Churn refers the continuous process of node arrival and departure in distributed peer-to-peer network. Enormous nodes joining the system concurrently will results in a flash crowd scenario for special nodes in the system, and enormous nodes crashing in a moment might come out a broken network. In fact, the joining and crashing always occur around some nodes at the same time, which will conduct strong dynamic environment and affect the detailed application over the overlay very much. In P2P networks under churn, We divide the new joining nodes into normal freshman, whitewasher and crowd attackers, and divide the departure nodes into normal dying nodes, outcast whitewasher and partition attackers. So the churn will be composed of tolerable normal lifespan behavior, the frightfully spiteful attack behavior or passive whitewashing behavior, which should be seriously noticed. In this paper, we present a novel protocol with positive communication policy among peers and conservative neighbor maintenance scheme under churn, to keep desirable properties such as a low network diameter and clustering. The protocol is resilient against different extend of churn and fit for P2P information dissemination and file sharing systems especially.
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