Ad hoc 網路是未來資訊傳輸新主流，由於移動式手機與手提電腦的便利性及無線寬頻數據服務需求日益增加，使TCP/IP在無線網路上的應用成為重要的研究項目，但隨意式網路(ad hoc network)因環境情況及IEEE 802.11協定的特性使得資訊傳輸在無線網路上必須克服許多困難，我們將針對MAC Layer作為研究的重點之一。
本論文主要參考Mesut Gunes[4]提出的RTS/CTS動態重傳機制，我們再提出一個解決IEEE 802.11在RTS/CTS訊息搶奪頻寬資源的競爭時會發生碰撞導致丟棄數據封包的問題來提升TCP效能，並且根據目前網路上壅塞的程度在TCP層重新制定一套新的Cwnd 計算公式，使發送端送出適當的封包數量，充分使用網路頻寬資源，改善了資源浪費與不足的問題，並且在路由器讀取封包標頭上的相關參數計算 flow number，更即時將相關的網路參數記錄在IP header及TCP header上，由路由器轉送到接收端，再利用回傳技術將這些參數傳到發送端來使用，所以本論文除了修改MAC Layer的軟體之外，也一併調整了IP Layer及TCP Layer相關之程式碼。
最後的模擬證明，我們提出的方法有效地改善了TCP效能，如封包遺失率的改善、增加 Congestion Window 送出去的封包數量與路由器上Buffer的使用率、RTS/CTS訊息的改進，使得整體的網路效能有顯著的提升。

Ad hoc network is a new tendency of data transmission in the future. Because of the convenience and necessity of mobile phone and/or portable computer coupled with wireless data services, TCP/IP has become an important topic for the study in wireless networks. However, there were a few difficulties in data transmission that must be overcome due to ad hoc environments and the characteristics of the IEEE 802.11 protocols. In these protocols, MAC layer is our primary research topic.
Based on the RTS/CTS signal of dynamic retransmission [4], this study presented an improvement to solve the problems: (1) media resources was easily robbed due to the RTS/CTS signal competition, (2) data frame would be dropped by the IEEE 802.11 protocol due to too many times collisions. In addition, this study modifies the CWND in TCP layer in accordance with congestion conditions. Sender can transmit data packets to the network, in which resources can be completely utilized without any waste or loss. We also use the related parameters from the IP and TCP header to calculate flow numbers. The calculated parameters are recorded in IP and TCP header, and then instantly forwarded to the receiver via routers. The receiver can forward these parameters back to the sender by using back transmission method.
The simulation result shows that the proposed methods can effectively improve TCP performance, such as packet loss rate, and fastly increase the CWND, the buffer utilization, and so forth. Thus, the network can perform more effectively while using the MAC-layer RTS/CTS signal.

第一章 導論…………………………………………….…….………..1 1.1研究動機……..…………………………………………………………….….…..1 1.2 研究方向與模擬………………………………………………………………….1 1.3 章節介紹…….…………………………………………………………….….…..2
第二章 有線及無線網路的TCP流量控制介紹……………...….…....3 2.1流量控制在增強多重跳躍的隨意式網路的TCP效能之改善方法…………….3 2.1.1路由器上使用回授機制作記號(Marking)之流量控制……………….………..3 2.1.1.1 EWLN：網路的第二層發生誤碼時作記號，透過回授機制之改善方法….3 2.1.1.2 BLUE：使用ECN回授機制之改善方法…………………………..………..4 2.1.1.3針對RED各種參數缺失再改善之方法…………………………….………..5 2.1.1.4 TCP-F：網路斷線時透過回授機制之改善方法….……………………...5 2.1.2 降低網路之延遲時間調整擁塞視窗………………………………….…….....6 2.1.2.1 LDM與TCP- RCWE 降低網路延遲時間之改善方法…….……………….6 2.1.3 發送端直接更改擁塞視窗之參數……………………………………………..7 2.1.3.1 DSRL：動態調整RTS/CTS重試次數之改善方法………….…….………...7
2.1.3.2 TCP-RC：發送端重新計算擁塞視窗之改善方法……………………….….8 2.1.3.3 CWL：限制擁塞視窗大小之改善方法……………..……………………….8 2.1.3.4 WS：調整擁塞視窗大小之改善方法.……………………………………….8 2.2 幾種多重跳躍的隨意式網路流量控制機制之比較整理…………...……..……9
第三章 在多重跳躍的隨意式網路之TCP流量控制………………..10 3.1 TCP 流量控制在多重跳躍的隨意式網路的介紹…………….………………..10 3.2 系統架構……………………………………………………………..………….11 3.3 NS-2 模擬程式的流程…………….…………………………..……….……….12 3.4 演算法…………………………………………………………………………...13 3.4.1解釋名詞….…………………….…………………….………………….…….13 3.4.2 Cwnd公式重新制定的部分…………………………………………….……..17 3.4.3在路由器上計算flow number…….…………………….………………....18 3.4.4 RTS/CTS訊號的改善部分…………………………………………..………...19 3.4.5 將DSRC參數轉為第三層參數………………………………………………19
3.4.6 將網路取得的參數調整擁塞視窗………………………………..……….….20第四章 實驗結果與分析………………………………………….…..21 4.1 實驗之網路拓樸…………………………………………………………..…….21 4.2 實驗數據及討論…………………………………………………………..…….22 4.2.1 Enhanced TCP 及 Original TCP 之平均Buffer Utilization 比較….….……22 4.2.2 Enhanced TCP 及 Original TCP 之平均Throughput 比較…..…….….……23 4.2.3 Enhanced TCP 及 Original TCP 之平均 Drop ratio比較……………….….24 4.2.4 Enhanced TCP 及 Original TCP 之平均 RTT比較………………..……….25 4.2.5 Enhanced TCP 之平均 RTS/CTS RETRY次數比較…………….…….….…26 4.2.6 Enhanced TCP 及 Original TCP之平均 Cwnd 比較….…………………....26
4.2.7 Enhanced TCP及TCP-RC[3]之平均Throughput比較………………………27 4.2.8 四種不同機制的TCP在不同DSRC之平均Throughput比較……………..28
第五章 結論與未來工作方向………………………………………………………30 5.1結論………………………………………………………………………………30 5.2未來工作方向…………...……………………………………………………….30參考文獻…………………………………………………………………….……….32索引……………………………………………………………………………….….35

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