For A-Plus Writer Only

Management Information Systems for The Information Age

Haag, S., & Cummings, M. (2013). Management information systems for the iriformation age.

New York: McGraw-Hill.

MANAGEMENT INFORMATION SYSTEMS FOR THE INFORMATION AGE

> > Ninth Edition

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EXTENDED LEARNING MODULE E

NETWORK BASICS

Identify and describe the four basic concepts on which networks are built

and describe what is needed to set up a small peer-to-peer network at home.

Describe the components used to build large business networks and define and

compare local area networks (LANs), wide area networks (WANs),

and metropolitan area networks (MANs).

Compare and contrast the various Internet connection possibilities.

Compare and contrast the types of communications media.

State the four principles of computer security and describe how different net'{Vork

security devices reflect those principles.

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ntroduction en you're surfing the Web, accessing software on your school's server, sending e-mail, ecting your roommate use his or her computer to access the files on your computer,

:rr computer is part of a network. A computer network (which we simply refer to as a ~·ork) is two or more computers connected so that they can communicate with each

r and share information, software, peripheral devices, and/ or processing power. y networks have dozens, hundreds , or even thousands of computers.

SIC PRINCIPLES OF NETWORKS

=;works come in all sizes, from two computers connected to share a printer, to the --m et, which is the largest network on the planet,joining millions of computers of all

all over the world. In between are business networks, which vary in size from a zen or fewer computers to many thousands. - ome basic principles apply to all networks, large or small.

I . Each computer on a network must have a network interface (either as an expansion card or integrated into the motherboard, or even through software for a modem) that provides the entrance or doorway in that computer for information traffic to and from other computers.

2 . A network usually has at least one connecting device (like a hub, switch, or home/broadband router) that ties the computers on the network together and acts as a switchboard for passing information.

3 . There must be communications media like cables or radio waves connecting network hardware devices . The communications media transport information around the network between computers and the connecting device(s).

4 . Each computer must have software that supports the movement of information in and out of the computer. This could be modem software and/or a network operating system.

'irst, we'll examine the smallest networks-a few computers connected in a home dorm room-and then move on to larger business networks . We'll discuss network ·ces, LANs, WANs, and MANs, communications media, and network security.

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~-___. Home Networks ~ If you have a computer at home with cable or DSL Internet access, you may already ;_;-

familiar with several network components. A typical home setup has

I

• An Ethernet network card in each computer, and/or a wireless Ethernet card in each laptop computer.

• Network cables to transmit signals, or no cables if you're using wireless.

• A DSL or cable line from your ISP, and a broadband or home router to pass messages and files back and forth.

NETWORK CARDS IN EACH COMPUTER

First, each computer needs a network interface. A network interface card (NIC) i expansion card for a desktop computer or a PC card for a notebopk computer that co·-- nects your computer to a network and provides the doorway for information to flow and out. The network interface card has a jack (or port) for a network cable that connec: your computer to a network. Most computers sold today have network interfaces b into their motherboards.

An Ethernet card is the most common type of network interface card. It has a ja usually an RJ-45 that looks like a telephone jack, only a little larger. You run a netwo cable from your Ethernet card to a hub or switch, or you can use a cable with differ< wiring called a crossover cable to plug straight into another computer or printer if ~­ have only two devices to connect.

WIRED AND WIRELESS TRANSMISSION MEDIA

The most common transmission medium for a home network is Cat 5 cable, which similar to phone cable (ordinary twisted-pair cable). Cat 5, or Category 5, cable i.;; better-constructed version of the phone twisted-pair cable. Each end of the Cat 5 cab has an RJ-45 connector. One end plugs into the Ethernet card in your computer and •· other end into a network switch or broadband router (which we'll discuss in a mome

If you'd like to access your home network wirelessly with your computer, you'll nee: another device on the network. A wireless access point (WAP) is a device that allows computer to use radio waves to access a network. A wireless access point has a tra:::..: - mitter and a receiver for the bidirectional flow of information. It also has an antenna capture the radio waves out of the air.

IHJnk • ..:~

If your wireless access point is a separate device, it connects to a wired network a cable to the hub or switch the same way wired computers do (see Figure E. l). M

T1 1.5Mbps

~ Internet

Reg ional or

National

Coaxial Cable or

Phone Line

I Cab le Modem

or DSL Modem

Horne Networks 411

Air

Printer Cable

bro adband routers (described in the next section) come with a wireless access point built in, so you may not need any extra cables.

Your notebook and any other device that accesses the network wirelessly must have a wireless adapter. Wireless adapters are available as PC Cards for notebook computers, or are built into notebooks. The wireless adapter incorporates a transmitter, receiver, and antenna,just like the wireless access point. If all your devices have wireless adapters, you can create a completely wireless network, in which the only cable used is the one connecting to the cable or DSL service.

HOME INTERNET SERVICE AND BROADBAND ROUTERS

A home network with no outside connections can still be used to share files and print- ers. But in order to access any services or sites outside your home, you need Internet service and equipment to connect it to your home network. Two common types of home Internet service are DSL, available through your telephone company, and cable Internet connection, available from your cable company.

A DSL or cable modem connection is designed to support only one computer, so if you want to connect more computers, you need another device, commonly called a broadband router or home router. A broadband router or home router is a device to connect several computers together to share a DSL or cable Internet connection in a home or small office. It has one port to plug in your Internet connection, and usually has several ports to plug in home computers or printers. Most broadband routers today include a built-in wireless access point.

Figure E.1 Typical Home Network

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Figure E.2 Switch

NETWORK SOFTWARE

As always , when you have hardware you need software to make it work. For a small net- work, Windows will do fine and must be installed on each network computer. To make the files on your computer available to the other computers on the network, you haYe to turn on the file-sharing option in Windows and indicate which drives, directories, or files to share. When you do this , the files on one computer will appear as additional fo ld- ers on the other computer.

Network Components Large networks are built in much the same way as small networks , using the same typ e of components. One difference is that home network devices often perform several dif- ferent functions that are separated onto separate devices in large networks. Let's take a closer look at two of these network components.

SWITCHES

A switch is a network device that connects computers and passes messages by repeating each computer's transmissions only to the intended recipient, not to all the computer connected. Several computers can have different conversations at the same1time through a switch, and such a network is called a switched network (see Figure E.2).

A switch works like a small business telephone system. When the marketing director needs to check on the status of a brochure, she calls the graphic artist to ask about it. At the same time , the shop supervis or can be giving a delivery date to the shipping manager. And the telephones all have speakers, so the operator can still get everyone's attention all at once if necessary.

Information transmitted over switches is generally private, unless it' s specifically meant to be broadcast to all the computers on the network. Switches are the most com- monly used components in networks today, and range in size from four- and eight-port models (connecting four or eight computers or printers) in home networks, to 24- and 48-port models (connecting 24 or 48 devices) common in business networks, to very large switches with hundreds of ports used to connect large call centers or run entire floors of office buildings.

