Measuring the state of ECN readiness in servers, clients,and routers

Better exposing congestion can improve traffic management in the wide-area, at peering points, among residential broadband connections, and in the data center. TCP's network utilization and efficiency depends on congestion information, while recent research proposes economic and policy models based on congestion. Such motivations have driven widespread support of Explicit Congestion Notification (ECN)in modern operating systems. We reappraise the Internet's ECN readiness, updating and extending previous measurements. Across large and diverse server populations, we find a three-fold increase in ECN support over prior studies. Using new methods, we characterize ECN within mobile infrastructure and at the client-side, populations previously unmeasured. Via large-scale path measurements, we find the ECN feedback loop failing in the core of the network 40% of the time, typically at AS boundaries. Finally, we discover new examples of infrastructure violating ECN Internet standards, and discuss remaining impediments to running ECN while suggesting mechanisms to aid adoption.