Research Of The Network Congestion Control Algorithm

Since the Internet has appeared, the development of Internet has been encumbered with the congestion problem caused by the lack of the network resources and the unbalance distribution of the network flows. The network congestion becomes more and more serious because of the increasingly expansion of Internet scale and the rapid growth of traffic flow.Congestion control has become the bottleneck witch hinders the Internet further develops.Network congestion is still inevitable in the present internet. The development of the internet requests us to adopt the effective control mechanism to reduce the possibility of the network congestion occurs as far as possible,attempt to make the network resume its normal work promptly even if the network congestion has happened,ensure the network stability and unimpeded. The network congestion control algorithm is the main way to avoid the network congestion, reform network performance and improve the network quality.The investigation on the network congestion control is important not only in the theory but also in the application.This work makes an intensive study of the network congestion control algorithm. We mainly carry on the multianalysis aimed at the TCP Vegas algorithm which belongs to the network congestion control algorithm based on the TCP port. We have made an improvement on the TCP Vegas algorithm in two aspects including the network asymmetry and the algorithm compatibility;Then we mainly research the queue management algorithm and the queue dispatch algorithm, witch belongs to the network congestion control algorithm based on the network port. the main research contents and innovative points are the follows:(1)Research of the algorithm compatible question based on TCP Vegas network congestion control algorithmTCP Vegas algorithm is one kind of network congestion control algorithms which is based on the measuring technology, TCP Vegas algorithm has made improvement in "slow start", "congestion avoided" and "fast re-transmit" three aspects compared with thetraditional congestion control algorithms.Specially it adjusts the congestion window size through the comparison between the actual throughput and the expectated throughput in the congestion avoided mechanism,which change the passive congestion avoided mechanism to the initiative prevention congestion avoided mechanism,thus enhanced the algorithm serviceability enormously.TCP Reno algorithm is the mainstream algorithm in the present network,it used the passive congestion avoided mechanism , through increase its congestion window continuously,until the network overload to guarantee the effective use network resource to avoid the mechanism; But TCP Vegas algorithm used the initiative congestion avoided mechanism,its goal is maintains the network band width at a stable level, therefore it will not continue expansion its congestion window. In the practical application, In the practical application,TCP Reno algorithm will steal the band width from TCP Vegas algorithm, which will cause TCP Vegas algorithm not to be able to play the actual role. In order to solve this problem, this article analysis the two parameters Alpha and Beta established by TCP Vegas,changes the fixed value to dynamic value,in addition changes the congestion window's exponential order growth linearity growth,the simulation result indicated that the improvement algorithm enhanced TCP Vegas algorithm's band width competitive ability and band width throughput stability.(2)Research of the network asymmetrical question based on TCP Vegas network congestion control algorithmTCP Vegas algorithm is a time-based algorithms, therefore the round-trip latency (RTT) accuracy is very important,Sketchy survey's RTT possibly causes an sketchy adjust to the congestion window.At present TCP Vegas algorithm had only considered take measures when the network congestion occurs on the data sending terminal,but if congestion occurs in the return route direction, also called the ACK direction, TCP Vegas algorithm mechanism will adopt the congestion avoided mechanism similarly, this will cause an underestimation to the actual throughput, thus causes congestion window nonessential reduction. In the practical application we are requested to be able to identify which direction do the congestion are occur, then adopts the correct measure to guarantee the network stability.In order to solve this problem, this article first analyzed the congestion avoid mechanism of TCP Vegas algorithm, obtained affects TCP Vegas algorithm RTT biggest factor is the reverse waiting time, therefore we can except this part to RTT's influence when computation. Simulation result indicated that the improvement algorithm eliminated the network asymmetrical problem of TCP Vegas algorithm.(3)Research of the Fusion of the reverse link jam and compatible question based on TCP Vegas algorithmWe have proposed corresponding improvement algorithm to the compatible problem and the network asymmetrical problem of TCP Vegas algorithm separately, the simulation testing has also proven the improvement algorithm validity. In the practical application we hope to find a "perfectly"algorithm as far as possible, this algorithm could solve all problems of TCP Vegas algorithm, met the present network development request.This article generalized analysis the improvement algorithm to the reverse link congestion problem,as well as the improvement algorithm to the compatible problem of TCP Vegas algorithm,then fusion them together,proposed TCP NewVegas algorithm. Simulation result indicated that this algorithm could maintain high band width competitive ability when uses with TCP Reno algorithm, also eliminate the influence of reverse link network congestion to the algorithm mechanism.(4)Research of the discrimination service question based on auto-adapted hypothesized formation algorithmThe adaptive virtual queuing (AVQ) algorithm judges the network congestion based on the system load situation,its algorithm mechanism is maintains an virtual queuing that capacity is smaller than the actual link capacity,compared with the traditional initiative queue management algorithm, this algorithm has solved the deadbolt lock problem, maintained the fair performance of the service class, may reduce the queuing detention. But this algorithm cannot provide discrimination service, this is a very big flaw to the increasing network service type and the network environment complex trend of development.In order to solve this problem,this article has analyzed the dynamic threshold value algorithm and the queue size threshold value algorithm firstly, then synthesized these two algorithm' thought to the AVQ algorithm.Specifically speaking,we makes an improvement to the queue management of AVQ algorithm with the dynamic threshold value algorithm,use the queue size threshold value algorithm's thought to improve the AVQ algorithm's dispatch,through setting different priority to the different service, gives the different grade of service according to the different priority,thus achieves the guarantee discrimination service to satisfy the timely service.