CHAPTER 8
COMMUNICATIONS AND NETWORKS
Objectives
After completing this chapter you will be able to:
1. Discuss the components required for successful communications
2. Describe use of computer communications
3. Differentiate among types of networks
4. Describe various types of lines for communications over the telephone network
5. Describe commonly used communication devices
6. Discuss different ways to set up a home network
7. Identify various physical and wireless transmission media
COMMUNICATIONS
USES OF COMPUTER COMMUNICATIONS
Internet, Web, E-mail, Instant messaging, Chat Rooms, Newsgroups, Internet, Telephony, FTP, Web Folders, Video Conferencing, and fax
Wireless messaging Service
Public Internet Accessing points
Global positioning System
Collaboration
Groupware
Voice Mail
Web Services
NETWORKS
LAN’s
MAN’s
WAN’s
Network Architectures
Network Topologies
Intranets
Network Communications Standards
COMMUNICATIONS SOFTWARE
COMMUNICATIONS OVER THE TELEPHONE NETWORK
Dial Up Lines
Dedicated Lines
COMMUNICATION DEVICES
Dial Up Modems
ISDN and DSL Modems
Cable Modems
Wireless Modems
Network Cards
Wireless Access Points
Routers
HOME NETWORKS
Wired Home Networks
Wireless Home Networks
COMMUNICATIONS CHANNELS
PHYSICAL TRANSMISSION MEDIA
Twisted Pair Cable
Coaxial Radio
Fiber optic Cable
WIRELESS TRANSMISION MEDIA
Infrared
Broadcast Radio
Cellular Radio
Microwaves
Communications Satellite
CHAPTER SUMMARY
COMPANIES ON THE CUTTING EDGE
Cisco Systems
Qualcomm
TECHNOLOGY TRAILBLAZERS
Robert Metcalfe
Patricia Russo
Computer communications describes a process in which two or more computers or devices transfer data, instructions, and information. Figure 8-1 shows a sample communications system. Some communications involve cables and wires; others are sent wirelessly through the air. As illustrated in this figure, communications systems contain all types of computers and computing devices. For successful communications, you need the following:
• A sending device that initiates an instruction to transmit data, instructions, or information.
• A communications device that connects the sending device to a communications channel.
• A communications channel, or transmission media on which the data, instructions, or information travel.
• A communications device that connects the communications channel to a receiving device.
• A receiving device that accepts the transmission of data, instructions, or information.
FIGURE 8-1 An example of a communications system. The commUfliCat channel consists of telephone lines, cable television and other underground lines, microwave stations, and satellites.
All types of computers and mobile devices serve as sending and receiving devices in a communications system. This includes mainframe computers, servers, desktop computers, notebook computers, Tablet PCs, smart phones, PDAs, and GPS receivers. One type of communications device that connects a communications channel to a sending or receiving device such as a computer is a modem. Two examples of communications channels are cable television lines and telephone lines.
Computer communications are everywhere. Many require that users subscribe to an Internet access provider. With other computer communications, an organization such as a business or school provides communications services to employees, students, or customers. The following pages discuss a variety of computer communications.
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Internet, Web, E-Mail, Instant Messaging, Chat Rooms, Newsgroups, Internet Telephony, FTP, Web Folders, Video Conferencing, and Fax
Previous chapters discussed many uses of computer communications as they related to a particular topic. In the course of a day, it is likely you use, or use information generated by, one or more of the previously discussed communications technologies, which are outlined in Figure 8-2.
The following pages discuss a variety of other uses of communications that have not been discussed previously. These include wireless messaging services, public Internet access points, global positioning systems, groupware, collaboration, voice mail, and Web services.
Worldwide collection of networks that links millions of businesses, government agencies, educational institutions, and individuals
Worldwide collection of electronic documents on the Internet that users access through a Web browser E-Mail Transmission of messages and files via a computer network
Real-time Internet communications service that notifies you when one or more people are online and then allows you to exchange messages, pictures, files, audio, and video
Real-time typed conversation that takes place on a computer connected to a network that also may allow the exchange of messages, pictures, files, audio, and video
Online areas in which users have written discussions about a particular subject
Conversation that takes place over the Internet using a telephone connected to a desktop computer, mobile computer, or mobile device
Internet standard that permits users to upload and download files to and from FTP servers on the Internet Web Folders Location on a Web server to which users publish documents and other files
Real-time meeting between two or more geographically separated people who use a network to transmit audio and video data
Transmits and receives documents over telephone lines
FIGURE 8-2 Uses of communications discussed in earlier chapters.
