延遲控制是現今網路服務中一種相當重要的研究議題，它是用來提升差異性服務品質的主要技術。目前，雖然已經有一些差異性延遲控制機制，例如，比例平均延遲(PAD)排程、等待時間優先序(WTP)排程、以及混合比例延遲(HPD)排程等能夠提供這方面的服務；然而，這些機制僅能對不同網路應用服務的傳輸延遲時間提供一個時間保證比例；對於封包的延遲時間，這些機制仍無法準確地去控制。此外，目前這些差異性服務機制多半都是實作在網路層上，換句話說，這些機制需要路由器提供額外的支援才能完成運作；這個限制，對於現今多變的網路環境而言，顯然非常地不切實際，因為我們無法確保在傳輸過程上的每個路由器都能提供這類的服務。
　　有鑑於此，為了改善以上這些問題，我們提出了一個「基於快速TCP機制之點對點延遲控制法」。在建立過程上，我們是先從快速TCP機制的特性分析開始。快速TCP機制是一種用來控制TCP傳輸速率的有效機制，它是藉由一個數學方程式來對TCP連線內的封包壅塞視窗(congestion window)大小做週期性的調整，並藉以達到控制封包傳送速率的功能。調整上，快速TCP會先針對封包傳送的延遲時間(round trip time)去加以量測，並藉由量測到的封包傳送延遲時間來估算出適合目前網路傳輸品質的壅塞視窗大小，再進而去控制TCP連線的封包傳輸速率。
　　因為封包佇列延遲時間(queuing delay)會反映在封包傳送延遲時間內，為此，我們便針對快速TCP機制內的壅塞視窗數學調整方程式加以分析。經過數學模式的建立和推導後，我們證明了快速TCP機制的操作參數設定和最終的封包佇列延遲時間有一定的數學關係。基於這項事實，我們發展出了一套封包延遲控制的方法 (DCA-FTCP)，此一方法可以準確地控制封包的時間延遲。此外，因為此延遲控制法是架構在TCP層上，為此，它不需要路由器的支援就可以直接實現在終端主機上。最後，藉由模擬實驗的測試，我們更進一步地驗證了此一延遲控制法的正確性跟可行性。相信此一控制延遲方法的提出，能為未來網路延遲控制的服務提供一個新的方向與作法。

　Delay control is an important service which belongs to Diffserv on Internet. Traditionally, mechanisms for delay control, like PAD scheduling, WTP scheduling, and HPD scheduling, are all deployed in IP layer and only offer a ratio of delay time for different applications. These mechanisms can not precisely control delay for a certain queuing delay request. Thus, in order to offer an accurate delay control service, we present DCA-FTCP, a delay control mechanism based on FAST TCP, in this thesis. On the basis of TCP layer, the proposed DCA-FTCP is easy to be installed in end hosts rather than current DiffServ mechanisms which need extra support from routers. And by mathematical analysis, DCA-FTCP is proven with its effectiveness of absolutely precise delay control service. Furthermore, a series of simulations are also conducted to verify the performance of DCA-FTCP. DCA-FTCP can indeed offer an absolutely accurate delay control service for Internet transmission.

[1] R. Gilligan, S. Thomson, J. Bound, J. McCann, and W. Stevens, “Basic Socket Interface Extensions for IPv6”, RFC 3493, IETF, Feb. 2003.

[2] comScore Networks, http://www.comscore.com/press/release.asp?press=849

[3] J. Postel, “User Datagram Protocol”, RFC 768, IETF, Aug. 1980.

[4] J. Postel, “Transmission Control Protocol DARPA Internet Program Protocol Specification”, RFC 793, IETF, Sep. 1981.

[5] J. Ström, “Digital Video over TCP/IP”, Master’s Thesis, Lund Institute of Technology, Sweden, Jul. 1995.

[6] P. H. Hsiao, H.T. Kung, and K. S. Tan, “Streaming Video over TCP with Receiver-based Delay Control”, IEICE Trans. on Communications, Nov. 2003.

[7] GoalSoft, “2Meeting Peer to Peer Video Conference Web Site”, http://www.goalsoft.com.tw/2meeting/

[8] F. Baker, R. Guerin, and D. Kandlur, “Specification of Committed Rate Quality of Service”, Internet Draft, Jun. 1996.

[9] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, and W. Weiss, “An Architecture for Differentiated Services,” RFC 2475, IETF, Dec. 1998.

