Practical Service Charge for P2P Content Distribution Jose Antonio Onieva 1 , Jianying Zhou 1 , and Javier Lopez 2 1 Institute for Infocomm Research 21 Heng Mui Keng Terrace, Singapore 119613 {onieva,jyzhou}@i2r.a-star.edu.sg 2 Computer Science Department, E.T.S. Ingenieria Informatica University of Malaga, 29071 - Malaga, Spain jlm@lcc.uma.es Abstract. With emerging decentralized technologies, peer-to-peer (P2P) content distribution arises as a new model for storage and transmission of data. In this scenario, one peer can be playing different roles, either as a distributor or as a receiver of digital contents. In order to incentivize the legal distribution of these contents and prevent the network from free riders, we propose a charging model where distributors become mer- chants and receivers become customers. To help in the advertisement of digital contents and collection of payment details, an intermediary agent is introduced. An underlying P2P payment protocol presented in [1] is applied to this scenario without total trust on the intermediary agent. 1 Introduction A crucial factor in the rapid growth of the Internet is electronic commerce: the ability to advertise goods and services, search for suppliers, compare prices and make payments, all being conducted at the click of a few computer mouse buttons. Nowadays several factors have lit a fire under the peer-to-peer (P2P) move- ment: inexpensive computing power, bandwidth, and storage. In a P2P architec- ture, computers that have traditionally been used solely as clients communicate directly among themselves and can act as both clients and servers, assuming whatever role is needed at each moment. The new P2P networking paradigms offer new possibilities for content distribution over the Internet. Customer peers interchange roles with provider peers, and compete in this new networked econ- omy. A major differentiating factor of P2P from traditional content distribution models is the lack of central management and control. This very important char- acteristic of P2P systems offers the ability to create efficient, scalable, anony- mous - when required, and persistent services by taking advantage of the fully distributed nature of the systems. If a peer distributing contents gets paid for this distribution, why is this peer going to distribute contents freely? This approach can incentivize a legitimate