141 24 112613 web caching 2 locally determine copy

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Unformatted text preview: = server agrees to handle client's request Yes! 2xx Success 200 = request succeeded; 204 = no content present 3xx Redirec8on 301 = page moved; 304 = cached page s8ll valid 4xx Client error 403 = forbidden page; 404 = page not found 5xx Server error 500 = internal server error; 503 = try again later 131 19 11/26/13 HTTP Protocol (4) •  Many header fields specify capabili8es and content –  E.g., Content- Type: text/html, Cookie: lect=8- 4- hfp Func.on Browser capabili8es (client à༎ server) Caching related (mixed direc8ons) Browser context (client à༎ server) Content delivery (server à༎ client) Example Headers User- Agent, Accept, Accept- Charset, Accept- Encoding, Accept- Language If- Modified- Since, If- None- Match, Date, Last- Modified, Expires, Cache- Control, ETag Cookie, Referer, Authoriza8on, Host Content- Encoding, Content- Length, Content- Type, Content- Language, Content- Range, Set- Cookie 132 Introduc8on to Computer Networks HTTP Performance (§7.3.4, §7.5.2) Computer Science & Engineering 20 11/26/13 PLT (Page Load Time) •  PLT is the key measure of web performance –  From click un8l user sees page –  Small increases in PLT decrease sales •  PLT depends on many factors –  Structure of page/content –  HTTP (and TCP!) protocol –  Network RTT and bandwidth 134 Early Performance •  HTTP/1.0 used one TCP connec8on to fetch one web resource –  Made HTTP very easy to build –  But gave fairly poor PLT… 135 21 11/26/13 Early Performance (2) •  Many reasons why PLT is larger than necess...
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