6-1. communications, networks, & safeguards 6.1 from the analog to the digital age 6.2 networks...

Communications, Communications, Networks, & Networks, & SafeguardsSafeguards

6.1 From the Analog to the Digital Age

6.2 Networks

6.3 Wired Communications Media

6.4 Wireless Communications Media

6.5 Cyberthreats, Hackers, & Safeguards

6.6 The Future of Communications

Chapte

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McGraw-Hill/Irwin © 2007 The McGraw-Hill Companies, Inc. All rights reserved.

6-3

From the Analog to the Digital AgeFrom the Analog to the Digital Age

Analog signals use variation of a wave form to send information

The wave forms look like the sine wave shown at right

In FM signals the Frequency is varied (Modulated)

In AM signals the Amplitude is varied (Modulated)

Radios send signals this wayLight works this wayHearing and phones work this

wayModems work this way

S1

-1

-0.5

0

0.5

1

Amplitude

Sine Wave

Frequency

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Digital signals send data in terms of 1s and 0s

A digital signal may look like this one at right

Notice how the signal goes up and down abruptly because the only values that matter are 0 and 1 and the timing of when they occur

Computers use digital signalsNewspaper photographs are

digital since they are made up of little dots

1 5 9

13 17 21 25 29 33 37 41

S10

1

Time

Data

Digital Signal

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Since computers use digital signals but phone lines use analog, modems must translate from digital to analog, send the signal along the phone line, then translate back from analog to digital at the other endThe process is called “modulation/demodulation”Modulation means to translate from digital to analogDemodulation means to translate from analog to digitalModems have to do all this just to use standard analog

voice phone lines

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Tape recorders, voices, and musical instruments are analog while CDs are digital

To burn a CD from a jam session, the digital recording equipment must convert from analog to digitalThe analog-to-digital converter samples the sound and

converts the height of the wave to a numberSamples of the sound wave are taken at regular intervals

– about 44,100 times each secondBecause the digital samples are played back faster than

our ears can react, it sounds to us like a single continuous sound wave

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Digital sampling is similar to showing moviesMovies show still pictures (frames)But they show them so fast that our eyes can’t react in

time So to us the series of still pictures look like continuous

motionDid you ever notice in movies when they show car tires in

motion they sometimes seem to move backwards? This is because the tires are moving at a rate that is

incompatible with the frame rate of the movie, so our eyes think the tires are really moving backwards when the car is actually moving forward!

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NetworksNetworks

A system of interconnected computers, telephones, or other communications devices that can communicate with one another and share applications and data

Before we had computer networks, people used “sneakernet” to share data between computersPerson 1 saved their document to a floppy diskThen they walked over to person 2’s desk (wearing

sneakers, of course) and handed over the disk to person 2

Person 2 loaded the disk into their computer to read and edit the document

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NetworksNetworks

Since the days of “sneakernet”, networks have become standard. They enable us to:Share peripheral devices such as laser printersShare programs and dataUse e-mail and other communication programsBackup critical information because it is stored centrallyAccess shared databases

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NetworksNetworks WAN – Wide Area Network

MAN – Metropolitan Area Network

LAN – Local Area Network

HAN – Home Area Network

PAN – Personal Area Network

Covers a wide geographic area, such as a country or the world

Covers a city or a suburb

Connects computers and devices in a limited geographic area such as an office, building, or group of nearby buildings

Uses wired, cable, or wireless connections to link a household’s digital devices

Uses short-range wireless technology to connect an individual’s personal electronics like cellphone, PDA, MP3 player, notebook PC, and printer

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NetworksNetworks

Client/ServerConsists of clients, which are computers that request

data, and servers, which are computers that supply dataFile servers act like a network-based shared disk driveDatabase servers store data but don’t store programsPrint servers connect one or more printers and schedule

and control print jobsMail servers manage email

Peer-to-PeerAll computers on the network communicate directly with

each other without relying on a serverFor fewer than 25 PCs

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NetworksNetworksPeer-to-Peer (continued)

Cheaper than client/server since servers are typically more expensive than PCs

There are often problems with knowing who has the current version of documents and files

Too slow for use in larger officesLegal considerations

Downloading copyrighted material without paying violates U.S. copyright laws

Server-based online file sharing sites such as Napster have been shut down

Peer-to-Peer file-sharing sites such as Kazaa, Grokster, and Gnutella have been more difficult to control since there is no central server to shut down

So publishers are suing individual downloaders instead

Watch out! Don’t download illegally!

