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In this paper, we study Skype video call in LAN, WAN, and WiMAX. Our main interest is on traffic characteristics and user experience. Using the standard Foreman video sequence (320×240, 30 fps, 8 second), we show that a Skype video call can adapt its source rate from <; 5 kBps up to ~60 kBps. The maximum achievable MOS (Mean Opinion Score) and EFR (Effective Frame Rate) is about 3.5 and 20 fps, respectively. Our experimental results also show that source rate is the dominating factor in determining both traffic characteristics and user experience of a Skype video call; while end-to-end delay or transport layer protocol, e.g. TCP or UDP, plays very little role. We also study the minimum RSSI requirement in a typical WiMAX network for achieving various levels of user experience: good, fair, and low, and derive the explicit logarithmic functions using the curve fitting technique to predict MOS and mean packet inter-arrival time (PIT) based on source rate.