Figures of merit for the placement (in) efficiency of interconnected CDNs

CDN interconnection is currently being debated across industry, academia and standards organizations, both in terms of proposing mechanisms for inter-CDN cooperation, such as architectures and protocols, and in terms of the conditions under which cooperation is advantageous. In this paper we focus on the second part and provide contributions to the fundamental problem of when two CDNs should cooperate. Given two CDNs, we aim at quantifying the loss in provisioning efficiency that arises from inter-CDN cooperation. We solve a CDN placement problem in interconnection scenarios, in order to compare the cost of centrally provisioning a network with the joint cost of provisioning the same topology but partitioned and with both sub-topologies independently and only locally optimally provisioned. Given the complexity of the topic (particularly the computational cost) but also aiming at general figures of merit, we use a non-capacitated K-median problem and solve the problem for a large number of topologies. Among other results, we show that the incurred inefficiency of provisioning the same topology partitioned in two independent CDNs, but locally optimal, can raise up to 30%. Overall, we demonstrate with exact solutions that interconnection may not be straightforwardly advantageous.