DBit: A Methodology for Comparing Content Distribution Networks

Content distribution networks (CDNs) are increasingly used to deliver high-performance web services. As the volume of content grows, these networks constantly evolve to improve performance. Their performance is difficult to characterize because it depends on factors including the distribution of clients, the geographical scope of the CDN, the specific way in which the content delivery is engineered, and so on. In this paper, we ask the following question: given two CDNs, how do we determine whether one CDN’s user-perceived performance is significantly better than another? In a departure from prior work, we propose a methodology called DBit that identifies distributional differences in user-perceived performance, and we apply it to several CDNs that serve photos. Using 14.5 million photo fetches on PlanetLab from three popular CDNs over a period of 8 months, we find that DBit can identify significant performance differences not just between CDNs, but also across time and location. To assess the robustness of our findings, we complement the PlanetLab dataset with data from home networks in 1470 ASes worldwide