Throughput Analysis and Measurements in IEEE 802.11 WLANs with TCP and UDP Traffic Flows

摘要

There is a vast literature on the throughput analysisof the IEEE 802.11 MAC protocol. However, very little has beendone on investigating the interplay between the collision avoidancemechanisms of the 802.11 MAC protocol and the dynamicsof upper-layer transport protocols. In this paper we tackle thisissue from an analytical, simulative and experimental perspective.Specifically, we develop Markov chain models to compute thedistribution of the number of active stations in an 802.11 WLANwhen long-lived TCP connections compete with finite load UDPflows. By embedding these distributions in the MAC protocolmodelling, we derive approximate but accurate expressions ofthe TCP and UDP throughput. We validate the model accuracythrough performance tests carried out in a real WLAN for a widerange of configurations. Our analytical model and the supportingexperimental outcomes show that: i) the total TCP throughput isbasically independent of the number of open TCP connections,and the aggregate TCP traffic can be equivalently modelled astwo saturated flows; and ii) in the saturated regime n UDP flowsobtain about n-times the aggregate throughput achieved by theTCP flows, independently of the overall number of persistentTCP connections. Index Terms--802.11 MAC protocol, TCP,UDP, performance modelling, Markov chain.