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Network Components 41 3

OUTERS

• ou ters connect together separate networks of computers, unlike switches that connect dividual computers. A router is a device that passes network traffic between smaller hnetworks (or subnets ) of a larger network. T hink of a large business with a warehouse in one building, management offices in other, and manufacturing in yet another. Long ago, each building had its own tele- one system with its own extensions- the warehouse has numbers 100- 199; manage-

ent has extensions 200-299; and manufacturing has numbers 400- 699. At first, the telephone systems weren't connected, and the telephones would call only

"thin the same building. But then the business ran telephone cables from each build- rr to a central phone system to tie them all together. Now the warehouse phone system

- Knows" that if it gets a call for any extension other than 100- 199, it routes the call to the :en tral system to direct to the proper building. And the central system knows to route m y call starting with 1 to the warehouse phone system, any call starting with 2 to man-

ement, and any call starting with 4, 5, or 6 to manufacturing. Ro uters work the same way. When a computer wants to send a message to another

::omputer on a different subnet (like in a different building), it actually sends the message :o the router on its subnet. The router then looks at the message's destination address-

here the message is going- and figures out how to get it there. Medium-sized networks ay have only one router at the center, in which case it can always deliver messages · ectly. Larger networks may have many routers connected together, in which case mes-

= ges may pass through several routers on their way from one computer to another (see : igure E.3).

It' s important to understand that even though you have a router, you still need a 5'\"i tch to p lug the computers into. Because large routers are expensive, it's not practi- cal to build them with enough ports to directly support all the computers on a network. Home routers that run your Internet connection usually have both a router and a switch

Figure E.3 Routers

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. .- Figure E.2 Switch

NETWORK SOFTWARE

As always, when you have hardware you need software to make it work. For a small ne<- work, Windows will do fine and must be installed on each network computer. To mah the files on your computer available to the other computers on the network, you ha,·e to turn on the file -sharing option in Windows and indicate which drives, directories. · files to share. When you do this, the files on one computer will appear as additional fo lrl- ers on the other computer.

Network Components Large networks are built in much the same way as small networks, using the same type of components. One difference is that home network devices often perform several dii- ferent functions that are separated onto separate devices in large networks. Let's take _ closer look at two of these network components.

SWITCHES

A switch is a network device that connects computers and passes mes1)ages by repeati _ each computer' s transmissions only to the intended recipient, not to all the compute~ connected. Several computers can have different conversations at the same time thro urr a switch, and such a network is called a switched network (see Figure E.2).

A switch works like a small business telephone system. When the marketing direc needs to check on the status of a brochure, she calls the graphic artist to ask about it. __ the same time, the shop supervisor can be giving a delivery date to the shipping manage= And the telephones all have speakers, so the operator can still get everyone's attention at once if necessary.

Information transmitted over switches is generally private, unless it's specifici.: meant to be broadcast to all the computers on the network. Switches are the most com- monly used components in networks today, and range in size from four- and eight-poc- models (connecting four or eight computers or printers) in home networks , to 24- 48-port models (connecting 24 or 48 devices) common in business networks , to w:- large switches vvith hundreds of ports used to connect large call centers or run emir.cc floors of office buildings.

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Network Components 413

UTE RS

·(ers connect together separate networks of computers, unlike switches that connect :-.-idual computers. A router is a device that passes network traffic between smaller etworks (or subnets) of a larger network. ~nk of a large business with a warehouse in one building, management offices in rher, and manufacturing in yet another. Long ago, each building had its own tele- ne sys tem with its own extensions- the warehouse has numbers 100-199; manage- r has extensions 200-299; and manufacturing has numbers 400-699.

At fi rst, the telephone systems weren't connected, and the telephones would call only -· · the same building. But then the business ran telephone cables from each build- = o a central phone system to tie them all together. Now the warehouse phone system

ws" that if it gets a call for any extension other than 100-199, it routes the call to the :ral sys tem to direct to the proper building. And the central system knows to route call starting with 1 to the warehouse phone system, any call starting with 2 to man- ent, and any call starting with 4, 5, or 6 to manufacturing.

Ro uters work the same way. When a computer wants to send a message to another p uter on a different subnet (like in a different building), it actually sends the message

::he router on its subnet. The router then looks at the message's destination address- ere the message is going-and figures out how to get it there. Medium-sized networks · have only one router at the center, in which case it can always deliver messages

n:ctly. Larger networks may have many routers connected together, in which case mes- - may pass through several routers on their way from one computer to another (see -~e E.3).

It's important to understand that even though you have a router, you still need a .rch to plug the computers into. Because large routers are expensive, it's not practi- ro build them with enough ports to directly support all the computers on a network.

- me routers that run your Internet connection usually have both a router and a switch

Hub or Switch

Figure E.3 Routers

414 Extended Learning Module E

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built into the same box. But even though they may be labeled routers, remember switching and routing are really two separate functions.

Switches can often be taken out of the box, hooked up to computers, and used wi1 · ·- out setting the configuration. But routers need to be programmed with informati about which computer addresses are on which subnets, so installing a router general.' requires someone with knowledge of network administration. Adding to or reconfigur- ing the network generally requires reconfiguring the router.

Classifying Networks by Distance We've discussed the different devices used to build networks, and next we'll talk abo ways networks are connected together. One way of describing large networks is · terms of the geographic area they cover. The size of a network can also impact whethe~ an organization owns the communicati ons lines or leases them from an independe provider.

LANS, WANS, AND MANS

A local area network (LAN) is a network that covers a building or buildings in clo5t: proximity, such as one campus of a university or corporation. The defining cha'racteri · of a LAN isn' t the actual size, but rather that the geographic area it serves is continuous So the large network on a two-square mile campus of an aircraft manufacturer would be considered all one LAN, but the small networks of a daycare center with two buildings city block apart would be considered separate LANs.

A wide area network (WAN), then, is a set of connected networks serving areas c: buildings not in immediate proximity to each other. Another way to think of a WM _ as a network of networks. WAN s generally use routers to connect LAN s together, just ~ LAN s can use routers to connect different subnets together.

Imagine a business that's large enough to have a production plant near a railroa and trucking depot, and separate corporate headquarters in a downtown office park. > has separate telephone systems on each site- in fact , the production plant has separa'~ telephone systems in the warehouse, the manufacturing building, and the packing an shipping plant. But they also have telephone lines connecting the production pl~ and the headquarters , and the telephone systems know how to send calls from one the other. In fact , except for using a different type of telephone line, sending calls fro one site to the other is set up exactly the same as sending calls from one building • another.

WANs work the same way to connect networks (LANs) on different sites. WANs ma-- connect networks at different locations around a city, or in different cities across a state a country, or even the entire world.

Because WANs connect areas that are some distance apart, organizations don' t usu- ally own the communications lines that WANs run over. Instead, the lines are usu- ally leased, often from a telephone or cable television company, or other commercia: communications provider. Some types of WAN circuits are 56 kilobits per secon (56 Kbps) leased lines; Tl, running at 1.544 megabits per second (1.544 Mbps); an DS3, running at 44. 736 Mbps. (Tl and DS3 are described in more detail in this mod- ule under Internet Connection Types.)

A metropolitan area network is a relatively recent term for a specific type ofW~ ­ A metropolitan area network or municipal area network (MAN) is a set of CO" - nected networks all within the same city or metropolitan area , but not in immedialc proximity to each other.

ternet

-em et, with a lowercase i, comes from the word internetworking, and is a network -:-works, connecting networks managed by different organizations. The largest inter- : all is the Internet (with a capital f) which is a vast network of computers that con- - millions of people all over the world.

- understand how computers send network communications across the Internet, _der the business described earlier that has telephone systems in separate b uildings

n separate sites. When employees place calls to other buildings, each building' s e system directs the calls through a central system that knows how to route the calls ir destinations.

;)C ides the connections to the different buildings, the company also h as connections e p ublic telephone system, so employees can make phone calls to p lace materials

- , and receive calls to accept orders for products. The company's ou tside telephone - d on't run directly to each building, but rather to the central system that knows how ute calls among all the buildings.

