Characterizing the Deployment and Performance of Multi-CDNs

Pushing software updates to millions of geographically diverse clients is an important technical challenge for software providers. In this paper, we characterize how content delivery networks (CDNs) are used to deliver software updates of two prominent operating systems (Windows and iOS), over a span of 3 years. We leverage a data set of DNS and ping measurements from 9,000 RIPE Atlas clients, distributed across 206 countries, to understand regional and temporal trends in the use of multiple CDNs for delivering OS updates. We contrast two competing methodologies for distributing OS updates employed by Microsoft and Apple, where the majority of Microsoft clients download Windows updates from their local ISP. But, 90% of Apple clients access iOS updates from Apple's own network. We find an approximate improvement of 70 ms in the latency observed by clients in Asia and Africa when accessing content from edge caches in local ISPs. Additionally, Microsoft provides lower latencies to its clients in developing regions by directing them to Akamai's rich network of edge caches. We also observe that clients in developing regions accessing Windows updates from Level 3 get poor latencies arising from the absence of Level 3's footprint in those regions.