Vegas Enhanced Congestion Control Algorithm And Imlementation In Linux Network

With the increasing development of the Internet, the limited network resource can not be satisfied with people's requirement of the high quality service of network. Network congestion problems are received extensive concern. TCP congestion control algorithm is an effective way, for solving the network congestion. But TCP Reno which is the most widely-used algorithm in the present network has some disadvantages. It uses Packet loss as the measure of congestion, so the sending rate changes greatly, and the average sending rate of the network is not very high. In contrast to Reno, Vegas uses delay as the measure of congestion and anticipates the onset of congestion by monitoring the difference between the actual throughput and the expected throughput. Vegas can avoid packet loss, and its throughput and stability are better than Reno. However, because of its conservative congestion avoidance, its throughput declines sharply coexiting with Reno. The purpose of this paper is to improve the performance of TCP Vegas.The main research contents and innovative points are as follows:(1) Research of the compatibility and fairness issues based on TCP Vegas algorithmTCP Vegas uses the initiative congestion avoided mechanism. Its goal is maintaining the network bandwidth at a stable level, therefore Vegas will not increase congestion window continuously. But TCP Reno will increase its congestion window until the network overloads. In the practical application, Reno will steal the bandwidth from TCP Vegas, which will cause Vegas not to be able to play the actual role. Besides, because of the BaseRTT estimation ways, Vegas is unfair towards older connections and higher bandwidth flows. The paper proposes Adaptive Vegas algorithm. The network operation condition is divided into different congestion states, and the parametersα,βand cwnd are regulated adaptively under different congestion states. When there are resources available in the network, using Adaptive Vegas algorithm can occupy available resources quickly. At the same time, it can maintain a certain degree of TCP-friendly with the data flows using Reno algorithm.Adaptive Vegas is evaluated under various network environments based on NS2 simulation platform, and compared to many TCP algorithms, such as TCP Reno, TCP Vegas, TCP Vegas-A. The result demonstrates that Adaptive Vegas not only enhances the bandwidth competitive ability, but also guarantees the fairness with TCP Reno under wired networks.(2) Implement Adaptive Vegas algorithm in Linux as a kernel moduleAdaptive Vegas algorithm is implemented in Linux as a kernel module, with which we can change the TCP congestion control machenism dynamically even though the Linux OS is online. The performance and the fairness with TCP Reno under wired networks of Adaptive Vegas are then evaluated in real networks. The result demonstrates that Adaptive Vegas performs better than Vegas and Vegas-A when the routers use Droptail algorithm. So we could infer that Adaptive Vegas has the value in real.