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研究生:鄭勝中
研究生(外文):Sheng-Chung Cheng
論文名稱:在Linux平台上實做動態調整DSCP的有效TCP傳輸機制
論文名稱(外文):Implementation of Dynamic DSCP Adjustment for Effective TCP Transmission on Linux Platform
指導教授:許蒼嶺
指導教授(外文):Tsang-Ling Sheu
學位類別:碩士
校院名稱:國立中山大學
系所名稱:電機工程學系研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:中文
論文頁數:65
中文關鍵詞:有效傳輸率動態調整DSCP
外文關鍵詞:DSCP dynamic adjustmentTCPCongestion WindowRound Trip Time
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IETF提出的差別式服務網路(Differentiated Service,DiffServ),奠定了下一代具有服務品質(Quality of Services,QoS)的網路架構。具有高度的延展性以及和相容性,是DiffServ網路最大的特色。不過對於個別資料流的傳輸率要求,仍缺乏一套有效的解決辦法。有鑑於此,我們提出有效率的TCP傳輸(Effective TCP Transmission)機制,依照TCP的傳輸特性,藉以改進在DiffServ網路上針對個別資料流所欠缺的傳輸服務品質。
我們提出的機制,是以TCP資料流的有效傳輸率為目標。我們考慮到真實的網路環境是時時刻刻都在變動的,因此必須有一套好的方法以掌握網路的即時狀況。首先我們將在入口端節點(Ingress Node)量測TCP的相關參數,此為 TCP的Congestion Window(cwnd)和Round Trip Time(RTT)。而在出口端節點(Egress Node)監測實際的傳輸率,並將得到的結果利用返回的TCP確認封包(Ack Packet)通知Ingress Node。在該資料流的傳輸率沒有達到預期目標時,我們利用量測的TCP參數做動態調整DSCP(DiffServ Code Point)。每個DSCP在Ingress Node都會有對應的延遲時間,這些延遲時間是由我們安排的Delayed-FIFO佇列所達成。故改變DSCP將使得資料流的RTT受到變化,因而我們可以調整傳輸率,讓TCP做有效的傳輸。
為了驗證我們的機制,我們將提出的方法實做于Linux平台上。並且透過實驗,量測與討論來分析理論和實做上的差距。並且以這種方式,說明了我們的機制在實際運作和與現有設備相容的可行性。
IETF proposes the Differentiated Service(DiffServ) architecture for next-generation QoS networks. The main features of a DiffServ network are high scalability and compatibility. However, lacking of supporting QoS for individual flows becomes a problem. To remedy this problem, we propose an effective TCP transmission (ETCP) scheme based on the characteristics of TCP.
The goal of this thesis is to make TCP transmission more effective. Because of the network complexity, we need to modify both the Ingress and Egress nodes. At Ingress node, we measure TCP congestion window(cwnd) and Round Trip Time(RTT), while at Egress node we monitor the throughput and embed a feedback ratio into TCP header of the acknowledge packets. When the throughput is below or over the target throughput, we adjust DSCP dynamically. The adjustment depends on both measured TCP congestion window and RTT. Each DSCP value is mapped with a delay time through Delayed-FIFO. Changing the delay time in Ingress node, we are able to control TCP transmission associated with RTT more effectively.
For the purpose of the demonstration, we implement our scheme on Linux platform. We discuss the performance difference between the theoretical and practical results through experiments. Besides, from the implementation, we have shown that our proposed architecture is workable and compatible with today’s network environment.
第一章 導論 …………………………………………………………………………1
1.1研究動機 ………………………………………………………………………1
1.2研究方向與實作 ………………………………………………………………1
1.3章節介紹 ……………………………………………………………………....2
第二章 網際網路的服務品質 ………….…………………………………………...3
2.1 差別式服務(Differentiated Services, DiffServ) ………………………………3
2.2 差別式服務網路架構 ………………………………………………………...4
2.2.1 DSCP的介紹 …………………………………………………..…………5
2.2.2 快速轉送(Expedited Forwarding) ….…………………………………….7
2.2.3 確保轉送(Assured Forwarding) ………………………….………………8
2.2.4預設轉送(Default Forwarding) …………………………….……………..8
2.3 差別式服務網路路由器(DiffServ Router)的介紹 …………….…………….9
2.4相關研究 ……………………………………………………….……………..11
2.4.1回授式控制的差別式服務網路(Feedback Controlled DiffServ) ………..11
2.4.2封包標記引擎(Packet Marking Engine,PME) …………………………12
2.4.3 DiffServ TCP Model ….…..…………………………………......………12
2.4.4 TCP-Friendly Traffic Marker ……………………………...……………..13
第三章 在DiffServ上的有效TCP傳輸機制 …………………………………….14
3.1 有效TCP傳輸機制 …………………………………………………………14
3.2 ETCP傳輸機制的架構 ………………………………………………………16
3.3 ETCP的控制訊息格式 ……………………………………………………....18
3.4 ETCP機制的運作 ……………………………………………………………20
3.4.1 ETCP 機制的演算法 …………...……………………………………....21
3.4.2 QoS資料流的建立 …………...…………………………………………23
3.4.3 mRTT和mcwnd ………………………………………………………….24
3.4.3.1 mRTT的量測過程 ………………………………………………….24
3.4.3.2 mcwnd的量測過程 ………………………………………………...26
3.4.3.3 mRTT和mcwnd量測的折衷方式 ………………………………...28
3.4.4 Delayed-FIFO的設計 …………………………………………………...30
3.4.5動態調整DSCP的演算法 ……………………………………………...31
3.4.5.1 DSCP的選擇 ……………………………………………………….31
3.4.5.2調整的時機 …………………………………………………………35
3.4.5.3壅塞封包的標記 ……..……………………………………………37
3.4.5.4演算法 ………………..……………………………………………37

第四章 ETCP的實做及結果討論 …………………………………………………39
4.1 實做ETCP于DiffServ的Linux平台 …………………………………… ..39
4.1.1 ETCP Controller模組 ………...…………………………………………39
4.1.2 Delayed-FIFO的實做 ………...…………………………………………42
4.1.3 ERED的實做 ………...………………………………………………….42
4.2 Linux實做的網路架構 ……………...……………………………………….43
4.3 實驗數據及分析討論 ………………...……………………………………..44
4.3.1 Delayed-FIFO和mRTT的量測 …………………………………………44
4.3.2 cwnd的量測 ………………………...…………………………………...45
4.3.3 動態調整DSCP的量測 ………………………………………………...46
4.3.3.1單方向的QoS資料流傳送 …………………………………………48
4.3.3.2雙方向的QoS資料流傳送 …………………………………………52
4.4與延遲ACK封包的效能比較………………………………………………..55
第五章 結論與未來工作方向 ………...…………………………………………...57
5.1結論 …………………………………...……………………………………...57
5.2未來工作方向 …………………...…………………………………………...59
參考資料 ………………...………………………………………………………...60
索引 …………….…………………………………………………………………63
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