Research On The Improvement Of TCP Congestion Control Mechanism For Satellite-terrestrial Hybrid Networks

Satellite-terrestrial hybrid network can cover very large area and has great capacity for emergency communication,but network structure is complex,and application scenarios keep changing,which cause a large range of round-trip time and packet loss rate.As a result reliable transmission data become a huge challenge.In this paper,we research the optimization problem of congestion control algorithm of TCP when transmission data in satellite-terrestrial hybrid network.The main contents are as follows:First,the hybrid network data transmission theory and its research status is discussed.We found out the network characteristics and the influence on the performance of the network.The progress and achievements of domestic and international organization were explored.Then we have an overview of research status on Network partition and end to end transmission acceleration.Second,a high speed algorithm was proposed to solve the problem of large range of round-trip time.The algorithm use fixed ratio,which can compress the round-trip time range,to speed up the slow start,and a cube function is used in the congestion avoidance phase,so that the congestion window can be maintained for a long time.This algorithm can keep high speed transmission in long round-trip time environment,so it can improve the transmission performance.Third,an adaptive mechanism based on round-trip time migration was proposed.By choose a reasonable upper and lower limits,the standard delay factor was calculated by the normalization treatment of round-trip time,which can reflect the residual of network resource.Then we use the standard delay factor to modify the congestion window growth and reduce factor,which can make the data transmission rate changing with the roundtrip time shift.The mechanism reduces the possibility of network congestion,also it can distinguish between random packet loss and network congestion,all of this is the reason why it improves the performance of transmission.In the end,the simulation environment is built,and the simulation experiments and analysis of the algorithms are carried out.The results show that the transmission performance of new algorithm increased by 20%.The high speed algorithm is mainly focused on the long round-trip time environment,while the adaptive mechanism has better performance in high PER environment.The fairness index of both algorithms is better than the CUBIC algorithm,so they are able to allocate bandwidth fairly for concurrent transmission flows.