Virtual Flow Queueing for Improving TCP Performance over IEEE 802.11 WLANs

We propose a packet scheduling discipline called virtual flow queueing (VFQ) to improve the end-to-end performance of TCP connections over IEEE 802.11 WLANs. VFQ is based on an inter-layer approach: the IP layer schedules packets over the wireless link according to the information coming from both the transport and MAC layers. The scheduler computes virtual transmission times that take into account the channel time at the MAC layer needed to transfer both TCP and ACK segments. The scheduling discipline achieves fair allocation of wireless channel capacity to TCP connections in both directions (upload and download). VFQ also supports different weights like in the classical WFQ scheduling so that the access point can for instance give preference to download connections. In this paper, we describe the VFQ implementation in the Linux kernel and present the results of measurements that show very good performance behavior of VFQ compared to the FIFO scheduling discipline currently deployed in 802.11 access points.