  The rapid growth of peer-to-peer (P2P) networks in the past few years has
brought with it increases in transit cost to Internet Service Providers (ISPs),
as peers exchange large amounts of traffic across ISP boundaries. This ISP
oblivious behavior has resulted in misalignment of incentives between P2P
networks--that seek to maximize user quality--and ISPs--that would seek to
minimize costs. Can we design a P2P overlay that accounts for both ISP costs as
well as quality of service, and attains a desired tradeoff between the two? We
design a system, which we call MultiTrack, that consists of an overlay of
multiple \emph{mTrackers} whose purpose is to align these goals. mTrackers
split demand from users among different ISP domains while trying to minimize
their individual costs (delay plus transit cost) in their ISP domain. We design
the signals in this overlay of mTrackers in such a way that potentially
competitive individual optimization goals are aligned across the mTrackers. The
mTrackers are also capable of doing admission control in order to ensure that
users who are from different ISP domains have a fair chance of being admitted
into the system, while keeping costs in check. We prove analytically that our
system is stable and achieves maximum utility with minimum cost. Our design
decisions and control algorithms are validated by Matlab and ns-2 simulations.
