On the effect of free-riders in P2P streaming systems

Peer-to-peer applications exploit the users willingness to contribute with their upload transmission capacity, achieving this way a scalable system where the available transmission capacity increases with the number of participating users. Since not all the users can offer upload capacity with high bitrate and reliability, it is of interest to see how these non-contributing users can be supported by a peer-to-peer application. In this paper we investigate how free-riders, that is, non-contributing users can be served in a peer-to-peer streaming system. We consider different policies of dealing with free-riders and discuss how performance parameters such as blocking and disconnection of free-riders are influenced by these policies, the overlay structure and system parameters as overlay size and source upload capacity. The results show that while the multiple-tree structure may affect the performance free-riders receive, the utilization of the transmission resources is still comparable to that of an optimized overlay.