Transcript What is a computer network?

9.1 The Need for a Computer Network
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What is a computer network?
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A system of interconnected computers,
peripherals and communication devices that
can exchange information and share
resources
The function becomes more extensive
when the computer is networked
9.1 The Need for a Computer Network
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Advantages of networking
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Better communication
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Users can communicate with each other by e-mail,
instant messaging or file transfer.
Communication through network
9.1 The Need for a Computer Network
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Advantages of networking
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Hardware sharing
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Networks allow users to share hardware resources
such as hard disks, printers and scanners.
The shared equipment can be better utilized and
saves the cost of repetitive hardware.
Sharing of hardware on a network
9.1 The Need for a Computer Network
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Advantages of networking
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Centralized data management
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Users can share centralized data files stored on a
network server.
Each user can access up-to-date and identical
information all the time.
Sharing of centralized file on a network
9.1 The Need for a Computer Network
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Advantages of networking
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Software sharing
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Application software can be shared among
computers on a network simultaneously.
A network licence makes multiple access to the
software legally.
9.1 The Need for a Computer Network
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Advantages of networking
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Software sharing
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Features of network licenses
Some are based
on the number of
computers on
which the
licensed program
can run.
The cost of a network
licence is usually lower
than the total cost of
individual software
licences.
Some may set a
limit on the
number of users
who use the
program
simultaneously.
There is no
need to carry
out the
installation on
each computer.
9.1 The Need for a Computer Network
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Advantages of networking
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Internet access service sharing
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Users can access the Internet via a computer
network with a single Internet service account.
Sharing of Internet access
9.1 The Need for a Computer Network
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Advantages of networking
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Efficient backup
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The information on individual computers can be
backed up and stored on a server via the network.
The backup files can be used to recover lost
information stored originally in a computer which
is found out-of-order.
9.1 The Need for a Computer Network
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Advantages of networking
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Efficient backup
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The information on individual computers can be
backed up and stored on a server via the network.
The backup files can be used to recover lost
information stored originally in a computer which
is found out-of-order.
9.2 LANs and WANs
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Networks are categorized according to the
area they cover.
local area network
(LAN): a network that
connects computers
within a relatively
limited area
wide area
network (WAN): a
network that
spans a wide
geographical area
9.2 LANs and WANs
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Local Area Network (LAN)
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Consists of networked computers, or
workstations, shared peripheral devices,
communication devices and links
Peer-to-peer and client/server are
two common architectures of LANs
9.2 LANs and WANs
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Two examples of peer-to-peer
network
Sharing printing service
Sharing Internet access
9.2 LANs and WANs
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Example of client/server network
A client/server network
9.2 LANs and WANs
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Comparison between peer-to-peer
network and client/server network
Peer-to-peer network
Client/server network
It is a network of
workstations without a
server, where all the
workstations can
communicate directly with
each other.
Client workstations are
connected to a central
server, or a host computer.
Each computer can access The clients can access the
the resources shared by all resources stored on the
the other peer workstations. server.
9.2 LANs and WANs
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Comparison between peer-to-peer
network and client/server network
Peer-to-peer network
A large and heavily loaded
network will result in
noticeable drop in
performance at each
workstation.
Client/server network
It provides better security
controls and network
services in a large-scale
network environment.
The set-up cost is relatively The set-up cost is relatively
low.
high.
It is usually found in small
companies and homes.
It is ideal for medium or
large organizations.
9.2 LANs and WANs
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Wide Area Network (WAN)
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A communication network that consists of
two or more remote LANs, which are
connected via public communication
channels
The Internet is the largest WAN in the
world
LANs are
interconnected
to form a WAN.
9.2 LANs and WANs
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Wide Area Network (WAN)
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A communication network that consists of
two or more remote LANs, which are
connected via public communication
channels
The Internet is the largest WAN in the
world
LANs are
interconnected
to form a WAN.
9.3 Connect to a Computer Network
 Network Interface Card (NIC)
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The hardware component needed to connect
the computer to a network
Each NIC has a medium access
control (MAC) address which is used
to identify the computer on the network.
Can be classified by the types of
connectors, expansion buses or the size of
its bandwidth.
Criterion for
classification
Examples
Bandwidth
10 Mbps, 100 Mbps and 1000 Mbps
Expansion bus
ISA, PCI, PCMCIA and USB
Connector
AUI, BNC and RJ-45
9.3 Connect to a Computer Network
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Different types of connectors
BNC
RJ-45
AUI
9.3 Connect to a Computer Network
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Different types of expansion bus
ISA
PCMCIA
PCI
USB
9.3 Connect to a Computer Network
 Five common types of connecting
devices
Switch
• It provides a central
connection point for
cables on a network.
