Abstract
The Internet and wireless networks are two of the most important technical developments that have had a direct effect on the lives of people over the past few years. The Internet allows easy and inexpensive access to useful information, independently of where that information was generated or is currently keep. The wireless networks on the other hand have broken the tie between location and access to communication. The next step is to combine these two technologies to provide wide-area wireless Internet access.Currently, Transport Control Protocol/Internet Protocol (TCP/IP) is the most important protocol that integrates a wide range of different physical networks into a global Internet. The environment of wireless networks violates many assumptions made by traditional TCP/IP. Compared with fixed and wired networks, the wireless networks have high bit-error rate (BER) and offer less available bandwidth. Furthermore, the host mobility also results in packet loss or delay during handoff procedures. Hence, the performance of TCP/IP over such wireless networks without any modification would suffer significant degradation of throughput and high interactive delay. In this paper, we propose some schemes to improve the performance of TCP/IP over wireless networks according to their characteristics. These improved mechanisms are as follows: First, the data-link layer retransmission without transport layer one to quickly recovery losses over the wireless networks, and the strategy of our data-link retransmission is flexible to adapt for different service classes with varying requirements. Second, a loss-tolerated TCP/IP header compression is used over the wireless link to reduce header overhead and resist packet loss or out-of-order problems. Third, an adaptive scheme for the size of MAC frame is also proposed to achieve optimal goodput under time-varying conditions of wireless networks. Finally, in order to provide seamless communication, a direction-based selective multicast handoff approach is used for real-time applications. On the other hand, the usual forward-based handoff procedures are used for non-real-time traffics to save scarce bandwidth of wireless networks.In this thesis, we analyze the performance of TCP/IP under different network conditions by using ns-2 simulator to facilitate comparisons with other previous studies. The simulation results show that our proposed mechanisms achieve better performance than other protocols.