mcgraw-hill 6-1. 6 mcgraw-hill communications, networks, & safeguards

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Communications, Networks, & Safeguards

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6.1 From the Analog to the Digital Age

© 2011 The McGraw-Hill Companies, Inc. All rights reserved.

• Digital• Computers use digital signals--0s and 1s, off and on.• All the data that a computer processes is a series of 0s

and 1s.• Each signal is a bit.

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• Analog• But most phenomena in life are analog.• Analog signals use wave variations.• Sound, light, and temperature are analog forms.• Traditional TV and radio use analog signals.• Humans’ vision operates in analog mode.

But analog data can be converted into digital form. Even though digital data is not as exact as analog data, it is easier to manipulate.


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For data transmission over telephone lines and cables, modems are needed to convert analog data into digital data that computers can use.

Modem is short for modulate/demodulate. Modems modulate (convert) a computer’s digital data to analog data, transmit it, then demodulate (reconvert) it back to digital data for the receiving computer.

Modems can convert data by modulating either a analog wave’s amplitude or its frequency.


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Converting Reality to Digital Form--Sampling Tape recorders, voices, and musical instruments are

analog; CDs are digital To burn a CD, the digital recording equipment must

convert from analog to digital The analog-to-digital converter samples the sound and

converts the height of the wave to a number Samples of the sound wave are taken at regular intervals –

about 44,100 times each second Because 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 movies. Movies 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

motion


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6.2 Networks

What’s a Network? A system of interconnected computers, telephones,

and/or other communications devices that can communicate with one another and share applications and data


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6.2 Networks

Benefits of Networks Share peripheral devices, such as printers, scanners, disk

drives Share programs and data Better communications, including email Security of information, because of improved backup

systems Access to shared databases


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6.2 NetworksCategory Description

WAN – Wide Area Network Covers a wide geographic area, such as a country or the world; largest WAN is the internet

MAN – Metropolitan Area Network Covers a city or a suburb

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

HAN – Home Area Network Uses wired, cable, or wireless connections to link a household’s digital devices

PAN – Personal Area Network Uses short-range wireless technology to connect an individual’s personal electronics, such as cellphone, PDA, MP3 player, notebook PC, and printer

Home Automatic Network Relies on very inexpensive, very short-range, low-power wireless technology to link switches and sensors around the house and outdoors


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6.2 Networks

How Networks Are Structured: Two Principal Structures 1. Client/Server

Consists of clients, which are computers that request data, and servers, which are computers that supply data File servers act like a network-based shared disk drive Database servers store data but don’t store programs Print servers connect one or more printers and schedule

and control print jobs Mail servers manage email


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6.2 Networks

How Networks Are Structured: Two Principal Structures (continued) 2. Peer-to-Peer (P2P)

All computers on the network are “equal” and communicate directly with one another, without relying on servers


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6.2 Networks


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6.2 Networks

Intranets, Extranets, & VPNs Intranets—use infrastructure and standards of the

internet and the web, but for an organization’s internal use only

Extranets—similar to intranets but allows use by selected outside entities, such as suppliers

VPNs—virtual private networks: use a public network (usually the internet) plus intranets and extranets to connect an organization’s various sites) but on a private basis, via encryption and authentication; regular internet users do not have access to the VPN’s data and information


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6.2 Networks

Network Components Wired/Wireless Connections

wired = twisted-pair, coaxial cable, fiber-optic cable wireless = infrared, microwave, Wi-Fi, satellite

Hosts and Nodes: Client/server network has a host computer, which controls the network; a node is any device attached to the network.

Packets– fixed-length blocks of data for transmission; reassembled after transmission; a packet is also called a datagram, a segment, a block, a cell, or a frame, depending on the protocol.


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6.2 Networks

Network Components (continued) Network Linking Devices

Protocol—set of conventions, or rules, governing the exchange of data between hardware and/or software components in the network; built into the hardware or software you are using

Hub—Common connection point for devices on a network; has multiple ports and can send to all connected devices

Switch—Device that connects computers to a network; sends only to intended recipients

Bridge—Interface that connects same type of networks Gateway—Interface that connects dissimilar networks


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6.2 Networks

Network Components (continued) Network Linking Devices(continued)

Router—Special computer that directs messages among several networks

Backbone—The main internet highway that connects all networks in an organization; includes gateways, routers, etc.

