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研究生:甘惠文
研究生(外文):Hui-Wen Kan
論文名稱:一個在行動隨意網路下適應於動態網路資訊的TCP壅塞控制機制
論文名稱(外文):An Adaptive TCP Congestion Control Scheme Based on Cross-layer Information for Mobile Ad Hoc Networks
指導教授:張軒彬張軒彬引用關係
學位類別:碩士
校院名稱:國立中興大學
系所名稱:資訊科學與工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
畢業學年度:96
語文別:中文
論文頁數:55
中文關鍵詞:行動隨意網路TCP壅塞控制802.11跨層式資訊
外文關鍵詞:ad hoc networksTCP congestion control802.11cross-layer information
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TCP是目前有線網路環境上最主流的傳輸層通訊協定,然而TCP的壅塞控制機制應用在行動隨意網路上往往會有一些不適當的表現。其原因在於TCP會把封包遺失當作是網路壅塞發生的一種警訊,進而啟動TCP壅塞控制機制去降低其傳送之速度。然而,行動隨意網路複雜的網路環境使得封包遺失行為除了中間節點發生buffer overflow之情況,更具有像是因節點任意移動而導致鏈結斷裂的斷線(disconnection)情況,因無線傳輸媒介特性所引起的通道錯誤(channel error)以及區域性競爭問題所引起的MAC contention等,這些因素都可能會導致封包遺失,使TCP誤解為buffer overflow之情形。
因此,在本篇論文中我們提出一個改善原本TCP壅塞控制之機制,稱之為TCP-CI (adaptive TCP based on Cross-layer Information),TCP-CI會在中間節點由802.11-based MAC layer試圖去偵測目前的動態網路情況,判斷封包遺失的確切原因,再由中間節點將此動態網路資訊告知傳送端,當傳送端實際了解網路的情形之後,便可以針對不同的狀態去啟動適當的反應機制對遺失的封包進行處理。由模擬實驗的結果顯示,無論是靜態的鏈狀拓樸或是動態的節點移動環境下,TCP-CI都能比原本的TCP以及另一個ADTCP獲得更進一步的效能改善。
TCP has been the dominant transport layer protocol used in the wired networks, but it faces some challenges when used in mobile ad hoc networks (MANET). The major problem is that legacy TCP treats packet loss as an indication of network congestion, and triggers the congestion control mechanism to alleviate the network overload. However, such a scheme is inappropriate in ad hoc networks because a packet loss in MANET is due to many kinds of reasons. Packet losses in MANET might be caused by link failures owing to node mobility, channel errors owing to wireless channel characteristics, or MAC contention owing to wireless shared medium. Because Legacy TCP interprets packet losses in all of these situations as a sign of congestion and attempts to shrink its congestion window size, it may cause a significant degradation in performance.
Thus, in this thesis, we propose a new TCP, called TCP-CI (adaptive TCP based on Cross-layer Information), to improve TCP congestion control scheme over MANET. By exploiting the cross-layer knowledge, TCP-CI attempts to find out the dynamic network states through the MAC layer information at the intermediate nodes. Once the intermediate node knows about the reason of a packet loss, it will use the explicit notification scheme to inform the sender about the exact network state. After receiving the information, the sending TCP may then adapt its congestion control mechanism to fit into the new network environment. Our simulation results demonstrate that TCP-CI can effectively improve TCP performance over Legacy TCP and ADTCP.
第一章 緒論............................................... 1
1.1 簡介.................................................. 1
1.2 研究動機.............................................. 5
1.3 論文架構.............................................. 7
第二章 背景知識與相關研究................................. 8
2.1 背景知識.............................................. 8
2.1.1 IEEE 802.11 媒介存取控制協定........................ 8
2.2 相關研究.............................................. 9
2.2.1 TCP-F and TCP-ELFN...................................9
2.2.2 ATCP ...............................................12
2.2.3 ADTCP...............................................15
2.2.4 LRED(Link RED) .....................................17
2.2.5 Preemptive routing .................................19
2.2.6 其他............................................... 22
第三章 研究方法.......................................... 23
3.1 系統架構............................................. 23
3.2 非壅塞狀態(non-congested state)之偵測程序............ 24
3.2.1 連線中斷狀態(Disconnected state)偵測............... 25
3.2.2 通道錯誤狀態(Channel error state)偵測.............. 26
3.3 壅塞狀態之偵測程序(congested state) ................. 27
3.3.1 Buffer overflow 偵測............................... 27
3.3.2 MAC 競爭狀態(MAC contention level)偵測............. 28
3.4 具有負面回應(negative acknowledgement)機制之媒介存取控制層...29
3.5 跨層訊息的回授機制(cross-layer feedback)............. 33
3.6 傳輸層針對動態網路狀態的反應程序..................... 34
第四章 實驗結果與討論.................................... 38
4.1 模擬環境設定......................................... 38
4.2 實驗結果............................................. 39
4.2.1 鏈狀拓樸(Chain Topology)........................... 39
4.2.2 節點隨意移動拓樸(Mobile Random Topology) .......... 46
第五章 結論與未來工作.................................... 50
5.1 結論................................................. 50
5.2 未來工作............................................. 50
參考文獻................................................. 52
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