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The growth in power and connectivity of today’s PCs promises a continued increase in streaming media over the Internet. Hand-in-hand with the increase in streaming media comes the impending threat of unresponsive traffic, often cited as the major threat to the stability of the Internet. The responsiveness of commercial streaming media applications will play an important role in the network impact of streaming media. Unfortunately, there are few empirical studies that analyze the responsiveness, or lack of it, of current streaming media products. In this work, we measure the responsiveness of RealVideo over UDP compared with RealVideo over TCP by simultaneously playing video clips selected from numerous RealServers on the Internet to two distinct video clients along the same network path. By varying the bottleneck bandwidth to the clients, we are able to analyze the “head-to-head” performance of RealVideo over UDP as compared to RealVideo over TCP, and correlate the results with network and application layer statistics. We find that most streaming RealVideo clips are not bandwidth constrained for typical broadband connections, resulting in a fair share of link bandwidth used by both RealVideo over TCP and RealVideo over UDP. In times of congestion, most RealVideo over UDP does respond to Internet congestion by reducing the application layer encoding rate, often achieving a TCP-Friendly rate. In times of severe congestion, RealVideo over UDP gets a proportionately larger share of available bandwidth than does the same video over TCP.