Ending the Anomaly: Achieving Low Latency and Airtime Fairness in WiFi

TL;DR

This paper introduces a novel queueing scheme and airtime fairness scheduler for WiFi that significantly reduces latency, improves throughput, and ensures fairness without requiring client modifications, validated through theoretical analysis and real-world experiments.

Contribution

The paper presents a new queueing scheme to eliminate bufferbloat and an airtime fairness scheduler for WiFi, implemented in Linux kernel and adopted into mainline.

Findings

Order of magnitude latency reduction under load

Large throughput improvements for multiple stations

Near-perfect airtime fairness for TCP and UDP

Abstract

With more devices connected, delays and jitter at the WiFi hop become more prevalent, and correct functioning during network congestion becomes more important. However, two important performance issues prevent modern WiFi from reaching its potential: Increased latency under load caused by excessive queueing (i.e. bufferbloat) and the 802.11 performance anomaly. To remedy these issues, we present a novel two-part solution: We design a new queueing scheme that eliminates bufferbloat in the wireless setting. Leveraging this queueing scheme, we then design an airtime fairness scheduler that operates at the access point and doesn't require any changes to clients. We evaluate our solution using both a theoretical model and experiments in a testbed environment, formulating a suitable analytical model in the process. We show that our solution achieves an order of magnitude reduction in latency under load, large improvements in multi-station throughput, and nearly perfect airtime fairness for both TCP and downstream UDP traffic. Further experiments with application traffic confirm that the solution provides significant performance gains for real-world traffic.We develop a production quality implementation of our solution in the Linux kernel, the platform powering most access points outside of the managed enterprise setting. The implementation has been accepted into the mainline kernel distribution, making it available for deployment on billions of devices running Linux today.