Covered in this tutorial:

• Overview of the WWW Service
• The WWW Client (browser)
• WWW Forms
• Web Servers (HTTP service)
• Web Server Configuration
• Configuring Multiple Web Sites
• Virtual Directories
• Client / browser Configuration
• Search Engines Overview

Overview of the WWW Service

The World Wide Web (WWW) service can be used to provide information in the form of text, pictures (graphics or video) and sounds. The inclusion of hyperlinks enables you to move between locations in a simple and intuitive manner. It was invented at CERN by Tim Berners-Lee, who is credited with the development of the HTML language.

Typical Uses of the WWW Service

The World Wide Web has many diverse uses, some of which include:

• advertising and information services
• E-commerce
• file download. However, HTTP is not as efficient as FTP because HTTP is optimized for HTML (text) transfer
• forms to collect information or query databases, using client input
• searching file data archives using search engines

How the WWW Service Works

The WWW service is based on a simple client/server architecture. It uses the hypertext transfer protocol (HTTP) to transfer Hypertext Markup Language (HTML) files, and other file types. HTTP is available in two versions: v1.0 and v1.1. The main improvements with the later version include:

• improvements in performance and usefulness; for example, the PUT command allows the posting of information to a web site
• several sites may be located on the same IP address. This is because each browser request contains a header with the site name. HTTP v1.0 required additional IP addresses to be assigned to the network interface, and the DNS was used to assign site names to each of the IP addresses
• multiple client requests may be handled on the connection without waiting for a response
• maintenance of persistent TCP connections, until the client or server request a connection close. This implies less overhead from opening and closing large numbers of sessions to download a page
• more flexible proxying services; support for mail, news and ftp through a proxy server

The WWW Client (or Browser)

Browsers provide the client software for the World Wide Web. The first browser (Mosaic) was invented by Marc Andreesen and subsequently evolved into Netscape Navigator. The most widely used browsers are Internet Explorer and Netscape Navigator; others include Opera and Lynx. Web browsers often allow the user to open other Internet applications such as News Readers and Mail clients.



In order to display a web page, a user either enters a uniform resource locator (URL) or clicks on a hyperlink which includes the URL. This specifies which HTML page to download and the server on which the file is located. The DNS is used to translate the FQDN of the web server to an IP address. The browser then connects to the web server and requests the download of the specified file.

To download a file, a browser performs the following steps:

1. GET /default.htm HTTP/1.0
   The GET command is used to request the file and announce the version of HTTP supported.
2. ACCEPT: text/HTML
   The ACCEPT command states that the browser is able to accept hypertext documents. Other file types could be listed using the MIME (Multipurpose Internet Mail Extensions) format.
3. The server responds with headers describing: the information to be transferred, a blank line and then the requested item.
4. The browser reads the page and displays the content. Different browsers and platforms (fonts) may interpret pages in different ways.
5. When the browser reads an embedded image, sound or java applet reference, it either opens another TCP connection and requests the file or, (in the case of modern browsers), it retrieves the file using the same connection.
6. Once the file download is complete, the browser breaks the connection to the server. (HTTP 1.1 has a persistent connection period which can be set by the server).

Uniform Resource Locators (URLs)

The URL (Uniform Resource Locator) is used as the addressing scheme of the Internet. It contains all the information required to locate any resource. A URL has a fixed structure with up to six components included. The following example shows the structure and the various components are described below.

HTTP://www.w3.org:80/WWW/addressing/Addr.htm#top



Capitalization is important in URLs, as most web servers differentiate between upper and lower case letters.