Web Caching and CDNs March 3 2004 Content
Web Caching and CDNs March 3, 2004
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
Scenario Content Provider origin server
Scenario Content Provider origin server proxy server
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
Drawbacks?
Drawbacks? • Latency – Cooperative caching = even greater latency • Cost of deploying proxy server • Stale data
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
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 • DNS lookup for www. cdn. com – DNS server maps to closest server • Request objects from www. cdn. com
CDNs vs. Caching?
CDNs vs. Caching? • 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
P 2 P • Relationship of CDNs, caching, and P 2 P model?
- Slides: 12