Yb.en employees at this company want to make outside calls, they dial a code start- = with 9 (a digit different from the first digit of any of their local extensions), and the

rral system knows to route their calls over the outside lines to the public telephone _·em. And when customers call, they dial one of the company's telephone numbers,

the public telephone system sends the calls over the company's outside phone lines the central system, which routes the calls to the correct departments . If customers n't know the right phone numbers to call, they can look up the company's name in a

- ephone directory and find the numbers they need. This is much the way the Internet works. When a computer needs to send a message ano ther computer somewhere else on the Internet, it sends the message to its local

- uter. If the router doesn't recognize the recipient as being attached to one of its LAN, ~-ll'l', or WAN connections, it sends the message over the connection to its Internet

.=en -i.ce Provider (ISP). The ISP has bigger routers that learn paths to get to even more ecworks. Even if they're not connected directly to the receiving network, the IS P's rout-

~. send the message to another router, which may send the message to still another, m d so forth, until the message finally gets to the receiving network. There, the receiving

uter will at last deliver the message to the computer at the ultimate destination. Computers and routers refer to each other using network addresses, commonly

m ternet Protocol (IP) addresses, like 192.168.1.1. This is similar to th e way teleph one ~-stems use telephone numbers , like+ 1 (414) 555-1212, to route calls. You probably r-emember the phone numbers of some of your friends and family, but no one knows all the different phone numbers in the world.

Similarly, you don't have to remember the low-level network address of every com- pu ter you send network messages to. Instead, you can use names for computers, like

\\W.mhhe .com, and your computer looks up the receiving computer's address for you in a directory called the Domain Name System, or DNS. Without DNS, the Internet would be virtually impossible to use.

BANDWIDTH

T he most common measurement used when comparing different types of communi- cations media is bandwidth, which refers to capacity. Bandwidth, or capacity of the communications medium, is the amount of information that a communications medium can transfer in a given amount of time. You can think of bandwidth as the thickness of a drinking straw: the thicker the straw, the more quickly yo u can move the liquid from the

Internet 41 5

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41 6 Extended Learning Module E

Figure.-E.4 Digital and Analog Signals

Digital

Analog

cup into your mouth. In fact, in the communications industry, bandwidth is sometim referenced informally as what size "pipe" you have between two locations.

Bandwidth is described as a quantity of data transferred in an amount of time, mo_ commonly as a number of bits per second. A bit is the smallest possible amount of da representing a single I or 0, and is abbreviated as the letter b. A byte is eight bits, and ::... used to store one letter or symbol of text, so the number of bits divided by eight giYe_ you the approximate number of text characters . (See Extended Learning Module A f: more info rmation about bits, bytes, and characters.)

Bandwidth is sometimes represented in bits per second, abbreviated bps. Because a sing_:: bit is such a small quantity, and communications media speeds are constantly increas- ing, the bandwidth of different media is more likely to be represented in thousands of b~ per second (kilobits per second-Kbps or kbps) , millions of bits per second (megabits per second-Mbps), or billions ofbits per second (gigabits per second- Gbps).

For example, if a particular communications medium has a bandwidth of 16 Mbps then 16 millions bits can be transferred in a single second. This module has ab oi..;.. 70 ,000 characters in it, which is approximately 560,000 bits, so it could be transferred in less than half a second across a 16 Mbps channel.

INTERNET CONNECTION TYPES

Like the circuits used to make wide-area connections, Internet circuits aren't usu owned by individual companies. Instead, the circuits are supplied by an Internet Seni.cc Provider. Types of Internet circuits include:

• Dial-up circuits, using an ordinary telephone line and a modem.

• Digital Subscriber Line (DSL) , which runs a high-speed connection over a telephone line without interfering with the voice telephone service.

• Cable modem, which runs a high-speed connection over a cable television line without interfering with television reception.

• Satellite modem, which runs a high-speed connection through your cable TV satellite without interfering with television reception.

• Dedicated high-speed lines such as Tl and DS3, which run on separate circuits and are generally used for business connections.

DSL, cable modem, and dedicated lines are classified as broadband connections. A broadband connection is a high-bandwidth (high-capacity) telecommunication.: line capable of providing high-speed Internet service. The Federal Communicatio- - Commission defines broadband as a capacity of 200 kbps (200 kilobits, or thousands bits, per second) both upstream (to the Internet) and downstream (from the Interne Other industry experts feel that broadband implies a speed of at least 750 kbps.

DIAL-UP CONNECTIONS To make a telephone or dial-up connection, you need _ computer, a phone line, a modem, and, of course, an Internet service p ro- vider. Just as people use telephones to talk over telephone lines, a teleph<tn modem (modem) is a device that connects a computer to your phone line that you can access another computer or network. And as is the case wi people and telephones, the computer at the other end needs a modem to o.

A modem converts the digital signals from your computer into an anal- = form (by modulating the signal) that can be transmitted over a phone line and then converts the analog signal back to digital signals (by demodula:- ing the signal) for the computer at the receiving end of the transmission ( Figures E.4 and E.5). The word modem is a contraction of the modem·, function of modulating outgoing and demodulating incoming transmis siolli

Digital uses discrete

electronic pulses to represent

information

Digital-to-Analog Conversion

Analog

Analog uses a continuous electronic stream to represent

information

Telephone Line

Analog-to-Digital Conversion

Modems are sometimes integrated into the motherboards of new computers, particularly .aptops and notebook. If your computer doesn't have a built-in modem, you can buy a card ·o plug into an expansion slot of your desktop, or a PC card for your notebook. A modem - the slowest type of Internet connection you can get. The fastest possible transmis- . on speed using a modem over a normal telephone line is 56 kbps, or about 56,000 bits

per second.

DI GITAL SUBSCRIBER LINE A Digital Subscriber Line (DSL) is a high-speed .Jiternet connection using phone lines, which allows you to use your telephone for voice communication at the same time. There are different kinds of DSL systems, including ADSL or asymmetric DSL, SDSL or symmetric DSL, and HDSL or high-bit-rate DSL, :hat offer different combinations of speeds from the Internet provider to the customer :rnd from the customer to the provider.

DSL works similarly to a traditional modem, modulating and demodulating the computer's digital signal into an analog form for transmission over the telephone line. H owever, unlike traditional modems which modulate into audible sounds (the screech ··ou hear if you pick up a telephone while your computer is connected to the Internet illrough its modem), DSL modems use frequencies too high for you to hear; this is how they can allow telephone conversations to happen at the same time. Even so , DSL modems sometimes cause clicks , pops , or buzzing on telephone lines , so most DSL con- nections use a splitter or filter to make sure that only voice calls go to the telephone and only DSL signals go to the DSL modem (see Figure E.6).

DDDDD DDDDD DDDDD DDDDD DDDDD DDDDD DDDDD DDDDD

amma mama

DSL Access Module

Internet 41 7

Figure E.5 The Role of a Telephone Modem

Figure E.6 DSL Internet Access

PHONE COMPANY YOUR HOME DSL Modem

41 8 Extended Learning Mo dule E

Figure E.7 Cab le Internet Access

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Because the high frequencies used by DSL are outside the range that telephone lin- were originally designed to carry, only telephone lines that meet certain criteria deliver DSL service. You need to live within about three miles of the phone company. C larger cities, phone companies have branch offices that can connect you throughou t th= metropolitan area.) The phone company may have restrictions about the type of equip- ment it uses to provide your phone line-a relatively recent central system, and a dire line to your house without any signal processing devices along the way. And the sp e of your connection may depend on the distance to the phone company and the quali of your line. Speeds may vary from 144 kbps to 1.5 Mbps, or even up to 6 Mbps fo r business-class DSL connection.

