Wireless Networking

Evaluation of IEEE 802.11e WLANs

M. Thottan and M.C. Weigle, Impact of 802.11e EDCA on Mixed TCP-based Applications, Proceedings of the International Wireless Internet Conference (WICON), Boston, MA, August 2006.


There has been an explosive growth in the use of wireless LANs (WLANs) to support network applications ranging from web-browsing and file-sharing to voice calls. It is difficult to optimally configure WLAN components, such as access points (APs), to meet the quality-of-service requirements of the different applications, as well as ensuring flow-level fairness. Recent work has shown that the widely-deployed IEEE 802.11 MAC Distributed Coordination Function (DCF) is biased against downstream flows. The new IEEE 802.11e standard introduces QoS mechanisms, such as Enhanced Distributed Channel Access (EDCA), that allow this unfairness to be addressed. So far, only limited work has been done to evaluate the impact of these MAC protocols on TCP-based applications. In this paper, through ns-2 simulations, we evaluate the impact of EDCA on TCP application traffic consisting of both long and short-lived TCP flows. We find that the performance of TCP applications is very dependent upon the settings of the EDCA parameters and buffer lengths at the AP. We also show that the performance of the admission control strategy employed depends on the buffer lengths at the AP and the traffic intensity.

Running Our Experiments

To replicate the experiments we ran in the paper, we have provided links to the ns source code changes we made as well as to our experiment scripts.

ns-2 Source

Experiment Scripts

Contents of
scripts.tgz (also available individually):

Scripts for Running the Experiment