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Français Ethernet generations, lane rates & electrical interfaces
Every Ethernet speed since 10G has been built from a small set of lane rates — 10G, 25G, 50G, 100G and now 200G per lane — combined in parallel. Knowing which lanes a given speed is made of explains the module's electrical interface, why breakout works or does not, why a 100G module can be either 4 × 25G or 1 × 100G, and what a host and a module have to agree on before the light means anything.
Timeline of IEEE 802.3 projects
| Year | Amendment | Speeds | Lane signalling | Notes |
|---|---|---|---|---|
| 1998 | 802.3z | 1000BASE-SX/LX/CX | 1.25 GBd 8B/10B | GBIC → SFP era |
| 1999 | 802.3ab | 1000BASE-T | 4 pairs, PAM5 | copper 1G |
| 2002 | 802.3ae | 10GBASE-SR/LR/ER/LX4 | 10.3125 GBd 64B/66B | XENPAK/X2/XFP → SFP+ |
| 2006 | 802.3an / aq | 10GBASE-T / LRM | — | copper 10G; MMF 220 m with EDC |
| 2010 | 802.3ba | 40GBASE-SR4/LR4/CR4, 100GBASE-SR10/LR4/ER4 | 4 × 10G / 10 × 10G / 4 × 25G | QSFP+, CFP |
| 2014 | 802.3bj | 100GBASE-CR4/KR4 | 4 × 25G NRZ | introduces RS-FEC (528,514) |
| 2015 | 802.3bm | 100GBASE-SR4, CAUI-4, 40GBASE-ER4 | 4 × 25G | QSFP28 becomes possible |
| 2016 | 802.3by | 25GBASE-SR/LR/CR | 1 × 25G | SFP28; CA-25G-L/S/N cable classes |
| 2017 | 802.3bs | 200GBASE-FR4/LR4/DR4, 400GBASE-SR16/DR4/FR8/LR8 | 50G PAM4 (8 × 50G electrical) | RS-FEC (544,514) KP4 |
| 2018 | 802.3cd | 50GBASE-SR/FR/LR/CR, 100GBASE-SR2/DR/CR2, 200GBASE-SR4/CR4 | 50G PAM4 lanes | SFP56, QSFP56 |
| 2019–21 | 802.3cn / cu | 50/200/400G 40 km ER; 100GBASE-FR1/LR1, 400GBASE-FR4/LR4-6 | 100G PAM4 optical lanes | adopted the 100G Lambda MSA |
| 2022 | 802.3ck / db | 100G/lane electrical (100GAUI-1, 400GAUI-4, 800GAUI-8); 100G/lane VCSEL (SR1, SR4, VR) | 106.25 GBd PAM4 | QSFP112, OSFP 800G |
| 2024 | 802.3df | 800GBASE-DR8/SR8/VR8, -DR4 (200G/lane optical) | 8 × 100G electrical | 800G in OSFP / QSFP-DD800 |
| ~2026 | 802.3dj | 200G/lane electrical and optical; 800GBASE-DR2, 1.6TBASE-DR8 | 212.5 GBd PAM4 | 1.6T OSFP-XD, OSFP |
MSA interfaces (CWDM4, PSM4, ZR…) filled the gaps between these: Optical interface MSAs.
How speeds are built from lanes
| Speed | Electrical lanes (host ↔ module) | Optical lanes (typical) | Module |
|---|---|---|---|
| 10G | 1 × 10G (XFI/SFI) | 1 × 10G | SFP+ |
| 25G | 1 × 25G (25GAUI) | 1 × 25G | SFP28 |
| 40G | 4 × 10G (XLAUI/XLPPI) | 4 × 10G (SR4, LR4) | QSFP+ |
| 50G | 1 × 50G PAM4 or 2 × 25G | 1 × 50G PAM4 | SFP56 |
| 100G | 4 × 25G (CAUI-4) | 4 × 25G (SR4, LR4, CWDM4, PSM4) | QSFP28 |
| 100G | 2 × 50G (100GAUI-2) or 1 × 100G (100GAUI-1) | 1 × 100G PAM4 (DR, FR1, LR1) | QSFP28/QSFP56/QSFP112, SFP112 |
| 200G | 4 × 50G (200GAUI-4) or 8 × 25G | 4 × 50G (FR4, SR4, DR4) | QSFP56 |
| 400G | 8 × 50G (400GAUI-8) or 4 × 100G (400GAUI-4) | 4 × 100G (DR4, FR4, LR4) or 8 × 50G (SR8, FR8) | QSFP-DD, OSFP |
| 800G | 8 × 100G (800GAUI-8) | 8 × 100G (DR8, 2×FR4) or 4 × 200G (DR4) | OSFP, QSFP-DD800 |
| 1.6T | 8 × 200G | 8 × 200G (DR8) | OSFP-XD, OSFP |
When electrical and optical lane counts differ, a gearbox in the module's DSP converts between them — 400GAUI-8 to DR4 is the classic case (Modulation & DSP). When they match (4 × 25G CAUI-4 to SR4), the module is a simple retimer or even unretimed.
Electrical interface names
| Name | Lanes × rate | Used with |
|---|---|---|
| XAUI | 4 × 3.125 GBd (8B/10B) | XENPAK, X2, early 10G |
| XFI / SFI | 1 × 10.3125 GBd | XFP / SFP+ |
| 25GAUI | 1 × 25.78 GBd | SFP28 |
| XLAUI / XLPPI | 4 × 10.3125 | QSFP+ (retimed / parallel physical interface) |
| CAUI-10 / CAUI-4 | 10 × 10.3125 / 4 × 25.78 | CFP / QSFP28, CFP4 |
| 50GAUI-2 / 50GAUI-1 | 2 × 25.78 / 1 × 26.5625 GBd PAM4 | SFP56 |
| 100GAUI-4 / -2 / -1 | 4 × 25.78 / 2 × 26.56 PAM4 / 1 × 53.125 PAM4 | QSFP28 → QSFP112 |
| 200GAUI-8 / -4 / -2 | 8 × 25.78 / 4 × 26.56 PAM4 / 2 × 53.125 PAM4 | QSFP56 → QSFP112 |
| 400GAUI-16 / -8 / -4 | 16 × 25.78 / 8 × 26.56 PAM4 / 4 × 53.125 PAM4 | CFP8 → QSFP-DD/OSFP |
| 800GAUI-8 | 8 × 53.125 GBd PAM4 | OSFP, QSFP-DD800 |
The GBd figures include FEC and 64B/66B overhead: 25.78 GBd carries 25 Gb/s of payload, 53.125 GBd PAM4 carries 100 Gb/s. These names appear in CMIS application descriptors as the host-interface half (SFF-8024).
What must match
- Lane rate and count on the electrical side — a 4 × 25G port cannot drive a 2 × 50G module even if both say "100G".
- Modulation — NRZ lanes and PAM4 lanes are different physical layers.
- FEC — RS(528) for 25G NRZ lanes, RS(544) for all PAM4; mandatory or optional per PMD (FEC & link training).
- Encoding — 8B/10B (1G) vs 64B/66B (10G+); a dual-rate module switches both.
- Optical PMD at both ends — the wavelength, fibre and reach in Optical interfaces and the PMD reference.
The module declares all of this in its identity — nominal rate, encoding, compliance or application codes — and the host refuses combinations it cannot drive (Speed & rate).
In CodingBox
The Check transceiver screen shows the nominal lane rate, encoding and, for CMIS modules, the host-interface IDs of each application, so you can see at a glance whether a module is 4 × 25G or 2 × 50G before it meets a port.