Urn models and peer-to-peer file sharing

We consider an open network, with constant rate of incoming ´peers´. A peer can contact and communicate with any other peer in the system, corresponding to an Internet´s overlay, where knowledge of peer´s IP-address enables communication with it. In this system one peer, the ´seed´, stays in the system and holds a file and wishes to distribute it to all its peers. One way of doing this, and suitable for large number of peers, is the idea of Bit-Torrent like systems: as soon as a peer receives the file, it becomes a seed itself. To enhance performance, the file is divided into small chunks that are spreaded in a similar fashion.