QSFP28 DAC vs Optical Fiber — 100 GbE Comparison
For 100 GbE links, you have two primary options: QSFP28 DAC (Direct Attach Copper) or QSFP28 optical with fiber patch cables. Each is optimal for different scenarios.
Quick Verdict
DAC for in-rack and adjacent-rack links (up to 5m active, 3m passive). Optical for cross-room, cross-floor, or long distances (up to 10 km LR, 80 km ER).
Side-by-Side Spec Comparison
| Spec | QSFP28 DAC Cable | QSFP28 Optical Fiber |
|---|---|---|
| Reach | 1-7m (3m passive, 5m active) | 100m (SR) / 10km (LR) / 80km (ER) |
| Latency | ~50ns | ~5μs (SR/LR) |
| Power per End | 0.5W passive / 1.5W active | 3.5W SR / 4W LR |
| Cost per 100G port pair | $50-300 (DAC) | $300-1,500 (optic + fiber) |
| Cable Flexibility | Fixed (cable + transceiver welded) | Modular (swap optics) |
Green-highlighted cells indicate the winner for that spec.
Frequently Asked Questions
When should I use DAC vs optical?
DAC for in-rack uplinks (ToR to leaf) where reach < 5m. Optical for any link over 5m, structured cabling deployments, or cross-room runs.
Are DAC cables cheaper?
Significantly — 100G DAC: $50-300. 100G optic + 5m fiber: $400-1,500. For short-reach in-row links, DAC saves 60-80% per port pair.
Our Recommendation
DAC for short-reach (under 7m) in-row interconnects. Optical for everything else.
Need help deciding?
Email sales@prodisknetwork.com with your specific requirements. Our team will match you to the right product based on your workload, budget, and existing infrastructure.