2001 - 08 - 02 Proceedings of the Sixth International Workshop on Web Caching and Content Distribution

In this paper we describe the Medusa proxy, a tool for exploring user-perceived Web performance. The Medusa proxy is a non-caching forwarding proxy used in conjunction with a user’s browser. The two key features that the Medusa proxy provides are (1) the ability to simultaneously mirror HTTP requests from the browser to different Web delivery systems and directly compare the results, and (2) the ability to transform requests, e.g., to transform Akamai URLs back into URLs to the customer’s origin server. We show how the Medusa proxy can be used to explore userperceived Web performance using two experiments that determine (1) to what extent using large-scale caching systems like the NLANR cache hierarchy improve user-perceived latency, and (2) to what extent content distribution networks like Akamai improve latency compared with using their customer’s origin server. We found that the NLANR cache hierarchy served 63% of HTTP requests in our workload at least as fast as the origin servers, resulting in a decrease of average latency of 15%. By transforming and mirroring Akamai URLs to both Akamai edge servers and their customer’s origin servers, we find that Akamai edge servers are able to serve HTTP requests an average of 5.7 times as fast as their customers. However, because requests to Akamai edge servers are only 6% of our workload, we find that using Akamai reduces overall mean latency by only 2% for our workload.