本篇論文針對TCP Vegas在無線網路環境中，修改CWND（Congestion Window, CWND）使其快速增量達到穩定狀態。TCP Vegas是以量測RTT為調整CWND依據，並且以預設的α與β值比較後作為調整CWND的大小，因此出現調整CWND的速率不夠快而無法有效利用頻寬的問題。依據無線網路環境參數的推算，其實無線網路的整體緩衝區（buffer），不像有線網路那麼多，還有從TCP Vegas公式和本篇文章對無線網路環境的觀察，得知Diff的值就是在預估線上整個還未完成的封包數量，所以還未收到ACK的封包數量，就幾乎相等於CWND值，因此，本篇提出的建議方法，將TCP Vegas的CWND值的變化控制介於α到β＋1之間。經由NS2（Network Simulator, version 2）模擬器實驗結果獲得驗證－在無線網路及受到背景干擾的情況下，我們的方法確實比TCP Vegas更快將CWND調整到穩定狀態並且獲得較高的吞吐量。 The main focus of this thesis is to utilize TCP Vegas by modifying the increment speed of congestion window (CWND) in wireless network environments. By doing so, TCP Vegas may rapidly increase its CWND and reaches the steady state sooner.Traditionally, TCP Vegas adjust its CWND based on the measurement of RTTs (Round Trip Time). It uses the CWND default value of α and compares it against β, and then adjusts the size of the CWND accordingly. This CWND adjustment approach is slow and inefficient, which may result in bandwidth underutilization. In fact, from the observation of wireless network as well as the TCP formula in this thesis, wireless network buffers are most likely less then wired network according to the wireless network environments parameters settings, and the Diff value is used to estimate the total amount of packets has been transmitted but still waiting for conformation, Hence, the amount of packets that are still waiting for conformation are very close approximation of the CWND value. Therefore, this thesis proposed a method that controls the variation of TCP Vegas CWND between α and β +1. From the results of NS2 simulations, we verified that the CWND adjustment of our proposed method not only adjust faster than traditional TCP Vegas, but also reaches the steady state sooner. The benefit of such changes gained higher throughput utilization ratio and also helps in decreasing the background interference issues.
