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10 0
30%
10 −1
10 −2
A Typical Video File Torrent
with 147 Peers
10 −3
10 0
10 1
10 2
AS Rank
Figure6.29
RatiobetweenASclustersizeandtorrentsize(141smalltorrents).
torrent. hese modiications will not only raise a remarkable overhead but also
affect the robustness of BT networks.
6.4.1 Measurement and Analysis of AS-Level Characteristics
In this section, we for the first time examine the video torrents exclusively in BitTorrent
networks in regards to the locality issues. he objective of this section is to investigate
the AS-level characteristics of torrents with different contents. Such properties have
the potential to address a more efficient locality scenario for the BitTorrent system.
In our study, we considered 30,415 video metainfo files and 44,317 nonvideo
metainfo iles. hese metainfo iles are manly advertised by www.btmon.com from
Feb. 12, 2007 to Aug. 12, 2008. We developed a script that can automatically detect
the “href ” field in a given HTML file and download files ending with “.torrent.”
Within the data set, there are 316 bad metainfo files, 1027 unavailable torrents
due to the tracker failure, and 3340 torrents have less than two peers. None of these
abnormal torrents is included in our study.
We carry out an Internet-based measurement using the PlanetLab [3] nodes.
We run a modified version of CTorrent [2] (CTorrent is a very typical BitTorrent
client in FreeBSD) on more than 200 PlanetLab nodes. his program was modiied
 
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