||Experimental Evaluation of TCP Performance in Multi-rate 802.11 WLANs
||EN615, Level 6, EN Building
||The goal of Rate Adaptation (RA) mechanisms in 802.11 WLANs is to provide optimum system throughput under varying channel conditions (e.g. in presence of noise) by carrying out run-time prediction and selection of the most appropriate bit-rate. The cross-layer interaction of TCP, as the major transport protocol in the Internet, with different RA mechanisms and DCF is yet to be thoroughly investigated. Previously reported efforts A) have never included real-life measurements of uplink TCP traffic; B) lack a practical view because they do not consider the RA mechanisms commonly deployed in today's off-the-shelf 802.11 devices; C) miss the study of RA mechanisms in low-noise environments. This paper covers all the above shortages, by conducting real-life measurements in two different test-beds (NDlab and Emulab) alongside with simulations, to study the performance of TCP coupled with different commonly deployed RA mechanisms. Our measurements reveal that 1) most conventional RA mechanisms are unable to distinguish frame errors due to collisions from channel noise/interference, and will respond to them negatively to some extent; 2) different than downlink TCP, uplink TCP can be adversely affected by collision-triggered rate downshifts that some RA schemes exhibit even under perfect channel conditions or in low-noise environments; 3) the relatively recent Minstrel RA mechanism can counter this negative uplink behavior well, yielding almost equal performance as in the downlink case.
This seminar is a trial run for a paper being presented at the IEEE International Symposium on a World of Wireless Mobile and Multimedia Networks (WoWMoM2012) - http://www.ieee-wowmom.org
||Naeem Khademi received a B.Eng degree in computer software from Kish University, Iran and his M.Sc degree from University Putra Malaysia in computer networks. He is currently a PhD student in the Networks and Distributed Systems group at the Department of Informatics, University of Oslo, Norway. His research interests include performance analysis, evaluation and optimization of wireless networks mainly by focusing on the cross-layer interactions e.g. between PHY/MAC and TCP, in 802.11 networks. As of May 2012, he is a visitor at the Centre for Advanced Internet Architectures (CAIA), Swinburne University of Technology.