Token bucket based traffic shaping and monitoring for WLAN-based control systems

In industrial automation, there is strong interest in using wireless technologies to run production environments, and in particular to build networked control systems. To operate such networks effectively, sufficient control over the communication system is needed, regarding, e.g., bandwidth usage, frame latency, and frame loss. In this paper, we present an approach for traffic shaping that applies a variant of the token bucket algorithm, and an approach for traffic monitoring in order to determine network overload. In particular, we introduce and apply a metric called unusable wasted bandwidth ratio, which is derived from the number of unusable wasted tokens to detect network overload locally. We have implemented both approaches on a commercial platform with WLAN adapters, and have conducted real experiments to assess their performance.