Study On The Construction Method Of Fuzzy Comprehensive Evaluation Based On Loss Differentiation Model

With the development of wireless application technology, the integration trend with the wired networks becomes more and more obvious. In the wireless network condition, owing to higher BER, complicated channel fading, burst equipment noise which characteristics can lead to packet loss constantly. All packet loss marked repetitive Ack or timeout are ascribed to congestion in traditional TCP would make flow control by starting congestion to control congestion control mechanism, such as increasing retransmission intervals, decreasing sending window and so on, but these methods are suited with the wired condition of well link quality. In the hybrid wired/wireless network, the bandwidth utilization would be decreased, and the meaningless deterioration of TCP performance would be caused. Therefore, the packet loss caused by wireless error or network congestion which should be distinguished correctly and simply that has the great significance.The relative one-way delay and average Ack-Timeout times ratio are combined in this paper, according to different network environments, by building the dynamic weight distribution function, fuzzy comprehensive evaluation model are adopted to distinguish the different packet loss reason. In addition, the construction of factor set membership function, initialization algorithm, and definition of dynamic weight are described in detail.(1)Establishment of fuzzy comprehensive evaluation packet loss distinguishing modelIn this paper, fuzzy logic is used to distinguish the packet loss reason more correctly in heterogeneous networks. In varying networks, single factor evaluation couldn't reach the satisfactory effect. To improve the distinguishing accuracy, the two factors are combined to consider, fuzzy comprehensive evaluation model isestablished and more reasonable congestion control and error control are given. On the one hand, this algorithm only modify the sender TCP, not change TCP of the intermediate node, ensure the integrity, interoperability and backward compatibility of TCP end to end semantic; on the other hand, the modifications only refer to the transmission layer, is not relative with others layers, this can ensure the independence of inter-protocol layer.(2) Study on the initialization algorithm of factor set membership functionThe packet loss reason can be judged independently by each factor membership function, so the evaluation value of each factor would be got about the current networks, the accuracy of the evaluation depends on factor set membership functions and the parameters estimation. In this paper, the probability distribution of relative one-way delay and average Ack-Timeout times ratio in different packet loss pattern are studied deeply, then the fuzzy evaluation factor set membership functions are built, finally the initialization algorithm of factor set membership function is proposed.(3)Study on dynamic weight algorithmEach weight coefficient of the fuzzy evaluation factor set is the probability function of judgement set results, the weight coefficient could reflect the reliability of each judgment set. In the practical environment, owing to the unknown probability value, and the influence of network environment is in time-varying state,so the fixed weight coefficient couldn't make the evaluation always in ideal state. In this paper, the weight distribution problems of factor set are studied deeply, then the determination algorithm of dynamic weight is proposed, so the well evaluation performance can be ensured in varying environment.