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研究生： 林益丞
Lin, Yi-Cheng
論文名稱： 傳輸層連線之緩衝區模糊控制
指導教授： 吳植森
Wu, Zhi-Sen
學位類別： 碩士
Master
系所名稱： 管理學院 - 資訊管理研究所
Institute of Information Management
論文出版年： 2003
畢業學年度： 91
語文別： 中文
論文頁數： 71
中文關鍵詞： 模糊比例-積分-微分控制器 、動態緩衝區管理
外文關鍵詞： ns-2, Fuzzy Proportional Integral-Derivative Controlle, Active Queue Management
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    • TCP/IP協定是目前網際網路上最被廣泛使用的通訊協定，而當中的傳輸層流量佔了網路頻寬的一大部分，其中包含了常見的TCP(Transmission Control Protocol)及UDP(User Datagram Protocol)流量。可預見的是，未來對網路頻寬的需求量將有增無減，且使用者對服務品質的要求也將更為嚴格，因此，如何在現有的頻寬下避免及控制網路壅塞，一直以來都是網路管理者所重視的課題。對於解決網路壅塞的問題可分為兩個部分來探討，第一為端對端(End-To-End)的控制，也就是傳送端及接收端之間的協調。當壅塞情形發生時，傳送端接收到壅塞的訊息(Congestion Indication)，即減少封包傳送的速率。常見的機制有TCP Tahoe、Reno、NewReno、SACK及Vegas等。Reno為網路上最為普遍建置的版本。第二為中介點(通常為路由器)的控制，根據RFC的分類分為封包的排程(Packet Scheduling)以及動態緩衝區管理(Active Queue Management)，前者常見的有FIFO、FQ、CBQ等，後者則有Drop-tail、RED、CHOKe等。本論文之主要研究對象在於動態緩衝區管理。我們利用模糊理論能夠解決非線性及不確定因素的特性，設計一個模糊比例-積分-微分控制器(Fuzzy Proportional Integral-Derivative Controller, FPID)來改進並應用在路由器緩衝區管理的控制上。本論文中使用ns-2網路模擬程式來實作此控制機制，並利用相關的工具來計算其效能並與其他著名之緩衝區管理機制作比較。經由模擬的結果顯示，FPID機制可以解決因發送端發送速率不同所造成的不公平現象，也可以解決在某些情況下較慢進入系統的連線會分配到較少頻寬的不公平現象。而與TCP-不友善流量共存時，並不會過度懲罰而使其流量不穩定，FPID機制可以調整將TCP-不友善流量維持在一較為平穩的狀態。而其餘的TCP流量也大致能獲得公平的頻寬，這對於需要穩定傳輸速率的影音、多媒體資訊流而言，是較為適合的。

    關鍵字：動態緩衝區管理(Active Queue Management)、模糊比例-積分-微分控制器(Fuzzy Proportional Integral-Derivative Controller)、ns-2

