BitTorrent (bt), a Peer-to-Peer (p2p) distribution system, is a major bandwidth consumer in the current Internet. This paper reports on a measurement study of bt traffic intended to identify potential traffic invariants. To this end, we employ high-accuracy packet capture hardware together with specialized parsing software. Important characteristics regarding bt sessions and messages as well as general system characteristics are reported. The results indicate that characteristics such as session inter-arrival times are corroborated to be exponentially distributed, while other characteristics are shown to differ from previously reported results. These differences are attributed to changes in the core bt algorithms. Further, it is observed that long- and heavy-tailed distributions can be used to model several characteristics. The log-normal, Pareto and mixtures of these distributions are used to model session sizes and durations, while the Weibull distribution has been observed to model message inter-arrival and inter-departure times for bandwidth-limited clients.