Measuring and Evaluating Large-Scale CDNs

CDNs play a critical and central part of today’s Internet infrastructure. In this paper we conduct extensive and thorough measurements that accurately characterize the performance of two large-scale commercial CDNs: Akamai and Limelight. Our measurements include charting the CDNs (locating all their content and DNS servers), assessing their server availability, and quantifying their world-wide delay performance. Our measurement techniques can be adopted by CDN customers to independently evaluate the performance of CDN vendors. It can also be used by a new CDN entrant to choose an appropriate CDN design and to locate its servers. Based on the measurements, we shed light on two radically different design philosophies for CDNs: the Akamai design, which enters deep into ISPs; and the Limelight design, which brings ISPs to home. We compare these two CDNs with regards to the numbers of their content servers, their internal DNS designs, the geographic locations of their data centers, and their DNS and content server delays. Furthermore, we study where Limelight can locate additional servers to reap the greatest delay performance gains. As a byproduct, we also evaluate Limelight’s use of IP anycast, and gain insight into a large-scale IP anycast production sys-