Abstract-Content distribution networks (CDNs) are a mechanism to deliver content to end users on behalf of origin Web sites. Content distribution offloads work from origin servers by serving some or all of the contents of Web pages. We found an order of magnitude increase in the number and percentage of popular origin sites using CDNs between November 1999 and December 2000. In this paper we discuss how CDNs are commonly used on the Web and define a methodology to study how well they perform. A performance study was conducted over a period of months on a set of CDN companies employing the techniques of DNS redirection and URL rewriting to balance load among their servers. Some CDNs generally provide better results than others when we examine results from a set of clients. The performance of one CDN company clearly improved between the two testing periods in our study due to a dramatic increase in the number of distinct servers employed in its network. More generally, the results indicate that use of a DNS lookup in the critical path of a resource retrieval does not generally result in better server choices being made relative to client response time in either average or worst case situations. A Content Disttibution Network (CDN) consists of a collection of (non-origin) servers that attempt to offload work from origin servers by delivering content on their behalf. The servers belonging to a CDN may be located at the same site as the origin server, or at different locations around the network, with some or all of the origin server's content cached or replicated amongst the CDN servers. For each request, the CDN attempts to locate a CDN server close to the client to serve the request, where the notion of "close" could include geographical, topological, or latency considerations. With content distribution, the origin servers have control over the content and can make separate arrangements with servers that distribute content on their behalf. While CDNs have been created by a number of companies and these CDNs are being used to serve content on behalf of popular origin server sites, there is little that has been published on the extent to which CDNs are being used and their relative performance in serving content. This work seeks to address this void by gathering use and
CONTENT DISTRIBUTION NETWORKS: Content distribution networks (CDNs REF ) are an alternate way of providing VoD to many clients.
On the use and performance of content distribution networks
IMW '01
Computer Science