File Replication-Based Technique For Discouraging Free Riding In Peer-to-Peer Networks

Most of peers in Peer-to-Peer (P2P) networks merely take what they need from others,and only a few altruistic peers provide services. These selfish behaviors are regarded asfree riding, and selfish peers are referred to as free riders. Free riding is a great challengefor P2P networks because it impairs robustness, availability, and lifetime of P2P systems.Some anti-free riding mechanisms are proposed, among which, the incentive mechanismsnot only degrade the Quality of Service (QoS) of free riders, but also decrease the numberof online users; the game theoretical approaches are too complicated to implement inlarge-scale P2P networks; the employment of social network/economic models in practiceis not fully investigated yet. Thus, a feasible, scalable and simple anti-free ridingmechanism is required.This thesis is dedicated to a distributed anti-free riding mechanism. The salient featureof our research is that peer's heterogeneity and inherent selfishness is given greatconsideration. P2P network is described with a novel model, which includes the networktopology, peers status, and files distribution. The efficiency criteria are defined formallyand clearly with the novel P2P network model, and different anti-free riding mechanismsare compared. Finally, the novel anti-free riding mechanism is employed in a scientificreferences sharing system, which shows that it is feasible and efficient.A file replication and workload balancing based anti-free riding mechanism (FRWBBA)is proposed in Chapter 2. The basic idea of FRWBBA is as follows. Every peer monitorsits workload status periodically and independently. If the workload is too heavy, theoverloaded peer transfers some frequently accessed files to neighbored free ridersproactively and transparently. As a result, these neighbored free riders share more popularfiles and make more contributions to P2P systems. The number of free rider is reduced,while the overloaded peers are well protected. Extensive simulations are carried out toverify the efficiency of FRWBBA. The results show that FRWBBA makes the whole P2Pnetwork robust and the shared files distributed appropriately.The strategies of file replication from overloaded peer to neighbored free riders areinvestigated in Chapter 3. As Zipf's law is suitable for modeling P2P file-accessedfrequencies, replicating the most popular files from overloaded peer to neighbored freeriders can decrease the workload effectively. Three strategies of target peers selection in terms of workload are proposed. Simulation results indicate that popular files should bereplicated to the least workload neighbors, which can eliminate overloaded peers rapidly.As an alternative, overloaded peer can transfer popular files to the ones near the serviceconsumers to reduce the hops of file access.P2P network modeling is important to evaluate anti-free riding mechanisms, which isdiscussed in Chapter 4. The essential metrics for P2P networks with respect to free ridingare identified. On this basis, a complex P2P graph is proposed, which can describe the P2Pnetwork topology, the heterogeneity of peers, and the relationship between shared filesdistributed in peers and the network topology. Since P2P networks are scale-free, theirrobustness and crispness is analyzed. The efficiency of FRWBBA and incentivemechanisms is evaluated by using the complex P2P graph and properties of scale-freenetworks. FRWBBA is shown superior to incentive mechanisms from the perspectives ofboth P2P users and suppliers.FRWBBA is implemented in JAVA and packaged as AntifreeridingWare. The softwaredevelopment methods of AntifreeridngWare are presented in Chapter 5. To illustrate theusage of the package, it is integrated into Semrex, a P2P scientific references sharingsystem, to deal with free riding. The development experiences suggest that anti-free ridingmethod cannot be separated from P2P applications completely, because it needs thesupports from P2P programs.The model analysis, Simulations, and applications in real P2P system all validate thatFRWBBA is an efficient anti-free riding approach. FRWBBA reduces the number of freeriders, and makes P2P networks provide services to all peers in best efforts. The abundantfiles in P2P network are maintained and distributed properly after anti-free riding control.Compared to the incentive mechanisms, FRWBBA offers better fairness to those peersbehind firewall and Network Address Translations, or peers with low speed Internetconnections. The software development experiences of FRWBBA help it be integrated intodifferent P2P applications quickly.