This document provides an overview of chapter 7 from the textbook Discovering Computers 2008. The chapter discusses computer communications and networks. It describes the components needed for successful communications including sending/receiving devices, communications devices, and transmission media. The chapter also covers network architectures like client/server and peer-to-peer, topologies like bus and star, standards such as TCP/IP and Wi-Fi, and transmission media including physical cables and wireless options. Uses of communications technology and common devices are also outlined.

1. Discovering Computers 2008
Chapter 7
Communications
and Networks
1

2. 2
Chapter 7 Objectives
Discuss the components required for
successful communications
Explain the purpose of
communications software
Identify various sending
and receiving devices
Describe various types of lines for
communications over the telephone network
Describe uses of computer communications
Describe commonly used
communications devices
List advantages of using a network
Discuss different ways to set up
a home network
Differentiate among client/server,
peer-to-peer, and P2P networks
Identify various physical and wireless
transmission media
Describe the various network
communications standards

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Communications
What are computer communications?
Process in which two or more computers/devices transfer
data, instructions, and information

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Communications
What is needed for successful communications?
Sending Communications Communications
device — initiates device — connects channel — media
instruction to the sending device to on which data,
transmit data, the communications instructions, or
instructions, or channel information travel
information
Communications Receiving
device — connects device — accepts
the communications transmission of data,
channel to the instructions, or
receiving device information

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Uses of Computer Communications
What are some uses of communications technology?
Instant
Internet Web E-Mail Messaging
Internet
Chat Rooms Newsgroups
Telephony
Fax Machine
Web Video
FTP or Computer
Folders Conferencing
Fax/Modem

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What are wireless messaging services?
TEXT MESSAGING
Limit messages to usually fewer
than 300 characters
Text messaging Mobile to Mobile
allows users to send Mobile to E-Mail
and receive short Web to Mobile
text messages Mobile to Provider: use common
(SMS) on a phone short code – 4 or 5 digit num
or PDA assigned to specific content or
wireless service provider, followed by
message – e.g. vote for TV prg
contestant

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What are wireless messaging services?
PICTURE MESSAGING
Video messaging: to send short video clips (about 15
seconds)
Smart phones & PDAs with picture/video messaging
also called MMS (multimedia message service)
Camera phone, video phone
Mobile to Mobile
Mobile to E-Mail
Picture messaging
allows users to send
graphics, pictures,
video clips, sound
Video
files, and short text
messaging
messages

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What are wireless messaging services?
WIRELESS INSTANT MESSAGING (IM)
Real-time Internet communications service that allow
wireless mobile devices to exchange messages with
one or more mobile devices or online users
Some WISP provide IM service: smart phone &
PDAs can be used to send & receive instant messages
AOL Instant Messenger (AIM),
Yahoo! Messenger
Mobile to Mobile Wireless instant
Mobile to PC messaging allows
Web to Mobile wireless mobile
devices to exchange
messages

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Uses of Computer Communications
What are wireless Internet access points
and cybercafés?
Wireless Internet access
point allows wireless
connection to Internet in
public location
Hot sport, 3G network
Cybercafé is coffee house
that provides computers
with Internet access – some
are also hot spots

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Uses of Computer Communications
What is a global positioning system (GPS)?
Navigation system consists of one or more earth-based
receivers that accept & analyze signals sent by satellites in
order to determine the geographical location
GPS receiver: handheld, mountable or embedded device
containing an antenna, a radio receiver and a processor –
many include screen display showing an individual’s
location on a map

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Uses of Computer Communications
What is a global positioning system (GPS)?
Step 2.
Step 1. A GPS receiver
GPS satellites orbit (such as in a car, a
Earth. Every wearable device, a
thousandth of a smart phone, a
second, each satellite handheld device,
sends a signal that or a collar)
indicates its current determines its
position to the GPS location on Earth
receiver. by analyzing at
least 3 separate
satellite signals
from the 24
satellites in orbit.

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Uses of Computer Communications
What are collaboration and groupware?
Collaboration or work
online is working with other
users connected to a server
A document management system
provides for storage and
management of a company’s
documents
Groupware is software that
allows people work together
and share information over a
network

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Uses of Computer Communications
What are voice mail and web services?
Voice mail is voice message
converted to digital form
Web services describe standardized
software that enables programmers
to create applications that
communicate with other remote
computers over the Internet or on an
internal business network
doesn’t specific require prg lang,
OS, or Web browser
By sending properly formatted
XML (eXtensive Markup
Language) files to Web services

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NETWORK

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Networks
What is a network
network?
Collection of
computers and devices
connected via
communications
devices and
transmission media
What are the advantages of using a network?