DSL circuits- the physical cabling to your house- are always provided by the ph one: company. The phone company usually provides the Internet service that you use over the DSL connection, too. However, in some areas , you may be able to buy your lnterne· service from an independent service provider instead. To connect to a DSL circuit, yo need the filter or splitter provided by the phone company (to k((,ep noise out of your tele- phone conversations) and the DSL modem. The cable from the DSL modem connec~ to your computer in one of two ways: either to an Ethernet card, or to a USB port.

DSL service has three big advantages over dialup connections:

1. DSL is much faster-up to 30 times faster than a traditional modem.

2. You can use the line for voice calls at the same time.

3. DSL can be an always-on connection- because it doesn't interfere with voice calls, you can leave it connected all the time , instead of having to wait for your modem to connect each time you want to use the Internet.

CABLE MODEM If you have wired cable television, you know it comes into your home on a coaxial cable that connects to your television set. This same cable can con- nect you to the Internet, too. Both cable TV signals and your Internet connection trave: from the cable company on one wire.

A splitter at your home splits the signals on the incoming cable, sending one pan to the TV and the other to your cable modem. A cable modem is a device that u seJ your TV cable to deliver an Internet connection (see Figure E.7). The cable from the cable modem attaches to either an Ethernet card (an expansion card that connects your

DDDDD DDDDD DDDDD DDDDD DDDDD DDDDD DDDDD DDDDD

000000 11 000000 CABLE COMPANY

Coaxial Cable to Subscribers

Sp litter

YOUR HOME

-- Cab le Mode m

puter to a network) or to a port on the motherboard. Like DSL, cable modems pro- e an always-on connection. However, unlike DSL, cable modems don't use a phone at all.

The speed of transmission with a cable modem is much faster than a phone modem, :..nning at about 10 Mbps (10 million bits per second). While the speed of a DSL con-

. on is guaranteed, though, the speed of a cable Internet connection depends on how y users are online, because the connection to the cable company is shared through-

• a neighborhood. If all your neighbors are surfing the Web with a cable connection at ame time you are, you may notice a reduction in your access speed.

- TELLITE MODEM If you have wireless cable television, that is, if you receive ur cable programming via a satellite, you can often also obtain your Internet service ough the same provider of your satellite cable. A satellite modem allows you to get ernet access from your satellite dish. In certain instances, you may not be receiving ur cable programming via satellite, but you may be able to receive your Internet

- rvi ce via a dedicated satellite dish. It really all depends on where you live and what ry es of services are offered for cable programming and Internet service.

T he concept and implementation of receiving your Internet service from your satel- e cable programming provider are the same as for using a cable modem. You would Ye a splitter with wiring for your cable programming going to your television and wir-

:ng for your Internet service going to your computer or a connecting device such as a uh or router.

1, DS3, FRAME RELAY, AND ATM A Tl is a high-speed circuit typically used or business connections, running at speeds up to 1.544 Mbps (1.544 million bits per -econd), and a DS3 is a high-speed business network circuit running at 44. 736 Mbps. T ls were originally designed to carry 24 telephone conversations on phone companies' ong-distance lines between cities. Later, equipment was developed to connect computer networks over Tl and DS3 lines. A Tl's speed of 1.544 Mbps is about 24 times the speed of an analog telephone modem. A DS3 line is equivalent to 28 Tl lines bundled together, and its total speed of 44. 736 Mbps is about 672 times the speed of an analog modem.

With some providers, a portion of the price of Tl and DS3 lines depends on the dis- tance they run. Because of this distance-based pricing and their overall higher cost than some other connection types , Tl and DS3 lines are most commonly used for metropoli- tan area network connections- between two branches of a business within the same city. One advantage of Tl lines is that, because of their origin in voice telephony, it' s possible to split their 24 channels between voice and computer communications, using the same T l circuit to connect both telephone systems and computer networks at two offices.

Frame Relay and Asynchronous Transfer Mode (ATM) are services that the phone company or other telecommunications providers can set up over high-speed lines like Tl s and DS3s to create "virtual circuits" connecting multiple offices. These virtual cir- cuits can provide network connections from each office to every other one without hav- ing to run physical lines directly between each pair.

For example, if a business had four offices that all needed to be connected to each other, it would take six Tl lines to hook them all up (see Figure E.8). With Frame Relay or ATM, each office has a single Tl line going to the communications provider (for a total of four), and the provider makes it work the same as it would if the six direct lines actually existed.

Remember that the price of Tl and DS3 lines can depend on the distance they run. With Frame Relay or ATM, the Tl or DS3 lines actually run from each office to the tele- communications provider, rather than from office to office, so the distance and price can both be lower than when Tl lines are run directly from office to office.

Internet 41 9

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Figure E.8 Frame Relay/ATM Virtual Circuits

...

T1 Lines without Frame Relay/ATM

T1 Lines for Frame Relay/ATM

Virtual Circuits

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!!!... ~··[ .!!!

Branch Office Connections without Frame Relay/ATM

Branch Office Connections Using Frame Relay/ATM

Because of this, Frame Relay and ATM are also used to connect many branch offices :o a single main office. If a business had six branch offices, it would take six Tl lines to connect all the branches back to the headquarters (see Figure E.9)- each potentially running a great distance. With Frame Relay or ATM, the business can instead install a DS3 from its headquarters to the communications provider and a Tl to each branch office. The provider makes it work as it would if the headquarters had a direct connec- cion to each branch office, and the business potentially spends less money than if it ran all of the Tl lines directly between offices. And the company has a single DS3 connec- cio n at its headquarters instead of six separate Tl connections , simplifying circuit man- agement and potentially increasing reliability.

VOICE OVER IP

We've just talked about different types of communications lines that can carry network information, but now it's time to turn that inside out. Several types of communications lines-telephone lines, Tls, and DS3s-were originally developed to transmit voice tele- phone calls, and later adapted to carry computer data. Voice over IP (VoIP) does the opposite-it's a means of transmitting a voice telephone call over a computer data network. Voice over IP (VoIP) allows you to send voice communications over the Internet and avoid die toll charges that you would normally receive from your long-distance carrier.

Why go to the trouble of sending voice calls over a computer network when they can already be sent directly through existing telephone systems and services? The answer has everything to do with overhead and with metered billing, meaning you pay an addi- cional amount for each call and/or for each minute of the call.

Offices in most businesses and universities today have at least two different cables run to them-one that goes back to a telephone system, and one that goes back to a network

Internet 421

Figure E.9 Frame Relay/ATM Circuit Aggregation

422 Extended Learning Module E

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= LEARNING OUTCOME 4 1 r

switch. On many telephone systems , the telephone extension number is assigned m _ particular port on the central equipmen t. So when an employee moves from one offic: to another, making his or her telephone extension work in the new office involves eith~ changing wiring or reprogramming the phone system.

In contrast, network addresses are assigned directly to the computer or other de\-iCT: regardless of which switch port it' s connected to. So moving a VoIP extension fro m on:: office to another is as easy as unplugging the network phone from one location, carryin~ it to another, and plugging it hack in. This reduction of maintenance effort can drama::- cally reduce the overhead of telephone system operation during office expansions anG'. moves. Additionally, office technicians no longer have to maintain two sets of wiring · two different systems, which can also reduce overhead.

