隨著網路技術的演進，網路頻寬與封包的傳輸距離均有所大幅度的增長。網路環境逐漸演進成高頻寬延遲乘積的環境。在高頻寬延遲乘積網路環境中，適用於低頻寬的TCP協定，已經無法勝任當下的網路環境。因此關於TCP 在高頻寬延遲乘積網路環境的傳輸效能，已經成為一個研究重點。 雖然TCP Vegas在穩定性、頻寬利用率與吞吐量方面均擁有較佳的表現。但是應用在高頻寬延遲乘積網路環境中， TCP Vegas卻有著提早離開緩啟動階段的問題與壅塞視窗調整速度太慢的問題。上述的問題將嚴重降低 TCP Vegas掌握網路頻寬的能力與吞吐量。 因此本文則提出一個基於TCP Vegas的改進機制，High Bandwidth-Delay Product Vegas（HBDP Vegas）。 HBDP Vegas在評估壅塞程度的方法部分，則是提出往返時間與最小往返時間的比例值作為衡量壅塞程度的依據。在緩啟動階段部分，HBDP Vegas藉由修改緩啟動階段中壅塞視窗的成長行為，來加強掌握網路頻寬的能力。同時在壅塞避免階段部分，也藉由動態調整TCP Vegas的α與 β值與修改壅塞視窗的控制方式，來強化適應網路環境變化的能力。 最後經觀察HBDP Vegas的緩啟動階段之表現、收斂時間、和其他連線競爭情形與公平性指數，均證實HBDP Vegas在掌握網路頻寬的能力、適應網路環境變化的速度與吞吐量均有所改進。 With the evolution of network technology, the network bandwidth and packet transmission distance have been greatly increased. The network environment has gradually evolved into high bandwidth-delay product environment. Low bandwidth TCP protocol has been unable to support the current network environment in high-bandwidth delay product network environment. Therefore, how to enhance TCP transmission performance with high bandwidth-delay product network environment has become a research focus now.Although TCP Vegas has better performance in stability, bandwidth utilization and throughput, it has the problems of early leaving in slow-start phase and slow adjusting speed in congestion window in high-bandwidth delay product network environment. This phenomenon will severely reduce the throughput of TCP Vegas and its ability of grasping network bandwidth.In this paper, we proposed a new enhanced mechanism based on TCP Vegas, High Bandwidth-Delay Product Vegas（HBDP Vegas）.HBDP Vegas assessed the degree of congestion by the ratio of round-trip time and minimum round-trip time. In slow-start phase, HBDP Vegas modified the growth of behaviors of congestion window to enhance the ability of grasping network bandwidth. In congestion avoidance phase, HBDP Vegas dynamically adjusted the value of α and β of TCP Vegas and modified the control method of congestion window to strengthen the ability of adapting to the fast change of network environments.In conclusion, simulation results showed that in slow-start phase, convergence time, competitive situation with other connections and fairness index, HBDP Vegas effectively improved the ability of grasping bandwidth, the response speed of adapting to the change of network environments, and the throughput.
