Joint content placement and lightpath routing and spectrum assignment in CDNs over elastic optical network scenarios

In this work, we address the problem of jointly deciding the placement of the contents delivered by a Content Distribution Network (CDN) among the available data centers, together with the allocation of the lightpaths required to serve the anycast demands initiated by the CDN network users, assuming an underlying high-capacity Elastic Optical Network (EON). We firstly present an Integer Linear Programming (ILP) formulation to optimally solve the targeted problem. This ILP formulation is of high complexity, though, and cannot be used to solve realistically sized problem instances. Hence, we also introduce a novel heuristic called CPRMSA-PD, which decomposes the problem into three sub-problems and applies greedy heuristics and simulated annealing meta-heuristic techniques to yield accurate solutions with practical execution times. We validate the performance of our CPRMSA-PD heuristic in medium-sized problem instances by comparing its results to the ones of the optimal ILP formulation. Next, we use it to give extensive insights into the effects of different key parameters identified in large CDN over EON backbone networks.