Both network companies like Cisco Systems and telephone companies like Nortel arr producing VoIP telephones that look like any other business phone, except they p lu.;, into a network jack instead of a telephone jack. Many even have an extra network jack o them for your PC, so your phone and computer can share a single connection hack c the building's huh or switch.

Voice over IP is gaining popularity with h ome users across the Internet. In mos~ parts of the world , traditional telephone calls made from on e local dialing area t another have metered hilling, and some large U. S. cities even have metered hilling fo. local calls.

Network access is often unmetered, though, particularly for broadband h ome acces.;: (cable modem and DSL). If you already have an Internet connection, you can use a nec- work telephone or network phone software for your PC to make calls to other VoIP user5 anywhere in the world at no additional cost per call or per minute-for the momem ... anyway. Most telephone hilling rates in the United States are set by federal and state gm·- ernments by regulations called tariffs, and it remains to he seen how long it will he befo re Voice over IP becomes tariffed as well.

Network Communications Media The objective of networks and telecommunications is to move information from one place to another. This may he as simple as sending information to the office next door, or as far- reaching as sending a message to the other side of the world. Whatever the case, informa- tion must travel over some path from its source to its destination. Communications media are the paths, or physical channels, in a network over which information travels.

All communications are either wired or wireless. Wired communications media transmit information over a closed, connected path. Wireless communications media transmit information through the air. Forms of wired and wireless communications media include:

Wired Wireless

• Twisted-Pair Cable • Infrared

• Coaxial Cable • Microwave

• Optical Fiber • Satellite

WIRED COMMUNICATIONS MEDIA

Wired communications media are those which tie devices together using cables of some kind. Twisted-pair, coaxial cable, and op tical fib er are the types of cabling you'd find in computer networks.

Network Communications Media 423

TWISTED-PAIR Twisted-pair cable is a bundle of copper wires used for transmitting voice or data communications and comes in several varieties. The Cat 5 that you already read about in connection with home networks earlier in this module is one type. Most of the world's phone system is twisted-pair and since it's already in place, it's an obvious choice for networks.

The simplest type of twisted-pair phone cabling (Cat 1) provides a slow, fairly reli- able path for information at up to 64 kilobits per second (Kbps) , while a better type (Cat 3) provides up to 10 megabits per second (Mbps). However, distance, noise on the line, and interference tend to limit reliability for most types of twisted-pair cabling. For example, a crackle that changes a credit card number from 5244 0811 2643 7 41 to 5244 0810 2643 7 41 is more than a nuisance; in business it means retransmitting the informa- tion or applying a charge to the wrong person's credit card.

Cat 5 or Category 5 provides a much higher bandwidth than ordinary phone cable, meaning it carries more information in a given time period, at least for distances up to 100 meters. It's commonly used for connections at 100 megabits per second (Mbps), and an enhanced version called Category Se is capable of carrying 1 gigabit per second (Gbps). Cat 5 is relatively inexpensive and is fairly easy to install and maintain. Because of these advantages, it's the most widely used cabling for data transfer in today' s LAN s. Note, however, that twisted-pair of any kind is relatively easy to tap into and so it's not very secure. It's even possible to access the information by simply detecting the signals that "leak" out.

COAXIAL CABLE An alternative to twisted-pair cable is coaxial cable (coax), which is one central wire surrounded by insulation, a metallic shield, and a final case of insulating material. (Coax is the kind of cable that delivers cable television transmissions and also carries satellite TV from the dish to your house.) While coaxial cable was once the cable of choice for internal LAN wiring, it has been almost completely replaced by twisted- pair cable. Coaxial cable is capable of carrying at least 500 Mbps, or the equivalent of 15,QOO voice calls, simultaneously. Because of its shielded construction, coaxial cable is much less susceptible to outside interference and information damage than twisted-pair cable. However, coaxial cable is generally more expensive than twisted-pair and is more difficult to install and maintain. Security is about the same with coaxial cable as with twisted-pair, except that the radiation, or leaking, of information is much less . Coax is commonly used for leased line private networks.

OPTICAL FIBER The fastest and most efficient medium for wired communication is optical fiber, which uses a very thin and flexible glass or plastic fiber through which pulses of light travel. Information transmission through optical fiber works rather like flashing code with a light through a hollow tube.

Op tical fiber's advantages are size (one fiber has the diameter of a human hair); capac- ity (easily hundreds of gigabits per second, and getting faster every year); much greater security; no leakage of information. It's very hard to "tap" into optical fiber. Attempts are pretty easy to detect since installing a tap disrupts service on the line- and that' s noticeable. Optical fiber is also used for nearly all connections between different build- ings, as it doesn't conduct electricity and so is immune to damage from lightning strikes. Optical fiber is more expensive than twisted-pair cable, however, and requires highly killed technicians to install and maintain.

WIRELESS COMMUNICATIONS MEDIA

For many networks, wired communications media are simply not feasible, especially for telecommunication across rugged terrain, great distances, or when one or more parties

_.

424 Extended Learning Module E

.--

may be in motion. For whatever reason , if wired communications media don't fi t Y' needs, wireless may be the answer. Wireless communications radiate information ir:- the air, either very narrowly beamed or in many directions like ripples from a pebi; - tossed into a pond. Since they radiate through the air, they don't require direct cab. - connections of any kind. Obviously, security is a big problem since the information available to anyone in the radiation's path. However, wireless encryption methods a=-:: good, and getting better.

INFRARED AND BLUETOOTH FOR VERY SHORT DISTANCES Infrared is the ol~­ est type of wireless communication. Infrared uses red light to send and receive inform=- tion. The light is invisible to humans, but snakes and some other animals can see it. Yo TV remote control uses infrared. You can use infrared to connect handheld devic~ such as pocket PCs , to peripheral devices such as printers. Wireless keyboards an~ mice usually connect to your PC with an infrared link. Infrared communication is to~ line-of-sight, meaning that you can't have anything blocking the path of the signal, or~ won' t work. Infrared transmission has very limited bandwidth (typically 1 Mbps).

A relatively new and competing wireless technology is called Bluetooth. Named fo:- a Viking king, Bluetooth is a standard for transmitting information in the form o: short-range radio waves over distances of up to 30 feet and is used for purposes such ~ wirelessly connecting a cell phone or PDA to a computer. Virtually all digital devices , lih keyboards,joysticks, printers , and so on, can be part of a Bluetooth system. Bluetooth is also adaptable for home appliances like refrigerators and microwave ovens.

OMNIDIRECTIONAL MICROWAVE (WIFI) FOR SHORT DISTANCES Another method of short-distance wireless communications is omnidirectional (all directio ns microwave transmission. Microwave transmission is a type of radio transmission. Microwaves occupy a portion of the electromagnetic spectrum between television sig- nals and visible light. Microwave ovens use high-powered microwaves to heat food and can interfere with some types of microwave wireless transmissions.

The mos t common types of wireless networking used today-802.1 lb and 802 . 1 l y (known to most people as Wi-Fi)-use microwave transmissions. Wi-Fi (wireles. fidelity) is a standard for transmitting information in the form of radio waves over distances 100 feet or so. With the right equipment, the reach can be several mileJ. Wi-Fi is actually a wireless industry alliance that provides testing and certification tha£ 802.11 devices communicate with each other properly. Several generations of Wi-Fi in common use are IEEE 802.11 b, running at up to 11 Mbps; 802. l lg, running at up to 54 Mbps and compatible with 802. l lb equipment at the slower rate; and 802.11 a, also running at up to 54 Mbps but no t compatible with 802.1 lb equipment. The lat- est Wi-Fi version , 802.11 n, can operate in several different modes , but is typicall:- used in a mode compatible with all previous versions at their slower rates and at up to 144.4 Mbps with other 802 . l ln devices.

