Optimal Delay for Media-on-Demand with Pre-loading and Pre-buffering

Abstract

Broadcasting popular media to clients is the ultimate scalable solution for media-on-demand. The simple solution of downloading and viewing the media from one channel cannot guarantee a reasonable startup delay for viewing with no interruptions. Two known techniques to reduce the delay are pre-loading and pre-buffering. In the former an initial segment of the media is already in the client buffer, and in the latter segments of the media are not transmitted in sequence and clients may pre-buffer later segments of the media before viewing them. In both techniques, the client should be capable to receive streams from channels at the same time of handling its own buffer and view the media from either one of the channels or the buffer.

In this paper we consider broadcasting schemes that combine pre-loading and pre-buffering. We present a complete tradeoff between (i) the size of the pre-loading; (ii) the maximal possible delay for an uninterrupted playback; (iii) the number of media; and (iv) the number of channels allocated per one media. For a given B the size of the pre-loading as a fraction of the media length, for m media, and for h channels per media, we first establish a lower bound for the minimal maximum delay, D, as a fraction of the movie length, for an uninterrupted playback of any media out of the m media. We then present an upper bound that approaches this lower bound when each media can be fragmented into many segments.