隨著時代日益變遷，使用者對網際網路依賴程度越來越大，網路系統中承載的網路服務也隨之增加，造成現有的傳統網路越來越複雜。不僅如此，傳統網路也缺乏蓬勃發展的網路所需要的彈性與適應性，所以近年來史丹佛大學提出軟體自定義網路(Software-Defined Networking, SDN)的概念，就是為了要解決傳統網路沒有彈性與適應性的缺點。SDN將控制網路的功能從網路設備中抽出，讓網際網路服務者透過集中的控制層操作多台網路設備，而且可以透過修改控制層的軟體內容來新增或修改管理功能，讓修改管理功能不再受限於難以更改的硬體，也比較易於管理整個網路的路由方式及清楚知道網路拓樸的狀況。因此，本論文提出基於任播動態路徑與伺服器選擇機制，將內容傳遞網路(Content Delivery Network, CDN)中的任播技術應用在SDN的環境下，並用演算法使整體網路頻寬和網路資源能夠平均的被分配和充分利用，改善傳統網路中無法了解整個網路的拓樸資訊、難以測量網路上的資訊和無法動態更改傳輸路徑的缺點，還有增加系統的穩定性及可擴展性。且所提出的系統在模擬環境中顯示比其他的演算法傳送所需的檔案速度來的還快。

Recently, most of people increasingly download files on Internet so that the network performance become an important component of management. Content Delivery Network (CDN) is an effective approach, which widely used by Internet Service Provider (ISP) to improve Internet service quality. However, traditional CDN hardly changes routing path based on network status and DNS-based proximity routing may cause redundant latency. The EDNS-client-subnet extension fixes this problem, but the solution isn’t fully implemented in all DNS resolvers, and it requires ISP to map the entire routing table, which is a much bigger challenge in traditional network. The concept of Software-Defined Networking (SDN) proposed by Stanford University turn out to be a solution. SDN decouple the control plane and data plane of network, which makes measuring network status easier than before and maintaining the global view of Internet in control plane. Based on the above mentioned, this research proposed a dynamic path and server selection mechanism based on Anycast in SDN. The mechanism solve the problems of DNS-based routing in traditional CDN and dynamically select the suitable path and server based on network status to make better network performance. The result shows that the dynamic path and server selection mechanism has better performance than closest-first algorithm and latency-first algorithm.

[1] Partridge, Craig, Trevor Mendez, and Walter Milliken, “Host anycasting service,” 1993, [Online]. Available: https://www.ietf.org/rfc/rfc1546.txt, RFC 1546, (2017, Jun. 28).
[2] Vakali, Athena, and George Pallis, "Content delivery networks: Status and trends," IEEE Internet Computing, vol. 7, no. 6, pp. 68-74, 2003.
[3] Nunes, Bruno Astuto A., et al, "A survey of software-defined networking: Past, present, and future of programmable networks," IEEE Communications Surveys and Tutorials, vol. 16, no. 3, pp. 1617-1634, 2014.
[4] Adhikari, Vijay Kumar, et al, "Vivisecting youtube: An active measurement study," in Proceedings of the IEEE INFOCOM, 2012.
[5] Casas, Pedro, et al, "When YouTube does not work—Analysis of QoE-relevant degradation in Google CDN traffic," IEEE Transactions on Network and Service Management, vol. 11, no. 4, pp. 441-457, 2014.
[6] Calder, Matt, et al, "Analyzing the Performance of an Anycast CDN," in Proceedings of the ACM Conference on Internet Measurement Conference, 2015.
[7] McKeown, Nick, et al, "OpenFlow: enabling innovation in campus networks." ACM SIGCOMM Computer Communication Review, vol. 38, no.2, pp. 69-74, 2008.
[8] “NOX.” [Online]. Available: https://www.bignox.com/ (2017, Jun. 28)
[9] “POX.” [Online]. Available: https://github.com/noxrepo/pox (2017, Jun. 28)
[10] “OpenDaylight.” [Online]. Available: https://www.opendaylight.org/ (2017, Jun. 28)
[11] “Floodlight.” [Online]. Available: http://www.projectfloodlight.org/floodlight/ (2017, Jun. 28)
[12] Jarschel, Michael, et al, "Interfaces, attributes, and use cases: A compass for SDN," IEEE Communications Magazine, vol. 52, no. 6, pp. 210-217, 2014.
[13] Khondoker, Rahamatullah, et al, "Feature-based comparison and selection of Software Defined Networking (SDN) controllers," in Proceedings of the IEEE World Congress on Computer Applications and Information Systems, 2014.
[14] “OpenFlow specification 1.5.” [Online]. Available: https://www.opennetworking.org/images/stories/downloads/sdn-resources/onf-specifications/openflow/openflow-switch-v1.5.0.noipr.pdf, (2017, Jun. 28).
