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When Can an Autonomous Reputation Scheme Discourage Free-riding in a Peer-to-Peer System?

When Can an Autonomous Reputation Scheme Discourage Free-riding in a Peer-to-Peer System?. Nazareno Andrade, Miranda Mowbray, Walfredo Cirne, Francisco Brasileiro. Why autonomous reputation?. A reputation scheme is a way of addressing the free-riding issue

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When Can an Autonomous Reputation Scheme Discourage Free-riding in a Peer-to-Peer System?

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  1. When Can an Autonomous Reputation Scheme Discourage Free-riding in a Peer-to-Peer System? Nazareno Andrade, Miranda Mowbray, Walfredo Cirne, Francisco Brasileiro

  2. Why autonomous reputation? • A reputation scheme is a way of addressing the free-riding issue • We consider the use of reputation to prioritize donations • Autonomous = Decisions are taken based on local information only • An autonomous reputation scheme is extremely lightweight • Easiness of deployment • We’re targeting OurGrid, a p2p CPU-sharing network

  3. Analyzing an Ideal Scheme • All peers have perfect information about who is free-riding • We measure the advantage to collaborators: • Advantage to collaborators = Mean utility of collaborators – Mean utility of free-riders

  4. Model: Peers • Interchangeable resources • CPU, Bandwidth, Storage, ... • It has D resources and can consume up to C in a time slot • It is either consuming or donating accordingly to a probability ρ • Consuming resources provides positive utility • Donating implies in negative utility • A peer may be a free-rider or a collaborator

  5. Model: System • Proportion f of free-riders in the system • Uniform distribution of resources • Based on our deployment scenario

  6. demand from free-riders demand from collaborators available resources Famine Middle Glut Analysis • Our model has three possible cases regarding the amount of resources available:

  7. Expected Dynamics • Ideal scheme:

  8. Autonomous Scheme X Ideal Scheme • Compare the autonomous scheme with an ideal reputation scheme • We compare the advantage to collaborators • System dynamics depends on it • Simulations of scenarios in all three cases and on the borders between them

  9. The autonomous reputation scheme • Each peer P1 keeps V(P1,P2) and V(P2,P1) • rP1(P2)=V(P2,P1)-V(P1,P2) • rP1(P2) is likely to be different from rP3(P2) • P1 prioritizes requesters based only on local rP1 • It never refuses to donate

  10. Simulation Results Summary • The performance of the autonomous scheme was similar to the ideal reputation scheme in most scenarios • The difference was greater in border cases • The autonomous scheme needs slightly more contention

  11. Graphical Comparison (1)

  12. Graphical Comparison (2)

  13. Conclusions • Donation prioritization drives free-riding out only when there is famine of resources • An autonomous reputation scheme performs very similarly to an ideal one in discouraging free-riding • Lightweight and easy to deploy solution

  14. Future Work • Mechanisms for causing famine • More skewed resource distributions • Getting feedback from OurGrid

  15. Contact: nazareno@dsc.ufcg.edu.br www.ourgrid.org

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