Transcript Computer Networks - Deyes High School

COMPUTER NETWORKS
GCSE ICT
LEARNING OUTCOMES:
 Understand
what a network is.
 Identify types of networks.
 Explore types of network formations.
NETWORKS
Networks are two or more machines linked
together to share files
 At home, your computer might be connected to its
own printer and scanner. This works well as you
are the only person who will be using them. A
computer which isn't connected to a network is
known as a 'stand-alone'
 In a school or an office, it would cost a lot of
money for every computer to have its own printer
and for the majority of the time, like your printer
at home, it wouldn't be used.
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NETWORKS
By joining computers together to form a network,
they are able to share one printer.
 This means that more money can be spent buying
a better quality printer and that the printer is
being used much more of the time.
 As well as sharing hardware, a network allows
computers or users to share software and
data.
 A computer connected to a network is known as a
'work-station'
 The computers can be connected by cables or
Wireless.
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There are two main types of Network…
LAN and WAN
LAN – LOCAL AREA NETWORK
WorkStation 3
Server
Printer
WorkStation 1
WorkStation 2
Scanner
LAN – LOCAL AREA NETWORK
When the computers are fairly close to one
another say, in a single office building, the
computers then form a Local Area Network
(LAN).
 Once the computers are connected together into a
LAN, many people (users) can share and use the
same resources at the same time.
 They can share files, software, hard disks
and peripherals such as a printer or CDROM.
 Users can also use the LAN to communicate with
each other by e-mail. Data can be transmitted
very quickly between networked computers.
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LAN – LOCAL AREA NETWORK
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A file server is used to store each person's data and
their files. This means that people can log onto any
machine on the network and access their files.
They are not restricted to just one machine. Another
advantage of having all of the files stored in one place
is that a back up copy of every users files can be
made easily.
To log onto a LAN, you usually need a user name
and password. The user name identifies you to the
file server so that it can 'serve' you the correct files.
Networks: LANs
What hardware do you need for a LAN network?
•File Server : Runs software,
stores files.
•Terminals : Workstations that
give network access.
•Print Server : Queues up all
print jobs from users in network.
•Cables (wire/optic) : Sends data
•Switch/Router – direct data
packets
ADVANTAGES OF NETWORKS
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Programs can be shared - software packages can be
installed onto the file server and accessed by all individual
workstations at the same time. This reduces cost,
maintenance and makes upgrades easier.
You can access your work from any workstation on
the network. Very handy if you have to change computer
every time you go to a different classroom.
Data can be shared by all users at the same time. Many
people can access or update the information held on a
database at the same time. Thus information is up to date
and accurate.
Users can communicate with others on the network by
sending messages and sharing files.
MORE ADVANTAGES…
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Individual workstations do not need a
printer, one high quality printer can now be
shared by everyone, thus cutting costs.
Networks provide security. A user must have
the correct Password and User ID in order to be
able to access the information on the network.
Private areas on the network can be set up
that allows each user to store their personal files.
The only other person who can access these files
is the 'system administrator' who looks after the
network.
DISADVANTAGES OF NETWORKS
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Networks can be expensive to set up. They often
involve taking up floors and ceilings to lay hundreds of
metres of cables - the File Server needs to be a powerful
computer, which often means that it is expensive. Plus
they need expert staff to look after them.
Networks are vulnerable to security problems.
Hackers, disgruntled employees or even competitors might
try to break into the system to read or damage crucial
information.
If the main File Server breaks down, then the whole
system becomes useless and no-one can carry on working.
As the number of users increase on the network, the
performance of the system can be affected and things
start to slow down.
TASK 1 - EXAM QUESTIONS
You have Five minutes to answer the following:
 Q1-Identify two disadvantages of setting up
and running a computer network (2 marks)
 Q2-Discuss the different methods used to
prevent people from gaining unauthorised
access to a computer network (3 marks)
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EXAM ANSWERS
Q1- Any two of the following points:
 -Networks can be expensive to install in terms of
cable and hardware such as routers and switches
 -Usually need specialist staff to run the network
 If the network is busy, accessing files and
hardware might be slower than a standalone
machine
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EXAM ANSWERS
Q2- Any two of the following points:
 Username
 Password
 Access rights
 Firewall
 Restrict physical access e.g. lock doors, security
cameras
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TASK TWO - COMPLETE THE WORKSHEET:
Fill in in the Gaps
 List Advantages and Disadvantages
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Network Topologies…
BUS NETWORK
This is one method of connecting computers
together and is the simplest one to connect
together.
 A single cable joins all of the workstations,
printer, file server and other components
together.
 At each end of the bus is a 'terminator'. This is a
piece of hardware which prevents signals
bouncing back and forth (echoes).
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ADVANTAGES AND DISADVANTAGES
Advantages
 Easy to install.
 Easy to add extra workstations.
 Uses less cable than a Star network.
 Best choice for temporary networks.
Disadvantages
 If there is a problem with the central cable, the entire
network stops working.
 If there are a lot of workstations on the network, data can
travel slowly.
 Data collisions can happen as the network becomes busy.
 Low security - every workstation can see all of the data in
the network.
 Limited cable length and a maximum number of
workstations.
RING NETWORK
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In a ring network layout, all of the computers are
connected to one another in a circle. The data
passes from one computer to the next one and
then all the way around the ring layout until it
reaches the destination computer.
ADVANTAGES AND DISADVANTAGES
Advantages
 Transmission of data is fairly simple as it only travels in one
direction.
 No data collisions.
 Extra computers can be added easily with little effect on
performance - although you have to shut down the network to
be able to do this.
Disadvantages
 If a single machine is switched off, the network doesn't work.
 If a cable breaks, the network doesn't work.
 Data must pass through every computer until it reaches its
destination. This can make it slower than other network
layouts.
 If there are any problems with the network, they can be
difficult to identify the cause.
STAR NETWORK
In a star network layout, each workstation
is connected by its own cable directly to the
server. Star networks are usually the layout
of choice in schools and offices because they
tend to be the most reliable of the
topologies.
ADVANTAGES AND DISADVANTAGES
Advantages
 Star networks are very reliable. If one connection fails, it
does not affect other users.
 Very few data collisions as each workstation has its own
cable to the server.
 Good security - no workstation can interact with another
without going through the server first.
Disadvantages
 The most expensive network layout to install because of the
amount of cables needed.
 Installing the network usually needs experts to set it up.
 Extra hardware such as hubs and switches may be needed.
 If the server crashes or stops working then nobody will be
able to access their files or use the network.
TASK 3 - EXAM QUESTIONS
The Manager of a Hospital is thinking about
installing a network so that different departments
can share data..
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Write the minimum of a paragraph what network
topology the hospital should buy. You should
think in terms of cost, installation, efficiency and
security. Explain your reasons.
INTRANETS AND EXTRANETS
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Intranet is similar to the
Internet but is internal to
an organisation. An
INTERNAL NETWORK
Users access the Intranet
through a user name and
password
Enables users to share
information and
communicate via
electronic messaging
View pages like webpages
– like an internal website
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An Extranet can be
accessed from outside the
Intranet by authorised
users via a user name and
password.
A NETWORK that can
accessed EXTERNALLY.
E.g. VLE
INTRANETS AND EXTRANETS
The Manager of a Hospital is thinking about
employees having access to the network internally
via an intranet and externally via an extranet.
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Write the minimum of a paragraph what the
advantages and disadvantages of having an
intranet and extranet. Give reasons.
WIRELESS NETWORKS
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Describe what is meant by the term WIFI.
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What are the main components of WIFI?
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Explain (in as much depth as possible) how a
wireless network works.
List and describe Advantages and Disadvantages
of using a Wireless network
TASK 4 - COMPLETE THE WORKSHEET

