Witals: AP-Centric Health Diagnosis of WiFi Networks

In recent years, WiFi has grown in capacity as well as deployment demand. WiFi system administrators (sysads) want a simple answer to the question “Is my WiFi network healthy?”, and a possible follow-up “What is wrong with it?”, if it is reported as “unhealthy”. But we are far from having such an interface today. It is this gap that this work attempts to fill. We present Witals, a system for WiFi performance diagnosis. We first design a causal diagnosis graph, that extensively identifies the underlying cause(s) of WiFi performance problems. Next, we identify a set of metrics corresponding to nodes in this causal graph. These metrics are measured in real-time by an operational AP, and help in quantifying the effect of each cause. We design a diagnosis algorithm based on the causal graph and the metrics, which ultimately presents a sanitized view of WiFi network health to the sysad. We have implemented a prototype of Witals on an enterprise grade 802.11n AP platform. Using a variety of controlled as well as real-life measurements, we show that our diagnosis framework follows ground truth accurately. Witals has also helped the sysads uncover some unexpected diagnoses.