Research On Congestion Contril In Large Bandwidth-Delay Network

With the rapid development of network technology, such as application of remote network connection and the popularity of satellite networks, the large bandwidth-delay networks have gradually developed into the mainstream of the Internet. The bandwidth-delay is an important indicator to reflect the network transfer rates. In this context, congestion control algorithms have shown their limitations and shortcomings.Thus, it has become very important to design a congestion control algorithm to adapt to the large delay-bandwidth network. To solve the above problems, the following aspects are to be stuied:Firstly, according to the most widely used AIMD algorithm, we study and improve Vegas algorithm which is based on delay. This thesis analyzes the problems of Vegas in the large delay-bandwidth network from the two stages of slow start and congestion avoidance In the slow start stage, we analyzes the reason of stoping slow start too fast, then introduce a rate control factor to adjust the growth rate of the congestion window, so as to solve the problem effectively; In the congestion avoidance stage, by dynamically adjusting the rate of the congestion window, the problem of a long linear increasing and decreasing can be avoided. In this thesis, the proposed algorithm is named for Vegas-f. Finally, we use NS2to test and verify performance of the improved algorithm. Simulation results show that the algorithm has a shorter convergence time and better fairness.Secondly, from the perspective of MIMD, we analyze the main performance of FAST TCP congestion control protocol in the large bandwidth-delay network, and propose improvements. FAST TCP is a new congestion control protocol, this thesis analyzes the dependence on network and the lack of fairness, the lack of fairness is due to different time flows. Through the analysis, we know the problem is caused by inaccurate estimation of the minimum link delay. Thus, the thesis proposes an improved algorithm which adjusts the minimum link delay according to the change of the congestion window and delay. And the simulation results show that the proposed algorithm has a good upgrade in terms of fairness.The above improved congestion control algorithm from the perspective of AIMD and MIMD provides an effective theoretical support for application and development in large delay-bandwidth product network.