Users can send and receive wireless messages to and from smart phones, cellular telephones, or PDAs using three techniques: text messaging, wireless instant messaging, and picture messaging (Figure 8-3).
TEXT MESSAGING A mobile device with text messaging, also called SMS (short message service), capability allows users to send and receive short text messages on a smart phone or PDA. Text messaging services typically provide users with several options for sending and receiving messages:
• Mobile to Mobile: send the message from your mobile device to another mobile device
• Mobile to E-Mail: send the message from your mobile device to an e-mail address anywhere in the world
• Web to Mobile: send the message from a text messaging Web site to a mobile device
WIRELESS INSTANT MESSAGING Wireless instant messaging (TM) is a real-time Internet communications service that allows wireless mobile devices to exchange messages with one or more mobile devices or online users. Some wireless Internet service providers partner with TM services so you can use your smart phone or PDA to send and receive wireless instant messages. With a compatible IM service, users have these TM options:
• Mobile to Mobile: use a wireless instant messenger to communicate between two mobile devices
• Mobile to Personal Computer: use a wireless instant messenger to communicate between a mobile device and a personal computer
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PICTURE MESSAGING Users can send graphics, pictures, video clips, and sound files, as well as short text messages with picture messaging, also called MMS (multimedia message service) to another smart phone or PDA or computer (read At Issue 8-1 for a related discussion). Picture messaging services typically provide users these options for sending and receiving messages:
• Mobile to Mobile: send the picture from your mobile device to another mobile device
• Mobile to E-Mail: send the picture from your mobile device to an e-mail address anywhere in the world
FIGURE 8-3 Users can send and receive text messages, wireless instant messages, and picture messages to and from their smart phones and other computers and devices.
Several schools have banned student cellular telephones claiming that they disrupt classes and sometimes are used for illegal activities, such as drug sales. Now, schools may have another reason to prohibit cellular telephones and other wireless devices among students.
Once, teachers only had to watch test-takers to make sure that no one was copying from a neighbor’s paper or secretly referring to notes concealed under a desk. Recently, however, students were caught using their cellular phones’ messaging service to send each other answers to test questions. Others have been caught using camera-enabled cellular phones to take pictures of tests and forwarding the images to other students who were scheduled to take the test at a later time. Some teachers fear that more students soon may be using wireless devices to communicate covertly with classmates during a test, or even to receive messages from sources outside the classroom. To eliminate this high-tech method of cheating, should cellular telephones, digital cameras, notebook computers, Tablet PC5, PDA5, and other wireless devices be banned during lectures and exams? Why or why not? Short of banning these devices, what, if anything, can schools do to prevent students from using them to cheat? Should schools seek a point of compromise so that they can both embrace the new technology and control it?
In many public locations, people connect wirelessly to the Internet through a public Internet access point using mobile computers or other devices. Two types of public Internet access points are hot spots and cybercafés.
A hot spot is a wireless network that provides Internet connections to mobile computers and other devices. Through the hot spot, mobile users check e-mail, browse the Web, and access any service on the Internet — as long as their computers or devices have built-in wireless capability or the appropriate wireless network card or PC Card (Figure 8-4). Hot spots are appearing in airports, hotels, schools, shopping malls, bookstores, restaurants, and coffee shops. Most hot spots span from 100 to 300 feet; some can extend to 15 miles and cover entire cities.
Some hot spots provide free Internet access, some charge a per-use fee, and others require users to subscribe to a wireless Internet service provider, to which they pay per access fees, daily fees, or a monthly fee. Per access fees average $3, daily fees range from $5 to $20, and monthly fees range from $30 to $50 for unlimited access.
When mobile users travel without their notebook computer or Internet-enabled mobile device, they can visit a cybercafé to access e-mail, the Web, and other Internet services. A cybercafé is a coffee house or restaurant that provides personal computers with Internet access to its customers. More than 6,300 cybercafés exist in cities around the world. Although some provide free Internet access, most charge a per-hour or per-minute fee. Some cybercafes also are hot spots.
FIGURE 8-4 Mobile users in this hot spot access the Internet through their notebook computers. One computer uses a wireless network PC Card. The other has Intel’s built-in wireless Centrino technology.
A global positioning system (GPS) is a navigation system that consists of one or more earth-based receivers that accept arid analyze signals sent by satellites in order to determine the receiver’s geo graphic location (Figure 8-5). A GPS receiver is a handheld, mountable, or embedded device that contains an antenna, a radio receiver, and a processor. Many include a screen display that shows an individual’s location on a map.