Wi-Fi hotspots are sites that offer wireless Internet access for your laptop. Such places have a link through a wireless router to an Internet service provider that make access available to the public. There may be a charge for this service or it may be free. You may have noticed signs offering Wi-Fi access at airports , restaurants like Starbucks. bowling alleys, and other public places. Be careful about using public networks thac don' t require a password and are not secure. Much of the data that moves around a net- work is clear text, meaning that it can be intercepted. Make sure that you use encrypted Web pages (the ones with https:// and a little padlock) and that you check your e-mail through a secure Web site rather than using an e-mail program like Thunderbird thac doesn't encrypt incoming and outgoing data. Some Webmail sites encrypt only the ID

Network Communicatio ns Media 425

and password but not the pages where you read and write e-mails messages, so watch fo r that. Others have the option of encryp ting all Webmail pages. You can encrypt files chat you are sending over a public network with programs such as Stuffit Deluxe. There are also encryption programs for specific systems such as Thunderbird.

DIRECTIONAL MICROWAVE FOR MEDIUM DISTANCES Microwaves may be rransmitted very directionally with a parabolic dish antenna or can be radiated in a wide curved path for broader use. Microwave transmission is a line-of-sight medium. That is, the microwave signal can- not follow the curved surface of the earth. So to send the information over a distance of more than about 20 miles you'd have to use repeaters (see Figure E.10). A repeater is a device that receives a radio signal, strengthens it, and sends it on. (You've probably seen microwave towers- they're the tall towers with lots of little dishes on them that stand near an industrial complex.) Microwave sig- nals have difficulty getting through walls or trees or other solid objects, so there must be a clear path from sender to receiver.

SATELLITES FOR LONG DISTANCES Communications satellites are microwave repeaters in space. They solve the problem of line-of-sight since the transmission shoots up into the sky in a straight line, bounces off, and shoots back down to earth again (see Figure E.11). Since satellites are so high, an array of them can cover essentially the whole earth (as the two dozen or so GPS satellites do). As with land-based repeaters , satellites receive information from one location and relay it to another. You'd usually use satellite communications to connect land-based networks in far-flung locations or to connect moving vehicles to each other or to the organizational network.

Satellite communications are cost effective for moving large amounts of information, especially given a large number of receiving sites. For example, K-Mart and other retail- ers place very small aperture terminal (VSAT) satellite dishes on the roofs of their stores. The VSATs allow individual stores to transmit information to the home office, and the

Sending Location

Receiv ing Locations

Figure E.10 Microwa ve

Figure E.11 Satellite

426 Extended Learning Module E

I LEARNING OUTCOME 5

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home office, in turn , can transmit information to all the stores simultaneously. Satellite radio is another example of far-flung satellite transmission. If you have satellite radio ~ your car, you'll never be completely out of range of your favorite satellite radio station.

---i Network Security

Thinking about network security may call to mind images from movies of computer rooms criss-crossed by laser beams, voice and handprint recognition, security cameras. and CDs or DVDs full of top-secret blueprints. Or it may make you think ofjumpsuic- wearing technicians clipping wires onto someone else's connection, greasy-haired teen- agers illuminated only by the green glow of their computer monitors , or an investigator frantically trying to guess the criminal's password as the footsteps in the hallway get ever closer.

These images, although dramatic, don' t give you much of an idea of the real threa to computer and network security and how to guard against them. In reality, co n- necting computers together can make it easier to take advantage of existing securi ty weaknesses-attacks can be performed from any distance away instead of only fr om within the same room-and introduces some new weaknesses.

PRINCIPLES OF COMPUTER SECURITY

The best way to understand network security is to look at the components of computer security, evaluate different threats in terms of these components, and then figure out how to reduce the effectiveness or damage of those threats. The basic principles of computer and network security are confidentiality, authenticity, integrity, and availability. Within the context of computer and network security

• Confidentiality means that information can be obtained only by those authorized to access it. In even simpler terms, it means keeping secrets secret. Confidential information includes things like bank statements, business plans, credit card reports, and employee evaluations. Threats to confidentiality include network transmissions that can be captured or monitored by unauthorized individuals, passwords that are easily guessed, and even printouts left lying out in plain sight. In the world outside of computers , confidentiality is protected by sealing envelopes and locking doors and file cabinets.

• Authenticity means that information really comes from the source it claims to come from. It's important to be sure of the authenticity of things like military orders, medical diagnoses , and buy/sell directions to your stockbroker. Threats to authenticity include fraudulent e-mail messages claiming to be from your bank (probably spoofing) , Web sites registered at names that are common misspellings of popular sites, and Web browsers that can be manipulated into making it look as though you're at a different site than you really are. Nonelectronic authenticity is provided by signatures (although they can be forged) , or by trusting only people you know personally.

• Integrity means that information has not been altered . This is closely related to authenticity. You would be concerned about the integrity of your bank balance, contents of your corporate Web site, medical prescriptions, and credit card charges. Threats to integrity include network transmissions that can be forged or taken over by unauthorized individuals and Web servers with flaws that allow their content to be rep laced . Integrity is hard to guarantee in the physical world - how can yo u really be sure that no one has changed

even a single word of your mo r tgage contract?-and is generally dependent on a certain degree of trust that' s much harder to apply to electronic communications.

• Availability means simply that a service or resource is available when it's supposed to be. If a mail-order Web site is unavailable during the Christmas season, a retailer could lose millions of dollars in sales. If a corporate e-mail server is frequently unavailable, the company may lose some of the trust of its business partners. Threats to availability include unintentional network failures, poorly written server software that stops working when presented with unusual inputs, and deliberate attempts to send so much traffic to a company's network that legitimate communications are unable to get through. Noncomputer-related availability is provided by designing buildings with multiple exits in case one is blocked by fire, making photocopies of important documents, and installing electrical generators in hospitals to keep life-critical equipment operating if the city power fails .

FIREWALLS AND INTRUSION DETECTION SYSTEMS

Networks are designed to connect computers together and move information between them. But what if attackers are trying to break into your computers through your net- work connection? Just as a company may install card readers or hire a guard to admit only staff wearing employee badges, afirewall is software and/or hardware that protects a computer or network from intruders (see Figure E.12). As hardware, a firewall is a device that permits or denies network traffic based on security policy. Firewalls provide protection against threats to confidentiality, authenticity, and integ;rity by blocking traf- fic that doesn't look like legitimate access to networked computers.

Some firewalls make their policy decisions based entirely on network addresses. For example, if you have caller ID on your telephone, you may choose to answer calls only if

Remote VPN User

~·----- Intrusion

Alarm

Corporate Network

VPN System

Netwo rk Security 427

Figure E.12 Firewall, Intrusion Detection System, and Virtual Private Network

428 Extended Learning Module E

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they come from your friends or family. Likewise, a simple firewall can examine networ. traffic and permit only the traffic coming from a known source.

Other firewalls may permit traffic from an unknown source if it appears to be a response to a request that was made by a computer on the protected network. For example, if you call a friend at the office but she's in a meeting, you might leave a message for her to car you back. When she does, you may recognize the phone number of her office as a number you just called and answer the call, even though the office number isn't on the list of phone numbers you'd normally answer.

