— In the last years peer-to-Peer (P2P) applications are emerging as potentially important structures for information, content management and distribution. The most popular P2P application in the Internet today is file sharing, which was initially popularized by the Napster system. One of the most used P2P network today allowing file sharing for Internet users is BitTorrent, which generates more than 53% of the P2P traffic in the Internet. Up to now very little efforts have been dedicated to develop analytical tools for performance evaluation of a peer in a BT network. The target of this paper is to propose an analytical model of a peer, called Tagged Peer (TP), with its peer set.