Communications and networks (NHẬP môn điện TOÁN SLIDE)

Chapter 9
Communications and
Networks

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Computing Essentials 2012: Making IT Work for You

Introduction
• We live in a truly connected society.
• Increased connectivity potentially
means increased productivity,
especially in business.
• You will learn more about the
concept of connectivity and
the impact of the wireless
revolution in this chapter.

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Communications
• Computer communications is the process
of sharing data, programs, and
information between two or more
computers
• Numerous applications depend on
communication systems, including
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–
–
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–

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E-mail
Instant messaging
Internet telephone
Electronic commerce
Global positioning systems (GPS)
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Communications Today

• Connectivity uses computer networks
to link people and resources
• The Wireless Revolution
– Single most dramatic change in
connectivity and communications
has been widespread use of mobile
telephones with wireless Internet
connectivity

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Communication
Systems
• Four
basic elements
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Sending and receiving devices
Communication channel
Connection devices
Data transmission specifications

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Communication
Channels
• Communication channels carry the
data from one computer to another
• Two categories of communication
channels
– Physical connection
– Wireless connection

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Physical Connections
• Ethernet cable
(Twisted pair cable)
ã Coaxial cable
ã Fiber-optic cable

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Wireless Connections
• Radio frequency (RF)
– Wi-Fi (wireless fidelity)
– Bluetooth (short-range)
– WiMax (extends Wi-Fi)
• Microwave
• Satellite
– Global positioning system (GPS)
• Infrared
– Short distances and line of sight

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Communication Channels
Summary

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Connection Device
Signals
• Types
of signals
– Analog

– Digital

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Connection Devices
• Types of modems
– Telephone modem
– DSL
(digital subscriber line)
– Cable modem
– Wireless modem
(WWAN)

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Computing Essentials 2012: Making IT Work for You

Connection Services

• Dial-Up services
– Uses phone lines

• Leased lines
– Replaced by
optical carrier
(OC) lines

• Digital
subscriber line
(DSL)
– Uses phone lines
– ADSL is most
widely used type
of DSL

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• Cable
– Uses existing TV
cable
– Speeds as fast as DSL

• Satellite connection
services
– Use almost anywhere
– Slower than DSL and
cable modem

• Cellular Services

– Use 3G and 4G
cellular network to
provide wireless
connectivity

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Computing Essentials 2012: Making IT Work for You

Connection Costs and
Speeds

• Typical user connection costs,
bandwidth speeds, and comparable
time required to download an image
in the USA

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Bandwidth
• Measurement of the width or capacity
of the communication channel
• Categories
– Voice band (or low bandwidth)
– Medium band
– Broadband
– Baseband

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Protocols
• Communication rules for exchanging
data between computers
• Internet standard: TCP/IP
(Transmission control
protocol/Internet protocol)
– Identification – unique IP address
– Packetization – broken down and
reassembled

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Networks
• A computer network is a communication
system that connects two or more
computers
• Allows exchange of information and
resources

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Computer Networks
•
•

•
•
•
•
•

Node
Client
Server
Directory server
Host
Switch
Network interface
cards (NIC)
ã Network operating
systems (NOS)
ã Network administrator

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Network Types
• Local area network (LAN)

• Home network
• Wireless LAN (WLAN)
• Metropolitan area
network (MAN)
ã Wide area network
(WAN)

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Network Architecture
• Arrangement is called topology
• Types of network topology
– Legacy
• Bus
• Ring

– Current

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ã Star
ã Tree

ã Hybrid
ã Mesh
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Bus Network
• Each device is connected to a
common cable, called a bus or
backbone
• All communications travel along this
bus
• There is no host; messages are
passed device-to-device in a
sequence

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Ring Network
• Each device is connected to two other
devices
• No central file server or computer
ã Useful in a decentralized environment

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Star Network
• Most widely used network topology
for both homes and large businesses
• Each device connects directly to a
central network switch

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Tree Network
• Each device is connected to a central
node, either directly or through
subordinate nodes
ã Also known as a hierarchical network

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Hybrid Network
• Combination of different topologies
• Large organizations have a complex
network of smaller networks
– These smaller networks use a
variety of configurations
– When connected together, they
form a hybrid

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Mesh Network
• Does not use a specific physical
layout, but requires that each node
have more than one connection to
other nodes
• Wireless technologies are frequently
used

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