The Content Delivery Networks (CDN) paradigm is based on the idea to transparently move third-party content closer to the users. More specifically, content is replicated on CDN servers which are located close to the final users, and user requests are redirected to the "best" replica (e.g., the closest) in a transparent way, so that users perceive a better content access service. In this paper we address user requests redirection and replica placement in CDNs. Differently from previous solutions our scheme considers the two problems jointly and relies on distributed and localized schemes that can be implemented with little complexity and overhead, thus providing a new overall solution that effectively trades-off among the number of replicas, their utilization (i.e., how many users requests they serve), the distance from the best replica and the number of replica adds and removals. An OPNET based thorough performance evaluation has allowed us to assess the effectiveness of the proposed solution. By properly tuning the distributed heuristics parameters the CDN provider can have a strict control on the CDN network operations so that the desired trade-off between all the relevant performance metrics is achieved.
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