DR (Direct Reach) and FR (Far Reach) are commonly used terms in Ethernet optical transceivers, referring to different types of transmission distances and implementations.
| Feature | DR (Direct Reach) | FR (Far Reach) |
|---|---|---|
| Definition | Directly modulated laser (DML) transceiver for shorter reach | Uses externally modulated laser (EML) for longer reach |
| Transmission Distance | Typically up to 500m (for DR4) | Typically up to 2km (for FR4) |
| Number of Lanes | DR4: 4 lanes, DR1: 1 lane | FR4: 4 lanes (MUX to 1 fiber pair) |
| Wavelengths | Uses a single wavelength per lane (e.g., 1310nm) | Uses CWDM4 wavelengths (1271nm, 1291nm, 1311nm, 1331nm) |
| Multiplexing | No WDM, uses parallel fibers (e.g., 4-fiber MPO) | Uses Wavelength Division Multiplexing (WDM) to combine 4 channels into 1 fiber pair |
| Typical Applications | Short-range, intra-datacenter connections | Longer-range datacenter interconnects |
| Example Standards | 400G DR4 (500m) | 400G FR4 (2km) |
Key Takeaways
- DR (Direct Reach) is used for shorter-distance links, usually within a single data center.
- FR (Far Reach) is used for longer data center interconnects (DCI) or campus networks.
- FR uses WDM technology to reduce fiber count, whereas DR uses parallel fiber connections.