Many mobile devices such as PDAs and smart phones have GPS capability built into the device or as an add-on feature. Some users carry a handheld GPS receiver; others mount a receiver to an object such as an automobile, boat, airplane, farm and construction equipment, or computer.
The first and most used application of GPS technology is to assist people with determining where they are located. The data obtained from a GPS, however, can be applied to a variety of other uses: creating a map, ascertaining the best route between two points, locating a lost person or stolen object, or monitoring the movement of a person or object. Many vehicles use GPSs to provide drivers with directions or other information.
Many software products provide a means to collaborate, or work online, with other users connected to a server. With Microsoft Office, for example, users can conduct online meetings (Figure 8-6). An online meeting allows users to share documents with others in real time. That is, all participants see the document at the same time. As someone changes the document, everyone in the meeting sees the changes being made. During the online meeting, participants have the ability to open a separate window and type messages to one another.
Instead of interacting in a live meeting, many users collaborate via e-mail. For example, if users want others to review a document, they can attach a routing slip to the document and send it via e-mail to everyone on the routing slip. When the first person on the routing slip receives the document, he or she may add comments to the document. As changes are made to the document, both the original text and the changes are displayed. When subsequent persons on the routing slip receive the document via e-mail, they see all the previous users’ changes and can make additional changes. Once everyone on the routing slip has reviewed the document, it automatically returns to the sender.
Groupware is software that helps groups of people work together on projects and share information over a network. Groupware is a component of a broad concept called workgroup computing, which includes network hardware and software that enables group members to communicate, manage projects, schedule meetings, and make group decisions. To assist with these activities, most groupware provides personal information manager (PIM) functions, such as an electronic appointment calendar, an address book, and a notepad. A major feature of groupware is group scheduling, in which a group calendar tracks the schedules of multiple users and helps coordinate appointments and meeting times.
Voice mail, which functions much like an answering machine, allows someone to leave a voice message for one or more people. Unlike answering machines, however, a computer in the voice mail system converts an analog voice message into digital form. Once digitized, the message is stored in a voice mailbox. A voice mailbox is a storage location on a hard disk in the voice mail system.
Web services describe standardized software that enables programmers to create applications that communicate with other remote computers over the Internet or over an internal business network. Businesses are the primary users of Web services because this technology provides a means for departments to communicate with each other, sup pliers, vendors, and with clients. For example, third- party vendors can use Web services to communicate with their online retailer’s Web site to manage their inventory levels.
FIGURE 8.6 When you start an online meeting from a Microsoft Office product, the participants use NetMeeting to collaborate on the document.
Test your knowledge of pages 296 through 302 in Quiz Yourself 8-1.
Instructions: Find the true statement below. Then, rewrite the remaining false statements so they are true.
1. A cybercafé is a wireless network that provides Internet connections to mobile computers and devices.
2. GPS is a navigation system that consists of one or more earth-based receivers that accept and analyze signals sent by satellites in order to determine the receiver’s geographic location.
3. Receiving devices initiate an instruction to transmit data, instructions, or information.
4. Users can send graphics, pictures, video clips, and sound files, as well as short text messages with text messaging.
Quiz Yourself Online: To further check your knowledge of required components for communications and uses of computer communications, visit scsite.com/dcf2e/ch8/quiz and then click Objectives 1 — 2.
As discussed in Chapter 1, a network is a collection of computers and devices connected together via communications devices and transmission media. Many businesses network their computers together to facilitate communications, share hardware, share data and information, share soft ware, and transfer funds.
A network can be internal to an organization or span the world by connecting itself to the Internet. Instead of using the Internet or an internal network, some companies hire a value-added network provider for network functions. A value-added network (VAN) is a third-party business that provides networking services for a fee.
Networks facilitate communications among users and allow users to share resources with other users. Some examples of resources are data, information, hardware, and software.
Networks usually are classified as a local area network, metropolitan area network, or wide area network. The main differentiation among these classifications is their area of coverage, as described in the following paragraphs.
LAN A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network, called a node, often shares resources such as printers, large hard disks, and programs. Often, the nodes are connected via cables. A wireless LAN (WLAN) is a LAN that uses no physical wires. Very often, a WLAN communicates with a wired LAN for access to its resources (Figure 8-7).
FIGURE 8-7 Computers on a wireless LAN often communicate via an access point with a wired LAN to access its software, printer, the Internet, and other resources.
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A metropolitan area network (MAN) is a high-speed network that connects local area networks in a metropolitan area such as a city or town and handles the bulk of communications activity across that region. A MAN typically includes one or more LANs, but covers a smaller geographic area than a WAN. The state of Pennsylvania, for example, has a MAN that connects state agencies and individual users in the region around the state capital.
