Optics in depth: lanes, reach codes, breakouts and FEC

Skills you'll practise

• Decode an Ethernet optic name into speed, reach class, media and lane count
• Choose an optic and fiber for a stated distance from the reach figures in a manufacturer's data sheet
• Plan a breakout from a QSFP port to four lower-speed ports, including the cable, the far-end optics and the port configuration
• Explain why some optics and DACs need FEC on the host port and diagnose a link that is down because FEC settings disagree

Course outline

1. 1.Optics in depth: lanes, reach, breakouts and FECVideo · 3 min
2. 2.Reading the name: speed, reach and lanesLesson · 20 min
3. 3.Choosing an optic and fiber for a distanceLesson · 20 min
4. 4.Breakouts and forward error correctionLesson · 20 min
5. 5.Optics in depth: lanes, reach codes, breakouts and FEC: knowledge checkKnowledge check · 18 questions
6. 6.Final exam8 questions · passing it completes the course, so people who already know the material can test out

Sources it draws on

The lessons and questions are written from these references, so learners can go back to the original.

• Cisco 10GBASE SFP+ modules data sheet (10GBASE-SR 300 m OM3 / 400 m OM4; LR 10 km; ER 40 km with attenuator note; COM/EXT/IND temperature ranges)
• Cisco 25GBASE SFP28 modules data sheet (25G SR 70 m OM3 / 100 m OM4; RS-FEC required on the host port)
• Cisco 40GBASE QSFP modules data sheet (SR4 MPO-12 100 m OM3 / 150 m OM4; 4x10G breakout to 10GBASE-SR; LR4 10 km)
• Cisco 100GBASE QSFP modules data sheet (SR4, SR1.2 BiDi, PSM4, DR, FR, CWDM4, LR4, ER4L reaches and connectors; QSFP to 4xSFP25G copper breakout)
• 100 Gigabit Ethernet: summary of IEEE 802.3 physical layers (naming: SR/LR/ER and lane-count suffix; SR4 and SR10 MPO connectors)
• NVIDIA Cumulus Linux 5.15 user guide: Switch Port Attributes (breakout ports swp1s0–swp1s3, FEC modes, IEEE 802.3by 25G DAC classes CA-25G-L/S/N)