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研究生:黃嘉佑
研究生(外文):Chia-Yu Huang
論文名稱:qtECN–一個改良的明確壅塞通知演算法
論文名稱(外文):qtECN – An Improved Explicit Congestion Notification Algorithm
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
論文出版年:2008
畢業學年度:96
語文別:中文
論文頁數:57
中文關鍵詞:佇列管理壅塞控制明確壅塞通知
外文關鍵詞:congestion controlqueue managementExplicit Congestion Notification
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ECN(Explicit Congestion Notification)是一種主動式的佇列管理機制(Active Queue Management, AQM),此協定的主要目的是為了減少路由器佇列中的壅塞現象,和目前使用最普遍的Drop-Tail機制相比,ECN能夠偵測早期的壅塞現象並利用明確的訊息通知TCP傳送端,使其降低傳送封包的速度以避免真正的壅塞發生。但在目前ECN的設計中,TCP傳送端是以封包遺失的方式來反應所收到的早期壅塞通知,使傳送速率過度的降低。另外,ECN機制在路由器中所使用的封包標記/丟棄規則會造成有效吞吐量、封包遺失率和傳送延遲在網路效能中相互的競爭,無法在獲得較高的有效吞吐量的同時也得到較低的傳送延遲。因此,在本篇論文中提出一個改良的明確壅塞通知演算法,稱為qtECN(Quantitatively Explicit Congestion Notification),qtECN以ECN的設計為基礎,修改封包在路由器被標記與丟棄的規則,同時在需要標記的封包中加上額外的資訊,使TCP傳送端在收到qtECN-ACK通知的同時,能夠知道壅塞路由器中的負載情況,藉以調整自身的壅塞視窗大小與封包的傳送速度。在本論文的實驗結果中顯示,qtECN不但能夠得到最佳的有效吞吐量、延遲抖動率與封包遺失率,同時具有不錯的封包傳送延遲,另外,使用qtECN的路由器因為佇列溢滿而將封包丟棄的數量趨近於零,代表qtECN比目前其它各種主動式佇列管理機制更適合用在有線無線並存的異質混合網路中。總結而論,當路由器發生無可避免的壅塞現象時,使用qtECN的設計可以使網路獲得更好的效能。
ECN (Explicit Congestion Notification) is an active queue management scheme for network routers. The purpose of this protocol is mainly aimed at solving the problem of queue management and relieving the congestion phenomenon on the network. Compared with the traditional method that drops packets when buffer is full, ECN could improve the network performance by noticing the TCP sender to reduce its sending rate in advance, i.e., before the congestion really happened on the network. However, in ECN algorithm, TCP sender could only invoke the same mechanism as that when it encounters a packet loss event and thus have the sending rate excessively reduced. In addition, the rule of ECN marking/dropping packets in routers will cause the transmission throughput and delay to compete with each other.
  In this thesis, we propose an improved ECN algorithm, named qtECN (Quantitatively Explicit Congestion Notification). The qtECN algorithm is based on the original design of ECN but modifies the rule that ECN uses for packets marking and dropping. Besides, qtECN adds additional information in the randomly marked packets to inform the TCP sender of the loading of the congested router, so the TCP sender could adjust its sending rate accordingly. The experimental results show that qtECN has a better performance at goodput, packet loss rate and delay jitter with acceptable transmission delay. In addition, packets’ dropping due to full queue is nearly zero when using qtECN. It means qtECN is more suitable for wired-wireless hybrid network than any other existing AQM schemes. In summary, applying the design of qtECN could make the performance of network further improved when unavoidable congestion happened in the router.