• Typically, one or more
computers are connected
to a switch with network
cables. The switch in turn
connects to a server.
Hub
• It provides a central
connection point for
cables on a network.
• It can be a low cost
substitution for a switch
in a network which has a
low transmission traffic.
9.3 Connect to a Computer Network
 Five common types of connecting
devices
Repeater
• It amplifies the received signals, removes unwanted
noises and then sends the amplified signals to the
connected device.
• It overcomes the problem of signal attenuation due to
the signal transmission over long distance.
9.3 Connect to a Computer Network
 Five common types of connecting
devices
Bridge
• It is used to interconnect
two distinct LANs of the
same type.
Router
• It translates signals from
different networks.
• It is responsible for the
connectivity between
different types of LANs
and between a LAN and
the Internet.
9.3 Connect to a Computer Network
 Hardware components of
networking
Hardware components of networking
9.3 Connect to a Computer Network
 Network cables
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In a network, computers and other network
devices are usually linked together by
network cables.
Common network cables include:
coaxial cable
optical fibre cable
twisted-pair cable
9.3 Connect to a Computer Network
 Twisted-pair cable
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Widely used in local area networks
Looks similar to a telephone cable and has
a RJ-45 connector on both ends
Two types of twisted-pair cables:
Shielded twisted-pair
(STP) cable
It has a metal wrapper
around each wire to
reduce noise.
Unshielded twisted-pair
(UTP) cable
It does not have metal
shielding. It is a low-cost
substitution for the STP cable.
9.3 Connect to a Computer Network
 Twisted-pair cable
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Several types of UTPs:
Category6 (Cat6)
• maximum data transfer
rate: about 1,000 Mbps
within 100 m distance limit
• commonly used network
cable in a LAN construction
9.3 Connect to a Computer Network
 Coaxial cable
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It is commonly used for VCR and cable
television connections.
It has a BNC connector on both ends.
9.3 Connect to a Computer Network
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Advantages of the coaxial cable
over the twisted-pair cable
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Has a higher ability to retain the strength
of a transmitting signal over a long
distance
Consists of a copper wire, a sheath of
insulation, a wire mesh that conducts and
shields against interference, and an
outside coating. This strengthened
insulation allows coaxial cable to transmit
more information
9.3 Connect to a Computer Network
 Optical fibre cable
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Made of a bundle of glass threads that
transmit light beams
9.3 Connect to a Computer Network
 Optical fibre cable
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Advantages of optical fibre cables over
twisted-pair cables and coaxial cables:
faster data
transmission
greater signalcarrying capacity
better security
for signal
transmission
reduced
susceptibility to
noise or
interference from
other devices
more
durable
lighter in
weight
thinner
9.3 Connect to a Computer Network
 Optical fibre cable
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Have replaced coaxial cables in telephone
networks
Disadvantages of optical fibre cables:
The cost is
very high.
A special device is
needed to
convert digital
signals to optical
light beams and
vice versa.
The installation
process is much more
difficult than that of
other network cables.
It is inflexible to
changes once
installed.
9.3 Connect to a Computer Network
 Characteristics of different types of
cables
Twistedpair cable
Coaxial
cable
Optical
fibre cable
Transmission 10 Mbps,
speed
100 Mbps
up to 200
Mbps
100 Mbps to
several Gbps
Transmission electrical
signal
electrical
optical
Cost
cheap
expensive
more
expensive
Topology
star, ring
bus
star, ring
9.3 Connect to a Computer Network
 Wireless networks
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Wireless local area network (WLAN)
uses high-frequency radio waves to
transmit and receive data without the
limitations of cables
Access point: a
device that allows a
wireless device to
communicate to other
wireless devices by
radio frequencies or to
a wired network
9.3 Connect to a Computer Network
 Wireless networks
A WLAN connects to a wired LAN by
means of an access point.
9.3 Connect to a Computer Network
 Features of WLANs
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Provide mobility.
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A wireless device
must equip with a
wireless network
interface card or a
wireless node
Wireless network interface
card
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Become an alternative for wired LANs
Set-up cost for a large-scale wireless LAN
is high and it poses security risks on the
whole network
9.3 Connect to a Computer Network
 Network topology
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The logical layout in which the computers
and other devices are connected together
Each computer or device on the network is
called a node
Common network topologies include:
bus
topology
star
topology
ring
topology
9.3 Connect to a Computer Network
 Bus topology
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All computers and other devices connect
to a single central cable known as the bus
Data is transmitted between the nodes
through the bus
Bus topology
9.3 Connect to a Computer Network
 Features of bus topology
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Set-up is simple and inexpensive
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Widely used in LAN constructions
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Very flexible as they allow computers and
other devices to be attached or detached
from the network, without disturbing the
rest of the network (at any point)
Failure of one device does NOT affect the
rest of the bus network
If the bus fails to work, the whole network
will not function properly.
