Experimental results on the support of TCP over 802.11b: an insight into fairness issues

Great attention has been dedicated, in the recent years, to the WLAN standards that are opening the market to the short range and high data rate wireless services in the local and hot spot areas. Technically speaking, the main strength of the most quoted standard, the IEEE 802.11, is the fully distributed nature of the access scheme, that provides cheap and easy-to-install components, able to operate in the unlicensed spectrum, still guaranteeing broadband capabilities. The aim of this paper is to deeply investigate traffic issues in 802.11b networks by emphasizing the interaction between WLAN link layer parameters or Access Point buffer provisioning with uplink/downlink TCP fairness. The novel aspect is that this investigation is fully made in an experimental environment. A great portion of flows that are exchanged in a WLAN are TCP-based (e.g. FTP flows). We prove, with real experiments, that TCP suffers of some inequalities that derive to unfair bandwidth sharing between uplink and downlink. Our extensive experimental analysis shows the main effects of these inequalities on the TCP behavior and highlights some performance anomalies that are difficult to be measured via simulations.