Rate Based Congestion Control For Semi-TCP In Multihop Wireless Networks

Multi-hop wireless network,which is simple configured,convenient and easy to use,has a strong resilience of fault-tolerant,so it is widely used.However,the TCP protocol and its variants designed for traditional wired network perform far from satisfactory in wireless network environment.Causing this is that TCP routinely misadjust the network condition due to packet loss in wireless networks,but the packet loss is relatively more frequently in wireless network and most packet loss is not caused by network congestion.Therefore,designs a wireless transport layer protocols adapts the wireless network environment is very meaningful.Semi-TCP is able to well adapt to the status of wireless network,which is a transport layer protocol base on hop-by-hop congestion control mechanism,but there are still some deficiencies.Firstly,on its shortcomings,using simulation analysis and study,pointing out that there is a serious medium contention in the vicinity of the source node,and aware of the source rate control mechanism is a feasible way to solve the deficiencies.Therefore,this paper proposes a rate control method based binary search method to improve network performance.This method has four States on transmission layer:(1)aggressive sending,(2)slow start(3)binary search,and(4)stable.Aggressive sending to measure the scope of network congestion levels;slow-start is used to probe the binary search range of send rate;binary search using bisection method to quickly find a transmission rate that match the conditions.Stable states monitors the changes of network status.If necessary,restart the search process.These four States are coherent and in order,and would convert to other states under certain conditions.According to the above description,implemented the rate control method in NS2 simulation platform.Simulation results show that the rate control method reduce the signal contention in all kinds of network topologies and under different network environment.Therefore,the source rate control method based on binary search can improve end-to-end throughput of Semi-TCP,reduce end-to-end delay,and improve network performance.