Priority inversion and queue management for 802.11 priority WLANs

All priority-based IEEE 802.11 networks use the 802.11e standard or one of its variants to improve the quality of service (QoS). An enhanced data link layer, which services packets in a manner that is consistent with their priority, is proposed by the standard. Buffer management and packet scheduling are two key components of a QoS mechanism operating at this layer. The 802.11e standard includes a well-defined packet scheduler, but it does not specify a buffer management policy. Buffer management policies determine which packets are discarded during network congestion. The drop tail algorithm is the traditional approach to buffer management and is both computationally simple and widely implemented. However, we show that drop tail can significantly reduce the throughput of a typical wireless network and lead to a priority inversion. We present the reasons for this performance degradation, propose several remedies, and recommend a new buffer management policy for 802.11e networks.