This paper reports on a measurement and modeling study of session and message characteristics of BitTorrent traffic. BitTorrent is a Peer-to-peer (P2P) replication and distribution system developed as an alternative to the classical client-server model to reduce the load on content servers and networks. Results are reported on measurement, modeling and analysis of application and link layer traces collected at the Blekinge Institute of Technology (BTH) and a local ISP in Sweden. Link layer traces and application logs were collected, modeled and analyzed using a dedicated measurement infrastructure developed at BTH to collect P2P traffic. New results are reported on important session and message characteristics of BitT...