A Measurement Study on the Topologies of BitTorrent Networks

BitTorrent (BT) is a widely-used peer-to-peer (P2P) application. Most of BT's characteristics (except the topology) have been studied extensively by measurement approaches. In this paper, we deploy a measurement system to examine some performance-related topology properties of BT. Our goal is to provide a measurement view of the real-world BT topologies and to verify the previous estimations via simulations and real-world experiments. We observe that at the steady stage, a BT topology has short distances and low clustering coefficients, and its degree-frequency exhibits a Gaussian-like distribution. These indicate that a BT network is very close to a random network rather than a scale-free network or a small world. The proportion of peers with large download percentages is very high at the steady stage, showing that the swarm is robust from the resource perspective. We also find out that most high-degree peers have a very fast download speed. However, the low Spearman's rank correlation coefficient indicates that there is no strong correlation between the peer connection degree and the download speed. Different from previous results, we find that the diameter of a BT network at the initial stage is small even when 95% of peers use the peer exchange extension.