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A single computer can be a useful tool, but the real power of computers becomes evident when they are connected to form a network . Computer networks enable such common functions as electronic mail (email) and browsing the World Wide Web. In this section, you'll learn some basic facts about computer networking.
Two major types of computer networks are the local area network (LAN) and wide area network (WAN). You will learn more about these types of networks in the coming sections. Pay particular attention to the differences as well as the similarities between a LAN and a WAN.
Understand the terms, local area network (LAN), wide area network (WAN). Understand the term client/server.
The distinction between a LAN and WAN is simple. When the computers at a single location are connected to form a network, that's a LAN. When computers at many locations are connected, that's a WAN. A WAN might link two LANs, or it might include thousands of computers at dozens of locations.
When computers are organized into networks, they can take advantage of client/server computing , a scheme in which some resources are held centrally on a computer called a server and shared by many users ( clients ). For example, your company might use a client/server database to store customer information. In that case, you work with customer information on your own personal computer (the client ), but all that information is actually stored on one central computer (the server ). When you need information on a particular customer, your client asks the server for the required information. If you make changes, those changes are sent back to the server. This scheme makes it easy for everyone on a network to share the same customer information.
List some of the advantages associated with group working such as: sharing printers, applications, and files across a network.
Why should your company's computers be connected into a network? Here are some of the benefits you can expect from a LAN:
Hardware sharing A network lets you share expensive hardware such as fast printers and plotters so that each user does not need his own printer or plotter.
Better communications A network enables group communication applications such as email and instant messaging (IM).
Application sharing A network lets users run applications from a central server, instead of having to install them on each individual computer.
Shared knowledge A network lets you share important files and information between users so that each user on the network has access to up-to-date information.
Another way to classify networks is by the number of companies that are connected together. This classification gives rise to the terms intranet, Internet, and extranet.
Understand what an intranet is and understand the distinction between the Internet and an intranet.
An intranet is a network that connects computers belonging to a single company. An intranet might be created as a LAN or a WAN, depending on how widespread the company's computers are.
But WANs can also connect computers belonging to more than one company. In fact, there is a single global WAN that connects millions of companies together. We refer to this WAN as the Internet .
Typically, intranets are used for company-specific tasks such as checking inventory, sharing documents with co-workers , and sharing printers. The Internet is useful for sending email to customers, browsing Web sites, and performing other tasks outside your organization.
Understand what an extranet is and understand the distinction between an intranet and an extranet.
A third type of network is intermediate between an intranet and the Internet. An extranet is a network that connects a company with its business partners . Unlike an intranet, which contains computers from a single company, an extranet might span 10 or 100 companies all working together. But unlike the Internet, an extranet isn't open to all comers. Companies closely control the business partners who have access to their extranet.
For example, Wal-Mart Stores, Inc., has implemented a large and successful extranet for communicating with its suppliers. Information such as inventory levels and purchase orders can be shared by Wal-Mart with selected suppliers over the extranet, without fear that competitors can read this information.
It's hard to get far these days without running across the Internet. Yet many people have only a vague idea of what the Internet is. You'll need more than a vague idea to pass the exam.
Understand what the Internet is and know some of its main uses.
The Internet is a global network of computers connected into one giant WAN. There are many uses for the Internet. For example, the Internet enables all of the following to take place:
Sharing information on Web sites
Moving files between computers at different locations
Sending email to recipients around the world
Holding private video and audio conferences
Working collaboratively with people at other locations
Although it was nearly nonexistent as recently as a decade ago, the Internet has now become an essential tool for all types of business.
Understand what the World Wide Web (WWW) is and distinguish it from the Internet.
Computers communicate with one another over the Internet using a variety of different codes and languages known as protocols . For example, you can move files between computers using the File Transfer Protocol (FTP).
One particularly important protocol is the Hypertext Transfer Protocol (HTTP). This protocol allows your computer to request a page of text and graphic information, called a Web page , from a distant server and to display the results of that request. Web pages can contain hyperlinks , words or images that you can click on to load other Web pages. The collection of all of the hyperlinked documents on the Internet is referred to as the World Wide Web (WWW) .
You'll learn much more about the World Wide Web in Chapter 8, "Information and Communication."
The Internet is an abstract concept, but there's a physical implementation beneath the concept. Computers are connected through a variety of communications circuits. You need to know about the use of the telephone network that is used to make some of these connections to the Internet as well as to other remote computers, such as remote computers used in an extranet or a corporate network.
Understand the use of the telephone network in computing. Understand the terms Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), Asymmetric Digital Subscriber Line (ADSL).
Many computers are connected to the Internet through the same network that carries our telephone conversations. You'll run across a variety of terms in conjunction with this network, including the following:
Public Switched Telephone Network (PSTN) This is simply a fancy term for the familiar network that lets you pick up a telephone, dial a number, and get connected ("switched") to another telephone.
Integrated Services Digital Network (ISDN) This is a special type of telephone circuit that connects you to your Internet provider at a higher speed than the regular PSTN circuits can support.
Asymmetric Digital Subscriber Line (ADSL) ADSL lines are a second special type of telephone circuit that are even faster than ISDN lines. They are asymmetric in that information flows faster to you than it does back to the network.
Depending on where you live and how recently the local phone company's equipment was upgraded, ISDN and ADSL circuits might or might not be available. ISDN circuits are normally more expensive than PSTN circuits, and ADSL circuits are more expensive still.
Understand the terms analog, digital, modem, transfer rate (measured in bpsbits per second).
There's a fundamental difference between computers and telephone lines: computers are digital , whereas telephone lines are analog . A digital device, such as a computer, represents information using a fixed number of values: computers use only the values 0 and 1. An analog device, on the other hand, uses a smoothly sliding scale of values. An old-fashioned mercury thermometer is a good example of an analog device; the mercury slides smoothly up and down the column to represent a near-infinite number of different temperatures .
When you send computer information over normal telephone lines, something has to change the digital information into analog information. At the other end of the line, the analog information must be converted back to digital information. The device that performs these conversions is called a modem . A modem is essential to send digital information over an analog network such as the PSTN.
Other telephone circuits, such as ISDN and ADSL, are inherently digital. When you send information over these circuits, there is no conversion between analog and digital involved.
Each type of network connecton is associated with a specific transfer rate that is, the speed with which information can flow across the network. Transfer rates are measured in bits per second , or bps. These days, an average modem works somewhere between 28,800bps and 57,600bps (often referred to as 28Kbps and 56Kbps). High-speed lines, such as ISDN and ADSL lines, can accommodate much faster modems.
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