Common TCP/IP Applications

You now know enough about the Transport layer, port numbering, and sockets to get into some of the gritty details of common TCP/IP applications. There's no pretty way to do this, so let's start with the big daddy of them all, the Web.

The World Wide Web

Where would we be without the World Wide Web? If you go up to a non-nerd and say "Get on the Internet," most of them will automatically open a Web browser, because to them the Web is the Internet. I think it's safe to assume you've used the Web, firing up your Web browser to surf to one cool site after another, learning new things, clicking links, often ending up somewhere completely unexpected . . . it's all fun! This section looks at the Web and the tools that make it function, specifically the protocols that enable communication over the Internet.

The Web is composed of servers that store specially formatted documents using a language called Hypertext Markup Language (HTML).

HTML has been around for a long time and as a result has gone through many versions. Today many pages are being written in an updated HTML version called eXtensible HTML (XHTML), which is HTML with an XML syntax.

NOTE XML is a markup language similar to HTML, but it provides more flexibility in how the data is described while being much more strict in its syntax.

Web browsers are designed to request HTML pages from Web servers and then open them. To access a Web page, you enter "http://" plus the IP address of the Web server. When you type the address of a Web server, such as http://192.168.4.1, you tell the browser to go to 192.168.4.1 and ask for a Web page. All Web servers have a default Web page that they open unless you enter something more complex like http://192.168.4.1/status.

NOTE Most Web browsers are pretty forgiving. If you only type in 192.168.4.1, forgetting the "http:" part, they usually just add it for you.

Granted, most people don't enter IP addresses into browsers, but rather enter text like www.totalsem.com or www.google.com. Memorizing text addresses is much easier than memorizing IP addresses. Web site text addresses use a naming protocol called Dynamic Naming System (DNS), which you will learn about in the next tutorial. For now, just enter the IP address.