1. Web Caching and CDNs March 3, 2004

2. Content Distribution Motivation –Network path from server to client is slow/congested –Web server is overloaded Web Caching –Store content in cache near client CDNs –Actively replicate content at servers in network Peer-to-Peer File Sharing

3. Scenario origin server Content Provider

4. Scenario origin server Content Provider proxy server

5. Benefits Reduce response time for client request Reduce traffic on an institution’s access link. Internet dense with caches enables “poor” content providers to effectively deliver content

6. Drawbacks?

7. Latency –Cooperative caching = even greater latency Cost of deploying proxy server Stale data

8. Content distribution networks (CDNs) origin server in North America CDN distribution node CDN server in S. America CDN server in Europe CDN server in Asia

9. CDNs Request base object from origin server –Objects to be fetched from CDN have URL http://www.cdn.com/www.foo.com/sports/ruth.gif http://www.cdn.com/www.foo.com/sports/ruth.gif DNS lookup for www.cdn.comwww.cdn.com –DNS server maps to closest server Request objects from www.cdn.com

10. CDNs vs. Caching?

11. Different business models –CDNs = no infrastructure required for client CDNs use push model to keep data fresh CDNs don’t incur latency of cache miss

12. P2P Relationship of CDNs, caching, and P2P model?