比例式延遲差異是相當著名的服務品質模型，因為它具有可控制性和可預測性，所以吸引眾多注目。這篇論文主要說明如何在無線網路上支援比例式延遲差異，並提出一個在無線網路環境下，能同時改善效能且支援比例式延遲差異的微調跨層排程機制（cross-layer fine-tuning scheduling，CFS）。CFS在考慮頻道傳輸率會隨著時間改變的情境下，微調競爭視窗（contention window）和後退時間(backoff time)，同時它是在完全分散式的環境跨層運作的機制。模擬結果驗證CFS在無線網路下，除了比802.11e更能提供比例式延遲差異，同時也有更佳的效能。

The proportional delay differentiation (PDD) is one of the most well-known QoS model and has drawn much attention because of its “controllable” and “predictable” characteristics. This paper addresses how to provide PDD in a wireless LAN (WLAN) and proposes a cross-layer fine-tuning scheduling (CFS) scheme with the goal to maintain PDD among all wireless stations while improving performance in a WLAN. CFS additionally considers the time-varying channel capacity to schedule packets, finely tunes the contention window, and properly arbitrates the backoff time. Also, it operates in a fully distributed manner among all stations and in a cross-layer approach in each station. The simulation results demonstrate that the CFS scheme can provide more satisfactory PDD and higher performance in a WLAN, compared with 802.11e.

[1] Christin, N., and Liebeherr, J.: ‘A QoS architecture for quantitative service differentiation’, IEEE Communications Magazine, June 2003, 41, (6), pp. 38- 45
[2] Dovrolis C., Stiliadis D., and Ramanathan P.: ‘Proportional differentiated services: delay differentiation and packet scheduling’, ACM SIGCOMM Computer Communication Review, October 1999, 29, (4), pp. 109-120
[3] Liebeherr, J., and Christin, N.: ‘Rate allocation and buffer management for differentiated services’, Computer Networks, September 2002, 40, (1), pp. 89-110
[4] Leung, M.K.H., Lui, J.C.S., and Yau, D.K.Y.: ‘Adaptive proportional delay differentiated services, characterization and performance evaluation’, IEEE/ACM Transactions on Networking, December 2001, 9, (6), pp. 801-817
[5] Ngin, H., and Tham, C.: ‘Achieving proportional delay differentiation efficiently’, Proc. IEEE International Conference on Networks, Singapore, August 2002, pp. 27-30
[6] Sankaran, S., and Kamal, A.E.: ‘A combined delay and throughput proportional scheduling scheme for differentiated services’, Proc. IEEE GLOBECOM 2002, Taiwan, November 2002
[7] Kleinrock, L.: Queueing Systems, Volume 2: Computer Applications, Wiley-Interscience, 1976
[8] IDC: ‘U.S. WLAN equipment 2005-2009 forecast by vertical market’, Market Report, IDC, August 2005
[9] Zhu, H., and Li, M., Chlamtac, I., and Prabhakaran, B.: ‘A survey of quality of service in IEEE 802.11 networks’, IEEE Wireless Communications, August 2004, 11, (4), pp. 6–14
[10] Ni, Q., Romdhani, L., and Turletti, T.: ‘A survey of QoS enhancements for IEEE 802.11 wireless LAN’, Journal of Wireless and Mobile Computing, John Wiley, 2004, 4, (5), pp. 547-566
[11] Cao, Y., and Li, V.O.K.: ‘Scheduling algorithms in broad-band wireless networks’, IEEE Proceedings of the IEEE, January 2001, 89, (1), pp. 76-87
[12] Xue, Y., Chen, K., and Nahrstedt, K.: ‘Achieving proportional delay differentiation in wireless LAN via cross-layer scheduling’, Wireless Communications and Mobile Computing, 2004, 4, (8), pp. 849-866
[13] Chang, A., and Lai, Y.C.: ‘A look-ahead scheduler to provide proportional delay differentiation in wireless network with a multi-state link’, IEICE Transactions on Communications, August, 2004, E87-B, (8), pp. 2281-2289
[14] Ramos, N., Panigrahi, D., and Dey, S.: ‘Quality of service provisioning in 802.11e Networks: Challenges, Approaches, and Future Directions’, IEEE Network, July/August 2005, pp. 14-20
[15] Romdhani, L., Ni, Q., and Turletti, T.: ‘Adaptive EDCF: enhanced service differentiation for IEEE 802.11 wireless ad hoc networks’, IEEE Wireless Communications and Networking Conference, New Orleans, Louisiana, March 16-20, 2003
[16] Bajaj, L., Takai, M., Ahuja, R., Tang, K., Bagrodia, R., and Gerla, M.: ‘GloMoSim: a scalable network simulation environment’, Technical Report 990027, UCLA Computer Science Department, May 1999