Decision Support for the Usage of Multicast versus Unicast in Broadband TV Networks

Internet Protocol Television (IPTV) is undoubtedly a killer application and when offered via wireless networks, it paves the way for quad-play in next generation networks. It has been argued for a long time that the popularity of TV channels can be modeled quite realistically using a Zipf-like distribution in which the top 10% of channels account for nearly 90% of viewers. Therefore, most channels are unpopular or rarely watched and it is not efficient to multicast a channel as long as there are less than a given number of viewers tuned into it. The interesting question arises at which bound multicast and unicast channels should be separated. In this article, we want to first introduce a performance criterion, called multicast gain, which can be used for computing multicast efficiency. Based on the measured gain, we define a threshold in order to identify cases in which unicasting might be a better choice. We show that although multicasting can usually outperform multiple unicasting in terms of bandwidth usage, due to the inherent overhead in establishing and maintaining multicast connections, in special cases, using multiple unicast flows can be preferable.