A Study On Network Congestion Control Stratigies

Internet has experienced an explosively growth since 1990's. Widespread use of computers networks, as well as the appearance of varied network applications has made network congestion a significant problem. Congestion often results in the decline of Quality of service (Qos) such as transmission delay and throughput, while the network resource utilization like bandwidth and buffers are also affected seriously. So it is important to solve the congestion problem effectively for improving network performance. How to avoid and control congestion is one of the most active fields in the computer networks.Current TCP/IP networks only provide best effort services and their resources allocation are mainly on end hosts. The end hosts use Transmission Control Protocol (TCP) to implement end-to-end congestion control. It can be said that the success of today's Internet primarily relies on TCP congestion control mechanisms. With the development of Internet and the problems in the implementation of TCP, the current TCP strategies couldn't meet various demands of users any longer. More and more researches indicate that the TCP congestion control mechanisms, while necessary and powerful, are substantively conservative and are not sufficient to provide good service in all circumstances.The traditional technique for managing router queue in Internet usually adopts first in first out (FIFO) scheduling and "Drop tail" queue management algorithms, which have no provision for the detection of incipient congestion when the queue is full. In fact, it will be more effective for detecting and preventing congestion if the routers peilbini congestion control strategies, so IP congestion control strategies has been discussed widely in recent years. The IETF has proposed the solution by deploying active queue management in Internet routers.In this paper, Chapter One gives a general introduction to the network congestion control. First the background and the cause of network congestion are introduced, and then the necessity of implementing congestion control is analyzed. We also discuss the research and development of congestion control strategies, and classify them from different aspects. Finally existing problems in current congestion control are proposed.In chapter two we focus on TCP end-to-end congestion control strategies and the mechanisms implemented in IP routers. First the four kernel algorithms of TCP congestion control are described, and the improved schemes such as New-Reno, SACK and TCP-Vegas are discussed either. Then we introduce "drop tail" algorithm and the principal idea of active queue management. Finally we discuss the related works in IP congestion control, in which RED and ECN Algorithm are emphasized.As the essential algorithm of TCP congestion control, slow start is used for avoid the busy traffic, which may exceed the network capacity. After lucubrating on this algorithm,we propose a new algorithm in chapter three, which is called HCTCP. In order to improve the startup behavior of TCP connections, HCTCP takes use of the parameters of history connections to set initial values for the new TCP connection. To avoid busy traffic, HCTCP also paces packets in the first RTT by using token technology. The simulation tests show that HCTCP could reduce the transmission time either in local or satellite networks especially for short connections such as Web traffic.As one of the active queue management algorithms, ECN changes the way of congestion indications. When detecting the incipient congestion, router provides explicit congestion indication to avoid dropping more packets later. It is found ECN couldn't solve the problem that the sender responds to congestion slowly, and the average queue length of router is sensitive to the static parameters of ECN. In chapter four we propose an algorithm called FECN, which provides congestion control and indication messages in router, so that the sender could response to congestion in good time. This algorithm can also adjust the max drop probability according to the ac...