GIT 335 Lecture 61 Arizona State University Department of Technology Management GIT 335 Computer...

GIT 335 Lecture 6 1

Arizona State University

Department of Technology Management

GIT 335Computer Systems Technology

Lecture 6

Communications

Dr. Thomas Schildgen, Professor

GIT 335 Lecture 6 2

Lecture 6

Introduction to Information Technology

Content taken from the McGraw Hill Textbook Chapter 6

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Communications, Networks, & Safeguards

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From the Analog to the Digital Age

• Analog signals use variation of a wave form to send information• In FM signals the Frequency is varied (Modulated)• In AM signals the Amplitude is varied (Modulated)• Radios send signals this way• Light works this way• Hearing and phones work this way• Modems work this way

GIT 335 Lecture 6 5


GIT 335 Lecture 6 6


• Digital signals send data in terms of 1s and 0sDigital signals send data in terms of 1s and 0s• The signal goes up and down abruptly because the only The signal goes up and down abruptly because the only

values that matter are 0 and 1 and the timing of when they values that matter are 0 and 1 and the timing of when they occuroccur

• Computers use digital signalsComputers use digital signals• Newspaper photographs are digital since they are made up Newspaper photographs are digital since they are made up

of little dotsof little dots

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

voice phone lines

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From the Analog to the Digital Age• 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 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– Did 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!

GIT 335 Lecture 6 10

Networks

• 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 computers– Person 1 saved their document to a floppy disk– Then 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


NetworksNetworks

• Since the days of “sneakernet”, networks Since the days of “sneakernet”, networks have become standard. They enable us to:have become standard. They enable us to:– Share peripheral devices such as laser printers– Share programs and data– Use e-mail and other communication programs– Backup critical information because it is stored

centrally– Access shared databases


Networks

• 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


Networks

• Client/ServerClient/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

• Peer-to-PeerPeer-to-Peer– All computers on the network communicate directly with

each other without relying on a server– For fewer than 25 PCs


Networks

• Peer-to-Peer (continued)Peer-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 offices

• Legal considerationsLegal 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 have been more difficult to control since there is no central server to shut down

– So publishers are suing individual downloaders instead


Networks Intranets, Extranets, VPNs

• IntranetsIntranets– An organization’s private network that uses the

infrastructure and standards of the internet and the web

• ExtranetsExtranets– Private internets that connect not only internal

personnel but also selected suppliers and other strategic parties

• Virtual Private NetworksVirtual Private Networks– Private networks that use a public network, usually the

internet, to connect remote sites


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NetworkNetwork ComponentsComponents

• ConnectionsConnections– Wired – twisted-pair, coaxial cable, or fiber-optic– Wireless – infrared, microwave (Bluetooth), broadcast

(Wi-Fi) or satellite• Hosts & NodesHosts & Nodes

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

• PacketsPackets– The format for sending electronic messages– A fixed-length block of data for transmission


NetworkNetwork ComponentsComponents

• ProtocolsProtocols– The 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 using– Govern the packet design and transmission standards– Examples 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


NetworkNetwork PacketsPackets

• TCP/IP Packets carry four types of informationTCP/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


NetworkNetwork DevicesDevices

• Daisy Daisy

ChainChain• HubHub

• SwitchSwitch

• BridgeBridge• GatewayGateway• RouterRouter

• BackboneBackbone

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

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

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

• Used to connect two networks of the same typeUsed to connect two networks of the same type

• Connects two networks of different typesConnects two networks of different types

• Connects multiple LANs together. Routers are Connects multiple LANs together. Routers are the internet backbonethe internet backbone

• The main route that connects all the gateways, The main route that connects all the gateways, routers, and other computers in an organizationrouters, and other computers in an organization


NetworkNetwork TopologiesTopologies

• Bus – all nodes are connected to a single wire or cableBus – all nodes are connected to a single wire or cable• Ring – all nodes are connected in a continuous loopRing – all nodes are connected in a continuous loop• Star – all nodes are connected through a central hostStar – all nodes are connected through a central host

Bus

Ring

Star


NetworkPacket Collision Schemes

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

• Ethernet – deals with collisionsEthernet – deals with collisions– All devices send data at once– Collisions happen regularly– Data is simply resent until it arrives

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


Wired Communications MediaWired Communications Media

• Communications media carry signals over a Communications media carry signals over a communications pathcommunications 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


Wired Communications Media

• Communications media continuedCommunications media continued– Fiber-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


Wired Communications Mediafor the home

• EthernetEthernet– 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

• HomePNAHomePNA– Uses existing telephone wiring and jacks– Requires HomePNA NIC in your PC– Speeds of about 320 megabits per second

• HomeplugHomeplug– Uses existing home electrical lines– Speeds of 200 megabits per second


Wireless Communications Media

• Electromagnetic spectrum of radiation is the basis of all Electromagnetic spectrum of radiation is the basis of all telecommunications signalstelecommunications 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


Wireless Communications MediaBandwidth

• Narrowband (or Narrowband (or Voiceband)Voiceband)– Used for regular telephone communications– Transmission rate 1.5 megabits per second or less

• Medium BandMedium Band– Used for long-distance data transmission or to connect

mainframe and midrange computers– Transmission rate 100 kb to 1 megabit per second

