Airtime Ping-Pong Effect in IEEE 802.11s Wireless Mesh Networks

Airtime is set as the default routing metric for the ongoing IEEE 802.11s wireless mesh networking standard. The metric is designed to minimize channel resource consumption by accounting for loss rate, bandwidth, and channel characteristics. However, the metric exhibits a noticeable ping-pong effect whose nature is still vague, and the very few references to this in the literature condemn it for being a perilous behavior. In this paper, we present a thorough study of the Airtime pingpong effect, and highlight its correlation to the underlying rate control algorithms. Using different rate control algorithms (e.g., ARF, AARF, ONOE, AMRR and Constant rate), we prove that transmission rate adaptation is the principal cause behind the effect. We show that the effect is an inherent behavior, and that an accurate characterization of it can help improve network performance. We present a ping-pong-aware mechanism that, by detecting when a link undergoes such an effect, adapts the routing protocol for better network performance. The mechanism is O(1), decentralized, and can be easily integrated into the IEEE 802.11s routing protocol.