A media-aware congestion control mechanism for real-time streaming media over wide area networks

Media streaming over wide area networks continue to be regarded as a challenging problem in spite of the widely available broadband Internet access and significantly improved compression algorithms. Due to its resource-intensive nature, transferring streaming media without proper congestion control would result in not only degraded media quality but also endangered network stability. Congestion control, therefore, is critical to both network stability and performance of streaming applications.; In this work, we first introduce a set of application-level video quality metrics which can be used in large scale studies. These metrics are derived from the behaviors of existing media applications. Our experiments demonstrate the correlation between these metrics and network-level performance metrics.; We then use these metrics evaluate streaming video quality when two of the major congestion control mechanisms, TCP and TFRC, are used. These mechanisms trade-off being responsive to network congestion and protective of the data streams: TCP emphasizes prompt response to congestion, while TFRC provides smooth send rate, but is progressively reactive to persistent congestion. We show that live streaming applications running TFRC still suffer from degraded video quality under bursty background traffic.; Based on our findings in evaluating TFRC, we design Media-Aware Rate Control (MARC), a TCP-friendly congestion control algorithm that takes the rate limited characteristics of live streaming applications into account in regulating traffic. MARC can shield live streaming applications from short-term transient congestion, such as those caused by TCP's bandwidth probing behavior, a part of normal Internet operating dynamics. As a result, MARC improves video quality of live streaming applications measured by our application-level metrics. As a congestion control protocol, MARC is fair to TCP and is responsive to persistent congestion.; MARC offers better streaming quality than TCP and TFRC to both single-layer video and multi-layer video. Multi-layered video generates multiple sub-streams with different priorities. MARC is able to provide smooth sending rate to the aggregate video stream. Leveraging the information provided by MARC, applications using layered video can further improve the performance of higher priority sub-streams.