An Experimental Study On TCP Performance In Wireless Networks

Recently, wireless network has developed rapidly with the expanding of IEEE 802.11 protocol family. A host of problems are created by various wireless network characteristics not found in wired network, and not all of these problems have been satisfactorily solved. Therefore TCP performance in wireless network is not as stable as in wired networks. Throughput and fairness are symbols of TCP performance. We proposed the Cross-layer TCP scheme to increase the TCP throughput and the D_NRED scheme to improve the TCP fairness.There are some characteristics different from wired network, such as channel exclusive, easy to be interference, high BER, and so on. TCP was designed to use in the reliable Communication Media. It assumes that the only reason of packets lost is due to network congestion. We proposed the Cross-layer TCP scheme to make the TCP adapt to wireless network. The scheme optimized the TCP congestion control arithmetic by using the MAC layer information. To validate the effectiveness of Cross-layer TCP, we implemented it in the simulation and experiment. Both of them showed that the performance of this sheme is better than original TCP.We found some problems of NRED through the experiment. In order to find the better way to improve TCP fairness, we propose the D_NRED scheme. The scheme detects congestion according to MAC layer delay and notifies the nodes which use too much channel to drop their packets. Thus the expressed node can get a chance to transmit. We actualized the D_NRED scheme both in NS2 simulator and in the testbed. This scheme includes three parts: how to find out the congestion center correctly and effectively; how to inform its neighbors about the congestion; and how the neighbors to calculate their local packet drop probability. The D_NRED scheme can be valid used because the testbed need not change the hardware.