what-when-how
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Figure 6.9
The block variation of the piece population in the PlanetLab-1
torrent.
are highly dynamic, a clear understanding of the characteristics and evolution of
the networks as peers arrive and depart, and during their entire lifespans, is critical
to their performance optimization.
We describe experiments that closely examine the underlying topologies of
torrents. hese experiments capture the intricacies of forming multiple complex
networks in BitTorrent, including the formation of four networks in a BitTorrent
download: Connection, Interest, Unchoked, and Download. Unlike previous
work, which was confined to the startup stage, we look at all four networks' char-
acteristics and dynamics throughout the entire lifespan of torrents. Our results
demonstrate that the networks exhibit fundamental diferences over time. his
suggests that the initial stage of a torrent is not sufficient to predict the overall
performance of the system, and in order to fully examine a torrent long-term mea-
surements are needed.
We find strong evidence of scale-free characteristics in the network of peers that
are unchoked by other peers. However, we find no clear evidence of persistent clus-
tering in any of the networks of peers that we studied, which suggests an interesting
venue for improving BitTorrent's performance.
Recently, several authors have examined the network topologies formed by
BitTorrent's neighbor selection algorithm. Urvoy-Keller and Michiardi [29] used
