What SR, DR, FR, LR, ER and ZR mean, typical distances by speed, and when copper DAC or AOC is the better choice.
Updated October 2026 · AltoChip team · General reference — project specifics are confirmed in each quotation.
The letters after the speed describe reach and optics: SR short reach over multimode fiber; DR about 500 m over single-mode, usually parallel; FR about 2 km single-mode; LR about 10 km single-mode; ER and ZR are longer-haul classes. A number after the code (SR4, DR4, SR8) is the count of optical lanes, which also decides the connector.
| Module | Fiber | Typical reach | Connector |
|---|---|---|---|
| 10G-SR | OM3 / OM4 | 300 m / 400 m | LC duplex |
| 10G-LR | OS2 | 10 km | LC duplex |
| 25G-SR | OM3 / OM4 | 70 m / 100 m | LC duplex |
| 100G-SR4 | OM3 / OM4 | 70 m / 100 m | MPO-12 |
| 100G-CWDM4 | OS2 | 2 km | LC duplex |
| 100G-LR4 | OS2 | 10 km | LC duplex |
| 400G-SR8 | OM4 | 100 m | MPO-16 |
| 400G-DR4 | OS2 | 500 m | MPO-12 |
| 400G-FR4 | OS2 | 2 km | LC duplex |
| 800G-DR8 | OS2 | 500 m | MPO-16 or 2 × MPO-12 |
Typical published classes; the exact reach and connector are confirmed against each module's datasheet in the quotation.
Inside a rack, a direct-attach copper cable (DAC) is often the simplest and lowest-power option, typically up to a few meters. Active optical cables (AOC) cover longer in-row runs with fixed ends. Separate modules plus patch cables give the most flexibility for structured cabling and longer distances. Tell us the distance and we will suggest which of the three fits.