A MAN usually is managed by a consortium of users or by a single network provider that sells the service to the users. Local and state governments, for example, regulate some MANs. Telephone companies, cable television operators, and other organizations provide users with connections to the MAN.
A wide area network (WAN) is a network that covers a large geographic area (such as a city, country, or the world) using a communications channel that combines many types of media such as telephone lines, cables, and radio waves (Figure 8-8). A WAN can be one large network or can consist of two or more LANs connected together. The Internet is the world’s largest WAN.
FIGURE 8-8 An example of a WAN.
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The design of computers, devices, and media in a network, sometimes called the network architecture, is categorized as either client/server or peer-to-peer.
CLIENTISERVER
On a client/server network, one or more computers act as a server; the other computers on the network request services from the server (Figure 8-9). A server controls access to the hardware, software, and other resources on the network and provides a centralized storage area for programs, data, and information. The clients are other computers and mobile devices on the network that rely on the server for its resources. For example, a server might store a database of customers. Clients on the network (company employees) access the customer database on the server.
Some servers, called dedicated servers, perform a specific task and can be placed with other dedicated servers to perform multiple tasks. For example, a file server stores and manages files. A print server manages printers and print jobs. A database server stores and pro vides access to a database. A network server manages network traffic (activity).
A client/server network typically provides an efficient means to connect 10 or more computers. Most client/server networks require a person to serve as a network administrator because of the large size of the network.
PEER-To-PEER
One type of peer-to-peer network is a simple, inexpensive network that typically connects fewer than 10 computers. Each computer, called a peer, has equal responsibilities and capabilities, sharing hard ware (such as a printer), data, or information with other computers on the peer-to-peer network (Figure 8-10). Each computer stores files on its own storage devices. Thus, each computer on the network contains both the network operating system and application software. All computers on the network share any peripheral device(s) attached to any computer. For example, one computer may have a laser printer and a scanner, while another has an ink-jet printer and an external hard disk. Peer-to-peer networks are ideal for very small businesses and home users.
FIGURE 8-9 On a client/server network, one or more computers act as a server, and the clients access the server(s).
INTERNET PEER-TO-PEER Another type of peer-to-peer, called P2P, describes an Internet network, on which users access each other’s hard disks and exchange files directly (Figure 8-11). This type of peer-to-peer network sometimes is called a file sharing network because users with compatible soft ware and an Internet connection copy files from someone else’s hard disk to their hard disks. As more users connect to the network, each user has access to shared files on other users’ hard disks. When users log off, others no longer have access to their hard disks.
Examples of networking software that support P2P are BitTorrent, Grokster, Gnutella, and Kazaa, which allow users to swap MP3 music files via the Web.
A network topology refers to the layout of the computers and devices in a communications network. Three commonly used network topologies are bus, ring, and star. Networks usually use combinations of these topologies.
Bus NETWORK A bus network consists of a single central cable, to which all computers and other devices connect (Figure 8-12). The bus is the physical cable that connects the computers and other devices. The bus in a bus network transmits data, instructions, and information in both directions. When a sending device transmits data, the address of the receiving device is included with the transmission so the data is routed to the appropriate receiving device.
Bus networks are popular on LANs because they are inexpensive and easy to install. One advantage of the bus network is that computers and other devices can be attached and detached at any point on the bus without disturbing the rest of the network. Another advantage is that failure of one device usually does not affect the rest of the bus network. The greatest risk to a bus network is that the bus itself might become inoperable. If that hap pens, the network remains inoperative until the bus is back in working order.
FIGURE 8-12 Devices in a bus network share a single data path.
RING NETWORK On a ring network, a cable forms a closed loop (ring) with all computers and devices arranged along the ring (Figure 8-13). Data transmitted on a ring network travels from device to device around the entire ring, in one direction. When a computer or device sends data, the data travels to each computer on the ring until it reaches its destination.
If a computer or device on a ring network fails, all devices before the failed device are unaffected, but those after the failed device cannot function. A ring network can span a larger distance than a bus network, but it is more difficult to install. The ring topology primarily is used for LANs, but also is used in WANs.
STAR NETWORK On a star network, all of the computers and devices (nodes) on the network connect to a central device, thus forming a star (Figure 8-14). The central device that provides a common connection point for nodes on the network is called the hub. All data that transfers from one node to another passes through the hub.
Star networks are fairly easy to install and maintain. Nodes can be added to and removed from the network with little or no disruption to the network.
On a star network, i...
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