Even more advanced firewalls make decisions based on the content of the netwof' traffic. Thinking back to the company with a security guard in the lobby, the guard ma;· allow a delivery person to enter the building if he's carrying envelopes or pizza, but no t ii he's carrying dynamite or bottles of acid. Of course, acid may be a regular delivery item in a chemical plant; not every company will want the same firewall policies .

While a firewall typically has a predefined policy about the network traffic it will allow. an intrusion detection system (IDS) is a device that watches network traffic for intru- sion attempts and reports them. An Intrusion prevention system (JPS) is a type of ID that also takes action against intrusion attempts, for example, by creating new policies in a firewall to block the source of the attack. Intrusion detection and prevention systems work by having information about many different types of network attacks and matching the current network traffic against their lists of attack characteristics. When they sense an attack in progress, they can e-mail or page network administrators about the ,attack, so they can take appropriate action.

Denial-of-service attacks simply interfere with network availability. A denial-of service (DoS) attack floods a server or network with so many requests for service tha' it slows down or crashes. (See Extended Learning Module H, Computer Crime and Forensics, for more details about denial-of-service attacks.) Imagine if someone called every pizza delivery service in town and ordered 20 pizzas delivered to your office. Eventually you'd manage to sort out the confusion and you wouldn't have to pay for the pizzas, but meanwhile you'd be too busy dealing with the situation to get any work do ne.

Firewalls and intrusion detection and prevention systems can protect availabili f) by preventing or reducing the effect of denial-of-service attacks. Some denial-of-service attacks use network capabilities that are technically permissible, but are almost never seen in legitimate network traffic; these attacks are easy to foil by denying those type of traffic. Other denial-of-service attacks send completely legitimate but useless traffic. Blocking those attacks involves recognizing an increase in network traffic beyond normal levels, determining the source or sources, and then blocking even legitimate-appearina traffic from those locations.

Most home broadband devices- for DSL and cable modem Internet connections- include a simple firewall. Home networking manufacturers have been packing more and more capabilities into their products, and even though the devices may be marketed as routers or firewalls , they generally contain a router, a firewall, and a switch or hub to con- nect multiple home computers. Some even include the DSL or cable modem , and some have a wireless access point, all in a device not much larger than a paperback book.

ENCRYPTED COMMUNICATIONS: SSL AND VIRTUAL PRIVATE NETWORKS

Earlier, we talked about types of network devices on which communications can be over- heard, for example wireless access points. This is a threat to confidentiality-unauthorized individuals could be watching your communications. So if you're using wireless acces5 or are somewhere that you don't know who has access to the communications lines and

equipment between you and your network destination, what can you do to protect the privacy of your communications?

The solution is encrypted communication. Encryption scrambles the contents of a ille so that you can't read it without having the right decryption key. It means scrambling -our communication in such a way that only the intended recipient can unscramble it.

you wanted to send the message, "Reschedule the grand opening for April 1 O,'' the encrypted version might look like

V'9:P)9@AI,i i>[D:J_sepnvlf.Xj2FAs_[Dhud+'. One way of using encryption to protect network transmissions is called Secure

ockets Layer (SSL), or somewhat less commonly, by the name of its successor, Transfer Layer Security (TLS). SSL is a security technology that encrypts each net- work conversation- between one network client and one server-individually. Web rraffic using SSL is called https, instead of just http. When you browse to a secure Web ite and see the padlock icon, it's telling you that your browser is using SSL/TLS to

encrypt your communications with the Web server. We cover more on SSL and other types of security technologies with respect to electronic commerce in Chapter 5.

In contrast, a virtual private network (VPN) uses encryption to protect the confi- d entiality of all network transmissions between two endpoints. Typically, one endpoint is a large office or headquarters, and the other endpoint may be a single computer, or it may be another office. All network communications between the two locations are routed through the VPN to be encrypted. This makes it look as though they have a dedi- cated network connection between them, even though they may really be communicat- ing over public network links, hence the name, virtual private network.

OTHER SECURITY THREATS: MALWARE

You've probably heard of computer worms, viruses , and spyware, collectively known as malware. Malware is a contraction of malicious software, and refers to software designed to harm your computer or computer security. Malware existed even before most computers were connected to networks, but increased connectivity between com- puters has made it dramatically easier for malware to transfer to new victims.

A virus is software that is written with malicious intent to cause annoyance or dam- age. The virus software is activated unintentionally by the computer user. A worm is a type of virus that replicates and spreads itself, not just from file to file, but from computer to computer via e-mail and other Internet traffic. Viruses spread by tricking users into running them, tor instance, by pretending to be an interesting program or e-mail mes- sage; worms spread by taking advantage of errors or weaknesses in computer programs. Viruses and worms most commonly threaten availability, by damaging or removing files, or by tying up a computer doing so much unauthorized work that it can't get its real job done.

Viruses and worms can be countered by running anti-virus software. Anti-virus soft- ware works very similarly to the intrusion detection systems described earlier. It has a long list of characteristics of known worms and viruses , and when it sees files being transferred or software running on the computer that has those characteristics, it alerts the user and often " quarantines" the file to part of the hard drive where it can't do any harm. Some anti-virus software can even remove the malicious instructions from com- puter files so that they are still useful once they're disinfected.

Anti-virus software can be run at different places in the network. Some viruses are transferred from computer to computer in e-mail messages, and anti-virus software on the e-mail server will help protect against them. It's very important to run anti-virus software on every PC, to protect against wo rms and viruses trying to attack the com-

Network Security 429

430 Extended Learning Module E

puter directly. And some companies have servers where customers can upload purchase orders or problem reports; they may run anti-virus software on those servers to screen all incoming files.

Spyware is a more recent type ofmalware than viruses and worms. Spyware (also called sneakware or stealthware) is malicious software that collects information about you and your computer and reports it to someone else without your permis- sion. Therefore, spyware is a threat to confidentiality. Spyware most often ge t installed on your computer secretly along with a piece of software you knew you were getting; for example, some peer-to-peer file sharing programs are notorious fo r including spyware.

The best defense against spyware is to install software only from trustworthy sources. but that can be hard to determine. Anti-spyware software is available that works just like antivirus software, recognizing patterns of known spyware and removing them from your computer. Two popular anti-spyware programs are Ad-Aware (www.lavasoftusa.com) and Spybot Search & Destroy (www.safer-networking.org).

Another category of malware is servers and bots. Sometimes. after breaking into a computer, attackers will set up unauthorized servers. These servers are often used to distribute illegal copies of movies, music , and software, or may even be used to distribute kits for breaking into other computers.

In the context of malware, bots are programs designed to be controlled by an attacker to perform unauthorized work over a period of time. Some bots are used to send spam, making it look like it's coming from the victim's computer instead of from the attack- er's. Other bots try to break into computers or perform denial-of-service (DoS) attacks against other networks or systems.

Bots and unauthorized servers can sometimes be detected by anti-virus or anti- spyware software-but they may be indistinguishable from legitimate servers. They can also sometimes be discovered by network intrusion detection systems. Sometimes they're even discovered by network administrators, noticing an unusual amount of network traffic coming from a single computer.

