Speaker: Arvind Krishnamurthy, University of Washington
Title: Incentive Mechanisms for Peer-to-Peer Systems

Abstract:

A fundamental problem with many peer-to-peer systems is the tendency
for users to "free ride"---to consume resources without contributing
to the system.  The popular file distribution tool BitTorrent was
explicitly designed to address this problem, using a tit-for-tat
reciprocity strategy to provide positive incentives for nodes to
contribute resources to the swarm.  While BitTorrent has been
extremely successful, we show that its incentive mechanism is not
robust to strategic clients.  We use these observations to drive the
design and implementation of BitTyrant, a BitTorrent client that
strategically allocates its bandwidth resources to exploit
BitTorrent's incentive mechanism.

Having exploited loopholes in BitTorrent's incentives, and with P2P
robustness ultimately dependent on incentivizing users to contribute
their resources, we performed a month-long measurement of millions of
users to determine the extent to which BitTorrent's incentive
mechanism has encouraged user participation.  We identify widespread
performance and availability problems, surprising given BitTorrent's
popularity.  These measurements motivate the design and implementation
of a new, one hop reputation protocol for P2P networks. Unlike
tit-for-tat, where no propagation occurs, or digital currency systems,
where contribution information is globally visible, one hop
reputations limit propagation to at most one intermediary. Through
trace-driven analysis and measurements of a deployment on PlanetLab,
we find that one hop reputations can provide wide coverage and
positive, long-term contribution incentives.