QoS-aware content management in P2P networks

Peer-to-peer (P2P) file sharing applications consist of nodes that share part of their local memory. A node can download a file (also called content,) from another node participating to the P2P community, and must allow others to download files stored in its own shared local memory. Since nodes join and leave the P2P community at their will in an uncoordinated way, copies of the same file must be stored in many nodes. By means of this redundancy, the probability that a given content cannot be retrieved because all nodes storing it are temporary inactive can be kept small. Content management policies are the distributed strategies implemented at the nodes to decide the set of files to be stored in the local memory. In this paper, we describe, analyze and compare different content management policies. The considered performance indices include the probability that a content cannot be retrieved due to lack of available copies of the content, the amount of traffic generated in the network and the efficiency of the search mechanism, i.e., the probability that a content is successfully downloaded if a peer looks for it in the network.