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Michael Sirivianos, Jong Han Park, Rex Chen and Xiaowei Yang
Main Idea In a sufficiently large swarm, a BitTorrent client that connects to many more peers than the protocol specifies can find more seeders, which do not abide by the tit-for-tat rule. It can also increase the likelihood of becoming optimistically unchoked, as more peers have it in their list of candidates to unchoke. Consequently, even if a client does not upload to its peers, it may be able to download at rates equal to or higher than those of tit-for-tat compliant clients.s
We study the behavior of BitTorrent networks in situations where selfish peers attempt to maintain high download rates without uploading. We use experiments in both public torrents and private torrents residing on PlanetLab to show that a client can free-ride and still attain performance equal to or better than protocol compliant clients. Our experimental results show the following: a) our modified free-rider client can achieve better download rates than a protocol compliant client in most common-case public torrents; and b) in ~300-leecher PlanetLab-residing torrents that consist of 10% free-riders, free-riders on average outperform compliant clients, while they perform slightly worse than clients in a swarm with only compliant client. Our results suggest that the large view exploit is effective and has the potential for wide adoption. Michael Sirivianos, Jong Han Park, Rex Chen and Xiaowei Yang. Free-riding in BitTorrent Networks with the Large View Exploit. IPTPS 2007. Note: This is an improved technical report version (UCI TR #07-01). Among others, it includes strengthened arguments on why free-riding could be a problem, and a better (we believe) method to prevent the exploit than the one included in the IPTPS paper. Download Free-rider Client The modified Enhanced CTorrent free-rider C/C++ source code can be found in large-view.tar.gz, under the directory Dandelion/ctorrent-dnh2. Instructions on how to build the free-rider client for FreeBSD and Linux can be found in the INSTALL and README files under Dandelion/ctorrent-dnh2. To run type: ctorrent <file.torrent> -p <incoming_port> -M 1000 -U 0 -s <save_file_as> Detailed instructions on how to use Enhanced CTorrent can be found at www.rahul.net/dholmes/ctorrent/userguide.html. The client has not been modified in any way other than what is required to aggressively obtain view of the network and connect to as many clients as possible. PlanetLab testbed scripts can also be found in large-view.tar.gz, under the directory bttest. Instructions on how to install and run the scripts in the README file under bttest. If you are new to PlanetLab check out these instructions.
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