Computer Networking

Origin of the WWW

• Invented in 1989 by Tim Berners-Lee at the Centre European pour Recherche Nucleaire (CERN) in Geneva

•  Two Central WWW ideas are hyperlinks and Uniform Resource Locators (URLs)

• Mosaic, the first web reader (browser) to gain widespread use, was written in 1993 at the National Centre for Supercomputing Applications (NSCA) by Marc Anderssen, who later founded Netscape

How the Web Works?

• Based on a Client-Server architecture

• The main Web communications protocol is Hypertext Transfer protocol

• Web Clients (browser) make HTTP requests to Web server. Web servers answer with HTTP responses

• Clicking on a hyperlink or typing a URL into a browser starts an HTTP request-response cycle

• An HTTP request-response cycle can have multiple steps since many web pages often contain embedded files, such as graphics, each requiring a separate respone

HTTP Request have 3 parts :

• Request line (requied): starts with a command and URL and ends with the http version number

• Request header (optional): contains information on the browser, date and the referring page from which the request originated. If the user types in the URL by themselves, then the referring page is blank

• Request body (optional): contains information sent to the server, such as from a form.

HTML

• Web pages are formatted using another protocol, usually HTML, also developed at CERN

• HTML documents include information on how to format the file imbedded in the document called tags

• HTML was initially developed for the text files, not multimedia files. This is why extensions to HTML have been needed.

• And also why other markup language formats have been vreated, such as Extensible Markup Language