1. On the Use and Performance of Content Distribution Networks Balachander Krishnamurthy Craig Wills Yin Zhang Presenter: Wei Zhang CSE Department of Lehigh University

2. What are Content Distribution Networks? 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.

3. Referenced CDNs and their URLs

4. CDN Techniques DNS redirection Full-site content delivery The origin server modifies its DNS zone file; The CDN server either serves the content from its cache or forwards on the request to origin server. Partial-site content delivery (primarily for images) i.e. www.foo.com/bar.gif -> foo.speedera.net/www.foo.com/bar.gif URL rewriting An origin server dynamically rewrites URL links in generated pages to redirect clients to different content servers.

5. Use of Content Distribution Networks Change Characteristics of CDN-Served Content CDNs are serving little dynamically generated content that is actually changing on each access.

6. Use of Content Distribution Networks Nature of HTTP-Request CDN content Images account for 96~98% of the CDN-served objects, but only 40~60% of the CDN-served bytes. Among the CDNs, Akamai servers over 85~98% of the CDN-served objects in the proxy logs and a comparable range of the CDN-served bytes.

7. Performance of CDNs Response Time Results

8. Performance of CDNs Performance for individual clients

9. Performance of CDNs DNS load balancing

10. Performance of CDNs DNS load balancing

11. Conclusion Most CDNs provide better download performance for the U.S. clients than the U.S. origin sites. CDNs should increase the DNS TTL given to a client unless the servers are known to be loaded.