Simulation and Analysis of TCP-ACK Prioritization Schemes

[[abstract]]近年來，無線網路已開始普及，無論是一般家庭或是公眾場合都看的到基地台(Access points , AP)的架設和無線網路的使用，網路的品質也開始受到重視。IEEE 802.11e提出了服務品質(Quality of Service , QoS) ，藉由不同的參數，達到不同優先權的區分。FTP、E-mail皆是使用TCP做傳輸，而TCP的連線必須要等待ACK回覆才算一次完整的傳送，若發生ACK延遲時間過長或是沒有回覆，不僅影響整體效能也可能發生重送，造成資源的浪費。在文中，我們將提出兩種情境的ACK優先權控制，針對TCP在Ad hoc環境下整體的Throughput，尤其是TCP常用的優先等級做改善。我們將藉由NS2模擬，由實驗一驗證ACK優先權控制對整體效能的影響，並探討不同優先權的ACK等待時間與隊列長度的變化，再由實驗二中分析我們所提出之兩情境在不同環境下的差異與效能。[[abstract]]In recent years, wireless network becomes popular. Base stations have been set up for wireless networks at home or public places. And quality of service begins to get much attention. IEEE 802.11e was proposed for quality of service (QoS) to achieve different transmission priorities. Transport Control Protocol (TCP) connections are confirmed through receiving Acknowledgments (ACKs), such as FTP and E-mail. If the delay of ACK is too long or there is no ACK received, not only it affects the overall performance but it may also cause retransmissions resulting in waste of resources. In this paper, ACK priority control schemes in wireless networks are studied using NS2, and we improve the overall throughput by adjusting the priorities of TCP connections. In the first experiment, ACK priority impacts on the overall performance have been monitored, and we particularly look into the changes of waiting time and the queue lengths among different priority ACKs. After that, we analyze the performance in the different wireless conditions through the second experiment