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Chapter 9

Communications

and Networks

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Communications

What is computer communications? A process in which one computer transfers data,

instructions, and information to another computer(s)

p.9.2 Fig. 9-1

Next

a

a

d

c

b

e

a

a

f

c

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Uses of Communications

Technologies

Voice mail

Fax

E-mail

Chatroom Instant Message

FTP

Newsgroup

Telephony

Videoconference

Groupware Global Positioning

System (GPS)

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share software

share

hardware

Networks

What is a network? A collection of

computers anddevicesconnected by

communicationschannels

Facilitatescommunicationsamong users

Allows users toshare resources

p.9.11

Next

facilitatecommunications

share data and

information

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Networks

What is a local areanetwork (LAN)?

Network that

connects

computers and

devices in a

limited

geographical

area.

Often usesEthernet

protocol

p.9.12 Fig. 9-9

Next

Click to view Web Link

then click LAN

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Networks

What is a node ? Each computer or device on a network

p.9.12

Next

often the nodes are

connected to theLAN via cables

a wireless LAN

(WLAN) is a LAN

that uses no

physical wires

node

node

node

node

node

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Administration

Adding, deleting, and organizing users

and performing maintenance tasks

File management

Locating and transferring files

Networks

What is a network operating system? The system

software that

organizes and

coordinates theactivities on LAN

Also called a

network OS or NOS

p.9.12

Next

Printer management

Prioritizing print jobs and reports sent to

specific printers on the network

Security

Monitoring and, when necessary,

restricting access to network resources

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Networks

What are servers and clients? Server

Controls access to thehardware and softwareon the network

Provides a centralizedstorage are for programs

Dedicated serversperform a specific task

Clients Other computers on the

network

Rely on the server for resources

p.9.14

Next

database server stores andprovides access to a database

network server

manages network traffic

print server manages

printers and print jobs

file server stores and

manages files

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Networks

What is a network topology? The configuration, or physical arrangement, of the

devices in a communications network

Networks usually use combinations of three topologies

p.9.16

Next

ring

star

bus

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Networks

What is a bus network? Consists of a single

central cable, towhich allcomputers and

other devicesconnect

The bus is thephysical cable

The bus is alsocalled thebackbone

Inexpensive andeasy to install

p.9.17 Fig. 9-15

Next

personal

computer

personal

computer

personal

computer

personalcomputer

personalcomputer

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Networks

What is a ring network? A cable forms a

closed ring, or loop,with all computers

and devicesarranged along thering

Data travels from

device to devicearound the entirering

p.9.16 Fig. 9-16

Next

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Networks

What is a star network? All of the devices

connect to a

central

computer/hub All data that

transfers from

one computer to

another passes

through the hub

p.9.17 Fig. 9-17

Next

host

computer

printer file server

personal computer

personal computer

personal computer

personal computer

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Networks

p.9.20

Next

uses TCP/IP

technologies

has a Web server

supports multimedia

Web pages coded in

HTML

accessible via a

Web browser

users can post and update

information on the intranet

by creating and posting a

Web page

An internal networkthat uses Internettechnologies

Generally makecompanyinformationaccessible toemployees andfacilitate working ingroups

Typically alsoincludes aconnection to theInternet

What is an intranet?

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Networks

What is an extranet? Allows customers

or suppliers to

access part of a

company¶s intranet

p.9.20 Fig. 9-18

Next

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Networks

What is a firewall? Hardware and/or software that restricts access to data

and information on a network

p.9.20 Fig. 9-19

Next

personal computer

personal computer

personal computer

personal computer

personal computer

personal computer

personal computer

printer

firewall

corporate

network Internet

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Networks

What is an intelligent home network? Extends the

basic home

network to

include features

such as lighting

control,

thermostat

adjustment, and

a securitysystem

p.9.23

Next

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Communications

Software

What is communications software? Consists of programs that help you establish a

connection to another computer or network

Manages the transmission of data, instructions, and

information

p.9.23

Next

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The Telephone Network

What is a dial-up line? A temporary connection that uses one or more analog

telephone lines for communications

A modem at the sending end dials the telephone

number of a modem at the receiving end

p.9.25

Next

Advantages

Costs no more than

making a regular call

Computers at any two

locations can establish a

connection using

modems and the

telephone network

Disadvantage

Cannot control the quality of the connection because the

telephone company¶s

switching office randomly

selects the line

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What is a dedicated line? A connection that always is

established between two

communications devices

The quality and consistencyof the connection is better

because dedicated lines

provide a consistent

connection

p.9.25

Next

Can be analog or

digital

Digital lines transfer data and information

at faster rates than

analog lines

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bits per second

(bps)


