The success of Skype has enlightened the future of peer-to-peer-based solutions for satisfactory real-time multimedia services over the Internet. However, fundamental questions, such as whether VoIP services like Skype are good enough in terms of user satisfaction, have not been formally addressed. One of the major challenges lies in the lack of an easily accessible and objective index to quantify the degree of user satisfaction.

In this work, we propose a model, geared to Skype, but generalizable to other VoIP services, to quantify VoIP user satisfaction based on a rigorous analysis of the call duration from actual Skype traces. The User Satisfaction Index (USI) derived from the model is unique in that 1) it is composed by objective source- and network-level metrics, such as the bit rate, bit rate jitter, and round-trip time, 2) unlike speech quality measures based on voice signals, such as the PESQ model standardized by ITU-T, the metrics are easily accessible and computable for real-time adaptation, and 3) the model development only requires network measurements, i.e., no user surveys or voice signals are necessary. Our model is validated by an independent set of metrics that quantifies the degree of user interaction from the actual traces.

Related paper:
- Tuning the Redundancy Control Algorithm of Skype for User Satisfaction
- An Empirical Evaluation of VoIP Playout Buffer Dimensioning in Skype Google Talk and MSN Messenger
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Kuan-Ta Chen, Chun-Ying Huang, Polly Huang, and Chin-Laung Lei, "Quantifying Skype User Satisfaction," In Proceedings of ACM SIGCOMM 2006, Pisa Italy, Sep 2006.

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