The Impact of Rts/cts Exchange on the Performance of Multi-rate Ieee 802.11 Wireless Networks
نویسنده
چکیده
All Rights Reserved iv Dedication This thesis is dedicated to my parents. They have supported me in my studies. and feedback on this thesis. I would also like to thank all the faculty members and staff of Indiana University South Bend who have taught and helped me during my studying. Finally, I would like to thank my parents for their support and patience. Abstract The RTS/CTS mechanism is an optional mechanism in DCF (Distributed Coordination Function) in IEEE 802.11 standard, which was designed to solve the hidden node problem. However, the RTS/CTS mechanism is turned off in most infrastructure-mode WLANs because the additional RTS/CTS frames exchange introduces transmission overhead. People commonly believe that the benefits of RTS/CTS might not be able to pay off the transmission overhead in 802.11 WLANs. While this is often true in 802.11 WLANs with a single transmission rate, this investigation led to an opposite conclusion for 802.11 WLANs when multiple transmission rates are exploited. A phenomenon called rate avalanche was found in the investigation if the RTS/CTS mechanism is turned off in a heavily-loaded 802.11 WLAN. Even if no hidden node is present, high collision rates not only lead to packet retransmissions but also drive the nodes to switch to lower data rates. The retransmissions and the longer time occupation caused by lower rates will increase the amount of channel contention, which yields more collisions. This vicious cycle could significantly degrade the performance of WLANs even though no hidden node problem is present. The research found that the effect of rate avalanche could be ameliorated by simply turning on the RTS/CTS mechanism in most cases of the investigation. Various scenarios/conditions are examined in studying the impact on the network performance for RTS/CTS on and off respectively. The investigation provides some insights about the impact of RTS/CTS exchange on the performance of multi-rate 802.11 WLANs.
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