[10] C. Davolis, D. Stiliadis, and P. Ramanathan, “Proportional differentiated services: delay differentiation and packet scheduling”, IEEE/ACM Trans. on Networking, Volume 10, Issue 1, Feb. 2002, pp. 12 – 26.

[11] C. Dovrolis, “Proportional differentiated services for the Internet”, Ph.D. dissertation, Dept. Computer Science, Univ. of Wisconsin, Madison, Dec. 2000.

[12] M. K. H. Leung , J. C. S. Lui, and D. K. Yau, “Adaptive proportional delay differentiated services: characterization and performance evaluation: Characterization and Performance Evaluation”, IEEE/ACM Trans. on Networking, Volume 9, Issue 6, Dec. 200, pp. 801 – 817.

[13] C. Jin, D.X. Wei, and S.H. Low, “FAST TCP: motivation, architecture, algorisms, performance”, in Proceedings of IEEE INFOCOM, Volume 4, Mar. 2004, pp. 2490-2501.

[14] C. Jin, D.X. Wei, S.H. Low, G. Buhrmaster, J. Bunn, D. H. Choe, R. L. A. Cottrell, J. C. Doyle, W. Feng, O. Martin, H. Newman, F. Paganini, S. Ravot, and S. Singh, “FAST TCP: from theory to experiments”, in Proceedings of IEEE Network, Volume 19, Issue 1, Jan.-Feb. 2005, pp. 4-11.

[15] J. Wang, D.X. Wei, and S.H. Low, “Modelling and stability of FAST TCP”, in Proceedings of IEEE INFOCOM, Volume 2, Mar. 2005, pp. 938-948.

[16] J. Wang, A. Tang, and S.H. Low, “Local Stability of FAST TCP”, in Proceedings of IEEE CDC, Volume 1, Dec. 2004, pp. 1023-1028.

[17] V. Jacobson, ”Congestion avoidance and control,” in Proceedings of SIGCOMM , Volume 18 , Aug. 1988, pp. 314-329.

[18] V. Jacobson, “Modified TCP Congestion Avoidance Algorithm”, end2end-interest mailing list, Apr. 1990.

[19] V. Jacobson, R. Braden, and D. Borman, “TCP Extensions for High Performance”, RFC 1323, IETF, May 1992.

[20] M. Allman, V. Paxson, and W. Stevens, “TCP Congestion Control”, RFC 2581, IETF, Apr. 1999.

[21] R. L. Cottrell, H. Bullot, and R. Hughes-Jones, “Evaluation of Advanced TCP Stacks on Fast Long-Distance Production Networks”, PFLDnet, Feb. 2004.

[22] J. Philippe, M. Flatin, and S. Ravot, “TCP Congestion Control in Fast Long-Distance Networks”, Technical Report CALT-68-2398, California Institute of Technology, Jul. 2002.

[23] E. He, P.V. Primet, and M. Welzl, “A Survey of Transport Protocols other than “Standard” TCP”, GFD-I.055, Data Transport Research Group, Nov. 2005.

[24] S. Floyd, “HighSpeed TCP for Large Congestion Windows”, RFC 3649, IETF, Dec. 2003.

[25] Y. T. Li and G. Fairey, "Implementing High Speed TCP (aka Sally Floyd's)", Oct. 2002, http://www.hep.ucl.ac.uk/~ytl/tcpip/highspeedtcp/hstcp/hstcp-ppncg-1209 2002.ppt

[26] L. Brakmo and L. Peterson, “TCP Vegas: End to End Congestion Avoidance on a Global Internet”, IEEE Journal of Selected Areas in Communications (J-SAC), Volume 13, Issue 8, Oct. 1995, pp. 1465-1480.

[27] CUBINlab, “FAST TCP simulator module for ns-2”, http://www.cubinlab.ee.unimelb.edu.au/ns2fasttcp/

[28] L. Tan, C. Yuan, and M. Zukerman, “FAST TCP: Fairness and Queuing Issues”, IEEE Communication Letters, Volume 9, Issue 8, Aug. 2005, pp. 762-764.

[29] Tony Cui, Andrew L. L. H., M. Zukerman, and L. Tan, “Improving the Fairness of FAST TCP to New Flows”, IEEE Communication Letters, Volume 10, Issue 5, May 2006, pp. 414-416.