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Networks
What is a local area network (LAN and a
LAN)
metropolitan area network (MAN
MAN)?
Network in limited geographical area such as
home or office building
Wireless LAN (WLAN
WLAN)
Metropolitan area network (MAN) connects LANs
in city or town

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Networks
What is a wide area
network (WAN)?
Network that covers
large geographic
area using many
types of media
Internet is world’s
largest WAN

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NETWORK ARCHITECTURES
peer-to-peer &
P2P

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Networks
What is a client/server
network?
One or more computers
act as server and other
computers, or clients,
access server

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Networks
What is a peer-to-peer
network?
Simple network
that connects
fewer than 10
computers
Each computer,
or peer, has equal
capabilities

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NETWORK TOPOLOGIES
bus, ring & star
(layout of devices in network)

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Networks
What is a bus network?
All computers and devices connect to central
cable or bus

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Networks
What is a ring network?
Cable forms closed
ring, or loop, with all
computers and devices
arranged along ring
Data travels from
device to device
around entire ring, in
one direction

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Networks
What is a star network?
All devices connect to
a central device (hub
or switch)
All data transferred
from one computer to
another passes
through hub or switch

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Networks
What is an intranet?
Internal network that uses Internet technologies
Makes information accessible to employees
Typically includes connection to Internet
Extranet allows customers or suppliers to access
part of company’s intranet

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Intranet

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NETWORK COMMUNICATIONS
STANDARDS
Ethernet, Token Ring, TCP/IP, 802.11 (Wi-Fi), Bluetooth,
UWB, IrDA, RFID, WiMAX, WAP

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Network Communications Standards
What are Ethernet and token ring?
Ethernet technology allows computers to contend
for access to network
If two computers send data at same time, a collision occurs and
computers must send the data again
Token ring technology controls access to network
by requiring devices to pass a special signal,
called token

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Network Communications Standards
What are TCP/IP and 802.11 (Wi-Fi)?
TCP/IP (Transmission Control Protocol/Internet
Protocol) technology transmits data by breaking it up
into small pieces, or packets
Commonly used for Internet transmissions
802.11 (Wi-Fi) is family of standards for wireless LANs

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Network Communications Standards
What is Bluetooth?
Short-range radio waves transmit
data between Bluetooth devices

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Network Communications Standards
What are UWB, IrDA, RFID, WiMAX, and Wireless
Applications Protocol (WAP)?
UWB IrDA
specification allows specification allows
data to be transferred data to be transferred Worldwide Interoperability
wirelessly via short-range wirelessly via infrared for Microwave Access (WiMAX
radio waves light waves or 802.16)
standard that specifies how wireless
devices communicate over the air
Radio Frequency in a wide area
Identification (RFID) Wireless Applications
uses radio signals to communicate Protocol (WAP)
with a tag placed in an object allow wireless mobile devices
to access Internet

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Communications Software
What is communications software?
System software
Programs that help users
establish connection to
Internet, other network,
or another computer Programs that help users Application
manage transmission of software
data, instructions,
and information
Programs that provide an
interface for users to
communicate with one
another
Application software for communication:
e-mail, FTP, Web browser, newsgroup/message
boards, chat rooms, instant messaging, video
conferencing, Internet telephony,…

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Communications Over the Telephone Network
Dial-Up Lines, Dedicated Lines

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Communications Over the Telephone Network
What is the public switched
telephone network (PSTN)?
Worldwide telephone
system that handles
voice-oriented
telephone calls

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Communications Over the Telephone Network
What is a dial-up line?
Temporary connection using telephone line for
communications
Computers at any two locations can establish a
connection using modems and telephone network
Costs no more than making regular call

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Communications Over the Telephone Network
What is a dedicated line?
Always-on connection
between two
communications
devices

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Communications Over the Telephone Network
Dedicated lines:
5 types:
1.ISDN (Integrated Service Digital Network) line
2.DSL (Digital Subscriber Line), ADSL (Asymmetric …)
3.FTTH & FHHB (Fiber to the Home/Building)
4.T-Carrier line (T1, fractional T1, T3)
5.ATM (Asynchronous Transfer Mode)
ISDN line technique
multiplexing of carrying 3 or more
signals at once through
the same line

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Communications Devices

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Communications Devices
What are examples of communications devices?
Common types are dial-up modems, ISDN and
DSL modems, cable modems, wireless modems,
network cards, wireless access points,
routers, and hubs
ISDN and DSL modems send
and receive data from ISDN
and DSL lines

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Communications Devices
What is a dial-up modem?
A dial-up modem converts digital signals to analog signals
and vice versa
Usually in the form of an adapter card

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Communications Devices
What are ISDN (Integrated Service Digital Network)
and DSL (Digital Subscriber Line) modems?
Communications devices that send and
receive digital ISDN and DSL signals
Usually external devices in which one
end connects to a telephone line and the other
end connects to a port on the system unit

