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router, creating a big, interwoven framework for communication. Figure 25-1 illustrates the decentralized and interwoven nature of the Internet. The key reason for interweaving the backbones of the Internet was to provide alternative pathways for data if one or more of the routers went down. If Jane in Houston sends a message to her friend Polly in New York City, for example, the shortest path between Jane and Polly in this hypothetical situation is this: Jane’s message originates at Rice University in Houston, bounces to Emory University in Atlanta, flits through Virginia Commonwealth University in Richmond, and then zips into SUNY in New York City (Figure 25-2). Polly happily reads the message and life is great. The Internet functions as planned.

Figure 25-1 Internet Tier 1 connections

Figure 25-2 Message traveling from Houston to NYC

But what happens if the entire southeastern United States experiences a huge power outage and Internet backbones in every state from Virginia to Florida go down? Jane’s message would bounce back to Rice and the Rice computers. Being smart cookies, the routers would reroute the message to nodes that still functioned—say, Rice to University of Chicago, to University of Toronto, and then to SUNY (Figure 25-3). It’s all in a day’s work for the highly redundant and adaptable Internet. At this point in the game (2009), the Internet simply cannot go down fully—barring, of course, a catastrophe of Biblical proportions.

Figure 25-3 Rerouted message from Houston to NYC

TCP/IP—The Common Language of the Internet

As you know from all the earlier chapters in this book, hardware alone doesn’t cut it in the world of computing. You need software to make the machines run and create an interface for humans. The Internet is no exception. TCP/IP provides the basic software structure for communication on the Internet.

Because you spent a good deal of Chapter 23, “Local Area Networking,” working with TCP/IP, you should have an appreciation for its adaptability and, perhaps more importantly, its extendibility. TCP/IP provides the addressing scheme for computers that communicate on the Internet through IP addresses, such as 192.168.4.1 or 16.45.123.7. As a protocol, though, TCP/IP is much more than just an addressing system. TCP/IP provides the framework and common language for the Internet. And it offers a phenomenally wide-open structure for creative purposes. Programmers can write applications built to take advantage of the TCP/IP structure and features, creating what are called TCP/IP services. The cool thing about TCP/IP services is that they’re limited only by the imagination of the programmers.

You’ll learn much more about TCP/IP services in the software and “Beyond A+” sections of this chapter, but I must mention one service that you’ve most likely worked with yourself, whether you knew them by that term or not. The most famous service is the Hypertext Transfer Protocol (HTTP), the service that provides the structure for the World Wide Web (“the Web,” for short), the graphical face of the Internet. Using your Web browser—a program specifically designed to retrieve, interpret, and display Web pages—an almost endless variety of information and entertainment is just a click away. I can’t tell you how many times I’ve started to look up something on the Web, and suddenly it’s two hours later and I still haven’t looked up what I started out wanting to know, but I don’t actually care, because I’ve learned some amazing stuff! But then when I do go look it up, in just minutes I can find information it used to take days to uncover. The Web can arguably claim the distinction of being both the biggest time-waster and the biggest time-saver since the invention of the book!

At this point, you have an enormous, beautifully functioning network. All the backbone routers connect with fiber and thick copper cabling backbones, and TCP/IP enables communication and services for building applications for humans to interface across the distances. What’s left? Oh, that’s right: how do you tap into this great