Learning About the Internet

What is the Internet?

Technically, the Internet is a "network of networks," the world's largest Wide Area Network. It started over 20 years ago as a project of the US Defence Department to link military research sites together. That brought in the Universities, then the companies that dealt with the military and the Universities, then everyone. Today the Internet includes hundred of thousands of local networks and millions of users. Popular applications on the Internet include electronic mail, news groups, the World Wide Web, FTP, and TELNET.

The Internet is a voluntary association of networks. It doesn't belong to the US government or anyone. No one is in charge of the Internet as a whole. If you have a dispute with the organization that is currently providing your Internet service, you can always link to another provider or lease a phone line to another Internet link in a different neighborhood, city, state or country.

The standard communication protocol used to interconnect these many networks is called TCP/IP. TCP/IP ensures that packets of informaton get to their destination reliably and are reassembled in the correct order as messages. The route that one of your packets takes need not be the same as that of your next or previous packet to the same place. Routing depends on the instantaneous load of the moment. The standards that define the Internet are developed interactively by the Internet users through RFC documents, where RFC stands for Request For Comment

Internet applications typically use a client/server design and exchange messages through a mechanism called sockets. For a fuller introduction to Internet technology and resources, read David Greer's paper "Client-Server, The Internet and WWW".

What is this "DNS"?

DNS stands for Domain Name System (sometimes Server because it is implemented using Client-Server techniques). DNS answers two questions about locations on the Internet:

Given a symbolic name such as daffy.robelle.com, what is the numeric IP address?
Given an IP address such as 192.40.254.8, what is the text name associated with it?

The DNS server lives either on your local LAN, somewhere on your network, or out on the Internet. Think of it like a telephone book for the entire Net. DNS maintains tables that map host names to IP addresses. Originally, every machine on Internet had a hard-coded "hosts" file that listed all the other machines that it wanted to network with. The hosts files became impossible to maintain once the Internet grew beyond a few hundred files, so DNS was invented to solve the problem. However, many PC systems still maintain a "hosts.txt" file to give the IP address of local machines, with a pointer to the IP address of a machine that contains the closest DNS server (note: in order to avoid an endless loop, the DNS pointer must be a numeric IP address, not a symbolic name).

DNS servers are linked in a hierarchy. The one closest to you many only know about names in your area of the Net. It you ask it to translate sam.unicode.org, it will have to query the DNS server for "organizations," which may query another server, and so on.

For fastest lookup time, it is best to have your own DNS server running on your local network. On UNIX the software that implements DNS servers is called named. Windows NT and MPE can be DNS clients, but do not appear to have DNS server capability as of 1995. If you are configuring a DNS server, we recommend the book DNS and Bind by Paul Albitz and Cricket Liu from O'Reilly.

Electronic Mail

Electronic mail (e-mail for short) allows users to send messages from desk-top to desk-top. If you have an Internet connection or use one of the commercial on-line services such as Compuserve, you can send messages all over the world. The most common addressing standard for e-mail is the Internet address: name@host.domain (for example, bgreen@robelle.com). If you know the host name, the domain is one of "com" (commercial), "org" (organization), "edu" (education), or "net" (network service), optionally followed by a two-letter country code. If you know the host name, common guesses for the user name are the person's first name, last name, or a combination of both with an underscore. For example, "green", "bob", "bob_green", "bgreen", "greenb", and so on. It is possible to define aliases which will accept mail addresses to all of these names and send them to a single user.

World Wide Web

The World Wide Web (WWW for short) is a means of providing hypertext access to all of the resources of the Internet. Hypertext is text that contains links to other resources. An example that you have probably experienced is a Windows help file. Web documents are called Web Pages; they aren't limited in size to a single page, but the units of information that are retrieved on the Web are still called pages. Web pages are coded in HTML (HyperText Markup Language) to specify headings, paragraph breaks, bold, italic, and most importantly, links.

If you follow a link on an Web page , you may end up on a computer half-way around the world from where you started. In fact, you seldom know where the resources are physically located. WWW is an umbrella application that sites on top of the many other information and communication tools of the Internet, giving them a consistent, machine-independent and accessible interface. The "links" aren't limited to text either, they can point to pictures, sounds, music, applications, or video. In order to access the WWW, you need an Internet connection and a Web browser, a program that follows links to retrieve "pages" from servers and display them on your client screen.

WWW is the application that caused the Internet's popularity to soar, especially once Mosaic was released as a free MS Windows "point and click" browser. There are now Windows versions of every conceivable Internet tool, including the Eudora e-mail reader, Netscape browser, and HTML editors. All of these applications run on top of a standard layer of socket interface called "winsock".

HyperText Markup Language (HTML)

HTML is the standard for coding documents on the World Wide Web. Instead of marking a heading as Centered, Helvetic 16-Point Bold with a blank line above and below, you put visible "tags" around your heading. The browser client program is responsible for deciding how best to display the heading on your screen. For example:

   <h1>My Great American Novel</h1>

The <h1> tag starts a level-one heading (the most bold) and the </h1> ends the heading. Most tags come as pairs, the ending tag being the same as the beginning one except for the addition of a slash character "/".

There are numerous tools to simplify the preparation of Web pages. This document was edited using HTML Writer and checked for errors with Weblint. A useful Web site is the HTML Validation Service. It will check your web pages for compliance with the HTML standard and send you a report of any errors.