Scalable communication cost reduction: The Chord case

In peer-to-peer (P2P) network system design a main focus is on efficient service discovery schemes, most frequently assuming permanent (or long-term stationary) positions for service facilities, neglecting communication costs due to the actual locations of the facilities. Since the problem of communication cost minimization is a large optimization problem (NP-hard) and requires global information (i.e., not scalable), in this paper the service migration philosophy is adopted which permits service facility movements and yields smaller communication cost in a scalable manner (i.e., based on local information). Service migration is incorporated in the Chord P2P system, imposing certain changes (e.g., the extension of the service discovery scheme of Chord) and introducing an extra system overhead (i.e., update messages) for the efficient operation of the (enhanced) system. As it is demonstrated here using simulation results, the communication cost corresponding to the extra system overhead is significantly small and more than enough compensated for by the communication cost reduction due to the introduction of service migration. As long as the network remains unchanged, the former communication cost is paid only once while the latter communication cost reduction is permanent.