    目錄 摘要.....................................................................Ⅰ 誌謝.....................................................................Ⅱ 目錄.....................................................................Ⅲ 圖目錄...................................................................Ⅳ 表目錄...................................................................Ⅶ 第一章 緒論..........................................................1 第一節 研究背景與動機................................................1 第二節 研究目的......................................................2 第三節 研究流程......................................................3 第二章 文獻探討......................................................4 第一節 TCP通訊協定.........................................................................4 第二節 UDP通訊協定........................................................................12 第三節 TCP壅塞控制演算法........................................................................13 第四節 緩衝區控制機制........................................................................24 第五節 模糊理論........................................................................30 第三章 研究方法........................................................................40 第一節 RED與TCP壅塞控制模式........................................................................40 第二節 模糊比例-積分-微分控制器........................................................................42 第三節 模糊比例-積分-微分控制器於緩衝區管理之設計……….........……43 第四章 實驗分析.....................................................52 第一節 同質流量之系統模擬........................................................................52 第二節 具HTTP流量之同質流量系統模擬........................................................................58 第三節 異質流量之系統模擬........................................................................63 第五章 結論........................................................................66 參考文獻........................................................................68 圖目錄 圖1.1 研究流程...................................................................................................................3 圖2.1-1 TCP連線狀態.........................................................................................................4 圖2.1-2 TCP連線建立的步驟...........................................................................................5 圖2.1-3 TCP連線中止的步驟...........................................................................................7 圖2.1-4 TCP封包格式.......................................................................................................9 圖2.1-5 TCP標頭格式.......................................................................................................9 圖2.2-1 UDP封包格式.....................................................................................................12 圖2.2-2 UDP標頭格式.....................................................................................................13 圖2.3-1 網路壅塞的現象.................................................................................................13 圖2.3-2 Tahoe機制的各階段...........................................................................................16 圖2.3-3 Reno機制的運作流程........................................................................................17 圖2.3-4 壅塞控制的範例.................................................................................................18 圖2.3-5 多個封包遺失的問題........................................................................................20 圖2.3-6 TCP NewReno的運作流程...............................................................................21 圖2.3-7 TCP SACK的運作流程.....................................................................................22 圖2.4-1 Drop-Tail機制的Lock-out現象........................................................................25 圖2.4-2 Drop-Tail機制下的視窗變化............................................................................26 圖2.4-3 RED機制的流程圖.............................................................................................28 圖2.4-4 RED機制的封包丟棄機率................................................................................28 圖2.4-5 RED機制下的視窗變化....................................................................................29 圖2.5-1 語言變數Speed的語言項歸屬函數................................................................32 圖2.5-2 模糊邏輯推論系統.............................................................................................34 圖2.5-3 模糊控制基本架構.............................................................................................35 圖2.5-4模糊化方法...........................................................................................................36 圖2.5-5 歸屬函數外型與分辨性的關係.......................................................................37 圖2.5-6 歸屬函數之間的重疊性....................................................................................37 圖2.5-7 重心解模糊化法圖示說明................................................................................38 圖2.5-8 中心平均解模糊化法圖示說明.......................................................................39 圖3.1-1 整體模式方塊圖.................................................................................................40 圖3.1-2 PI控制器控制方塊圖.........................................................................................41 圖3.1-3 模糊比例-積分微分控制系統..........................................................................42 圖3.2-1 輸出輸入變數之模糊歸屬函數.......................................................................44 圖3.2-2 腳本檔(Script file)範例......................................................................................45 圖3.2-3 模擬實驗圖...................................................................................................46 圖3.2-4 緩衝區大小變化圖(a)........................................................................................46 圖3.2-5 緩衝區大小變化圖(b)........................................................................................47 圖3.2-6 模糊推論過程...............................................................................................49 圖3.2-7 模糊推論結果之合成........................................................................................49 圖3.2-8 本機制流程圖...............................................................................................50 圖4.1-1 同質流量模擬環境圖...................................................................................52 圖4.1-2 DropTail流量輸出圖(a)................................................................................53 圖4.1-3 DropTail中流量1及流量7的cwnd變化圖(a)..............................................54 圖4.1-4 RED流量輸出圖(a).......................................................................................54 圖4.1-5 RED中流量1及流量7的cwnd變化圖(a)....................................................55 圖4.1-6 FPID流量輸出圖(a)......................................................................................55 圖4.1-7 FPID中流量1及流量7的cwnd變化圖(a)................................................56 圖4.1-8 各個機制下流量的輸出圖...........................................................................56 圖4.1-9 緩衝區大小變化圖(a)...................................................................................57 圖4.2-1具HTTP流量之同質流量模擬環境圖.........................................................58 圖4.2-2 DropTail流量輸出圖(b).................................................................................59 圖4.2-3 DropTail中流量1及流量7的cwnd變化圖(b).............................................59 圖4.2-4 RED流量輸出圖(b)........................................................................................60 圖4.2-5 RED中流量1及流量7的cwnd變化圖(b)........................................................60 圖4.2-6 FPID流量輸出圖(b)......................................................................................61圖4.2-7 FPID中流量1及流量7的cwnd變化圖(b)................................................61 圖4.2-8 緩衝區大小變化圖(b)...................................................................................62 圖4.3-1 異質流量模擬環境圖...................................................................................63 圖4.3-2 CHOKe機制之各流量輸出圖......................................................................64 圖4.3-3 FPID機制之各流量輸出圖...........................................................................64 表目錄 表4.3-1 各個流量的平均值與標準差.......................................................................65

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