Loaded latency: the number a speed test can hide
Loaded latency measures responsiveness while the connection is actively transferring data. It is one of the clearest ways to expose queueing problems.
Idle vs loaded latency
Idle latency is measured while the line is relatively quiet. Loaded latency is measured while download or upload traffic is deliberately filling the path. The useful comparison is the increase: loaded latency minus the idle baseline.
| Example | Idle | Loaded | Added latency |
|---|---|---|---|
| Responsive line | 18 ms | 31 ms | +13 ms |
| Noticeable queueing | 18 ms | 132 ms | +114 ms |
| Severe queueing | 18 ms | 430 ms | +412 ms |
Why we show p95 too
A median describes the typical measured latency, but real-time apps can be hurt by spikes. Connection Vitals therefore also exposes the 95th percentile in Advanced Details. It means 95% of the observed samples were at or below that value.
Download and upload are different
Many consumer connections are asymmetric. Upload capacity may be much lower than download capacity, so an upload can fill its bottleneck queue quickly even when download-loaded latency looks fine. Connection Vitals measures the two directions separately.