SUMMARY: STUDENT LEARNING OUTCOMES REVISITED

<"'

I. Identify and describe the four basic concepts on which networks are built and describe what is needed to set up a small peer-to-peer network at home. There are four basic concepts on which almost all networks are built. They are

• Network inteiface cards (NICs) in each computer

• A connecting device like a hub, switch, or home/broadband router

• At least one communications medium

• Network operating system software

To set up a peer-to-peer network at home , you'd need

• Ethernet cards (as the NI Cs) in each computer

• A home/broadband router

• Cat 5 cables

• A network operating system, like W in dows

Summary: Student Learning Outcomes Revisited 431

2. Describe the components used to build large business networks and define and compare local area networks (LANs), wide area networks (WANs), and metropolitan area networks (MANs). Large business networks are built using

• Network interfaces in each computer

• Switches to connect the computers together into subnetworks

• Routers to connect the subnetworks together

A local area network (LAN) covers a geographically contiguous area. A wide area network (WA.h) is a set of connected networks serving areas not in immediate proximity. A metropolitan area network (MA.h) is a set of connected networks all within the same city or metropolitan area, but not geographically continuous.

3. Compare and contrast the various Internet connection possibilities. There are five ways described in this book to connect a computer or network to the Internet. They are

• Phone line and modem, which uses a phone line and prevents your using the same line for voice communication at the same time. It's the slowest type of connection.

• Phone line and DigiJal Subscriber Line (DSL), which, although it uses the phone line, does not prevent simultaneous voice communication. A DSL connection is a broadband connection.

• Cable TV line and cable modem, which brings Internet access in with your cable modem and doesn't use the phone line at all. It's also broadband.

• Cable programming via a satellite and satellite modem, which supports both cable television programming and Internet access.

• Tl, a high-speed business circuit running at l.544Mbps, or DS3, a very-high- speed business circuit running at 44. 736Mbps.

4. Compare and contrast the types of communications media. Communications media are the paths, or physical channels, over which information travels in a network. There are two options: wired and wireless. Wired communications media include twisted-pair cable, coaxial cable, and optical fiber. Of these, optical fiber is the fastest and the most secure. Wireless communications media include infrared, Bluetooth, Wi-Fi, microwave, and satellite. Infrared and Blu'etooth are for very short distances only, Wi-Fi is for short distances, microwave has short and medium distance versions , and satellite is for long distance.

5. State the four principles of computer security and describe how different network security devices reflect those principles. The four principles of computer security are

• Confidentiality, meaning that information can only be obtained by those authorized to access it

• Authenticity, meaning that information really comes from the source it claims to come from

• Integrity, meaning that information hasn' t been altered

• Availability, meaning that a service or resource is available when it' s supposed to be

Firewalls protect confidentiality, authenticity, and integrity by blocking traffic that doesn't look like legitimate access to networked computers. Intrusion

4 3 2 Extended Learning Module E

detection systems (IDSs) p rotect all type s of comp uter security by watching for network intrusion attemp ts and reporting them; intrusion prevention sys tems (IPSs) take action to block them. Encryption methods, including SSL and virtual private network; (VPNs), p ro tect confidentiality by scrambling your communication in such a way that only the in tended recipient can unscramble it.

- --· KEY TERMS AND CONCEPTS

Bandwidth, 415 BI uetooth, 424 Broadb~ nd, 416 Broadband router (home

rout er), 411 Cable modem, 418 Cat 5 (Category 5), 410 Coaxial cable (coax), 423 Communications media, 422 Communications satellite, 425 Computer network, 409 Denial-of-service (DoS)

attack, 428 Digital Subscriber Line (DSL), 4 17 DS3, 419 Encryption, 429 Ethernet card , 410 Firewall, 427 Infrared, 424

Internet, 415 Intrusion detection system

(IDS), 428 Intrusion prevention system

(IPS), 428 Local area network (LAN), 414 Malware, 429 Metropolitan area network

(municipal area network, MAN), 414

Microwave t ransmission, 424 Network interface card (NIC), 410 Optical fiber, 423 Repeater, 425 Router, 413 Satellite modem, 419 Spyw are, (sneakware,

stealth w are), 430 Switch, 412

T1, 419 Telephone modem, 416 Twisted-pair cable, 423 Vi rtua l private network

(VPN), 429 Virus, 429 Voice over IP"

(VoIP), 421 Wide area network

(WAN), 414 Wi -Fi (wireless fidelity), 424 Wi-Fi hotspot, 424 Wired communications

media, 422 Wireless access point

(WAP), 410 Wireless communications

media, 422 Worm, 429

- --· SHORT-ANSWER QUESTIONS

1. What are the four basic princ iples that apply to 7. What impact does Frame Relay have

all networks? on a metropolitan area network?

2. What is an Ethernet card? 8. What is Cat 5 cable used for?

3. What does a network switch do? 9. What is Bluetooth?

4. What is bandwidth? 10. What does Wi-Fi do?

5. What do you need to have a dia l-up 11. How does a VPN protect confidentiality?

co rrm ection to the Internet? 12. What are the four principles of computer

6. How is a DSL Internet connection different security?

from a telephone modem connection?

ASSIGNMENTS AND EXERCISES

1. WHAT ARE THE INTERNET ACCESS OPTIONS

IN YOUR AREA? Write a report on what sort

of Internet connections are available close to

you . How many ISPs offer telephone modem

access? Is DSL available to you? Is it available

to anyone in your area? Does your cable

company offer a cable modem? If your school

has residence halls, does it offer network

connections? Compare each available service

on price, connection speed, and extras like

a help line, list of supported computers and

operating systems, and people who will come

out to your home and help you if you're

having difficulties. What type of Internet

connection do you currently use? Do you plan

to upgrade in the future? If so, to what type

of connection? If not, why not?

2. INVESTIGATE BUILDING YOUR OWN HOME

NETWORK Build your own home network

on paper. Assume you have the computers

already and just need to link them together.

Find prices for switches and routers on the

Web. Also research Ethernet cards and cables .

If you were to get a high-speed Internet

connection like DSL or cable modem, how

much would it cost? Can you buy your own,

or would you have to rent the modem from

the phone or cable company?

3. DEMONSTRATE THE IMPACT OF WIRELESS

TECHNOLOGY How many devices do you own

or use that transmit signals (not just computer

data) wirelessly? Think of as many as you

can, and make a list showing the different

types of signaling used by each device. Don't

forget that some devices use multiple wi reless

technologies, like cell phones with both

cellular signals for voice transmissions and

Bluetooth for syncing their address books .

Hint: Don't forget cordless phones, TV and

stereo remotes, radios, and portable computers

and smartphone with infrared capability (look

for a small, glossy black window somewhere

on the edge of the case). Can any of your

devices communicate with each other?

Assignments and Exercises 433

4. CONSIDER THE IMPORTANCE OF NETWORK

SECURITY Write a report about the importance

of computer and network security in your daily

life, in terms of the four principles of computer

security. If you have a job in addition to being

a student, write about computer security in

your workplace. If you don't work outside the

classroom, write about how computer security

affects you at school and in your personal life.

You may be surprised at how man~,things

you do that depend on some aspect of secure computer records and communications, like

banking, grades, e-mail, timesheets, library and

movie rental records, and many more .

5. FIND OUT ABOUT FIREWALLS Go to the Web

and find out about software and hardware

that protect your computer and home

network, respectively.

If you have only one computer connected to

the Internet, then a software firewall like Zone

Alarm will most likely be enough protection

from intruders . Find three different firewall

software packages on the Web . A good place

to start looking would be the sites that sell anti-virus software. Compare the firewall

software on price and features . Some sites to

try are

• Symantec at www.symantec.com

• Trend Micro at www.trendmicro.com

• McAfee at www.mcafee.com

If you have a home network, look into

hardware firewall options . How many different

hardware firewalls can you find on the Web

site of your favorite electronics retailer? (Hint:

Look in the feature lists of home routers and

broadband routers, even if they don't have the

word firewall in their name.)