Combining replica placement and caching techniques in content distribution networks

Caching and replication have emerged as the two primary techniques for reducing the delay experienced by end-users when downloading web pages. Even though these techniques may benefit from each other, previous research work tends to focus on either one of them separately. In particular, caching has been studied mostly in the context of proxy server systems, while replication is the technology behind Content Distribution Networks (CDNs). In this paper we investigate the potential performance gain by using a CDN server both as a replicator and as a proxy server. We develop an analytical model to quantify the benefit of each technique, under various system parameters, and propose a greedy algorithm to solve the combined caching and replica placement problem. Our simulation results indicate that a simple LRU caching scheme can improve significantly the response time of HTTP requests, when utilized over a replication-based infrastructure. Moreover, due to its simplicity, this hybrid approach does not affect the administrative overhead of the CDN architecture. q 2005 Elsevier B.V. All rights reserved.