摘要 1
Abstract 2
目錄 3
圖表目錄 4
第一章 導論 6
1.1 簡介 6
1.2 研究動機 8
1.3 論文架構 10
第二章 背景知識 11
2.1 壅塞與網路效能 11
2.2 TCP壅塞控制簡介 13
2.3 Drop-Tail機制簡介 20
2.4 RED機制簡介 22
2.5 ECN機制簡介 24
第三章 系統架構 29
3.1 欲解決的問題 29
3.2 qtECN演算法設計 31
第四章 模擬實驗 43
4.1 實驗拓樸與設定 43
4.2 實驗(一):改變佇列容量 45
4.3 實驗(二):改變連線數 52
第五章 結論與未來的研究方向 59
參考資料 60
[1] K. Ramakrishnan and S. Floyd , “A Proposal to add Explicit Congestion Notification (ECN) to IP ,” RFC 2481 , January 1999.
[2] K. Ramakrishnan, S. Floyd, D. Black, “The addition of explicit congestion notification (ECN) to IP”, RFC 3168, September 2001
[3] S. Floyd, “TCP and explicit congestion notification,” ACM Computer Communication Review, vol. 24, no. 5, pp. 8–23, October 1994, http://www.aciri.org/floyd/.
[4] Jun Lai, Wu Ye, Sui-Li Feng, “LQRD: An Improved ECN Algorithm,” Eighth ACIS International Conference on Software Engineering, Artificial Intelligence, Networking, and Parallel/Distributed Computing, Volume 1, pp.239-244, July 2007
[5] Van Jacobson and Michael J. Karels, “Congestion Avoidance and Control,”ACM Computer Communication Review, In Proceedings of ACM SIGCOMM ’88 Symposium in Stanford, CA, August 1988
[6] M. Allman, V. Paxson, W. Stevens, “TCP Congestion Control,” RFC 2581, April 1999
[7] V. Jacobson. “Modified TCP Congestion Avoidance Algorithm,” Technical Report, April 1990
[8] S. Floyd and T. Henderson, “The New Reno Modification to TCP’s Fast Recovery Algorithm,” RFC 2582, IETF, April 1999
[9] J. Hoe, “Improving the Start-up Behavior of a Congestion Control Scheme for TCP,” In Proceedings on Applications, Technologies, Architectures and Protocols for Computer Communications, Pages 270–280, ACM Press, 1996
[10] B. Braden , D. Clark , J. Crowcroft , B. Davie , S. Deering , D. Estrin , S. Floyd , V.Jacobson , G. Minshall , C. Partridge , L. Peterson , K. Ramakrishnan , S. Shenker ,J. Wroclawski , & L. Zhang , “Recommendations on Queue Management and Congestion Avoidance in the Internet ,” Internet draft , work in progress, 1998
[11] S. Floyd and V. Jacobson, “Random early detection gateways for congestion avoidance,”IEEE/ACM Transactions on Networking, vol. 1, no. 4, pp. 397–413, Aug. 1993
[12] C. Liu and R. Jain,“Improving explicit congestion notification with the mark-front strategy,”Submitted to Computer Networks, May 2000 http://www.cis.ohio-state.edu/jain/papers/ecnfront.htm
[13] Kai Xu, Ye Tian, and Ansari N.,“TCP-Jersey for Wireless IP Communications,”Selected Areas in Communications, IEEE Journal, Vol. 22, Issue 4, Pages 747-756, May 2004
[14] M. Kwon and S. Fahmy,“TCP Increase/Decrease Behavior with Explicit Congestion Notification (ECN),”Proceedings of IEEE ICC(Symposium on High-Speed Networks), Vol. 4, pp. 2335-2340, April 2002
[15] 柯志亨、程榮祥、謝錫(方方土)、黃文祥(2005):《計算機網 路實驗-以NS2模擬工具實作》,台北:學貫行銷股份有限公司。
[16] D. Chiu, R. Jain, “Analysis of the increase and decrease algorithms for congestion avoidance in computer networks,” Computer Networks and ISDN Systems, Vol. 17, No. 1, pp.1-14, 1989
[17] S.Floyd,”RED : Discussions of setting parameters,” http://www.icir.org/floyd/REDparameters.txt
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