Streaming Variable Bit-Rate Media Streams - Scalable Continuous Media Streaming Systems - page 119

7

Streaming Variable Bit-Rate
Media Streams

Compared to streaming constant bit-rate media streams, it is substantially more complex to
stream variable bit-rate media streams due to the inherent bit-rate variations and the need
to maintain playback continuity at the media client. If the network supports bandwidth
reservation, then the challenge is to determine howmuch bandwidth to reserve for streaming
the VBR media stream. Obviously it will be wasteful to reserve the peak bandwidth of the
VBRmedia stream for the entire duration of the media stream, and so it is necessary not only
to reserve bandwidth, but also to adjust the amount of bandwidth from time to time to reduce
bandwidthwastage. In this chapter we first introducemedia bit-rate smoothing techniques to
smooth out the rate variations for more efficient bandwidth utilization. Next, we investigate
media streaming in mixed-traffic networks where traffics from data services as well as other
continuous media streams compete for the same pool of network resources. We develop a
monotonic decreasing rate scheduler that can guarantee streaming performance in mixed-
traffic networks and evaluate its performance.

7.1 Introduction
Future broadband networks will support a wide variety of services with very different traffic
characteristics. Among them, multimedia applications such as video-on-demand (VoD) are ex-
pected to consume a significant portion of the bandwidth. Therefore, the efficient transmission
of delay-sensitive variable bit-rate (VBR) video data [1] is likely to be one of the key challenges
in managing resources in such networks. Apart from the frame-by-frame bit-rate fluctuations
that are also found in constant bit-rate (CBR) videos, VBR videos tend to exhibit long-range
bit-rate variations in time scale of minutes. Such fluctuations complicate the admission of video
streams and the scheduling of video data transmission to provide performance guarantee.
To tackle this problem, researchers have studied various ways to reduce the bit-rate variations
of prerecorded VBR videos - video bit-rate smoothing [2-14]. Video bit-rate smoothing is a
technique to reduce bit-rate variations in the retrieval and transmission of VBR encoded videos.