Research On Available Bandwidth Measurement And TCP Cong Estion Control Algorithm

With the developpment of the Internet,,Experts do the research about Network problems more deeply. Auther do research from two fields:estimation of available bandwidth and network congestion control. Available bandwidth is very improtant resource in network business.We can fully expoilt the bandwidth in network links if we can measure available bandwidth arrcuately.When we can not accurately measure the value, TCP congestion control is the key to guarantee the network business. So research about the estimation of available bandwidth and TCP congestion control are the hot issues all the time.This paper introduces the basic concept of estimation of bandwidth and congestion control,the background of this two fields. A improved pathChirp is proposed in the paper,making the result of estimation more accurately. Then, this paper describes the relationship between one-way delay and sending rate of packets: the value of sending rate of packet which one-way delay is the biggest equals to the value of available bandwidth of a path. Based on this theory, a decreasing rate chirp algorithm (DRChirp) is proposed to measure end-to end available bandwidth. Firstly, this algorithm searches appropriate upper bound of available bandwidth using fast probe technology. Then, the exponential decreasing chirp is sent and the available bandwidth of path on the basis of the weighted average rates between the sending rate of packets with the biggest and the second biggest one-way delay is calculated. The experiments with NS2tool indicate this algorithm’s accuracy is higher than classic algorithm based on probe rate mode in multi-hop networks.This paper also study the mechanism of TCP congestion control and proposed a imporved congestion control algorithm called TCP Vgeas-L.This algorithm improved the compatibility and competitiveness,proving it well through the experiment.