What is transfer rate? The speed with which a line carries data and information

The faster the transfer rate the faster you can send and

receive data and information

Usually are expressed as bits per second (bps)

p.9.26

Next

kilobits per second(Kbps)

megabits per second

(Mbps)

gigabits per second

(Gbps)

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What are popular types of digital dedicated lines? ISDN

DSL

T-carrier

CATV ATM

p.9.26 Fig. 9-25

Next

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Communications

Devices

What is a communications device? Any type of hardware capable of transmitting data,

instructions, and information between a sending

device and a receiving device

Sometimes the device must convert the data,instructions, and information from analog to digital

signals or vice versa

p.9.27

Next

dial-up modems

ISDN and DSL

modems

cable

modems

network

interface cards

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Communications

Devices

What is a modem? A communications device that converts a computer's

digital signals to analog signals before they are

transmitted over standard telephone lines

Sometimes called a dial-up modem

p.9.28

Next

Click to view

Web Link

then click

Modems

modulate

To change into

an analog signal

demodulate

To convert an

analog signal into a

digital signal

mo + dem

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DSL modem

Sends and receives

digital data to a DSL line

Communications

Devices

What is a digital modem? One that sends and receives data and information to

and from a digital telephone line such as ISDN or

DSL

p.9.28

Next

ISDN modem

Also called an ISDN adapter

Sends and receives digital data to

an ISDN line

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Communications

Devices

What is a cable modem? A modem that sends and receives data over the cable

television (CATV) network

Currently muchfaster than a

dial-up modemor ISDN

Usually attachesto a USB port or a port on a

network interfacecard

p.9.29 Fig. 9-28

Next


then click Cable Modems

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Communications

Devices

What is a network interface card (NIC)? A card you insert into

an expansion slot of a

personal computer or

other device, enablingthe device to connect

to a network

p.9.29 Fig. 9-29

Next


then click Network Interface Cards

NIC for desktop

computer

NIC for notebookcomputer

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Communications

Channel

What is a channel? The communications path between two devices

p.9.31

Next


then click Bandwidth

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twisted pair cable

twisted pair cable twisted pair wire

Physical Transmission

Media

What is twisted-pair cable? Consists of one or more twisted pair wires bundledtogether

Each twisted pair wire consists of

two separateinsulated copper wires

Twisted together to reduce noise

Noise is anelectricaldisturbance thatcan degradecommunications

p.9.33 Fig. 9-33

Next

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coaxial cable

plastic outer coating

woven or braided wire

insulatingmaterial

copper wire


Media

What is coaxial cable? Consists of a single copper wire surrounded by at least

three layers

Often called

coax Often used

for cable

television

wiring

p.9.33 Fig. 9-34

Next

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fiber-optic cable betweenfloors of a building

cable

contains

many optical

fibers

outer

covering

jacket


Media

What is fiber-optic cable? Contains a core of dozens or hundreds of thin strands of

glass or plastic

Uses light to transmit signals

Each strandis called an

optical fiber

Thin as

a human

hair

p.9.34 Fig. 9-35

Nextprotective

coating

glass

cladding

opticalfiber core

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transmitter

sends thebroadcast radio

signal

Wireless Transmission

Media

What is broadcast radio? A wireless transmission medium that distributes radio

signals through the air over long distances such asbetween cities, regions, and countries and shortdistances such as within an office or home

Slower and more susceptible to noise than physicaltransmission media

p.9.35

Next

receiver

accepts the broadcast

radio signal

must have an antenna that

is located in the range of

the signal

transceiver

both sends and receives

signals from wireless

devices

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Media

What is cellular radio? A form of broadcast radio that is used widely for mobile

communications, specifically wireless modems and

cellular telephones

Acellular telephoneis a telephone

device that uses

radio signals to

transmit voice and

digital datamessages

p.9.36 Fig. 9-39

Next

mobile telephone

switching office

(MTSO)

cell

cell

cell

cell

calling party

in auto

calledparty

public switched

telephone

networkbase station

(microwave

station)

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Media

What is a microwave station? An earth-basedreflective dish thatcontains the equipmentnecessary for

microwavecommunications

Microwaves areextremely high-speedsignals

Line-of-sight towers Must transmit in a

straight line

p.9.38 Fig. 9-40

Next

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Media

What is a communications satellite?

p.9.38 Fig. 9-40

Next

Click to

view video

A space station that receivesmicrowave signals from anearth-based station, amplifiesthe signals, and broadcasts

the signals back over a widearea to any number of earth-based stations

Transmission to asatellite is an uplink

Transmission from asatellite to anearth-based stationis a downlink

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Media

What is infrared (IR)? A wireless transmission

media that sends signals

using infrared light waves

Requires a line-of-sighttransmission

Many computers and

devices have an IrDA port

that enables the transfer

of data using infraredlight rays

p.9.39 Fig. 9-42

Next

Click to

view video

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