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.
Abstract
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
# helper function for accessing queue in the wireless node Node/MobileNode instproc get-ifq {} { $self instvar ifq_ return $ifq_(0) }