBASE-SR4/LR4/ER4, InfiniBand FDR, 4×10G breakout

Specifications

  • SFF-8436 — QSFP+ 4X 10 Gb/s Pluggable Transceiver 4.9 (electrical, mechanical,

original management).

  • SFF-8635 — QSFP+ 4X 10 Gb/s Pluggable Transceiver Solution; SFF-8685 —

QSFP+ 14 Gb/s 4X Transceiver Solution (FDR).

  • SFF-8679 — QSFP+ 4X Hardware and Electrical Specification 1.8.
  • SFF-8661 — QSFP+ 4X Module; SFF-8682 — 4X Connector; SFF-8683 — Cage.
  • SFF-8636 — Management Interface for Cabled Environments.
  • SFF-TA-1004 — Tunable QSFP+/QSFP28 Memory Map for ITU Frequencies.

Management interface

Paged SFF-8636: lower page 00h (status, monitors, controls) plus upper pages 00h (identity), 01h/02h (thresholds, vendor) and 03h, selected via byte 127. Per-lane Rx power and Tx bias are reported for all four lanes, and per-lane Tx disable / loss-of-signal flags allow individual lane control. Codes come from SFF-8024.

Compatibility notes

  • Fits QSFP28 and later cages; most 100G ports fall back to 40G with a QSFP+ module.
  • 4×10G breakout to four SFP+ links uses an MPO-to-4×LC harness (SR4/PSM4 only —

LR4 multiplexes four wavelengths onto one fibre pair and cannot be broken out).

In CodingBox

Fully supported: SFF-8636 pages appear as tabs in the EEPROM editor, per-lane DDM on the DDM screen. The classic hidden fault — one degraded lane masked by aggregation — is visible here per lane (see Failures).