Hypertext Transfer Protocol (HTTP) Contents ◼ HTTP and Client-Server model ◼ DNS and URL ◼ HTTP Request and response ◼ Character encoding ◼ Media type HTTP ◼ HTTP = Hypertext Transfer Protocol  Application-level protocol for distributed, collaborative, hypermedia information systems.  Used for retrieving inter-linked resources led to the establishment of the World Wide Web.  HTTP is a request/response standard of a client and a server.  Client is the end-user using web browser  Server is the web site. Between client and server there may be several intermediaries: proxies, gateways, and tunnels. ◼ Typically, an HTTP client initiates a request to server over TCP ◼ An HTTP server listens at a particular port (80 by default) waits for the request messages from clients. ◼ Standardization: RFC2616 (HTTP 1.1): ◼ http://www.w3.org/Protocols/rfc2616/rfc2616.html Examples of Web server and client ◼ Web server  IIS: windows  Apache HTTP server (Apache): windows, linux ◼ Web client (Browser)  Internet Explorer: Free with Windows license, started in 1995 ◼ Support Windows ◼  Mozilla Firefox from Mozilla Corporation free browser, ◼ Support: Linux, Mac OS X, Microsoft Windows, and many other Unix-like operating system ◼  Safari: developed by Apple Inc. ◼ Support Mac OS, Windows, iPhone OS  Chrome: from Google Free ◼ Support ◼ Usage share of web browsers ◼ Wikipedia: http://en.wikipedia.org/wiki/Usage_share_of_web_browsers Server Client model ◼ Server client model of Web system ◼ HTTP protocol between Client, Server Web Server Store webpage, Process web request 2 1 Return HTML document 3 Browser display the web page Request a web page User (Web Client) HTTP request and response How to display download progress bar for 1 HTTP request/response? HTTP request and response v.1.0 HTTP request and response ◼ Procedure:  HTTP Client (Web Browsers) opens the connection  HTTP Client sends the request message to an HTTP s