9.3 Connect to a Computer Network
 Star topology
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All devices on the network are connected
to a central computer or a switch to form
a star
All data transferred from one computer to
another passes through the central
computer
Star topology
9.3 Connect to a Computer Network
 Features of star topology
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Each device connects directly to the
central computer
If one device of the system fails, only that
device will fail to work while other devices
remain unaffected
If the central computer fails, the whole
network will become inoperative
9.3 Connect to a Computer Network
 Ring topology
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All devices on the network are connected
on a circular path that allows data to flow
in one direction only
A computer transmits
data packets to the
computer next to it
until all data packets
arrive at their
destination
Ring topology
9.3 Connect to a Computer Network
 Features of ring topology
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Control data transmission with a tokenpassing scheme
Token:
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Advantages of the token-passing scheme:
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A control signal passing from one device to the
next
Only the token-holding device is allowed to
transmit data
Ensures only one device can transmit data at a
time
Ensures no data collisions occur
If any device fails, no device can transmit
data properly as the token cannot be passed
around the ring any longer.
9.3 Connect to a Computer Network
 Intranet and Extranet
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Intranet: a local area network built with
Internet technology, forming a private,
small-scale Internet inside an organization.
Features of the intranet:
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Applications such as internal e-mail systems,
message boards, web sites and videoconferencing may be available.
Users can use the web browser, FTP application or
any Internet access tools to retrieve information
from the intranet.
9.3 Connect to a Computer Network
 Intranet and Extranet
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Extranet :a network connection that
allows external users to access the
intranet through the Internet and the
public telecommunication channels
Connection is usually protected by a
firewall
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Extranet
ensures the access is secure and under control
9.3 Connect to a Computer Network
 Network Operating Systems
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Functions of a network operating
system (NOS):
to control
the flow
of data
to manage
network
resources
to maintain
security
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Two components of a NOS:
network
server
software
network
client
softwar
e
9.3 Connect to a Computer Network
 Basic functions of a network server
software
control the access to the
server’s resources such
as hard disks, printers,
Internet access and
application software
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track and record
the activities of
users with log
files
manage user
accounts
Basic functions of a network client
software
gather login
information
access the shared
resources on the
network
9.3 Connect to a Computer Network
 Some examples of network
operating systems developed by
different companies
Company
Network client
software
Network server
software
Apple
Mac OS X
Mac OS X Server
IBM
OS 2 Warp
OS 2 Warp Server
Microsoft
Windows XP
Professional
Windows .NET
Server
Novell
Netware 6
Netware 6
9.3 Connect to a Computer Network
 Server and client software
components
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The server and client software
components do not have to match each
other
Network client
software
• Windows 98
• NT Workstation
• XP Professional
allow to
access
Network server
software
• Windows NT Server
• Windows 2003 Server
• Linux
• UNIX
• Novell Netware
9.3 Connect to a Computer Network
 Server and client software
components

The server and client software
components do not have to match each
other
Network client
software
• Windows 98
• NT Workstation
• XP Professional
allow to
access
Network server
software
• Windows NT Server
• Windows 2003 Server
• Linux
• UNIX
• Novell Netware
9.4 Common Services Available in a
Network Environment
 Services available on different
servers
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Different server computers provide
different services on a client/server LAN.
The servers include:
File servers
Print servers
Application servers
9.4 Common Services Available in a
Network Environment
 File server
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Shares programs and data files stored on
its hard disk with other workstations
Workstations
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access the network
File server shares programs
hard disk just as
and data with workstations in
they do for their
a LAN
local hard disks
process data or execute
programs using their own
processor and main memory
9.4 Common Services Available in a
Network Environment
 Print server
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Manages the printing services
Receives print jobs from workstations and
then forwards them to a network printer
Functions of a print server:
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Maintains the print queue which stores print jobs
until they are processed successfully
Able to keep track of the printing activities and bill
the users accordingly
It can be a file server, or a workstation in the
network
9.4 Common Services Available in a
Network Environment
 Print server
A print server manages print jobs
by a print queue.
9.4 Common Services Available in a
Network Environment
 Application server
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It runs a specific application software
package and forwards the processed
results to the requested workstations.
The interaction cycle of an application
server and its client
9.4 Common Services Available in a
Network Environment
 Application server

It runs a specific application software
package and forwards the processed
results to the requested workstations.
The interaction cycle of an application
server and its client