Research Of Congestion Control Mechanism For Bandwidth Fair Sharing On The Different Access Links

With the development of the Internet, especially the rise of the Mobile Internet. A variety of multimedia applications are emerging, it is mainly reason that a large number of new kind of media services spring up and a variety of portable terminals access the services through the wireless way that makes the network become much more overcrowding, thus affecting the quality of network services. The reasons that making the internet much more congestion are due in part to network congestion control mechanism unreasonable that affecting the bandwidth possession. Therefore, researching how to protect the reasonable and equitable share of the network bandwidth, making the network environment does not affect the respective protocol stream data transmission quality and appear serious network congestion because of excessive network connections is a challenge issue to research.This thesis reviews the development of the congestion control technology research and discusses classification of network congestion control schemes in detail, on this basis, this thesis has been presented two improvement schemes, specifically including the following two parts of work.1. Congestion control mechanism of TCP Vegas-V based on bandwidth sharing friendly is proposed. It summarizes the reasons that cause such much more vulnerable network bandwidth possession ability when sharing the bandwidth with other protocol flows. At last, it is proposed a new scheme that be based on the variation between the congestion window size and the threshold of congestion control program for changing the transmission rate. So that it can get a moregood share of the network bandwidth and low transmission delay in the based on guaranteed network bandwidth share friendly when TCP protocol flows share network bandwidth with other protocols. According to the analysis of simulation, TCP Vegas-V has a much stronger network bandwidth possession ability than TCP Vegas in the based on network bandwidth share friendly.2. Congestion control mechanism of NewTFRC based on bandwidth sharing friendly in wireless link environment is proposed. Such scheme is intended for the part of wireless network in the heterogeneous network environment. Through analyzing the two phases of slow start and congestion avoidance in TFRC protocol and its limitations and shortcomings in the wireless network environment, and then proposing an improvement scheme (NewTFRC) to make it fit into the wireless network environment. Such scheme mainly analyzes the affect that packet loss rate which is in the congestion avoidance stage brings impact to the sending rate and scheme that filters out the cause of packet loss due to wireless bit error, so that to improve the performance of TFRC network bandwidth sharing fairness and rate smoothness. According to the simulation analysis by NS2, it is indicated that the performance of improved scheme is much better than that of the original one in the aspects of sharing of network bandwidth capacity and the smoothness of the sending rate in the wireless environment.Two improved congestion control schemes discussed above show much better performance than that of the original schemes in terms of bandwidth possession, bandwidth fairness and friendliness in the specific work environment, then achieves a good performance in the actual prototype system, which can lay the theoretical foundation for the practical application of the late.