On the practical feasibility of fair TCP communications in IEEE 802.11 based multihop ad hoc wireless networks

In the center of this dissertation is the question whether it is practically feasible to achieve deterministically good quality for traditional network services such as file transfer and Web browsing in multihop wireless mobile ad hoc networks (MANETs). Despite the straight forward benefits of MANETs such as quick installation due to the absence of wireline infrastructure, and the virtue of dynamic re-configuration, these networks mainly exist in research labs so far. One of the stumbling blocks which prevents MANETs from wide deployment and popularization, is the poor and unstable performance of the TCP protocol which underlies file transfer and Web traffic. In particular, the problem considered in this thesis is the severe unfairness between multiple TCP sessions in a wireless context. Overall, the thesis explores the operational range of MANETs in which the quality of network services is acceptable for an end user. The first part of our work reveals that this range is extremely narrow for the plain combination of TCP and wireless communication according to IEEE 802.11. The second part of this work studies the interactions of TCP and IEEE 802.11 assuming static routing in the network. It gives a systematic view on fairness in MANETs. The max-min fairness model from the wireline Internet is adapted to the specifics of the wireless environment. The resulting solution presented in this thesis is an adaptive distributed capacity allocation scheme for multihop wireless networks. It leads to a dramatic improvement of TCP performance and a significant extension of the operation range. The third part analyzes the effect of ad hoc routing on the quality of TCP sessions. The routing traffic itself is one of the reasons for unfair TCP communications. Finally, the thesis addresses implementation issues of the suggested fairness model. It describes a distributed protocol for the dynamic control of the network load, which is implemented both for a network simulator and a real-world operating system.