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Communications Devices
What is a cable modem?
Sends and receives data
over cable television
(CATV) network
Much faster than dial-
up modem or ISDN;
speed similar to DSL
Sometimes called a
broadband modem
Placed after cable splitter
System unit has network
card – e.g. Ethernet card

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Communications Devices
What is a wireless modem?
Allows access to the Web
wirelessly from a
notebook computer, a
PDA, a smart phone, or
other mobile device
Typically use the same waves used by cellular telephones
Has external or built-in antenna
Available as PC Cards, ExpressCard modules and flash
cards

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Communications Devices
What is a network card?
Is an adapter card, PC Card,
ExpressCard module, USB
network adapter, or flash card
that enables computer or device to
access network
Coordinates the transmission and
receipt of data, instructions &
information to & from the
computer or devices containing
the network card Wireless network card
Sometimes called network
interface card (NIC)

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Communications Devices
What is a wireless access point?
Central
communications
device that allows
computers and
devices to transfer
data wirelessly among
themselves or
wirelessly to a wired
network

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Communications Devices
What is a router?
Connects computers and
transmits data to correct
destination on network
Routers forward data on
Internet using fastest
available path
Some routers have a built-in
hardware firewall

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Communications Devices
What is a hub or switch?
Device that provides central
point for cables in network
Some hubs include routers –
hub receives data from many
directions and then forwards it
to one or more destinations
What are the differences between a hub & a switch & a router?

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Home Networks
What is a home network?
Multiple computers
connected in home
Several types of home
networks
Ethernet — connect
computers via cable
Powerline cable —
use electrical lines in house
Phoneline — use
telephone lines
Wireless Home Network
HomeRF network, Wi-Fi home network

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Communications Channel

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Communications Channel
What is a communications channel?
Transmission media on which data travels in
communications system
Bandwidth is amount of
Transmission media data that can travel
are materials capable of over a communications
carrying one or more channel
signals
Latency is the time it
takes a signal to travel
from one location to
another on a network

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Transmission Media
Transmission media
category
Baseband media Broadband media
transmit only one transmit multiple signals
signal at a time at much faster speed
Download transfer rates are
faster than upload
DSL, cable television Internet
service, satellites,…

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Communications Channel
How is a request sent over the
Internet using a communications
channel?

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Transmission Media
Transmission media
types
Physical transmission media Wireless transmission media
Twisted-Pair Cable, Coaxial Infrared, Broadcast Radio,
Cable, Fiber Optic Cable Cellular Radio, Microwave

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Physical Transmission Media
What is physical transmission media?
Wire, cable and other
tangible materials used to
send communications signals

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Physical Transmission Media
What are twisted-pair cable and coaxial cable?
Twisted-pair cable is used for telephone systems and network cabling
(LAN)
Reduced noise – electrical disturbance that can degrade
communication

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Physical Transmission Media
What are twisted-pair cable and coaxial cable?
Coaxial cable is often used for cable television wiring – long distance
Single copper wire surrounded by at least 3 layers: an insulation
material, a woven or braided metal, a plastic outer coating

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Physical Transmission Media
What is fiber-optic cable?
Capable of carrying
significantly more
data at faster speeds
than wire cables
Less susceptible
to interference
(noise) and, therefore,
more secure
Smaller size (thinner
and lighter)

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Wireless Transmission Media
What is wireless transmission media?
Used when inconvenient, impractical, or impossible to
install cables
Includes Bluetooth and IrDA

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Wireless Transmission Media
What are broadcast radio and cellular radio?
Broadcast radio distributes radio signals over long distances (btw
cities, countries,…) and short distances (within an office or home)
- Flexible & portable but slower, more susceptible to noise
- used by Bluetooth, UMB, HomeRF, Wi-Fi, and WiMAX
* Bluetooth & UMB are alternatives to infrared communications
* Hot spots use Wi-Fi & WiMAX networks
Cellular radio
is form of broadcast radio used for
mobile communications – wireless
modems & cellular telephones (use high-
frequency radio waves to transmit voice
& digital data messages)
- 1G, 2G & 3G

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Wireless Transmission Media
What is a microwave station?
Earth-based reflective dish contains antenna, transceivers
and other equipments for microwave communications
Microwave: radio waves at high-speed signal transmission
(fixed wireless)
Must be transmitted in
straight line with no
obstructions

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Wireless Transmission Media
What is a communications satellite?
Space station that receives microwave
signals from earth-based station, amplifies
(strengthens) signals, and broadcasts
signals back to any number of earth-based
stations (microwave stations, smart phones
& GPS) - uplink down link
Air navigation, television and radio
broadcast, & Internet connections use
communications satellites
Satellite Internet connection needs a
satellite dish & a satellite modem card

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Summary of Communications and Networks
Communications terminology
and applications
Various communications
devices, media, and procedures
How to join computers into a network
Chapter 7 Complete