Discovering Free-riders Before Trading: A Simple Approach

MPhil Thesis Defence


Title: "Discovering Free-riders Before Trading: A Simple Approach"

By

Mr. Lei Xia


Abstract

BitTorrent is one of the most widely used Peer-to-peer (P2P) file sharing 
systems, which has proved to be a robust and scalability approach for 
delivering large files to several users. Each peer in BitTorrent system 
plays two roles: server and client. This model decreases the server’s 
burden a lot. However, free-rider, a peer just downloads without any 
upload contribution, has become one of the most serious problems in 
Peer-to-peer (P2P) system. Free-riders’ behavior has influenced the system 
perform seriously. Some incentive mechanisms, like reputation system, have 
been proposed to deal with this problem, but it shows that they are not 
good enough on preventing free-riders finishing downloading. The reason is 
that those policies discover free-riders’ behavior after or during the 
process of trading with free-riders, so it gives opportunities to 
free-riders to download freely from other nodes. In this thesis, we 
propose a novel approach named PreDiscover to prevent the free-riding 
behavior in BitTorrent file sharing system. In PreDiscover, regular peers 
and free-riders can be recognized before trading, which means a regular 
peer knows its neighbors are free-riders or not without sending any blocks 
to them, so it gives little opportunities for free-riders to get blocks 
from others freely. We implement PreDiscover in a simulator based on 
BitTorrent Protocol, and we compared the results of Original BitTorrent 
and PreDiscover. Our experiment results show that this new mechanism is 
very effective on discouraging free-riders and therefore fosters fairness.


Date:			Tuesday, 5 January 2010

Time:			10:00am – 12:00noon

Venue:			Room 3501
 			Lifts 25/26

Committee Members:	Dr. Jogesh Muppala (Supervisor)
 			Dr. Brahim Bensaou (Chairperson)
 			Dr. Lin Gu


**** ALL are Welcome ****