On the Use and Performance of Content

Distribution Networks

Balachander Krishnamurthy

Craig Wills

Yin Zhang

Presenter: Wei Zhang

CSE Department of Lehigh University

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.

Referenced CDNs and their URLs

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 cac

he 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.

Use of Content Distribution Networks

Change Characteristics of CDN-Served Content CDNs are serving little dynamically generated conten

t that is actually changing on each access.

Use of Content Distribution Networks

Nature of HTTP-Request CDN content Images account for 96~98% of the CDN-served o

bjects, 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.

Performance of CDNs

Response Time Results

Performance of CDNs

Performance for individual clients

Performance of CDNs

DNS load balancing

Performance of CDNs

DNS load balancing

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.