with UDP and TCP Application Layer 2 18 Web and HTTP First a review web

With udp and tcp application layer 2 18 web and http

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with UDP and TCP
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Application Layer 2-18 Web and HTTP First, a review… web page consists of objects object can be HTML file, JPEG image, Java applet, audio file,… web page consists of base HTML-file which includes several referenced objects each object is addressable by a URL, e.g., host name path name
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Application Layer 2-19 HTTP overview HTTP: hypertext transfer protocol Web s application layer protocol client/server model client : browser that requests, receives, (using HTTP protocol) and displays Web objects server: Web server sends (using HTTP protocol) objects in response to requests PC running Firefox browser server running Apache Web server iPhone running Safari browser
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Application Layer 2-20 HTTP overview (continued) uses TCP: client initiates TCP connection (creates socket) to server, port 80 server accepts TCP connection from client HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server) TCP connection closed HTTP is stateless server maintains no information about past client requests protocols that maintain state are complex! past history (state) must be maintained if server/client crashes, their views of state may be inconsistent, must be reconciled aside
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Application Layer 2-21 HTTP connections non-persistent HTTP at most one object sent over TCP connection connection then closed downloading multiple objects required multiple connections persistent HTTP multiple objects can be sent over single TCP connection between client, server
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Application Layer 2-22 Non-persistent HTTP suppose user enters URL: 1a . HTTP client initiates TCP connection to HTTP server (process) at on port 80 2 . HTTP client sends HTTP request message (containing URL) into TCP connection socket. Message indicates that client wants object someDepartment/home.index 1b . HTTP server at host waiting for TCP connection at port 80. accepts connection, notifying client 3 . HTTP server receives request message, forms response message containing requested object, and sends message into its socket time (contains text, references to 10 jpeg images)
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Application Layer 2-23 Non-persistent HTTP (cont.) 5 . HTTP client receives response message containing html file, displays html. Parsing html file, finds 10 referenced jpeg objects 6. Steps 1-5 repeated for each of 10 jpeg objects 4. HTTP server closes TCP connection. time
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Application Layer 2-25 Persistent HTTP non-persistent HTTP issues: requires 2 RTTs per object OS overhead for each TCP connection
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