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

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Presentation on theme: "When Can an Autonomous Reputation Scheme Discourage Free-riding in a Peer-to-Peer System? Nazareno Andrade, Miranda Mowbray, Walfredo Cirne, Francisco."— Presentation transcript:

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 Analysis Our model has three possible cases regarding the amount of resources available: demand from collaborators demand from free-riders FamineMiddle Glut available resources

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) r P1 (P2)=V(P2,P1)-V(P1,P2) r P1 (P2) is likely to be different from r P3 (P2) P1 prioritizes requesters based only on local r P1 –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:


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