Analytical Modeling of TCP clients in wi-fi hot spot networks

The channel utilization of 802.11-based wireless local area networks has been studied extensively from an analytical perspective. However, these studies consider wireless networks formed by saturated stations that transmit UDP-like traffic to randomly selected destinations. This model cannot be easily applied to hot spots since: i) the majority of Internet applications are based on the TCP protocol; ii) the TCP traffic is rate-controlled and the TCP flow control mechanisms impede the stations to saturate; and iii) the users' traffic is either sent towards or received from the access point. This paper is the first to provide an analytical model of the channel utilization in hot spots when there are M users which use TCP connections to download traffic from the Internet. Specifically, in this work we analytically investigate the complex interaction of the TCP flow control mechanisms and MAC collision avoidance techniques in 802.11b-based hot spot networks. We validate our model by means of simulations, and we exploit it to provide thorough reasons of the following counter-intuitive observations: i) the channel utilization is almost independent of the number of TCP connections, ii) on average the access point contends with few users for the channel bandwidth.