To enhance web browsing experiences, content distribution networks (CDNs) move web content "closer" to clients by caching copies of web objects on thousands of servers worldwide. Additionally, to minimize client download times, such systems perform extensive network and server measurements, and use them to redirect clients to different servers over short time scales. In this paper, we explore techniques for inferring and exploiting network measurements performed by the largest CDN, Akamai; our objective is to locate and utilize quality Internet paths without performing extensive path probing or monitoring. Our contributions are threefold. First, we conduct a broad measurement study of Akamai's CDN. We probe Akamai's network from 140 PlanetLab vantage points for two months. We find that Akamai redirection times, while slightly higher than advertised, are sufficiently low to be useful for network control. Second, we empirically show that Akamai redirections overwhelmingly correlate with network latencies on the paths between clients and the Akamai servers. Finally, we illustrate how large-scale overlay networks can exploit Akamai redirections to identify the best detouring nodes for one-hop source routing. Our research shows that in more than 50% of investigated scenarios, it is better to route through the nodes "recommended" by Akamai, than to use the direct paths. Because this is not the case for the rest of the scenarios, we develop lowoverhead pruning algorithms that avoid Akamai-driven paths when they are not beneficial. * Drafting is a technique commonly used by bikers and longdistance runners to reduce wind resistance by moving into the air pocket created behind the leader.
More recently, through a detailed measurement of the Akamai CDN, we show that CDN redirections are primarily driven by network conditions, specifically network latencies on the paths between clients and the Akamai servers, and are updated frequently enough as to be useful for control REF .
Drafting behind Akamai (travelocity-based detouring)
SIGCOMM '06
Computer Science