HERMES: Repurposing User-Driven Speed Tests to Monitor the Internet

Diagnosing performance degradations and pinpointing their source is crucial for operators to make informed routing decisions and for policymakers and researchers to assess the Internet's stability, yet no publicly available observatories currently provide this capability. Existing solutions rely on coarse-grained signals that fail to capture end-user performance, while proprietary solutions are inaccessible and offer limited attribution for identifying the source of a problem. We introduce HERMES, the first open system to fill this gap. HERMES uses publicly available M-Lab speed tests—data that has existed for years but has not previously been used to automatically detect and explain end-user performance degradations at scale. To achieve these goals, HERMES combines statistical techniques to detect performance degradation with novel tomography methods and forward and reverse path measurements to localize the source of a problem. Despite relying only on public data, HERMES matches a reimplementation of a large cloud provider's monitoring system for 94.5% of events visible to both systems, agreeing on the degradation source in the path. HERMES also surfaces 11× more publicly discussed events than existing public observatories. We demonstrate its ability to track weather- and cable-cut disruptions, diagnose routing inefficiencies, and identify persistently congested links.