e. The Web began in 1989 at CERN, the European Center for Nuclear Research. In 1994 the World Wide Web Consortium was founded for developing the Web and its protocols. In the mid-1990s, Netscape Communications Corporation launched a browser available to anybody free of charge and use of the Internet exploded. With a WWW browser (client program) Internet users can download pages containing various types of information including text, graphics, pho- tos, video, and audio. The three main questions are: (1) how does the user locate a piece of information in which he or she is interested? (2) how is information requested and delivered? and (3) how is the format of a Web page created? We attempt to address these questions next. 6.6.11.1 Uniform Resource Locators (URLs) To access information or a resource, it must have a unique identification. A URL is used to indicate where the specific resource is found and which pro- tocol should be used to fetch it. The structure of a URL is illustrated in Figure 6.55. When the user provides a URL, the Web server transfers the requested file to the browser for display. The user may then click an item on screen, which the page designer has linked to another URL that may identify Introduction to Telecommunications Network Engineering http://www.w3.org/public/courses/internet.html Protocol Search path computer Figure 6.55 Structure of a URL. a page that is then fetched from the other side of the world. The host part in Figure 6.55 is translated by the DNS to an IP address, which is in this case 18.23.0.24, and the protocol section defines HTTP and the TCP connec- tion is established to port 80, the default port for HTTP, of the destination host. Search path defines where in the file hierarchy the file of interest is found. The file type .html in the example defines a file type that the browser shows on screen. 6.6.11.2 HTTP HTTP is an ASCII-type application protocol primarily intended for cli- ent-server communication. A client is an application program, or browser, which sets up a con