NIC—Network interface card; inserted in a slot on the motherboard, enables computer to operate as part of a network

NOS—network operating system; the system software that manages network activity


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6.2 Networks

Topologies: Bus, Ring, Star Bus – all nodes are connected to a single wire or cable


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6.2 Networks

Topologies Ring – all nodes are

connected in a continuous loop


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6.2 Networks

Topologies Star – all nodes are

connected through a central host


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6.2 Networks

Packet Collision Schemes (Protocols) Collisions happen when two data packets are going

opposite directions on shared media Ethernet – deals with LAN collisions

All devices send data at once Collisions happen regularly Data is resent until it arrives

Token ring – avoids LAN collisions Devices take turns sending data Token is sent around the ring Wait to get the token, then send data


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6.3 Wired Communications Media

Communications media carry signals over a communications path Twisted-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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Communications media (continued) Fiber-optic cable

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

Can transmit up to 2 gigabits per second Have lower error rate than twisted-pair or coax 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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For The Home Ethernet

Pull Cat5 cables through the house 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 about 320 megabits per second

Homeplug Uses existing home AC electrical lines Speeds of 200 megabits per second


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6.4 Wireless Communications Media

Electromagnetic spectrum of radiation is the basis of all telecommunications signals, wired and wireless Radio-frequency (RF) spectrum is the part of the

electromagnetic spectrum that carries most communications signals


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Bandwidth: range (band) of frequencies that a transmission medium can carry in a given period of time Analog bandwidth is expressed in hertz, digital bandwidth

usually in bits per second (bps) Narrowband (Voiceband): used for regular telephone

communications Transmission rate 1.5 megabits per second or less

Broadband: For high-speed data and high-quality audio and video Transmission rate 1.5 megabits per second to 1 gigabit per

second or more© 2011 The McGraw-Hill Companies, Inc. All rights reserved.

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TC/IP (Ch. 2) is the protocol for getting wired devices connected to the internet

WAP (wireless application protocol) gets wireless handheld devices, such as cellphones, connected to the internet


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Five Types of Wireless Communications Media Infrared Transmission

Sends signals using infrared light Frequencies are too low to see (1-16 Mbits per second)

Broadcast Radio AM/FM, CB, ham, cellphones, police radio Sends data over long distances using a transmitter and a

receiver (up to 2 Mbits per second) Cellular Radio

Form of broadcast radio Widely used in cellphones and wireless modems Transmits voice and digital messages


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Five Types of Wireless Communications Media (continued) Microwave Radio

Superhigh-frequency radio waves (2.4 gigahertz or higher) Requires line-of-sight transmitters and receivers More than ½ of today’s telephones systems use microwave

Communications Satellites Microwave relay stations in orbit around the earth Basis for Global Positioning Systems (GPS) Cover broad service area


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Communications Satellites (continued) Can be placed at different heights: GEO, MEO, LEO

GEO – geostationary earth orbit 22,300 miles above earth; travel at the same speed as the

earth and so appear to us to be stationary Always above equator Transmission delay can make conversations difficult

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

LEO – low-earth orbit 200 – 1,000 miles up Has no signal delay


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Long-Distance Wireless: One-Way Communication GPS (Global Positioning System)

24 to 32 MEO satellites continuously transmitting timed radio signals

Each satellite circles earth twice each day at 11,000 miles up

GPS receivers pick up transmissions from up to 4 satellites and pinpoint the receiver’s location

Accurate within 3 – 50 feet, with a norm of 10 feet accuracy


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Long-Distance Wireless: One-Way Communication (continued) One-way Pagers

One-way pagers are radio receivers that receive data sent from a special radio transmitter Radio transmitter sends out signals over the special frequency Pagers are tuned to that frequency When a particular pager hears its own code, it receives and

displays the message


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 one another.

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Long-Distance Wireless: Two-Way Communications 1G: First-Generation Cellular Service

Analog cellphones Designed for voice communication using a system of

hexagonal ground-area cells around transmitter-receiver cell towers

Good for voice – less effective for data because of handing off

2G: Second-Generation Cellular Service Uses digital signals First digital voice cellular network


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Long-Distance Wireless: Two-Way Communications (continued) 3G: Third-Generation Cellular Service

3G cellphones are more like PDAs Broadband technology Carries data at high speeds High speed data: 144 kilobits per second up to 2.4 megabits

per second Accepts e-mail with attachments Displays color video and still pictures Plays music


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Long-Distance Wireless: Two-Way Communications (continued) 4G: Fourth-Generation Cellular Service

A nationwide 4G network in development Uses the WiMax (Worldwide Interoperability for Microwave

Access) standard May provide broadband to rural areas First 4G phone, the EVO, released in March 2010


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

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Short-Range Wireless: Two-Way Communications Local Area Networks

Range 100 – 228 feet Include Wi-Fi (802.11) type networks Wi-Fi n is the latest and fastest Wi-Fi technology

Personal Area Networks Range 30 – 32 feet Use Bluetooth, ultra wideband, and wireless USB

