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Unformatted text preview: server –  Based on 8mestamp of copy such as “Last- Modified” header from server –  Or based on content of copy such as “Etag” header from server –  Content is available aher 1 RTT Cache Network Server 143 25 11/26/13 Web Caching (4) •  Pu‚ng the pieces together: 144 Introduc8on to Computer Networks CDNs (Content Delivery Networks) (§7.5.3) Computer Science & Engineering 26 11/26/13 Context •  As the web took off in the 90s, traffic volumes grew and grew. This: 1.  Concentrated load on popular servers 2.  Led to congested networks and need to provision more bandwidth 3.  Gave a poor user experience •  Idea: –  Place popular content near clients –  Helps with all three issues above 148 Popularity of Content •  Zipf’s Law: few popular items, many unpopular ones; both mafer George Zipf (1902- 1950) Zipf popularity (kth item is 1/k) Rank Source: Wikipedia 151 27 11/26/13 Content Delivery Network 153 Content Delivery Network (2) •  DNS resolu8on of site gives different answers to clients –  Tell each client the site is the nearest replica (map client IP) 154 28 11/26/13 Business Model •  Clever model pioneered by Akamai –  Placing site replica at an ISP is win- win –  Improves site experience and reduces bandwidth usage of ISP Consumer site ISP Replica User . . . User 155 Topic •  The Future of HTTP –  How will we make the web faster? –  A brief look at some approaches request Network 156 29 11/26/13 Modern Web Pages •  Waterfall diagram shows...
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