On the Use and Performance of Content Distribution Networks
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Transcript of On the Use and Performance of Content Distribution Networks
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.