Form factors: overview & comparison

An optical transceiver's form factor fixes its size, connector, electrical interface, lane count and — crucially for CodingBox — the management specification that defines where every field lives in module memory. CodingBox supports the 14 form factors below; each has its own reference page.

The single-lane family (SFP lineage)

The four-lane family (QSFP lineage)

The eight-lane family (double density)

Three generations of management

• Two-address (SFF-8472) — SFP-class modules expose identity at A0h and diagnostics at A2h. See SFF-8472.
• Paged (SFF-8636) — QSFP-class modules use one address with a lower page and selectable upper pages. See SFF-8636.
• CMIS / MIS — QSFP-DD, OSFP, QSFP112 and SFP-DD use the form-factor-independent CMIS model (or its SFP-DD sibling MIS) with banked pages and a module state machine. See CMIS and MIS.

Codes shared by all of them — identifiers, connectors, interface codes — live in SFF-8024.

Why it matters

The form factor tells CodingBox which decoder to apply, so identity and DDM are read from the right addresses; reading an SFP as if it were a QSFP would misinterpret every field. CodingBox detects the form factor automatically. How a module protects its memory is a separate axis — see Write-protection types & programming.

Which cages accept which of these form factors, and what speeds the port behind the cage can run: Port types and cages.

Power class ladders and real consumption for each form factor: Power & consumption.

Which of these form factors and PMDs fits which fibre, distance and connector — the matching table from the plant's point of view, with the common module-to-plant mismatches: Transceivers in the link.