Chapter 9
Communications
and Networks
“The hardest thing to learn in life is which
bridges to cross, and which to burn”
Communications
What are computer communications?

Process in which two or more computers or devices transfer data,
instructions, and information via cables and wires or wirelessly
mainframe computers
notebook
computers
smart
phones
servers
Web-enabled
PDAs
GPS
receivers
desktop
computers
mainframe
computers
set-top boxes
Tablet PCs
p. 9.02 Fig. 9-1
Next
Communications
What is needed for successful communications?
sending device
Initiates an instruction to transmit
data, instructions, or information
communications device
Converts or formats the data, instructions, or
information from the sending device into
signals carried by a communications channel
communications channel
A path on which the signals travel
communications device
Next
p.9.2
Receives the signals from the communications
channel and converts or formats them so the
receiving device can understand
the signals
receiving device
Accepts the data, instructions, or information
Uses of Computer Communications
What are some uses of communications technology?
Web
Internet
Instant
Messaging
Web
Folders
p. 9.04
Chat Rooms
E-Mail
Newsgroups
Video
Conferencing
FTP
Fax Machine
or Computer
Fax/Modem
Next
Uses of Computer Communications
What are collaboration and
groupware?

Collaboration is working
with other users connected
to a server


Microsoft’s NetMeeting
allows collaboration
Groupware is software
that allows people
to share
information
p. 9.07 Fig. 9-5
Next
Uses of Computer Communications
What is a global positioning system (GPS)?
Step 1.
GPS satellites orbit
Earth. Every
thousandth of a
second, each satellite
sends a signal that
indicates its current
position to the GPS
server.
Click to view video
Step 2.
A GPS receiver
(such as in a car,
a PDA, a watch,
a handheld
device, or a
collar)
determines its
location on Earth
by analyzing at
least 3 separate
satellite signals
from the 24
satellites in orbit.
Click to view Web Link,
then click GPS below
Chapter 9
p. 9.08 Fig. 9-7
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Networks
What is a network?

Collection of
computers and
devices connected
via communications
devices and
transmission
media
p. 9.11 Fig. 9-9
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Networks
What is a local area
network (LAN)?

Network in limited
geographical area such
as home or office
building

Metropolitan area
network (MAN)
connects LANs in city
or town
Click to view Web Link,
then click LAN below
Chapter 9
p. 9.13 Fig. 9-10
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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
p. 9.14 Fig. 9-11
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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
p. 9.14 Fig. 9-12
Next
Networks
What is a peer-to-peer
network?


Simple network
that connects
fewer than 10
computers
Each computer,
or peer, has equal
capabilities
p. 9.15 Fig. 9-13
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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
bus
ring
star
Next
p.9.16
Networks
What is a bus network?


All computers and
devices connect to
central cable,
or bus
Example of network
topology (layout of
devices in network)

p. 9.16 Fig. 9-15
Popular topologies are
bus, ring, and star
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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
p. 9.16 Fig. 9-16
Next
Networks
What is a star network?


All devices connect to
a central device, called
hub
All data transferred
from one computer to
another passes
through hub
p. 9.17 Fig. 9-17
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Networks
What are network communications technologies?
Specific combinations of hardware and software that allow
the different devices on several types of networks to be
able to communicate
Ethernet
token ring
TCP/IP
Next
p.9.18
WAP
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
p. 9.19
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Communications Software
What is communications software?
Programs that help users
establish connection to
Internet, other network,
or another computer
Programs that help users
manage transmission of
data, instructions,
and information
Programs that provide an
interface for users to
communicate with one
another
p. 9.20
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Communications Over the Telephone Network
What is a dial-up line?

Temporary connection
using telephone line for
communications


p. 9.22 Fig. 9-23
Costs no more than
making regular call
Computers at any
two locations can
establish a
connection using
modems and
telephone network
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Communications Over the Telephone Network
What is a dedicated line?
Always-on connection
between two
communications
devices


p. 9.23 Fig. 9-24
Four types are ISDN
line, DSL, T-carrier
line, and ATM
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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
cable
modems
dial-up modems
Next
p.9.27
ISDN and DSL
modems
network
interface cards
Communications Devices
What is a network card?


Adapter card or PC
Card that enables
computer or device
to access network
Sometimes called
network interface
card (NIC)
p. 9.27 Fig. 9-29
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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
Click to view Web Link,
then click Routers
below Chapter 9
p. 9.28 Fig. 9-31
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Communications Devices
What is a hub?

Device that provides central
point for cables in network
Click to view animation
p. 9.28 Fig. 9-32
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Communications Channel
What is a channel?

Transmission media on which data travels in
communications system
Transmission media
are materials capable of
carrying one or more
signals
p. 9.31
Bandwidth is amount of
data that can travel
over channel
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Physical Transmission Media
What is physical transmission media?

Wire, cable,
and other
tangible
materials used
to send
communications
signals
p. 9.32 Fig. 9-35
Transfer Rates for Various Types of LANs Using Physical Transmission Media
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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
Coaxial cable is often used for cable television wiring
p. 9.32 Fig. 9-36—9-37
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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)
p. 9.33 Fig. 9-38
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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
p. 9.33 Fig. 9-39
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Wireless Transmission Media
What are broadcast radio and cellular radio?


Broadcast radio
distributes radio
signals over long
and short distances
Cellular radio
is form of
broadcast radio
used for mobile
communications
Click to view Web Link,
then click Cellular
Communications
below Chapter 9
p. 9.34 Fig. 9-40
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Wireless Transmission Media
What is a microwave station?


Earth-based
reflective
dish used for
microwave
communications
Must transmit in
straight line with
no obstructions
p. 9.35 Fig. 9-41
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Wireless Transmission Media
What is a communications satellite?

Space station
that receives
microwave signals
from earth-based
station, amplifies
signals, and
broadcasts signals
back to any
number of earthbased stations
p. 9.36 Fig. 9-42
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Direction of transmission
Simplex channel – transmits
data in one direction only
Half-duplex channel –
transmits data in both
directions but only one
direction at a time
Full-duplex channel –
transmits data in both
directions at the same time
Chapter 9 Complete