Bufferbloat Test
Bufferbloat is extra delay caused by packets waiting in oversized buffers while the link is busy. The test loads the link in each direction and reports the increase.
Bufferbloat Test
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How this test works
Phases: idle latency, loaded download, loaded upload. During each transfer a latency probe starts every 200 ms. Only probes that start inside the measurement window count; the start-up discard is the same as for throughput. Delta = the larger of the two loaded medians minus the idle median.
How to read the result
Grade by delta: A+ below 5 ms, A below 30, B below 60, C below 200, D below 400, F otherwise; comparison is strict. Partial means only one direction was graded. Without idle latency or without a loaded value the grade is "no data". The delta itself is reported in ms.
What is typical
Grade boundaries come from a published bufferbloat grading scale cited in the code. The gaming and call estimates on the speed test page use the worse loaded latency when it exists, and idle latency otherwise.