  The BitTorrent mechanism effectively spreads file fragments by copying the
rarest fragments first. We propose to apply a mathematical model for the
diffusion of fragments on a P2P in order to take into account both the effects
of peer distances and the changing availability of peers while time goes on.
Moreover, we manage to provide a forecast on the availability of a torrent
thanks to a neural network that models the behaviour of peers on the P2P
system. The combination of the mathematical model and the neural network
provides a solution for choosing file fragments that need to be copied first,
in order to ensure their continuous availability, counteracting possible
disconnections by some peers.
