The Research On Algorithm For Congestion Control Based On Active Queue Management

With the evolvement of Internet based on TCP/IP, the scale, users and traffics of Internet have experienced an explosive growth since 1990's. The network congestion has become more serious and complex due to the ever-increasing network application types and dynamic network parameters such as active sessions and round trip time. Congestion often results in decline of quality of service (QoS) in terms of transmission delay and throughput, which affects the utilization of network resource like bandwidth and buffers. Therefore, 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 is mainly on end hosts. The end hosts use Transmission Control Protocol (TCP) to implement end-to-end congestion control. 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 substantially 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 perform congestion control strategies, so IP congestion control strategies has been discussed widely in recent years. The IETF(Internet Engineering Task Force) has proposed the solution by deploying active queue management in Internet routers.Congestion control schemes of IP Networks are studied in the routers on the basis of simulation.The followings are the main contents.(1) The RED active queue management algorithm is studied deeply. The advantages and disadvantages of algorithms are summed up theoretically. The simulation experiments are given by using NS-2 and the improved algorithm's performance is verified. Adaptive RED, by adapting the RED parameter maxp and automatically setting the RED parameter wq, maintains a predictable average queue size and reduces RED's parameter sensitivity.(2) The GREEN algorithm is investigated. Its improved algorithm, GREEN+, is analyzed. GREEN+ correct the utilization limitation by introducing the parameter, K(t), which is able to effectively utilize the link bandwidth in the presence of short lived and low bandwidth flows. GREEN+ is able to provide superior fairness to other schemes, while simultaneously maintaining high link utilization, low packet loss, and short queues. For now, we use the IP priority field as a convenience to implement embedded RTTs.