TCP Fairness Enhancing Mechanisms In Wireless Ad Hoc Networks

Nowadays, wireless ad hoc networks have become a hot-point in science and industry, more and more specialists and scholars involved in the researches on it. Comparing with wired networks, it has some unique characteristics which induce many problems on network transmission. Specially, the TCP unfairness is one of the most significant problems. In order to solve this TCP unfairness problem, Dr. Xu Kaixin of UCLA proposed a Wireless Neighborhood theory and gave a network layer solution called Neighborhood Random Early Detection (NRED). The simulation results show that the NRED mechanism can improve the TCP fairness in wireless ad hoc network effectively. However, it has some limitations such as weak compatibility, hard for application, parameter sensitivity and weak robustness.In order to solve these aforementioned problems and seek for better solutions, we investigated the TCP unfairness in ad hoc networks systemically. We found that there are three main causations for this problem: the limitation of spatial reuse, the impact of the DCF protocol in MAC layer and the side-effect of TCP congestion control. Therefore, we probed into two main factors of the TCP fairness mechanism: Neighborhood Congestion Detection (NCD) and Neighborhood FairnessImprovement. At last, we proposed several new mechanisms in both aspects. In this dissertation, we firstly analyzed channel utilization measuring based NCD and improved it to queue length broadcasting based NCD. We also proposed two new neighborhood congestion detection schemes: packet sniffing based NCD and MAC delay measuring based NCD, and contrasted them in details by theoretic analysis, simulations and testbed experiments.Secondly, we worked on two potential neighborhood fairness improving schemes: NRED scheme and PAUSE scheme.Finally, after thorough studies and precise experiments, we draw a conclusion that TCP fairness in wireless ad hoc network can be greatly improved by using our improved mechanisms. In addition, we also described and analyzed some problems remained.