在本篇論文中描述了現今行動網路的架構，並且指出在無線存取網路中，流量分布 極度不均衡造成的網路壅塞問題。針對此問題，我們提出三個希望達成的目標:(1)降低 無線網路中多餘的資料流量。(2)減少網路流量超出負荷及壅塞的情形發生。(3)替個人 最大化下載的資料價值。
為了達成這三個目的，我們引進代理伺服器此元件並設置於手機及網際網路上。位 於網際網路上的代理伺服器負責收集應用程式的更新資訊，而手機上的代理伺服器則擁 有快取和流量控管的能力。憑藉這兩種設備所提供的功能，得以實現我們的研究目標。
代理伺服器進行流量控管的方式是根據效能函數來決定。效能函數是一種評估網路 效能、服務品質，或是用戶滿意度的計算方式。經由效能函數可將抽象的概念量化後，
進行運算及比較。我們以過去的研究為基礎提出了適當的效能函數形式，設定了頻寬、
封包遺失率、延遲三個影響服務品質的參數與效能的關聯性，以量化服務品質的效能，
得出對應的服務品質效能函數。基於多屬性效能定理，可將這三個單一參數的效能以合 理的方式整合成為總體效能函數，用來評估在不同網路條件下的用戶滿意程度。
代理伺服器從應用層觀測對外連線情況，因此可直接操作各個連線，不需考慮下層 的封包排程方式。我們設計了一個排程演算法，於網路狀況變化、新工作加入或是現有 工作結束時，自動選擇應執行的工作列表及其對應的傳輸速率。工作排程的順序基於最 大潛在效能，而傳輸速率的控制則以邊際效能決定。我們並證明了此種區域搜尋方式可 於工作皆只有一種速率需求的情況下獲得最大效能。
在本論文的實驗分析和結果中，呈現出在有代理伺服器以及適當的演算法的情況下，
對於降低網路的負擔有明顯的助益。除了整體網路流量降低之外，網路壅塞的情形也顯 著減少。從用戶的角度來看，則可感受到應用程式的反應時間明顯變短，以及服務品質 提升等優點。進一步透過個人化的設定，使得有限的頻寬可以運用於重要的資料傳輸，
大幅提升用戶獲得的資料價值。
在經過更嚴謹的模擬驗證後，下一步即可考慮將代理伺服器實際部署至行動網路上。
手機代理伺服器可加入手機內建的程式，或是放進應用程式商店裡供用戶免費下載。雲 端代理伺服器則應架設於網際網路之上，並且需有足夠的數量及頻寬以確保所有手機都 能獲得支援。對網路服務商來說，建立以上系統將帶來若干好處。最重要的是無線網路 壅塞的問題將能有效的解決，不需添購大量的額外線路，使成本可大幅降低。利用代理 伺服器的快取和排程機制，使得現有的網路資源能被妥善的運用，達到網路使用率最佳 化的目標。由於服務品質的提升，讓舊有的使用者願意繼續選擇此服務商，同時吸引更 多的客戶群加入，形成用戶及服務商雙贏的局面。
36
參 考 資 料
[1] Shenker, S. (1995). "Fundamental design issues for the future Internet." IEEE Journal on Selected Areas in Communications 13(7): 1176-1188.
[2] Shi, L., C. Liu, et al. (2008). "Network utility maximization for triple-play services." Computer Communications 31(10): 2257-2269.
[3] Dharwadkar, P., H. J. Siegel, et al. (2001). "A Heuristic for dynamic bandwidth allocation with preemption and degradation for prioritized requests." ICDCS '01:
Proceedings of the The 21st International Conference on Distributed Computing Systems: 547-556.
[4] Zimmermann, S. and U.Killat (2002). "Resource Marking and Fair Rate Allocation." 2002 IEEE International Conference on Communications:
1310-1314.
[5] Kelly, F. P., A. K. Maulloo, et al. (1998). "Rate control for communication networks shadow prices, proportional fairness and stability." Journal of the Operational Research Society 49: 237-252.
[6] Harks, T. and T. Poschwatta (2005). "Priority Pricing in Utility Fair Networks. "
ICNP '05 Proceedings of the 13TH IEEE International Conference on Network Protocols:311-320.
[7] Chang, C.-S. and Z. Liu (2004). "A Bandwidth Sharing Theory for a Large Number of HTTP-Like Connections." IEEE/ACM Transactions on Networking 12(5): 952-962.
