``A Performance Study of BitTorrent-like Peer-to-Peer Systems"
Lei Guo, Songqing Chen, Zhen Xiao, Enhua Tan, Xiaoning Ding, and Xiaodong Zhang
IEEE Journal on Selected Areas in Communications, Vol. 25, No. 1, 2007,
This paper presents a performance study of BitTorrent-like P2P systems by
modeling, based on extensive measurements and trace analysis. Existing
studies on BitTorrent systems are single-torrent based and usually assume
the process of request arrivals to a torrent is Poisson-like. However, in
reality, most BitTorrent peers participate in multiple torrents and file
popularity changes over time.
Our study of representative BitTorrent traffic provides insights into the
evolution of single-torrent systems and several new findings regarding the
limitations of BitTorrent systems: (1) Due to the exponentially decreasing
peer arrival rate in a torrent, the service availability of the corresponding
file becomes poor quickly, and eventually it is hard to locate and download
this file. (2) Client performance in the BitTorrent-like system is unstable,
and fluctuates significantly with the changes of the number of online peers.
(3) Existing systems could provide unfair services to peers, where a peer
with a higher downloading speed tends to download more and upload less.
Motivated by the analysis and modeling results, we have further proposed a
graph based model to study interactions among multiple torrents. Our model
quantitatively demonstrates that inter-torrent collaboration is much more
effective than stimulating seeds to serve longer for addressing the service
unavailability in BitTorrent systems. An architecture for inter-torrent
collaboration under an exchange based instant incentive mechanism is also
discussed and evaluated by simulations.