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NetworksNetworks Intranets, Extranets, VPNsIntranets, Extranets, VPNs

IntranetsAn organization’s private network that uses the

infrastructure and standards of the internet and the webExtranets

Private internets that connect not only internal personnel but also selected suppliers and other strategic parties

Virtual Private NetworksPrivate networks that use a public network, usually the

internet, to connect remote sites

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NetworkNetwork ComponentsComponents

ConnectionsWired – twisted-pair, coaxial cable, or fiber-opticWireless – infrared, microwave (Bluetooth), broadcast

(Wi-Fi) or satelliteHosts & Nodes

Host: the central computer that controls the networkNode: a device that is attached to the network

PacketsThe format for sending electronic messagesA fixed-length block of data for transmission

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NetworkNetwork ComponentsComponents

ProtocolsThe set of conventions governing the exchange of data

between hardware and/or software components in a communications network

Built into the hardware or software you are usingGovern the packet design and transmission standardsExamples are:

TCP/IP for LANs and internet AppleTalk for older Mac networks SIP for Voice over IP (VoIP) CDMA for cellphones IPX for older Novell networks

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NetworkNetwork PacketsPackets

TCP/IP Packets carry four types of information Sender’s address (source IP number) Address of intended recipient (destination IP number) Number of packets the original data was broken into

This happens because the amount of data the PC is sending can be much larger than the space in a single packet

So the data has to get broken up in one or more packets Then the packets have to be assigned a number like 1 of 6, 2 of 6,

3 of 6, 4 of 6, 5 of 6, and 6 of 6 Packet number and sequence info for each packet

Packets may arrive out of order (1, 6, 3, 2, 5, 4 for example) This information is used to resequence the packets and put them

back in the correct order (1, 2, 3, 4, 5, 6) so they can be read

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NetworkNetwork DevicesDevices

Daisy ChainHub

Switch

BridgeGatewayRouter

Backbone

Used in peer-to-peer networks – direct connections from one PC to the next

Used in small LANs to connect PCs and LAN segments to each other. Forwards to all ports

Used in larger, busy LANs – faster than hubs because it forwards only to correct destination

Used to connect two networks of the same typeConnects two networks of different typesConnects multiple LANs together. Routers are

the internet backboneThe main route that connects all the gateways,

routers, and other computers in an organization

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NetworkNetwork TopologiesTopologies

Bus – all nodes are connected to a single wire or cableRing – all nodes are connected in a continuous loopStar – all nodes are connected through a central host

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NetworkNetworkPacket Collision SchemesPacket Collision Schemes

Collisions happen when two data packets are going opposite directions on shared media

Ethernet – deals with collisionsAll devices send data at onceCollisions happen regularlyData is simply resent until it arrives

Token ring – avoids collisionsDevices take turns sending dataToken is sent around the ringWait to get the token, then send data

$$$ Pricier than Ethernet

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Wired Communications MediaWired Communications Media

Communications media carry signals over a communications pathTwisted-Pair Wire

2 strands of insulated copper wire twisted around each other Twisting reduces interference (crosstalk) from electrical signals Data rates are 1 – 128 Megabits per second

Coaxial Cable Insulated copper wire wrapped in a metal shield and then in an

external plastic cover Used for cable TV and cable internet electric signals Carries voice and data up to 200 megabits per second

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Wired Communications MediaWired Communications Media

