Reducing Handover Latency And Improving Tcp Performance In Wireless Networks

Modern network technologies first evolved in wired networks and subsequently entered the wireless network field. Applications may work in pure wired network, pure wireless network or hybrid network. Improving performance in these network infrastructures has been a continuous effort for decades. In this dissertation, we tackle two important challenges: (1) improving handover performance in heterogeneous wireless network, and (2) improving TCP performance in multi-hop wireless network. In heterogeneous network, users expect uninterrupted services moving from one network to another. IEEE proposed Media Independent Handover (MIH) to make it possible to achieve better handover performance. Currently, Mobile IPv4 (MIP) is the dominant mechanism for mobility management and is expected to persist into the future. However, when multiple interfaces of a mobile client are connected to a Foreign Agent (FA), MIP and its existing improvements do not perform well when the active interface fails unexpectedly. In this dissertation, we propose novel mechanism and MIP extension with MIH support. We prove experimentally that the new approach eliminates the FA-HA latency and achieves much faster handover, compared with existing mechanism. Our method also allows FA-bicasting, which can improve transmission reliability by combining traffic from different links, through the same FA. In multi-hop wireless networks, the main network factor that affects TCP performance is the medium-access contention, complicated by other factors like hidden terminal. We analyze the TCP congestion window and provide a more accurate estimate of its optimal value than those reported in the prior work. We also show that the much shorter TCP-ACK packets consume comparable channel capacity as the much longer data packets. We therefore propose two methods to improve TCP throughput, as follows. (1) Segregate the flows of data and ACK using static routing in grid wireless network, (2) Develop an improved variant of delayed TCP ACK by minimizing the number of ACK packets. Our evaluation validates the effectiveness of the proposed method, which can enhance TCP performance significantly. In terms of throughput, it achieves up to 204% improvement over the regular TCP in chain-topology wireless networks, and about 35% improvement in a complex grid wireless network. We also propose a new architecture to achieve higher throughput when multiple TCP connections exist.