博碩士論文 etd-0827104-203122 詳細資訊


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姓名 林俊賢(Chun-Hsien Lin) 電子郵件信箱 E-mail 資料不公開
畢業系所 電機工程學系研究所(Electrical Engineering)
畢業學位 碩士(Master) 畢業時期 92學年第2學期
論文名稱(中) 在Ad Hoc無線網路上具有ACK路徑重繞用以改進TCP效能的改良式AODV
論文名稱(英) A Modified AODV with Ack-Path Traffic Rerouting for TCP Performance Improvement in Ad Hoc Wireless Networks
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    摘要(中) 在本篇論文中,我們藉著修改Ad Hoc網路上的一個routing protocol,AODV (Ad Hoc On-Demand Distance Vector),來達成利用ACK路徑reroute的方法,並且將這個修正過的機制稱為MAODV (Modified AODV)。MAODV中增加幾個新的routing information,用來告知TCP網路上的情況。在route failure發生後,會在來源端monitor是否有目的地端來的ACK封包,如果有的話就用這ACK封包的資訊來更新routing table,使得TCP可以利用回傳的ACK路徑將資料傳出去。TCP利用回傳的ACK路徑開始傳送資料後,還必須處理因為斷線而丟掉的封包,因為這些丟掉的封包與網路壅塞造成的不同需要另外處裡,所以TCP在收到第1次duplicate ACK時就會重傳丟掉的封包,並且不會降下cwnd,直到因為route failure丟掉的封包都重傳完時,才回到原來TCP的機制。我們實際用NS來模擬,模擬的結果中可以看出,當斷線的位置在資料路徑的前端,也就是靠近來源端的地方,MAODV比起TCP-BuS (BUffering capability and Sequence information) 與原來的TCP都有較好的表現。因為此時AODV要重建路徑需要花很多的時間,尤其是來源端離目的地端的hops數越多的時候越顯的明顯,MAODV早就利用ACK的路徑將封包傳出去,而TCP-BuS與TCP都要等到路徑找好才能傳資料。至於斷線在資料路徑的後端的話,MAODV比起TCP-BuS和原來的TCP差別就不明顯。這是因為AODV會啟動local repair的功能,減少了找尋路徑的時間,在極端的狀況下,當local repair重試多次依然找尋不到路徑時,會返回到來源端重新尋找路徑,此時MAODV就可以看出效果。
    摘要(英) In this thesis, a modified routing protocol, MAODV (Modified Ad Hoc On-Demand Distance Vector), is proposed for wireless Ad Hoc networks. MAODV uses ACK paths for rerouting data traffic whenever there is a route failure. We create new flags in the routing information of AODV to timely notify TCP layer the network status. After a route failure, the source node monitors ACK packets from the destination node. Every ACK packet when it is received from the destination node, its carried information is used to update the routing tables. Thus, without any interruption, TCP can take the reverse route of the ACK forwarding paths to continue to transmit the rest of data packets. In our proposed scheme, without decreasing the size of TCP congestion window (CWND), a lost packet can be immediately retransmitted as soon as the first duplicate ACK is received. We use NS-2 to simulate the proposed MAODV. From our simulation results, we have shown that when the position of route failures is near the source node, it may take more time to find new data paths. Hence, MAODV has the advantages by taking the reverse ACK paths to transmit data packets before new routing paths are found. Finally, we have demonstrated that MAODV performs better than TCP-BuS (BUffering capability and Sequence information) and the original TCP, when there are many hops between the source node and the destination node. On the other hand, when the position of route failures is near the destination node, the advantages of MAODV become not so significant because there exists some local repair mechanisms to be applied.
    關鍵字(中)
  • 重繞
  • 斷線
  • 關鍵字(英)
  • Reroute
  • Ad Hoc
  • TCP performance
  • AODV
  • Route failure
  • 論文目次 第一章 導論………………………..…………………………………………………1
    1.1 研究動機…………….………..……………………………………….….…1
    1.2 論文簡介…………………………………………………………………….1
    1.3 論文架構…………………………………………………………………….3
    第二章 Ad Hoc網路上改進TCP效能的相關研究……………….……..…………..4
    2.1 Ad Hoc網路上的routing protocol介紹.……………………………………4
    2.1.1 AODV的封包格式.…………..………………………………….…...4
    2.1.2 AODV的路徑建立與維持…………………..……………………….5
    2.2 在Ad Hoc網路上各種改進TCP效能的方法…..………….………………7
    2.2.1 藉由routing information…….………….……………….…………...7
    2.2.2 分辨Ad Hoc網路上不同的狀況…………………………..………..9
    2.2.3 限制cwnd的大小…………………………………….……..……..11
    2.2.4 將TCP分段………………………………………..……………….12
    2.2.5 其他方法………………………………………..……….………….12
    2.3 各個方法的比較…………………………………………………………...13
    2.4 本論文的方法………………………..……………….………….….……..14
    第三章 具有ACK路徑重繞的AODV…………………..…………………………15
    3.1 修改AODV的部分…………….………………………..............………..15
    3.2 修改TCP的部分……….…………………………………………………..17
      3.3 MAODV完整的流程……………………………………………...……….18
      3.4 MAODV的演算法………………………………………………..…….…22
    第四章 模擬結果………………………………………………………..…….…….27
    4.1 Ad Hoc網路模擬器…….…………………………………………..…..…..27
    4.1.1 修改過的NS模組…………….…………………………….………27
    4.1.2 新增加的NS模組…………….…………………………………….27
    4.2使用者自訂的網路拓樸……………………..……………….……………29
    4.2.1 結果分析………………………………………………..………….30
    4.2.2 斷線在資料路徑的上游………………………………………….30
    4.2.3 斷線在資料路徑的下游……………………………………...……35
    4.3使用亂數產生的網路拓樸………………………………………………...38
    4.3.1結果分析…………………………………….……………….…..….39
    第五章 結論與未來工作……………………………………………………………41
    5.1 結論………………………………………………………………………...41
    5.2 未來工作………………………………………………………………...…42
    Reference………………………………………..……………………………………43
    Index………………………………………………………………………………….47
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  • 許蒼嶺 - 指導教授
  • 口試日期 2004-07-15 繳交日期 2004-08-27

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