彈性封包環是一種發展於都會型網路的傳輸技術，由IEEE 802.17制定相關協定並已推出正式版本。先前在都會型網路廣泛被使用的SONET和乙太網路技術分別有頻寬無法有效被利用和不支援公平性的問題，彈性封包環提供了一些加強的機制以克服上述缺失。彈性封包環發展至今，壅塞控制與公平性機制是主要被廣為探討的議題，對於單一彈性封包環網路，許多研究在探討頻寬永久震盪問題並提出更有效率的公平性演算法。近幾年來，有文獻針對橋接式彈性封包環的架構提出全域式公平性的概念與機制，用以確保跨環訊務流之間的公平性。
本篇論文提出一個在彈性封包環網路上以公平性機制為基礎的壅塞感知重新繞徑策略，目標是提升整體網路吞吐量。當環上發生壅塞且經由公平性機制運作使得競爭壅塞鏈結頻寬的訊務流收斂至穩定速率時，我們嘗試為造成壅塞的部分訊務找尋另一條有更多可利用頻寬的替代路徑並將其重新繞徑以提升傳輸速率，此外，由於競爭者減少，流經壅塞鏈結的訊務流亦可獲得較多頻寬。
為了評估所提出的方法，我們進行一系列包含單一彈性封包環與橋接式彈性封包環架構的模擬來驗證，模擬結果顯示壅塞感知重新繞徑策略在多種不同情境中皆可明顯提升網路吞吐量。

The Resilient Packet Ring (RPR), which has been standardized as IEEE 802.17, is a technology developed in Metropolitan Area Networks (MANs). The previous MAN technologies, SONET and Ethernet, have underutilization and unfairness problems, respectively. RPR provides some strong mechanisms to overcome the shortcomings. Congestion control and fairness in RPR is a main topic that has been frequently discussed. For the single RPR network, many researchers have resolved the permanent oscillation problem and improved the efficiency of fairness algorithm. In resent years, there have been literatures on global fairness to ensure fairness for inter-ring traffic in the bridged RPR network.

In this thesis, we propose a congestion-aware rerouting (CAR) strategy based on the fairness mechanism to increase the network throughput. When congestion is detected and all flows competing for the bandwidth of congested link converge to the steady rate, we try to find an alternate path to gains more bandwidth than the current path for partial traffic crossing the congested link. Moreover, the throughput of flows traversing through the congested link will increase due to the competitors for the bandwidth is decreasing.

To evaluate the proposed scheme, we perform a series of simulations with the network topologies of the single RPR and the bridged RPR. Our simulation results show that CAR can significantly increase the throughput in various scenarios.

[1] ANSI/IEEE Std. 802.3, 2000 Edition, “IEEE standard for Ethernet,” 2000.
[2] ANSI T1.105.06-1996 Synchronous Optical Network (SONET) - Physical Layer Specification (Revision of ANSI T1.106-1988), 1996.
[3] IEEE Standard 802.1D, “Media Access Control (MAC) Bridges,” 2004.
[4] IEEE Standard 802.17, “Resilient Packet Ring (RPR) access method and physical layer specifications,” 2004.
[5] IEEE Standard 802.17b, “Part 17: Resilient packet ring (RPR) access method and physical layer specifications Amendment 1: Spatially aware sublayer,” 2007.
[6] IEEE Standard 802.1Q, 2003 Edition. “IEEE standards for local and metropolitan area networks. Virtual bridged local area networks.”
[7] F. Alharbi and N. Ansari, “Distributed bandwidth allocation for resilient packet ring networks,” Computer Networks: The International Journal of Computer and Telecommunications Networking, vol. 49, no. 2, pp. 161-171, October 2005.
[8] F. Alharbi and N. Ansari, “SSA: simple scheduling algorithm for resilient packet ring networks,” IEEE Proceedings on Communications, vol. 153, no. 2, pp. 183-188, April 2006.
[9] F. Davik, M. Yilmaz, S. Gjessing, and N. Uzun, “IEEE 802.17 Resilient Packet Ring Tutorial,” IEEE Communications Magazine, vol. 42, no. 3, pp. 112-118, 2004.
[10] F Davik, A Kvalbein, and S Gjessing, “Improvement of resilient packet ring fairness,” IEEE International Conference on Global Telecommunications, GLOBECOM ’05, St. Louis, MO, U.S.A., vol. 1, pp.581-586, 2005.
[11] V. Gambiroza, P. Yuan, L. Balzano, Y. Liu, and S. Sheafor, and E. Knightly, “Design, Analysis, and Implementation of DVSR: A Fair, High Performance Protocol for Packet Rings,” IEEE/ACM Transactions on Networking, vol.12, no.1, pp.85-102, 2004.
[12] A. Kvalbein, S. Gjessing, and F. Davik, “Performance Evaluation of an Enhanced Bridging Algorithm in RPR Networks,” Proceedings 3rd International Conference on Networking (ICN’04), pp. 760-767, 2004.
[13] T.J. Kim, “An enhanced fairness algorithm for the IEEE 802.17 resilient packet ring,” IEICE Transactions on Communication, 2005.
[14] T.J. Kim, “Bandwidth Reallocation Scheme for the IEEE 802.17 Resilient Packet Ring,” The Fourth IEEE and IFIP International Conference on Wireless and Optical Communications Networks, 2007.
[15] C.G. Liu and J.S. Li, “A fast-convergent fairness scheme for resource allocation in RPR networks,” International Journal of Communication Systems, 2008.
[16] D.H. Lee and J.H. Lee, “A novel fairness mechanism based on the number of effective nodes for efficient bandwidth allocation in the resilient packet ring,” IEICE Transactions on Communication, 2006.
[17] O. Lysne and S. Gjessing, “Java based RPR simulator,” Available at http://simula.no/research/networks/software/rpr
[18] N. Nongnuch, W. Kwanmetakun, P. Setthawong, and S. Tanterdtid, “Efficient Bandwidth of Multicast Packets in RPR Topology for Supporting Wireless and Mobile Devices,” ACM International Conference Proceeding Series, 2006.
[19] Y.F. Robichaud and C. Huang, “Improved fairness algorithm to prevent tail node induced oscillations in RPR,” IEEE International Conference on Communications, ICC ’05, Seoul, Korea, vol. 1, pp. 402-406, 2005.
[20] P. Setthawong and S. Tanterdtid, “Inter-ring traffic management for global fairness in bridged resilient packet rings,” Global Telecommunications Conference, 2005.
[21] P. Setthawong, C. Siriakkarap, and S. Tanterdtid, “Inter-Ring Traffic Engineering for Bridged IEEE 802.17 Resilient Packet Rings,” Information and Telecommunication Technologies, 2005.
[22] P. Setthawong and S. Tanterdtid, “Inter-ring Traffic Management in Bridged Resilient Packet Rings: Global Fairness and Buffer Overflow Prevention,” IJCSNS International Journal of Computer Science and Network Security, vol. 6, no. 11, pp. 190-201, November 2006.
[23] P. Setthawong and S. Tanterdtid, “Non-Flooding Bridging Solutions for Resilient Packet Rings,” ECTI Transactions on Electrical Eng., Electronics, and Communications, vol. 6, no.1, February 2008.
[24] P. Setthawong and S. Tanterdtid, “Flood avoidance mechanisms for bridged resilient packet rings,” Journal of Computer Science and Technology, vol. 23, no.5, September 2008.
[25] W.S. Tang and C.J. Chang , “Intelligent Interring Route Control in Bridged Resilient Packet Rings,” Journal of Lightwave Technology, vol. 27, pp. 5631-5638, December 2009.