Communications media continuedFiber-optic cable

Dozens or hundreds of thin strands of glass or plastic that transmit beams of light, not electricity

Can transmit up to 2 gigabits per second More expensive than twisted-pair or coax Lighter and more durable than twisted-pair or coax More difficult to tap into than twisted-pair or coax

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Wired Communications MediaWired Communications Mediafor the homefor the home

Ethernet Pull Cat5 cables through the house (yourself or contractor) Connect to PC’s Ethernet network interface card (nic) For several PCs, get a hub or switch to connect them all 10 or 100 megabits per second

HomePNA Uses existing telephone wiring and jacks Requires HomePNA nic in your PC Speeds of 10 – 240 megabits per second

Homeplug Uses existing home electrical lines Speeds of 14 megabits per second

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Wireless Communications Wireless Communications MediaMedia

Electromagnetic spectrum of radiation is the basis of all telecommunications signals Includes the longest radio waves (9 kHz) and audio waves (sound), up

through gamma rays that come from nuclear decay (thousands of gigahertz)

Radio-frequency spectrum is the part of the electromagnetic spectrum that we use for radio communication

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Wireless Communications MediaWireless Communications MediaBandwidthBandwidth

Narrowband (or Voiceband)Used for regular telephone communicationsTransmission rate < 100 kilobits per second

Medium BandUsed for long-distance data transmission or to

connect mainframe and midrange computersTransmission rate 100 kb to 1 megabit per second

BroadbandFor high-speed data and high-quality audio and videoTransmission rate 1 megabit per second to 100

megabits per secondUS households get 4 – 5 MB while Japanese get 100

MB per second

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Wireless Communications MediaWireless Communications Media

Infrared TransmissionSends signals using infrared lightFrequencies are too low to see (1-4 Mbits per second)

Broadcast RadioAM/FM, CB, ham, cellphones, police radioSends data over long distances using a transmitter and a

receiverMicrowave Radio

Superhigh frequency radio waves (1 gigahertz)Requires line-of-sight transmitters and receivers

Communications Satellites

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Wireless Communications MediaWireless Communications Media

Communications Satellites These are microwave relay stations in orbit around the earth -

Uplinking: transmitting a signal from ground station to a satellite Cover broad service area Cost $300 million to $700 million each + launch costs Can be placed at different heights: GEO, MEO, LEO

GEO – geostationary earth orbit 22,300 miles up above earth Always above equator

MEO – medium-earth orbit 5,000 – 10,000 miles up

LEO – low-earth orbit 200 – 1,000 miles up Has less signal delay than GEO, MEO satellites

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Wireless Communications MediaWireless Communications MediaGPSGPS

Global Positioning System24 earth-orbiting satellites continuously transmitting timed

radio signalsEach satellite circles earth twice each day at 11,000 miles

upGPS receivers pick up transmissions from up to 4 satellites

and pinpoint the receiver’s locationAccurate within 3 – 50 feet, with a norm of 10 feet accuracyGPS receivers contain map files that are displayed based

on the GPS position to guide usersMany GPS receivers have speech chips, too

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Wireless Communications MediaWireless Communications MediaOne-wayOne-way PagersPagers

One-way pagers are radio receivers that receive data sent from a special radio transmitterRadio transmitter sends out signals over the special

frequencyPagers are tuned to that frequencyWhen a particular pager hears its own code, it receives

and displays the messageDiscussion Question: Why do airplane rules require you to turn off pagers and cellphones during flight?Answer: Pilots use radar and radio to determine their position and communicate with ground control. Pager and cellphone signals use radio, too, and competing signals can interfere with each other

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Wireless Communications MediaWireless Communications MediaLong-Distance WirelessLong-Distance Wireless

Two-way pagers: Blackberry and Treo1G: First Generation Cellular

Analog cellphonesDesigned for voice communication using a system of

hexagonal ground-area cells around transmitter-receiver cell towers

Good for voice – less effective for data due to handing off2G: Second Generation Cellular

