Figure 7: The content lifetime versus the number of seeds after 10 days for over 14,000 files. the average download speed of 240 kbps allowed peers to fetch even large files in one day. An important observation
is the power-law relation between the average download speed and the number of downloads at that speed. In BitTorrent the availability of content is unpredictable. When the popularity drops and the last
peer/seed with certain content goes offline, the content dies. Figure 7 shows the content lifetime of all large files (at least 500 MByte) on BitTorrent/Suprnova we have followed. Each file is represented as a data point with on the horizontal axis the number of seeds for the file 10 days after its injection time, and on the vertical axis its content life time. Important observations are that the number of seeds after 10 days is not an accurate predictor for the content lifetime, and that files with only a single seed can
still have a relatively long content life time. BitTorrent itself does not have incentives to seed, but
there are Suprnova-like websites that do so. For instance, the software from Yabtuc.org consists of such a website with an integrated tracker which registers seeding behaviour.When users do not upload sufficiently, their access is temporarily denied. However, this system is even more centralized then Suprnova due to the integration of website and tracker at a single location.