Based On The Tcp Performance Of The Adsl Network Optimization

The rapid development of Internet has supplied expansive market field for data transfer service aiming at home and enterprises. In order to satisfy the rapidly increasing market, different broadband access technologies have been concerned. Asymmetric digital subscriber line (ADSL) is one of these technologies capable of delivering large bandwidth over existing copper telephone line infrastructure, and it is widely applied in home and enterprises now. This thesis aims to characterize and analyze TCP/IP performance in presence of a new algorithm promoted for ADSL network architecture. This new method can solve the problem caused by TCP Asymmetric and so optimize the performance of ADSL and boost the transfer rate of the downstream.In this thesis, we study the effects of network asymmetry on end-to-end TCP performance and suggest some techniques to improve it. The network investigated in this study is ADSL (Asymmetric Digital Subscriber Line) network. In recent literature, asymmetry has been considered in terms of a mismatch in bandwidths in the two directions of a data transfer. We generalize this notion of bandwidth asymmetry to other aspects of asymmetry, such as latency and media-access, and pAcket error rate, which are common in wide-area wireless networks.Although Network asymmetry does affect the performance of reliable transport protocols such as TCP, the main reason is that these protocols rely on feedbAck in the form of cumulative Acknowledgments from the receiver to ensure reliability. In addition, TCP is Ack-clocked, relying on the timely arrival of Acknowledgments, to make steady progress and fully utilize the available bandwidth of the path.Thus, any disruption in the feedbAck process could potentially impair the performance of the data transfer.In this thesis, we pay our attention to bandwidth asymmetry. We discuss all kinds of algorithm and compare their advantages and weakness. After that, we introduce AMP mode that describes the performance degradation affected by TCP protocol. Based on this mode, we provide a new algorithm called SDA (Selective Drop Ack). That is: by suppressing Acknowledgements on the reverse channel suitable for avoiding TCP bursts,we improve network performance. We also define a constant/variable called Ack_Max as a limiting factor.We use both simulating tools and real networks to establish our experiment environment. We analyze TCP performance in networks where the achieved throughput is not solely a function of the link and traffic characteristics in the direction of data transfer (the forward direction), but depends significantly on the reverse direction as well. Focusing on bandwidth asymmetries, we propose and evaluate several schemes to improve end-to-end performance in these cases. These include some techniques to decrease the rate of Acknowledgments on the constrained reverse channel (Ack congestion control and Ack filtering), and techniques (Ack Regeneration) to reduce source burst when Acknowledgments are infrequent (TCP sender adaptation).