What Happens on the Internet
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. 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 22 and 23 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.
Figure 16.2. On the Internet, a computer typically acts as a client or a server.
Figure 16.3 shows the whole teaming ecosystem at a glance. A user sitting at a single computer anywhere in the world can connect to any of thousands of servers elsewhere in the world. A hierarchy of DNS servers resolves the target domain name to an IP address (in a process that is invisible to the user), and the client software on the user’s computer establishes a connection. The server might provide web pages for the user to browse and view, instant messaging, or files to download with FTP. Or perhaps the user is connecting to a mail server to download incoming messages.
Figure 16.3. The Internet is a vast sea of services accessible from anywhere on the Earth.
From the simple beginning of a few networked mainframes, the Internet has morphed into a sprawling jumble of services that the original professors and researchers couldn’t have imagined. In addition to sending email and surfing the web, a new generation of Internet users can make phone calls, connect webcams, watch television, download music, listen to podcasts, and blog their deepest emotions—all through the miracle of TCP/IP. You’ll learn more about many of these new web technologies in later hours.