QoS-Controlled Dynamic Replication in Peer-to-Peer Systems

ABSTRACT

This paper presents a study of dynamic replication for peer-topeer networks. We take an availability-centric view on quality of service (QoS) and focus on the issues of satisfying availability requirements for distributed multimedia services running on large Peer-to-Peer (P2P) systems. We especially tackle the replica placement problem where our focus is on choosing dynamically the number and location of replicas while (1) satisfying the availability QoS requirement for all individual peers and (2) taking the intermittent connectivity of peers explicitly into account. For this purpose, we model P2P systems as a dynamic stochastic graph in which the nodes go up and down depending on their assigned up probability and issue content access events with a certain level of availability requirement. Through an event-driven simulation study we compare and evaluate replication schemes which are fully distributed and adaptive and which satisfy the availability QoS requirements. Simulation results show that (1) satisfying availability QoS requires more replicas than for only increasing the hit rate, (2) the location of replicas is a more relevant factor than their number for satisfying availability QoS, and (3) even simple heuristics can achieve reasonably high availability QoS. Our proposed replication model can be used for further study on the dual availability and performance QoS for dynamically changing, large-scale P2P systems.