Effective message routing in unstructured peer-to-peer overlays

There is a lack of efficiency in flooding-based unstructured peer-to-peer overlays, where loosely coupled nodes require high local autonomy. Two routing improvements are compared based on answer caching, where the cached metadata facilitates content-based routing of queries. Since peer nodes keep joining and leaving the overlay, a mechanism to keep the metadata valid is analysed. The problem area is reviewed, an overlay network model described, and related message routing issues and the simulation environment explained. Simulation results confirm expectations about the traffic reduction, while the user experience does not deteriorate.