QoS content management for P2P file-sharing applications

Peer-to-peer (P2P) file-sharing applications allow large communities of users to share multimedia contents. According to their willingness to participate in the P2P community, nodes can switch on and off. An active node participates in the community by downloading content from other nodes and by allowing others to download content which are stored in its own memory. In this paper, we focus on the design of content management at the nodes. Basically, whenever a node retrieves some new content, it may store it in the shared memory and make it available to other users, or it may “consume” it on the fly. The storing policy impacts the effectiveness of the application to provide content to users. Indeed, if only few copies of a given content are available, it may happen that, while the nodes storing those copies are off, the content is not available. Based on the probability that this content unavailability occurs, we define a notion of Quality-of-Service (QoS) and we propose criteria for the QoS design of content management policies. Moreover, we consider a simple policy based on these criteria and we evaluate its performance by an analytical model based on a Markovian approach.