1. Motivation Due to the development of new Internet access technologies (DSL's and HFC's), VoD services have become increasingly popular Despite the continuous effort done on the client server architecture, it still remains restricted, in terms of scalability, for this type of service Personal computers have incredibly evolved, offering the same resources that are scarce in the servers, in a abundant and idle way P2P networks exploit such resources, offering a new and scalable architecture for VoD services

2. Problem In P2P networks, clients are autonomous to decide whether to cooperate or not As resources like bandwidth are expensive, they tend to behave selfishly (cooperating the least), trying to maximize their utility Indeed, research done in P2P file sharing has shown that only 30% clients are altruistic Considering the time dependent constraint of streams, higher levels of cooperation are essential Therefore, incentive mechanisms are necessary for P2P media stream

3. Project We are studying how far different incentive mechanisms improve scalability and QoS in VoD systems over P2P networks Barter trade (bit-for-bit) and Reputation have been analyzed in Live Streaming context (synchronized content distribution in application level multicast) ● Barter trade is being used to balance the offered and consumed bandwidth in the system, improving scalability ● Reputation is being used as a means of stimulate longer session times, in order to minimize tree disruptions and hence improve QoS

4. Results and Contributions Results: ● Results show that barter trade brings considerable improvements to the system, ensuring that clients cooperate as much as they consume ● Not so optimistic are the results about reputation and longer session times: the price of the policy's impl. sometimes exceeds its gain, in terms of tree disruptions Contributions: ● A cooperation framework has been proposed and evaluated, considering different incentive patterns ● A P2P network simulator has been developed and will be made available as open source as soon as possible