The paper reports on a modeling and evaluation study of session characteristics of BitTorrent traffic. BitTorrent is a second generation Peer-to-Peer (P2P) application recently developed as an alternative to the classical client-server model to reduce the load burden on content servers and networks. Results are reported on measuring, modeling and analysis of application layer traces collected at the Blekinge Institute of Technology (BIT) and a local ISP. For doing this, a dedicated measurement infrastructure has been developed at BIT to collect P2P traffic. A dedicated modeling methodology has been put forth as well. New results are reported on session characteristics of BitTorrent, and it is observed that session interarrivals can be accurately modeled by the hyper-exponential distribution while session durations and sizes can be reasonably well modeled by the lognormal distribution.