The Research Of Congestion Control For Network QoS

With the development of Internet, many applications have come forth, such as VOD, network conference. All of these applications have a common feature, i.e. they require network to provide QoS. However, Internet witch is based on "best effort" cannot guarantee QoS. To solve this problem, various network QoS technologies were presented, such as Integrated Service, Differentiated Service, and Multiple Protocol Label Switch. Because these technologies need to modify the infrastructure of current network, there is a long way to go before they become applicable.There are many factors to influence network QoS. An important one is network congestion. As a crucial method to avoid and control network congestion, congestion control is not only the critical factor of network performance and efficiency improvement, but also the premise of improving network QoS.This dissertation explores methods of how to administer and control diverse network traffics efficiently and impartially to enable network to provide undetermined QoS guaranty. On the basis of systematic summarization of up to date network congestion control work, this dissertation researches three primary fields of congestion control in depth; describes the author's creative viewpoints and obtains several breakthroughs. The primary innovations of this dissertation are as follows:1) Presenting a new algorithm of high-speed network packet schedule-EWFQ, which redefines the virtual time calculation function, and uses SEFF as the schedule rules. Simulated experiments show that EWFQ has many advantages, such as lower computational complexity, fairer bandwidth assignment, and lower WFI.2) Presenting an equation-based real time media stream congestion control mechanism-EBCC, which uses TCP rate response function under stable status as the control equation, and processes the control parameter RTT and p with-in-distinctive smooth method. EBCC can accomplish congestion control task for real time media steams preferably.3) Presenting a rate-based multicast congestion control mechanism-RJBMCC initiated unitedly by sender and receiver, which assigns the response duties to receiver, intermediate node and sender in order to accomplish fast and accurate responses for dynamic network condition. Simulated experiments show that RBMCC is scalable and fair.In addition, the contributions of this dissertation are:1) Giving a systematic and in-depth survey of current research of congestion control, which has three focuses: (i) improving the current TCP congestion control algorithm; (ii) studying some policies which were applied in the network device, such as router or switch, to avoid and control network congestion;(iii) studying new end-to-end congestion control protocol.2) Giving a systematic and in depth summary of the progress of multicast congestion control. Analyzing the major difficulties of reliable multicast congestion control, related proposals and their advantages and disadvantages.3) Systematically analyzing the TCP's principle, implementation and improvement. This dissertation researches two popular implementations of TCP: TCP Tahoe and TCP Reno, and introduces two TCP rate response models: simple model and complex model.Congestion control is a sophisticated task that cannot be absolutely resolved by monolithic protocol or algorithm. The only way to guarantee the steadiness and efficiency of network is to use various mechanisms to control the congestion from multiple aspects of the whole network.