The Internet and World Wide Web: E-commerce Infrastructure

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T he Internet: Technology Background 119 FIGURE 3.6 ROUTING INTERNET MESSAGES: TCP/IP AND PACKET SWITCHING To: From: 1 The TCP protocol breaks data into packets 2 The packets travel from router to router over the internet according to the IP protocol 3 The TCP protocol reassembles the packets into the original whole To: From: Router Router Router Sender Router Router Router Recipient The Internet uses packet-switched networks and the TCP/IP communications protocol to send, route, and assemble messages. Messages are broken into packets, and packets from the same message can travel along different routes. name3.org. We discuss domain names and URLs further in Section 3.4. Table 3.1 summarizes the important components of the Internet addressing scheme. TABLE 3.1 IP addresses Domain names DNS servers Root servers ICANN PIECES OF THE INTERNET PUZZLE: NAMES AND ADDRESSES Every computer connected to the Internet must have a unique address number called an Internet Protocol address. Even computers using a modem are assigned a temporary IP address. The DNS (domain name system) allows expressions such as aw.com (Addison Wesley’s Web site) to stand for numeric IP locations. DNS servers are databases that keep track of IP addresses and domain names on the Internet. Root servers are central directories that list all domain names currently in use. DNS servers consult root servers to look up unfamiliar domain names when routing traffic. The Internet Corporation for Assigned Numbers and Names (ICANN) was established in 1998 to set the rules for domain names and IP addresses and also to coordinate the operation of root servers. It took over from private firms such as NetSolutions.com.
120 CHAPTER 3 The Internet and World Wide Web client/server computing a model of computing in which very powerful personal computers are connected together in a network with one or more servers. client a very powerful personal computer that is part of a network. They are capable of displaying rich graphics, storing large files, and processing graphics and sound files server networked computer dedicated to common functions that the client machines on the network need, such as storing files, software applications, utility programs such as Web connections, and printers Client/Server Computing. While packet switching exploded the available communications capacity and TCP/IP provided the communications rules and regulations, it took a revolution in computing to bring about today’s Internet and the Web. That revolution is called client/server computing and without it, the Web — in all its richness — would not exist. In fact, the Internet is a giant example of client/server computing in which over 70 million host server computers store Web pages and other content that can be easily accessed by nearly a million local area networks and hundreds of millions of client machines worldwide (Computer Industry Almanac Inc., 2001.) Client/server computing is a model of computing in which very powerful personal computers called clients are connected together in a network together with one or more server computers. These clients are sufficiently powerful to accomplish complex tasks such as displaying rich graphics, storing large files, and processing graphics and sound files, all on a local desktop or handheld device. Servers are networked computers dedicated to common functions that the client machines on the network need, such as storing files, software applications, utility programs such as Web connections, and printers. (See Figure 3.7.) To appreciate what client/server computing makes possible, you must understand what preceded it. In the mainframe computing environment of the 1960s and 1970s, computing power was very expensive and limited. For instance, the largest commercial mainframes of the late 1960s had 128k of RAM and 10 megabyte disk drives, and occupied hundreds of square feet. There was insufficient computing capacity to support graphics or color in text documents, let alone sound files or hyperlinked documents and databases. With the development of personal computers and local area networks during the late 1970s and early 1980s, client/server computing became possible. Client/server FIGURE 3.7 Client THE CLIENT/SERVER COMPUTING MODEL Client NETWORK Client Server Computer Shared Database Applications Files In the client/server model of computing, client computers are connected in a network together with one or more servers.
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