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Improving File Sharing Experience
with Incentive Based Coalitions
M.V. Belmonte, M. Dıaz, and A. Reyna
E.T.S.I. Informatica, Bulevar Louis Pasteur, N.35
Universidad de Malaga, 29071 Malaga, Spain
{
mavi,mdr,reyna
}
@lcc.uma.es
Abstract.
The natural selfish behavior of P2P system users, has given rise to the
appearance of freeriding. These users download but don't contribute to the sys-
tem, leading to a degradation of the system, and the user experiences. It becomes
mandatory to find proper mechanisms to incentive cooperation among users in
these systems. In this paper we provide an incentive based coalitions to improve
the system welfare and users experiences. A peer that participates in a coalition
lends “bandwidth” to other peers of the coalition, in exchange for utility and con-
sequently a far better experience. Taking concepts from game theory we provide a
solid ground upon which we build our mechanism . Simulated experiments sup-
port the approach, showing how encouraging participation stops freeriding and
therefore improve the system performance and the user experience.
Keywords.
P2P, Coalition, Game theory, File sharing, Free-riding, Incentive
mechanisms.
1
Introduction
In general, a P2P content distribution system creates a distributed storage medium that
allows the publishing, searching and retrieval of files by members of the network [11].
Traditionally, the main problem of the P2P systems is limited to file search. However,
the efficient download of content and the fairness in the bandwidth contribution is also
an important aim in the design goal of these kind of systems. The early P2P systems
(Gnutella, Kazaa,...) lack mechanisms for fairness in bandwidth usage. For this reason,
these systems suffer from free-loaders, peers that consume many more resources or con-
tents (bandwidth) than they contribute. In [6] and [17] empirical studies have observed
this behaviour in Napster, Gnutella or even eDonkey.
One of the reasons for this problem is that the mechanisms used for downloading and
sharing in the P2P systems, do not take the selfish behaviour of the peers into account
at the design stage. P2P system users act rationally trying to maximise the benefits
obtained from using the system's shared resources [3]. Therefore, it is important to find
mechanisms that provide incentives and encourage cooperation. One possible solution
could be to use an economic framework that provides incentives. In this sense game
theory may be a good tool on which to model the interactions between peers in a P2P
file sharing system. The idea is to define “the rules of the game” so that the system