[15] “OpenFlow specification 1.3.” [Online]. Available: https://www.opennetworking.org/images/stories/downloads/sdn-resources/onf-specifications/openflow/openflow-spec-v1.3.0.pdf, (2017, Jun. 28).
[16] Hinden, Robert M., Larry Masinter, and Brian E. Carpenter, "Format for Literal IPv6 Addresses in URL's," 1999, [Online]. Available: https://www.ietf.org/rfc/rfc2732.txt, RFC 2372, (2017, Jun. 28).
[17] Katabi, Dina, and John Wroclawski, "A framework for scalable global IP-anycast (GIA)," ACM SIGCOMM Computer Communication Review, vol. 30, no. 4, pp. 3-15, 2000.
[18] Ballani, Hitesh, and Paul Francis, "Towards a global IP anycast service," ACM SIGCOMM Computer Communication Review, vol. 35, no. 4, 2005.
[19] Bhattacharjee, Samrat, et al, "Application-layer anycasting." in Proceedings of the IEEE Computer and Communications Societies, 1997.
[20] Ge, Jingguo, et al, “Performance Analysis of Load-Aware Anycasting Based on OpenFlow,” in Proceedings of the IEEE International Conference on Trust, Security and Privacy in Computing and Communications, 2013.
[21] Othman, Othman MM, and Koji Okamura, "Improvement of Content Server with Contents Anycasting Using OpenFlow," in Proceedings of the Asia-Pacific Advanced Network, pp. 37-44, 2010.
[22] “Akamai Technology.” [Online]. Available: https://www.akamai.com/ (2017, Jun. 28).
[23] Krishnamurthy, Balachander, Craig Wills, and Yin Zhang, "On the use and performance of content distribution networks," in Proceedings of the ACM SIGCOMM Workshop on Internet Measurement, 2001.
[24] Flavel, Ashley, et al, "Fastroute: A scalable load-aware anycast routing architecture for modern cdns," in Proceedings of the USENIX Symposium on Networked Systems Design and Implementation, 2015.
[25] Qin, Feng, Zhifeng Zhao, and Honggang Zhang, "Optimizing routing and server selection in intelligent SDN-based CDN," in Proceedings of the International Conference on Wireless Communications and Signal Processing, 2016.
[26] Chandrakanth, Jagannath, Pradeepti Chollangi, and Chung-Horng Lung, "Content Distribution Networks Using Software Defined Networks," in Proceedings of the IEEE International Conference on Trustworthy Systems and Their Applications, 2015.
[27] Chen, Longbin, et al, "Supporting high-quality video streaming with SDN-based CDNs," Journal of Supercomputing, pp. 1-15, 2016.
[28] Wichtlhuber, Matthias, Robert Reinecke, and David Hausheer, "An SDN-based CDN/ISP collaboration architecture for managing high-volume flows," IEEE Transactions on Network and Service Management, vol. 12, no. 1, pp. 48-60, 2015.
[29] “Ryu.” [Online]. Available: https://osrg.github.io/ryu/ (2017, Jun. 28)
[30] Larson, Matt, et al, "Protocol modifications for the DNS security extensions," 2005, [Online]. Available: https://www.ietf.org/rfc/rfc4035.txt, RFC 4035, (2017, Jun. 28).
[31] Tarjan, Robert, "Depth-first search and linear graph algorithms," SIAM journal on computing, vol. 1, no. 2, pp. 146-160, 1972.
[32] Huang, Cheng, et al, "Public DNS system and global traffic management," IEEE INFOCOM, 2011.
[33] Opricovic, Serafim, and Gwo-Hshiung Tzeng, "Compromise solution by MCDM methods: A comparative analysis of VIKOR and TOPSIS," European journal of operational research, vol. 156, no. 2, pp. 445-455, 2004.
[34] Chatterjee, Prasenjit, and Shankar Chakraborty, "Investigating the Effect of Normalization Norms in Flexible Manufacturing System Selection Using Multi-Criteria Decision-Making Methods," Journal of Engineering Science and Technology Review, vol. 7, no. 3, pp. 141-150, 2014.
[35] Chen-xiao, Cui, and Xu Ya-bin, "Research on load balance method in SDN," International Journal of Grid and Distributed Computing, vol. 9, no. 1, pp. 25-36, 2016.
[36] Qin, Feng, Zhifeng Zhao, and Honggang Zhang, "Optimizing routing and server selection in intelligent SDN-based CDN," International Conference on Wireless Communications and Signal Processing, 2016.
[37] Curtis, Andrew R. et al, "DevoFlow: Scaling flow management for high-performance networks," ACM SIGCOMM Computer Communication Review, vol. 41, no. 4, pp. 254-265, 2011.