The age of impatience: optimal replication schemes for opportunistic networks

• Authors: Joshua Reich;Augustin Chaintreau
• Venue: Proceedings of the 5th international conference on Emerging networking experiments and technologies
• Year: 2009

Multimedia content dissemination in mobile settings requires significant bandwidth. Centralized infrastructure is often either inadequate or overly expensive to fill the demand. Here, we study an alternative P2P content dissemination scheme for mobile devices (e.g., smart-phones), which leverages local dedicated caches on these devices to opportunistically fulfill user requests. In our model, the allocation of content in the global distributed cache comprising the union of all local caches, determines the pattern of demand fulfillment. By selectively replicating local content at node meetings, the global cache can be driven towards a more efficient allocation. However, the allocation's efficiency itself is determined by a previously overlooked factor - the impatience of content requesters. By describing user impatience in the form of any monotonically decreasing delay-utility functions, we show that an optimal allocation can be efficient computed or approximated. As users become increasingly impatient, the optimal allocation varies steadily between uniform and highly-skewed towards popular content. Moreover, in opportunistic environments, the global cache state may be difficult or impossible to obtain, requiring that replication decisions be made using only local knowledge. We develop a reactive distributed algorithm, Query Counting Replication (QCR) that for any delay-utility function drives the global cache towards the optimal allocation - without use of any explicit estimators or control channel information. We validate our techniques on real-world contact traces, demonstrating the robustness of our analytic results in the face of heterogeneous meeting rates and bursty contacts. We find QCR compares favorably to a variety of heuristic perfect control-channel competitors.