Reseach On Congestion Control Algorithm Based On Available Bandwidth Estimation

As an important transport layer protocol, Transmission Control Protocol(TCP) is widely used on the current Internet, which is oriented to the connection and provides the stable reliable data transmission service. The TCP congestion control mechanism is one of the key factors to ensure the normal and reliable data transmission technology. However, TCP congestion control mechanism, which performs better performance in wired networks, is facing the huge challenge and a sharp decline in performance in mixed wired/wireless heterogeneous networks with the high bit error rate, narrow bandwidth, asymmetric link and long delay. Therefore, this paper details analysis of the decline of the network performance, and proposes an improved congestion control mechanism based on the available bandwidth estimation to improve the network bandwidth utilization and network throughput. The main research work and research results are as follows:1 、 This paper improves the available bandwidth estimation method which combines the advantages of TCP Westwood algorithm and TCPW RE algorithm. On the one hand, this paper adaptively estimates bandwidth by using the bottleneck link utilization. On the other hand, this paper selects more precise time interval of ACK to improve the accuracy of available bandwidth estimation.2、TCP Westwood algorithm still obeys the rules of blind linear growth pattern to increase the congestion window size during the congestion avoidance phase, resulting in more congestion times and reducing bandwidth utilization. In view of the problems, this paper improves the congestion avoidance mechanism utilizing the buffer queue length and the bandwidth ratio factor to adaptively adjust the increments of cwnd.3 、 It is necessary to identify the predominant cause of packet loss, and appropriately set the ssthresh and cwnd to take full advantages of bandwidth resource. Therefore, this paper improves faster retransmission and faster recovery mechanism by using the queue length based on the estimated available bandwidth to choose more reasonable ways to set cwnd and sshtresh. In addition, since the performance of TCPW significantly decreases under the network environment of multiple packet losses in the same window, this paper adopts the partial ACK to detect lost packets in the same window to improve the performance.4、As used in Lw IP protocol stack is still the traditional Reno congestion control mechanism, therefore this paper implements the improved TCP_New BR algorithm based on the available bandwidth estimation in Lw IP protocol stack. Furthermore, this paper builds the actual network environment to test the improved performance. The experimental results show that the improved the algorithm of Lw IP protocol stack obtains better throughput.