Home Automation networks Range 100 – 150 feet Use Insteon, ZigBee, and Z-Wave standards


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Short-Range Wireless: Two-Way Communications (continued)

Wi-Fi b, a, g, and n networks Named for variations on the IEEE 802.11 standard

(802.11b, 802.11a, 802.11a) Data ranges: 11 megabits per second up to 126 feet

indoors (Wi-Fi b) to 54 megabits per second up to 120 feet (Wi-Fi a and g)

Wi-Fi n with MIMO extends range of Wi-Fi using multiple transmitting and receiving antennas – 100 - 320 megabits per second for up to 228 ft


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Short-Range Wireless: Two-Way Communications (continued)

Wi-Fi Security 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.” Make sure to turn your Wi-Fi software off when you are not using it.


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Short-Range Wireless: Two-Way Communications (continued) Personal Area Wireless

Bluetooth Short-range wireless standard to link cellphones, PDAs,

computers, and peripherals at distances usually up to 30 ft Transmits up to 3 megabits per second When Bluetooth devices come into range of each other, they

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


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Short-Range Wireless: Two-Way Communications (continued) Personal Area Wireless (continued)

Ultra Wideband (UWB) Developed for military radar systems Operates in 480 megabits per second, range up to 30 ft Uses a low power source to send out millions of bursts of radio

waves each second Wireless USB

USB is the most used interface on PCs Range of 32 ft and maximum data rate of 480 megabits per

second; used in game controllers, printers, scanners, cameras, MP3 players, hard disks, and flash drives


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Short-Range Wireless: Two-Way Communications (continued) Short-Range Wireless for Home

Insteon Combines electronic power line and wireless technology Can send data at 13.1 kilobits per second with 150 ft range

ZigBee Entirely wireless sensor 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


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6.5 Cyberthreats, Hackers, & Safeguards

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 criminals 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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Cyberthreats Denial of Service Attacks

Consist of making repeated requests of a computer or network device, thereby overloading it and denying access to legitimate users

Used to target particular companies or individuals


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Cyberthreats (continued) Worms (Malware)

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

May copy itself so much it crashes the infected computer Primarily target PCs running Microsoft Windows


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Cyberthreats (continued) Viruses (Malware)

Deviant program that hides on a disk, in an e-mail, or in a web link that causes unexpected effects such as destroying or corrupting data

Viruses are released at the rate of about one per day To see what the latest ones are, go to

www.symantec.com/avcenter/vinfodb.html


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Cyberthreats (continued) Trojan Horses (Malware)

Programs that pretend to be a useful program such as a free game or a screensaver but that carry viruses or malicious instructions that damage your computer or install a backdoor or spyware

Backdoors and spyware allow others to access your computer without your knowledge


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Cyberthreats (continued) How they spread

Via e-mail attachments By infected disks By clicking on infiltrated websites By downloading infected files from websites Through infiltrated Wi-Fi hotspots From one infected PC on a LAN to another

What can you do about it? Install antivirus software and subscribe to the

manufacturer’s automatic antivirus update service


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Cyberthreats (continued) Cellphone Malware

Spread via internet downloads, MMS attachments, and Bluetooth transfers

Usually show up disguised as applications such as games, security patches, add-on functionalities, erotica, and free programs

Protect your phone: Turn off Bluetooth discoverable mode Check security updates to learn about filenames to

watch out for Install security software


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Cyber Villains Hackers are either

Computer enthusiasts, people who enjoy learning about programming and computers

People who gain unauthorized access to computers or networks, often for fun or just to see if they can

Two types: Thrill-seeker hackers: do it for the challenge White-hat hackers: do it to expose security flaws that can be

fixed


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Cyber Villains 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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Online Safety Use antivirus software, and keep it current Install a firewall to monitor network traffic and filter out

undesirable types of traffic and undesirable sites Don’t use the same password for multiple sites Don’t give out any password information Use robust passwords:

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


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Online Safety (continued) Install antispyware software Encrypt financial and personal records so only you can

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

reformatted, you can restore your data Never download from a website you don’t trust Consider biometric authentication


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Online Safety (continued) Biometrics: science of measuring individual body

characteristics Used in security devices Examples; hands, fingerprints, iris recognition, face

recognition, voice recognition Now available on laptops


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Online Safety (continued) Encryption

Process of altering readable data into unreadable form to prevent unauthorized access Uses powerful mathematical ciphers to create coded

messages that are difficult to break Unencrypted messages are known as plain text Encrypted text is known as cybertext Either private keys or public keys are used to encrypt

and send and then to receive and decrypt messages


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Online Safety (continued) 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 recipient’s public key is given to the sender to encrypt the message; the receiver uses a private key to decrypt it


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