In this paper, we identify several common pitfalls that
lead to measurement error. We carefully address these dif-
ficulties and present a detailed study using three widely-
deployed P2P systems: an unstructured file-sharing system
(Gnutella), a content-distribution system (BitTorrent), and
a Distributed Hash Table (Kad). Our analysis reveals sev-
eral properties of churn: (i) overall dynamics are surprisingly
similar across different systems, (ii) session lengths are not
exponential, (iii) a large portion of active peers are highly
stable while the remaining peers turn over quickly, and (iv)
peer session lengths across consecutive appearances are cor-
related. In summary, this paper advances our understanding
of churn by improving accuracy, comparing different P2P file
sharing/distribution systems, and exploring new aspects of
churn.
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