: Providing Incentives in Cooperative Content Distribution Systems

1. I got  I repaid  I repaid  Scrivener Scrivener • Maintain history for asynchronous exchange • Extend trading to allow multiple parties • Allow exchanges of different content I owe Animesh Nandi, Tsuen-Wan “Johnny” Ngan, Atul Singh, Peter Druschel, and Dan S. Wallach I owe : Providing Incentives in Cooperative Content Distribution Systems Computer Security Lab: Rice University http://seclab.cs.rice.edu/ FreePastry Project http://freepastry.rice.edu/ Solution Content Distribution System I want . has it, but he doesn’t know me… What can I do? • Assume users are selfish; create a playground for selfish users • Design a system to translate selfish behaviors into maximizing common welfare • E.g., employing “tit-for-tat” policy, letting those contributing more to get better service • Make content available for download • Peer-to-peer: everyone stores a little • Rely on user cooperation and altruism Can you send me? Can you ask to give me ? Can you give to ? Sure! BitTorrent Rationality Results • People are “rational”, i.e., selfish • Best of users’ interest to consume, but do not provide, resources • They become “freeloaders” • Technically easier to freeload than malicious attacks • Exists expensive mechanism for the latter Hey, you don’t have this. Take it! • Users get only to the extend they contribute • System is scalable and effective, with only modest overhead • Figure shows service levels of cooperative users and users alternating between cooperative and non-cooperative Non-cooperative period Cooperative period • Design for situations where everyone wants the same content • Attempt to find simultaneous exchange partners • Very popular file sharing application on the Internet today Users always cooperate gets nearly perfect service You’re so kind! Have this! Can you send me? Let’s keep exchanging!!! Users cooperate 50% of time get good service 50% of time Conclusion Drawbacks • Majority becomes freeloaders • Result: “Tragedy of the common” • System may not function at all • Both sides need to want something from the other • Unlikely unless they want the same content • Cannot leverage credit earned from one peer to another peer • Decentralized system to provide incentives to cooperate • Effectively preventing freeloading while not affecting cooperative users • Relatively low overhead • We also have other designs for different applications