Chinese Journal of Computers   Full Text
Title	A Survey on Overcoming Free Riding in Peer-to-Peer Networks
Authors	YU Yi-Jiao JIN Hai
Address	(Key Laboratory of Services Computing Technology and System of Ministry of Education, Huazhong University of Science and Technology, Wuhan 430074) (Key Laboratory of Cluster and Grid Computing of Hubei Province, Huazhong University of Science and Technology, Wuhan 430074)
Year	2008
Issue	No.1(1—15)
Abstract &   Background	Abstract Since the first report of free riding on Gnutella in 2000, large amounts of network measurement results show that free riding is prevalent in almost all Peer-to-Peer (P2P) networks, which reduces the robustness, availability and lifetime of P2P networks. Overcoming free riding becomes a hot research issue both in academic and industrial communities. The traffic measurement mechanisms in P2P networks are overviewed, which include active measurement and passive measurement. Some detailed traffic measurement results of Gnutella overlay network are illustrated, which indicate the development of free riding in P2P network in recent 6 years. The modeling of P2P network is introduced, and the impacts to system performance of free riding are discussed. Moreover, the authors focus on the mechanisms avoiding free riding and categorize the proposed approaches into incentive mechanisms, game theoretical approaches, and social network or economic models based methods. Each category is discussed in detail, and some typical work is introduced. Especially, the features of these three categories of solutions are analyzed and compared from the aspect of engineering implementation, which is helpful to both the P2P software developers and academic researchers. Finally, future works about the mechanisms discouraging free riding in P2P networks are outlined. keywords P2P network; free riding; incentive mechanism; game theory; utility function background This work is supported by National Basic Research Program of China (973 Program) under grant No.2003CB317003, which focuses on semantic storage technologies and high performance of services in grid and Peer-to-Peer (P2P) network environments. P2P applications are popular in recent years, in which peers are not only eager to enjoy services, but also expected to contribute to the P2P network. Some traffic measurement experiments are carried out since 2000 and the results, however, show that free riding is prevalent in almost all P2P networks. Free riding is a new challenge for P2P network, and a lot of overcoming mechanisms have been proposed. Unfortunately, most of proposed mechanisms are not employed in real P2P networks, due to the complexities or unreasonable assumptions in modeling. The main objectives of this paper are to introduce the measurement of free riding, its impacts on P2P networks, and the proposed typical overcoming approaches. The authors categorize the proposed solutions, discuss the key ideas and features of solutions in each category, and summarize the future research issues. To the best of our knowledge, this paper is the first survey on the mechanisms avoiding free riding. In the past years, the authors have proposed a workload balancing based approach to discourage free riding in P2P network, and submitted a related national patent.