| Due to the rapid development of network technologies, the network bandwidth and the rate of network transmission has been enhanced greatly. However, the data that need to be transmitted has also incremented with the same rate, even exceed the incrementing rate of network bandwidth. This fact indicates that the network bandwidth is still a key issue for network transmission. At the same time, some new applications (such as multimedia transmission and multicast etc.) that are developed recently not only increased the amount of traffics, but also changed the properties of the traffics. So, these applications require new service, which result in the requirement of network improvement.The current Internet only provides the service called best-effort, in which, all traffics are treated indistinguishably and compete for the network resources equally. This service model is insufficient for those applications that have special requirements for bandwidth, delay and delay jitter, and these requirements result in the emergence of concept of quality of service (QoS).This dissertation made a summarization of the research of QoS, and made a view for the trend of future research of QoS. Based on this, this dissertation made a research on the fairness of bandwidth sharing in QoS, and pointed out the factors that impact the fairness. In this dissertation, we tried to improve the fairness of bandwidth sharing from two aspects: marking algorithm in DiffServ and the implementation of TCP protocol. In summarize, this dissertation includes the following outcomes:1) Made a summarization that covers several models of quality of service (QoS) provided in the Internet, which include IntServ, DiffServ and MPLS etc. This dissertation analysed the architecture and technological characteristics of each model. After an introduction of each model, the dissertation summarized what QoS requests they can fulfil and how they implement them. The emphasis of this overview is on the total architecture of a Top-to-Bottom, End-to-End QoS system. It also described the support of multicast in QoS models. On the basis of the preceding analysis, the part finally put forward the likely trend for more research of QoS;2) For marking algorithm, this dissertation pointed out the factors that impact the fairness of bandwidth sharing, and analyzed the inefficiency of the current marking algorithms in the fairness of bandwidth sharing. Based on this, we put forward a new marking algorithm - adaptive fair marker (AFM). Differentiated from the former markers, AFM neither aims at some certain factors, nor tries to establish a precise mathematic model. On the contrary, AFM follows a rule of result-oriented and reallocates the network resources in an adaptive manner, and thus gains high performance in the fairness of bandwidth sharing;3) The congestion control mechanisms of the current TCP have been proved to be effective for prevention of network collapse. However, with thedevelopment of network technologies, the insufficiencies of TCP are becoming increasingly severe, especially in the environment of heterogenous networks, the throughput performance of TCP is disappointing. This dissertation made a review of the research of TCP, and analyzed some typical implementations of TCP that aims at the problems under heterogenous networks. Based on this, we put forward a new TCP implementation which is called receiver advertisement based TCP (TCP-Rab). Rab can estimate the available bandwidth dynamically, and it can also distinguish the type of error when packet loss occurs, which helps for the choice of different recovery policies. For packet loss result from network congestion, Rab adopts the same recovery mechanisms as the original TCP; for packet loss result from link error, it adopts a recovery mechanism which is called immediate recovery, and the value of congestion window of the source is set to a value that corresponds to the available bandwidth.We made some simulation experiments with the network simulator NS2 to validate the ma...
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