SFP56

SFP56 pushes a single lane in the SFP footprint to 50 Gb/s by switching from NRZ to PAM4 signalling — four voltage levels per symbol, so twice the bits at the same symbol rate as SFP28.

Key facts

Specifications

• Mechanical: the SFP28 definition of SFF-8402 and the SFF-8432 module and cage.
• Electrical: 50GAUI-1 (IEEE 802.3cd) — one PAM4 lane.
• SFF-8472 — Management Interface, with the extended rate and application codes

required for PAM4 modules.

Management interface

Still the two-address SFF-8472 model, but with PAM4-era additions: extended compliance codes from SFF-8024 and FEC expectations (RS-FEC is mandatory for 50GbE PAM4 optics). Because the host must know the module is PAM4 and enable RS-FEC, correct identity coding is essential — a module identified as the wrong type simply will not link.

Compatibility notes

• An SFP56 port typically accepts SFP28 and SFP+ modules at their rates.
• SFP56 is the single-lane sibling of QSFP56

(4×50G) and of the two-lane SFP-DD (2×50G).

In CodingBox

Supported per SFF-8472 with the extended PAM4 codes; identity, DDM, editing and writing work as for SFP28. When recoding an SFP56, keep the compliance and FEC-related codes consistent with the target platform's expectations.