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QoS Enhancements for Streaming Media

Streaming Audio: Bursty errors in a streaming audio application can either cause interruptions to an audio stream or cause gaps in an audio stream for periods of time easily perceptible by the human ear. We consider the case where a RealServer streams a .wav/.mp3 audio file to an end-host using RTP. The audio stream can use OverQoS to smooth out bursty losses i.e., spread a bursty loss over time.

MPEG Streaming: An MPEG video stream consists of a Group of Pictures (GOP) each comprising of I-frames, P-frames and B-frames [6]. Among these, I-frames are the most important since they represent the start of a video sequence in a GOP while P-frames and B-frames are inter-coded frames. Each frame is typically larger than a packet and a frame is sent across multiple consecutive packets. All packets corresponding to an I-frame occur in succession. A single bursty network loss can eliminate an I-frame completely which can cause an MPEG player like Mplayer [5] to disconnect since a GOP cannot be reconstructed. The B-frame and P-frame of a GOP are useless without the corresponding I-frame.

Using OverQoS, one can associate packets belonging to I-frames with higher priority and recover packets within an I-frame at the expense of B or P-frame packets. Additionally, bursty dropping of $ B$ and $ P$ frame packets affects the quality of one GOP in an MPEG stream, smoothly dropping $ B$ and $ P$ packets can affect the quality of multiple GOPs. The type of frame of a packet is embedded in the MPEG Video-Specific header within the payload of a packet.


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Next: Evaluation Up: Streaming Media Applications Previous: Streaming Media Applications
116 2004-02-12