Modelling the population dynamics and the file availability in a BitTorrent-like P2P system with decreasing peer arrival rate

Many measurement studies of P2P file sharing systems suggest that the request rate for a file changes over time and the system is thus non-stationary. For this reason we study the population dynamics and the availability of a file in a BitTorrent-like file sharing system, when the arrival rate for file requests decreases exponentially. We study the system first by a deterministic fluid model and then by a more detailed Markov chain analysis that allows estimating the life time of a single chunk exactly. Simple approximation for the life time is also derived. In addition, we simulate the life time of a file consisting multiple chunks in order to verify the analytical results to be applicable also to a more complex system.