The proliferation of the Internet is leading to high expectation on the fast turnaround time. Clients abandoning their connections due to excessive downloading delays translates directly to profit losses. Hence, minimizing the latency perceived by end-users has become the primary performance objective compared to more traditional issues, such as server utilization. The two promising techniques to improve the Internet responsiveness are caching and replication. In this paper we present an overview of recent research in replication. We begin by arguing on the important role of replication in decreasing client perceived response time and proceed by illustrating the main topics that affect its successful deployment on the Internet. We analyze and characterize existing research, providing taxonomies and classifications whenever possible. Our discussion reveals several open problems and research directions. 1

Abstract—Notoriously high delays in accessing Web pages loaded with massive multimedia objects are highly undesirable. Inspired by the requirements of news agencies and other information providers to include multimedia content in their pages, this paper proposes a new solution to the problem of minimizing the Web response time. We consider an environment that consists of a central multimedia repository and various sites physically dispersed. Our approach is based on simultaneous downloading of some of the embedded multimedia objects from the repository, and the rest from the regional servers. We propose a cost model to formalize the relative benefits of the proposed scheme, and design an algorithm that replicates multimedia objects so as to take advantage of concurrency in data transferring. An extensive simulation study evaluates the performance of the proposed replication policy under storage and processing capacity constraints, as well as with various network transfer rates. Comparisons are carried out with alternative schemes. Index Terms—Parallel downloads, replica placement, multimedia repository, Web, Internet. 1