Ian Kash, John K. Lai, Haoqi Zhang, and Aviv Zohar
Over the years, private file-sharing communities built on the BitTorrent protocol have developed their own policies and mechanisms for motivating members to share content and contribute resources. By requiring members to maintain a minimum ratio between uploads and downloads, private communities effectively establish credit systems, and with them full-fledged economies. We report on a half-year-long measurement study of DIME -- a community for sharing live concert recordings -- that sheds light on the economic forces affecting users in such communities. A key observation is that while the download of files is priced only according to the size of the file, the rate of return for seeding new files is significantly greater than for seeding old files. We find via a natural experiment that users react to such differences in resale value by preferentially consuming older files during a `free leech' period. We consider implications of these finding on a user's ability to earn credits and meet ratio enforcements, focusing in particular on the relationship between visitation frequency and wealth and on low bandwidth users. We then share details from an interview with DIME moderators, which highlights the goals of the community based on which we make suggestions for possible improvement.
In WWW 2012 (to appear)