On churn and communication delays in social overlays

Peer-to-peer systems based on an overlay network that mirrors the social relationships among the nodes' owners are increasingly attracting interest. Yet, the churn induced by the availability of users raises the question-still unanswered-of whether these social overlays represent a viable solution. Indeed, although constraining communication to take place only among “friends” brings many benefits, it also introduces significant limitations when healing the overlay in the presence of churn. This paper puts forth two contributions. First, we show through simulation on real datasets that churn induces relevant delays in information dissemination, which may ultimately hamper the practical application of social overlays. Yet, identifying opportunities for improvement and evaluating design alternatives through simulation is impractical, due to the size of the target networks, the large parameter space, and the many sources of randomness involved. Therefore, in our second contribution we combine analytical and simulation techniques to enable the estimation of dissemination delays at a practical cost.