The Implementation And Improvement Of TCP/NC Under Linux

The wireless network has been large-scale used in recent years. However, with the characteristics of signal fading, external interference, multiple access competition and mobility, wireless link bit error rate is higher. Thus, TCP performs poorly under it. The study on this question put forward many improvement measures such as modifying TCP through mono-layer, modifying TCP with cross layer controlling and end-to-end improvement method, but these solutions don't improve fundamentally the poor performance of TCP under wireless network with high packet loss rate.Network coding provides a new idea to solve the problem. Sundararajan proposed TCP/NC based on network coding. Theoretical analysis and simulation have proved TCP/NC can improve throughput under high packet loss rate environment, but hadn't implemented and verified it under practical wireless environments.To evaluate and improve the performance of TCP/NC in practical wireless network, we firstly proposed to realize TCP/NC under Linux OS using Linux kernel module and inserted NC layer between TCP layer and IP layer. This method basically not modifies the original TCP/IP protocol stack of Linux. Because the inability of TCP/NC to change redundancy factor automatically influences the performance of TCP/NC, we put forward an algorithm which can adjust redundancy factor according to changes of throughput. We implemented ad R-TCP/NC protocol which can adjust redundancy factor dynamically under Linux kernel. Lastly several wireless Ad-Hoc network testbeds were constructed to evaluate, compare and analyze the performance of TCP, TCP/NC and ad R-TCP/NC. This paper also studies the impacts on TCP/NC and ad R-TCP/NC by redundant factor and coding window separately.Experimental results show that TCP/NC can improve the performance compared with TCP when applied to high packet loss rate environments. Coding window and redundancy need comprehensive consideration because they have a significant impact on the performance of TCP/NC. With the ability of adjusting redundancy factor dynamically,ad R-TCP/NC can further improve the performance in the networks with dynamic packet loss rate compared with TCP/NC.