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6

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Communications, Networks, &
Safeguards

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6.1 From the Analog to the Digital
Age

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•
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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6.1 From the Analog to the Digital
Age


•
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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6.1 From the Analog to the Digital
Age


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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6.1 From the Analog to the Digital
Age

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6.1 From the Analog to the Digital
Age

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6.1 From the Analog to the Digital
Age


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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6.1 From the Analog to the Digital
Age


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 Networks

Category

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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Components of Networks

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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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6.3 Wired Communications Media


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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6.3 Wired Communications Media


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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6.4 Wireless Communications
Media

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6.4 Wireless Communications
Media

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6.4 Wireless Communications
Media


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

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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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

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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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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

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

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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.4 Wireless Communications
Media


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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6.5 Cyberthreats, Hackers, &
Safeguards


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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-
Hill Companies, Inc. All rights reserved.