Jae Chung, Mark Claypool, Yali Zhu
The growth in power and connectivity of today's PCs promises a continued increase in the growth of streaming media over the Internet. Hand-in-hand with the increase in streaming media comes the impending threat of unresponsive UDP traffic, often cited as the major threat to the stability of the Internet. The responsiveness of commercial streaming media applications, such as RealNetworks' RealPlayer, 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 commercial streaming media. In this work, we measure the responsiveness of RealVideo over UDP by measuring the performance of numerous streaming video clips selected from a variety of RealServers on the Internet. By varying the bottleneck bandwidth to the player, we are able to analyze the TCP-Friendliness of RealVideo over UDP 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. In times of congestion, most RealVideo UDP streams respond to Internet congestion by reducing the application layer encoding rate, and streams with a minimum encoding rate less than the fair bandwidth share usually achieve a TCP-Friendly rate. In addition, our analysis suggests that a reason streaming applications choose not to use TCP is that the TCP API hides network information, such as loss rate and round-trip time, making it difficult to estimate the available bandwidth for effective media scaling.
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