[8] Chen, J., S. He, et al. (2009). "Optimal flow control for utility-lifetime tradeoff in wireless sensor networks." Computer Networks 53(18): 3031-3041.
[9] Singh, S. (1996). "Quality of service guarantees in mobile computing." Computer Communications 19(4): 359-371.
[10] Kroner, H. (2001). "Radio Resource Allocation for Data Services in UMTS
Networks." AEU - International Journal of Electronics and Communications 55(1):
55-62.
[11] Mahadevan, I. (2000). "A Hierarchical Architecture for QoS Guarantees and Routing in Wireless/Mobile Networks." Journal of Parallel and Distributed Computing 60(4): 510-520.
[12] Campbell, A. T., M. E. Kounavis, et al. (1999). "Programmable mobile networks." Computer Networks 31: 741-765.
[13] Chandramathi, S., S. P. P. Raghuram, et al. (2008). "Dynamic bandwidth
allocation for 3G wireless systems—A fuzzy approach." Applied Soft Computing 8(1): 274-284.
[14] Yang, X., J. Bigham, et al. (2005). "Resource Management for Service Providers
37
in Heterogeneous Wireless Networks." IEEE Wireless Communications and Networking Conference. 3: 1305-1310.
[15] Song, Q. and A. Jamalipour (2005). "A Network Selection Mechanism for Next Generation Networks." IEEE International Conference on Communications. 2:
1418-1422.
[16] Lu, S., V. Bharghavan, et al. (1999). "Fair Scheduling in Wireless Packet Networks." IEEE/ACM Transactions on Networking 7(4): 473-489.
[17] Wang, Y., S. Ye, et al. (2005). "A fair scheduling algorithm with traffic classification for wireless networks." Computer Communications 28(10):
1225-1239.
[18] Shi, J., G. Fang, et al. (2006). "Improving Mobile Station Energy Efficiency in IEEE 802.16e WMAN by Burst Scheduling." IEEE international conference on global telecommunications conference: 1-5.
[19] Mendez, A., R. Aquino, et al. (2010). "Performance evaluation of the
RQMA-CDMA scheme for multimedia traffic with QoS guarantees." AEU - International Journal of Electronics and Communications 64(10): 916-923.
[20] Choi, Y., J. Choi, et al. (2007). "Upper-level scheduling supporting multimedia traffic in cellular data networks." Computer Networks 51(3): 621-631.
[21] (2010). "Fall 2010 Global Internet Phenomena Report", Sandvine.
[22] (2011). "Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2010–2015", Cisco.
[23] "LTE Encyclopedia." Retrieved Aug, 2011,
from http://sites.google.com/site/lteencyclopedia/home.
[24] Kelly, F. (1997). "Charging and rate control for elastic traffic." European Transactions on Telecommunications 8: 33-37.
[25] Jiang, Y., C.-K. Tham, et al. (2001). "A Probabilistic Priority Scheduling Discipline for High Speed Networks." 2001 IEEE Workshop on High Performance Switching and Routing: 1-5.
[26] Massoulié, L. and J. Roberts (2002). "Bandwidth Sharing: Objectives and Algorithms." IEEE/ACMTransactions on Networking 10(3): 320-328.
[27] Kim, J.-H. and Y. Y. Kim (2003). "Analysis of User Utility Function in the Combined Cellular/WLAN Environments." Proceedings of the 2nd international conference on Human.society@internet: 725-730.
[28] Derbel, H., N. Agoulmine, et al. (2007). "Service Utility Optimization Model Based on User Preferences in Multiservice IP Networks." Globecom Workshops, 2007 IEEE: 1-5.
[29] Choi, Y.-J. and S. Bahk (2006). "Delay-Sensitive Packet Scheduling for a Wireless Access Link." IEEE Transactions on Mobile Computing 5(10):
38
1374-1383.
[30] Li, Y., A. Papachristodoulou, et al. (2011). "Congestion control and its stability in networks with delay sensitive traffic." Computer Networks 55(1): 20-32.
[31] Klemm, A., C. Lindemann, et al. (2001). Traffic modeling and characterization for UMTS networks. Global Telecommunications Conference, 2001.
GLOBECOM '01. IEEE. 3: 1741-1746 vol.1743.
[32] Tran-Gia, P., D. Staehle, et al. (2001). "Source Traffic Modeling of Wireless Applications." AEU - International Journal of Electronics and Communications 55(1): 27-36.
[33] Keeney, R. L. and H. Raiffa (1993). "Decisions with Multiple Objectives:
Preferences and Value Tradeoffs", Cambridge University Press.