以使用者感受導向對於Skype的前向錯誤控制機制之分析

A QoE-Centric Analysis of Skype's FEC Mechanism

王博榮(Po-Jung Wang)

指導教授 ： 黃寶儀

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01437

摘要

近年來Skype驚人的成長已經超越眾人的預期。其應用程式成功的主要原因是一在於他的前向錯誤控制機制，也就是增加冗餘的語音封包，在網路封包掉落造成語音封包損壞的情況下，得以維持穩定的語音品質。運用考量使用者感受 (QoE - Quality of Experience) 的方法，也就是測量平均意見分數 (MOS - Mean Opinion Score)。我們去檢驗Skype帶有冗餘封包的數量，並且系統化的探索針對不同語音壓縮格式與不同的網路損害程度所需要加冗餘封包的量。本篇研究論文顯示出Skype所使用的前向錯誤更正機制之控制方法與編碼方法符於我們的假設。藉由有線與無線網路的量測，也發現到連續掉落的特徵發生在無線網路相當頻繁，使得針對連續掉落更精確去調整前向錯誤控制機制不可或缺。Skype尚有一定可觀的程度可以被改善以更進一步確保穩定的使用者滿意度。

關鍵字

Skype ； 前向錯誤更正機制 ； 使用者感受品質 ； 網路服務品質 ； 網路語音電話

並列摘要

The phenomenal growth of Skype in recent years has surpassed all expectations. Much of the application’s success is attributed to its FEC mechanism, which adds redundancy to the voice streams to sustain audio quality under network impairments. Adopting the quality-of-experience (QoE) approach, i.e., measuring the Mean Opinion Scores (MOS), we examine how much redundancy Skype adds to its voice streams and systematically explore the optimal level of redundancy for different network and codec settings. This study reveals that (1) Skype’s FEC control and coding mechanism, not so surprisingly, falls in the ballpark, but (2) a surprisingly significant margin we can improve to ensure consistent user satisfaction. By surveying packet loss patterns under different network types and environments, we found that most of the wireless loss pattern cannot be recover well by Skype’s FEC. A more sophisticated FEC mechanism adaptive to variety of loss pattern is required to achieve consistent user satisfaction.

並列關鍵字

Skype ； Forward Error Correction ； Quality of Experience ； Quality of Service ； VoIP

參考文獻

[5] S. Baset and H. Schulzrinne, “An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol,” in Proceedings of IEEE INFOCOM’06, Barcelona, Spain, Apr. 2006.

[8] D. Bonfiglio, M. Mellia, M. Meo, D. Rossi, and P. Tofanelli,“Revealing Skype traffic: when randomness plays with you,” in Proceedings of ACM SIGCOMM’07, Kyoto, Japan, Aug. 2007, pp. 37–48.

[9] K.-T. Chen, C.-Y. Huang, P. Huang, and C.-L. Lei,“Quantifying Skype User Satisfaction,” in Proceedings of ACM SIGCOMM’06, Pisa, Italy, Sep. 2006.

[10] K.-T. Chen, C. C. Tu, and W.-C. Xiao, “Oneclick: A framework for measuring network quality of experience,” in Proceedings of IEEE INFOCOM 2009, 2009.

[11] E. Gilbert, “Capacity of a Burst-Noise Channel,” The Bell System Technical Journal, vol. 39, pp. 1253–1265, SEP 1960.