What Happens on the Internet
What is the point of this whole lavish labyrinth of technology? A far greater number of readers would have asked that question a few years ago. Almost anyone able to buy this book probably has some idea of what the Internet is and what it's for. Still, a short summary of the principal activities is a useful beginning for the study of the Internet landscape that begins in this hour and continues in Hours 17 and 18.
The Internet really is a big TCP/IP network, and if you're not worried about security or time delays, you can use the Internet for almost anything you can do on a routed corporate LAN.
By the Way
Of course, the security considerations are substantial. You definitely should not use the Internet for anything you could do on a routed corporate LAN, but you could if you wanted to. Hours 19 and 20 discuss some of the reasons why you need to be more careful about security in an unprotected space like the open Internet.
It is important to remember that all computers participating in a networking activity (on the Internet or on any other network) have one thing in common: They are running software that was designed for the activity in which they are engaged. Networking doesn't just happen. It requires protocol software (such as the TCP/IP software described in Hours 2–7), and it also requires applications at each end of the connection that are specifically designed to communicate with each other. As shown in Figure 16.2, most computers on the Internet can be classified as either clients (computers that request services) or servers (computers that provide services). A client application on the client computer was written specifically to interact with the server application on the server computer. The server application was written to listen for requests from the client and to respond to the requests. Most of the major Internet activities fit closely with this paradigm. The principal activities include the following:
The World Wide Web, for example, is really a combination of Web clients (Web browsers) that are able to request, receive, and present data supplied in a predetermined format and Web servers, which listen for requests and transmit the Web data requested by the client.
The following sections take a closer look at the World Wide Web, email, newsgroups, chat, and remote access. See Hour 14 for more on FTP. It is important to keep in mind, however, that the possibilities for Internet services are endless. Computers can now use the Internet for anything from a classroom to an operating room. In every case, a connection is successful because a client application and a server application know exactly what to expect from each other.
The World Wide Web
It is no secret that the past few years have witnessed an explosion in the development of the phenomenon known as the World Wide Web. Millions of organizations now make documents available through Web sites. Some younger users think that the Web is the Internet.
The Web is not really a place or a thing. It is more like a method for communication. As you'll learn in the next hour, a Web server is a server that communicates using Hypertext Transfer Protocol (HTTP). When a client application that can communicate using HTTP (a Web browser) connects to the Web server, it receives a burst of data that is assembled by the browser into the image of a Web page.
Web browsers are constantly growing more sophisticated, adding still more features to the rich set of Web activities. The browser is evolving into something like a universal user interface for network applications, and many believe that in a few years, average users will be able to conduct all of their digital business without ever having to leave the browser window.
By the Way
Remember that the Internet is a big TCP/IP network connecting computers all over the world. The Web is a collection of Internet resources that use the HTTP protocol.
Email (short for electronic mail) was the first truly revolutionary innovation to emerge from the Internet culture, and it might yet prove to be the most enduring. The user writes a letter using an email client application and sends that letter over the Internet to another user, who might be on the other side of the world.
As you'll learn in Hour 18, each user on an email system has a mailbox on a mail server computer. The mailbox is a file or directory where messages collect until the user wants to read them. When the user checks for mail, the messages are downloaded to the user's home computer.
Another rich source of information on the Internet is through Internet news servers. Unlike Web servers, which typically do not allow the user to add or alter Web content, news servers enable remote users to post messages. News servers provide what are called newsgroups. Each newsgroup is targeted at a specific topic, interest, or concern. A client application called a newsreader connects to the news server. The newsreader lets the user view the list of available newsgroups and subscribe to newsgroups in which the user has an interest. After a user has subscribed to a newsgroup, she can display messages posted by others or post new messages to the newsgroup.
Some newsgroups are moderated to ensure that inappropriate messages are not available. However, other newsgroups are not moderated.
A newsreader requires some initial setup before you can view news messages. First the newsreader must download the names of available newsgroups. Then the user can select the newsgroup(s) that he is interested in joining. Finally, news messages are downloaded from the selected newsgroup(s) for viewing, as shown in Figure 16.3.
Chat and Instant Messaging
Chat groups (sometimes called chat rooms) are commonly organized around a shared interest. For instance, you might find a chat room for Solaris admins or medieval musicologists. Recently, online magazines have begun to use the chat format for real-time interviews with celebrities. Chat groups differ from newsgroups in that chat is interactive. If you post a message with a newsgroup, you might have to come back later to get a response. If you enter the message in a chat room, you might get a response immediately, but that response can only be from someone else who happens to be visiting the chat room at the time.
A further refinement of the chat concept is instant messaging. Instant messaging does not require a preconstructed chat room for interactive, text-based conversations. Instead, the participants can establish their own interactive dialogs. In a typical instant messaging scenario, one user attempts to contact another user. If the other user is currently online, she can elect to join the conversation, in which case a dialog window appears on both screens, and the participants type their instant interactive messages in the dialog window.
The Internet was once considered unsafe for direct access to secured resources. Internet access was limited to insecure public sites, such as Web servers and FTP servers, and private places behind the firewall were accessed through a more secure point-to-point connection, such as a phone connection. Recently, however, the development of encryption technology and Virtual Private Networking (VPN) techniques have allowed the development of products that let the user establish the equivalent to a point-to-point connection through the Internet. VPN tools let users access remote networks through the Internet over a secure and private connection. You'll learn more about VPNs in Hour 20, "TCP/IP Security."