Use same network of cell towers to send voice and data in digital form over the airwaves

Required digital receivers on original analog celltowers

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Wireless Communications MediaWireless Communications Media2G Wireless2G Wireless

There are two competing, incompatible standardsCDMA – Code Division Multiple Access

Transmission rates 14.4 kilobits per second Used by Verizon and Sprint

GSM – Global System for Mobile Communications Transmission rates of 9.6 kilobits per second Used by Cingular and T-Mobile, as well as Western Europe,

Middle East and Asia US GSM and European GSM use different frequencies

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Wireless Communications MediaWireless Communications Media2.5G Wireless2.5G Wireless

Data speeds of 300–100 kilobits per secondGPRS – General Packet Radio Service

An upgrade to 2.5G Speeds of 30 – 50 kilobits per second

EDGE is Enhanced Data for Global Evolution A different 2.5G upgrade Speeds of up to 236 kilobits per second

6-32

Wireless Communications MediaWireless Communications Media3G Wireless3G Wireless

Third generation wirelessHigh speed data: 144 kilobits per second up to 2

megabits per secondAccept e-mail with attachmentsDisplay color video and still picturesPlay music Two important upgrades:

EV-DO – Evolution Data Only Average speeds of 400 – 700 kilobits per second, peaks of 2

megabits per second UMTS – Universal Mobile Telecommunications System

Average speed of 220 – 320 kilobits per second

Discussion Question: If your cellphone can download and play music, do you still need an i-pod?

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Wireless Communications MediaWireless Communications MediaShort-range WirelessShort-range Wireless

Local Area NetworksRange 50 – 150 feetInclude Wi-Fi (802.11) type networks

Personal Area NetworksRange 30 – 32 feetUse Bluetooth, Ultra wideband, and wireless USB

Home Automation networksRange 100 – 250 feetUse Insteon, Zigbee, and Z-Wave standards

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Wi-Fi (802.11) networksWi-Fi b, a, and g correspond to 802.11b, 802.11a, and

802.11g802.11 is an IEEE wireless technical specification802.11b is older, transmits 11 megabits per second 802.11a is faster than b but with weaker security than g802.11g is 54 megabits per second and transmits 50 ftWi-Fi n with MIMO extends range of Wi-Fi using multiple

transmitting and receiving antennas – 200 megabits per second for up to 150 ft

Warning! Security is disabled by default on Wi-Fi

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Wi-Fi SecurityWhy is it disabled by default?

So non-technical users can get Wi-Fi working more easilyWhy should this bother me?

A person with a $50 antenna can eavesdrop on everything your computer sends over wireless from a block or two away

This is called “wardriving”To read more about this problem, follow these links

http://www.webopedia.com/TERM/W/wardriving.html http://www.wardriving.com/

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Wireless Communications MediaWireless Communications MediaPersonal Area WirelessPersonal Area Wireless

BluetoothShort-range wireless standard to link cellphones, PDAs,

computers, and peripherals at distances up to 30 ftNamed after King Harald Bluetooth, the Viking who

unified Denmark and NorwayTransmits 720 kilobits per secondWhen Bluetooth devices come into range of each other,

they negotiate. If they have information to exchange, they form a temporary wireless network

Bluetooth can also be used to eavesdrop on networksTurn it off on your cellphone unless you need it at that

time

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Wireless Communications MediaWireless Communications MediaPersonal Area WirelessPersonal Area Wireless

Ultra Wideband (UWB)Developed for military radar systemsOperates in 480 megabit per second range up to 30 ftUses a low power source to send out millions of bursts of

radio waves each second100 times as fast as Bluetooth

Wireless USBUSB is the most used interface on PCsThe wireless version could be a hitRange of 32 ft and maximum data rate of > 480 megabits

per second

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Wireless Communications MediaWireless Communications MediaShort-Range Wireless for HomeShort-Range Wireless for Home

Insteon Combines electronic powerline and wireless technology Can send data at 13.1 kilobits per second with 150 ft range Replaces X10

ZigBee Entirely wireless very power-efficient technology Can send data at 128 kilobits per second with 250 ft range

Z-Wave Entirely wireless power-efficient technology Can send data at 127 kilobits per second to range of 100 ft Allows you to remotely program your house!

