It measures both "Write" (Upload) and "Read" (Download) speeds.
| Observed Speed | Likely Cause | |----------------|----------------| | 900–1000 Mbps | Optimal gigabit performance | | 100–110 Mbps | Cable or switch limited to Fast Ethernet | | 10–30 Mbps | Wi-Fi interference or half-duplex collision | | Highly variable speed | Auto-negotiation failure, driver issue, or disk I/O bottleneck | | Packet loss >0.1% | Faulty cable, duplex mismatch, or switch buffer overflow | lan speed test v350ph link