• BroadbandBroadband– For high-speed data and high-quality audio and video– Transmission rate 1.5 megabits per second to 1 gigabit per

second or more• US households get 4 – 5 MB while Japanese get 63 – 64 MB US households get 4 – 5 MB while Japanese get 63 – 64 MB

per secondper second


Wireless Communications Media• Infrared TransmissionInfrared Transmission

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

second)• Broadcast RadioBroadcast Radio

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

and a receiver• Cellular RadioCellular Radio

– Form of broadcast radio– Widely used in cell phones and wireless modems– Does not interfere with other cellular phone calls


Wireless Communications Media

• Microwave RadioMicrowave Radio– Superhigh-frequency radio waves (2.4 gigahertz

or higher)– Requires line-of-sight transmitters and receivers

• Communications SatellitesCommunications Satellites– “sky stations”– Microwave relay stations in orbit around the earth– Launch costs between $50 and $400 million– Basis for Global Positioning Systems (GPS)


Wireless Communications MediaWireless Communications Media

• Communications SatellitesCommunications 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


Wireless Communications MediaGPS

• Global Positioning SystemGlobal Positioning System– 24 to 32 earth-orbiting 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– GPS receivers contain map files that are displayed

based on the GPS position to guide users– Many GPS receivers have speech chips too


Wireless Communications MediaWireless Communications MediaOne-wayOne-way PagersPagers

• One-way pagers are radio receivers that One-way pagers are radio receivers that receive data sent from a special radio receive data sent from a special radio transmittertransmitter– 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


Wireless Communications MediaWireless Communications MediaLong-Distance WirelessLong-Distance Wireless

• Two-way pagers: Blackberry and TreoTwo-way pagers: Blackberry and Treo• 1G: First Generation Cellular1G: First Generation Cellular

– 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 due to handing off

• 2G: Second Generation Cellular2G: 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 cell towers


Wireless Communications MediaLong-Distance Wireless

• 3G: Third Generation Cellular– Broadband technology– Based in the U.S.– Carry data at high speeds

• 4G: Fourth Generation Cellular– A nationwide 4G network in development– Uses the WiMax (Worldwide Interoperability for

Microwave Access) standard– Hope to provide broadband to rural areas


Wireless Communications MediaWireless Communications Media2G Wireless2G Wireless

• There are two competing, incompatible There are two competing, incompatible standardsstandards– CDMA – 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


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

• Data speeds of 300–100 kilobits per Data speeds of 300–100 kilobits per secondsecond– GPRS – 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


Wireless Communications MediaWireless Communications Media3G Wireless3G Wireless

• Third generation wirelessThird generation wireless– High speed data: 144 kilobits per second up to 2

megabits per second– Accept e-mail with attachments– Display color video and still pictures– Play 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


Wireless Communications Media4G Wireless

• Fourth generation wireless– The latest standard– Uses WiMax (Worldwide Interoperability for

Microwave Access) standard– Transmission at a range of 6-10 miles– Transmission speed up to 20 mbits/sec – Transmits farther than Wi-Fi– Two varieties: one fixed/one mobile– Hoped to provide broadband in rural areas– Several communications firms developing a

nationwide 4G network


Wireless Communications MediaWireless Communications MediaShort-range WirelessShort-range Wireless

• Local Area NetworksLocal Area Networks– Range 100 – 228 feet– Include Wi-Fi (802.11) type networks

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

USB

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


Wireless Communications MediaShort-range Wireless

• Wi-Fi (802.11) networks– Wi-Fi b, a, and g correspond to 802.11b, 802.11a, and

802.11g– 802.11 is an IEEE wireless technical specification– 802.11b is older, transmits 11 megabits per second – 802.11a is faster than b but with weaker security than g– 802.11g is 54 megabits per second and transmits 50 ft– Wi-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


Wireless Communications MediaShort-range Wireless

• Wi-Fi SecurityWi-Fi Security– Why is it disabled by default?

• So non-technical users can get Wi-Fi working more easily

– Why 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 this link

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


Wireless Communications MediaPersonal Area Wireless

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

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

unified Denmark and Norway– 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

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

time


Wireless Communications MediaPersonal Area Wireless

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

of radio waves each second– 100 times as fast as Bluetooth

• Wireless USB– USB is the most used interface on PCs– The wireless version could be a hit– Range of 32 ft and maximum data rate of > 480 megabits

per second


Wireless Communications MediaShort-Range Wireless for Home

• InsteonInsteon– Combines electronic power line and wireless technology– Can send data at 13.1 kilobits per second with 150 ft

range– Replaces X10

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

• Z-WaveZ-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!


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 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.



• Denial of Service Attacks– Consist 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 individuals

• Worms– A program that copies itself repeatedly into a computer’s

memory or disk drive– May copy itself so much it crashes the infected computer– Famous worms include: Code Red, Nimda, Klez, Sasser,

Bagle– Primarily target PCs running Microsoft Windows



• Viruses– A 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” virus– Viruses are published at the rate of about one per day– To see what the latest ones are, go to

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



• 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 spyware

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



• How they spread– Via e-mail attachments– By infected floppies or CDs– By clicking on infiltrated websites– By downloading from 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 anti-virus software and subscribe to the automatic

anti-virus update service



• 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



• Safeguards– Use antivirus software, and keep it current– Install a firewall to monitor network traffic and filter out

undesirable types of traffic and undesirable sites– Use robust passwords:

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

– 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



• Encryption– The 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– Two 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

GIT 335 Lecture 61 Arizona State University Department of Technology Management GIT 335 Computer...

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