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Cyberthreats, Hackers, & Cyberthreats, Hackers, & SafeguardsSafeguards

Problem: internet was begun to foster collaboration among universities and scientists. They trusted each other. No security was built into the internet.

Problem: the internet is open-access and is used by some people who are not trustworthy, who take advantage of the lack of built-in safeguards.

Problem: Most people connect to the internet and use their computers in LANs. All it takes is one computer on a LAN that has been compromised for all computers on it to be vulnerable.

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Denial of Service AttacksConsist of making repeated requests of a computer or

network device, thereby overloading it and causing legitimate requests to be ignored

Used to target particular companies or individualsWorms

A program that copies itself repeatedly into a computer’s memory or disk drive

May copy itself so much it crashes the infected computerFamous worms include: Code Red, SQL Slammer,

Nimda, MyDoom, SasserPrimarily target PCs running Microsoft Windows

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VirusesA deviant program that hides on a floppy, hard drive, CD,

or e-mail that causes unexpected side effects such as destroying or corrupting data

Viruses self-replicate and try to secretly distribute themselves to other systems

Famous viruses include the “I Love You” virusViruses are published at the rate of about one per dayTo see what the latest ones are, go to

http://www.symantec.com/avcenter/vinfodb.html

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Trojan Horses Programs that pretend to be a useful program such as a

free game or screensaver.Carry viruses or malicious instructions that damage your

computer or install a backdoor or spywareBackdoors and spyware allow others to access your

computer without your knowledge

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How they spreadVia e-mail attachmentsBy infected floppies or CDsBy clicking on infiltrated websitesBy downloading from infected files from websitesThrough infiltrated Wi-Fi hotspotsFrom one infected PC on a LAN to another

What can you do about it?Install anti-virus software and subscribe to the automatic

anti-virus update service

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Hackers are either Computer enthusiasts, people who enjoy learning about

programming and computers (good) People who gain unauthorized access to computers or

networks, often for fun or to see if they can (not good)Crackers

Malicious hackers who break into computers for malicious purposes Script kiddies are technically unsophisticated teenagers who use

downloadable software for perform break-ins Hacktivists are hacker activists who break into systems for a

political purpose Black-hat hackers are those who break into computers to steal or

destroy information or to use it for illegal profit Cyberterrorists attack computer systems so as to bring physical or

financial harm to groups, companies, or nations

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SafeguardsUse antivirus software, and keep it currentInstall a firewall to monitor network traffic and filter out

undesirable types of traffic and undesirable sitesUse robust passwords –

Minimum 8 characters with letters, numbers, characters 4cats is not a good password, but f0UrK@tTz is

Install antispyware softwareEncrypt financial and personal records so only you can

read themBack up your data, so if your PC is attacked and must be

reformatted, you can restore your dataNever download from a website you don’t trustConsider Biometric authentication

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EncryptionThe process of altering readable data into unreadable

form to prevent unauthorized access Uses powerful mathematical ciphers to create coded

messages that are difficult to breakTwo forms:

Private Key encryption means the same secret key is used by both the sender and receiver to encrypt and decrypt a message

Public Key encryption means that two keys are used The public key of the recipient is published and is used by the

sender to encrypt the message The private key of the recipient is secret and is the only way to

decrypt the message

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Future of CommunicationsFuture of Communications

This is a big area of developmentThere is a lot of money to be made from faster and

more secure broadband communicationsAreas of development include

Global high-speed low—orbital satellite networks for rural internet and voice connectivity

4G wireless technologyPhotonics to speed up fiber-optic linesSoftware-defined radioGrid computing

6-1. communications, networks, & safeguards 6.1 from the analog to the digital age 6.2 networks...

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