Complete the work sheet describing Advantages
and disadvantages of Network Topologies
WAN – WIDE AREA NETWORK
WAN – WIDE AREA NETWORK
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Many modern companies have offices, shops or
factories in various locations around the country,
and for large corporations, across the world. Even
though staff work in different places, they often
need to be able to access the same information no
matter where they are.
It would not be possible to connect computers in
different buildings or countries together using
LAN cables.
WAN – WIDE AREA NETWORK
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Computers on LANs in one building can be
connected to computers on LANs in another
building usually through the telephone system,
often using a modem. They can also be
connected via fibre optic cables or satellite.
By linking LANs together, the network is no
longer local to one building, it is now spread over
a wide area. It is known as a Wide Area Network
(WAN)
The largest WAN in existence is the Internet?
Networks: WANs
What extra hardware do you need for a WAN
network?
• Modems : To connect up to a
telephone system (instead of cable).
How a modem
works…
PROTOCOLS
Computers on a network must all have a way of
being able to 'talk' or 'communicate' with one
another and they do this by following a protocol.
A protocol is a set of rules which define:
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How to establish communication between the
machines
The format of any data which is to be exchanged
between the machines
How errors in the data will be detected
How errors will be corrected
Methods of compressing the data to transmit it faster
and more efficiently
How the connection between the machines is to be
terminated
PROTOCOLS
The protocol that is used on most LANs and the
Internet is known as the TCP/IP protocol.
If any computers on the Internet are not using this
standard then they will not be able to communicate
with others that are.
Another extremely common protocol in use on the
web is HTTP - Hyper Text Transfer Protocol. which
is what most page URLs start with. See what you
can find out about this.
RESEARCH
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Use the internet and your books to write an
explanation of TCP/IP
Use the internet and your books to write an
explanation of HTTP
TASK 5 - COMPLETE THE WORKSHEET

Complete the task 5 worksheet using the internet
or your books to find the description of the
different Network Components.
NETWORK COMMUNICATIONS
GCSE ICT
LEARNING OUTCOMES:
 Understand
the term Bandwidth.
 Learn the different ways we can
communicate on a network.
 Know how we connect to the Internet and
what is required.
THE TELEPHONE NETWORK IN
COMPUTING
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A modem is required for a computer to
communicate over telephone lines
Data is converted from digital to analogue and
then back again
The speed at which data is transmitted and/or
received is measured in bits per second
NETWORK COMMUNICATIONS
Bandwidth tells us the
rate at which data can
be transmitted down the
communications line in
a given period of time.
The current standard is
56,000 bits per second
FAST BANDWIDTH
SLOW BANDWIDTH
NETWORK COMMUNICATIONS
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The higher the bandwidth, the quicker the data
will flow along the line…
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Web pages loaded quicker.
Multimedia is downloaded faster.
Internet connection is faster.
Less network traffic.
Quicker response time.
NETWORK COMMUNICATIONS
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There are a number of connection types available
to us when we want to access the services from
the Internet… Each one has a different
BANDWIDTH.
PSTN : Public Switched Telephone Network.
 ISDN : Integrated Services Digital Network.
 ADSL : Asymmetric Digital Subscriber Line.
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PUBLIC SWITCHED TELEPHONE
NETWORK
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PSTN for short.
Uses traditional telephone system to allow access to the
Internet. This is the telephone system used for making
day-to-day telephone calls
It is the main reason why computers have become so
popular in recent years!
Low Bandwidth
Dial Up Connection.
INTEGRATED SERVICES DIGITAL
NETWORK
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ISDN for short.
Has a greater range of frequencies than PSTN, at least as
twice as fast. Typical transfer rate of 128,000 bits per
second
Data is transmitted simultaneously
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Special connection and modem required
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Supports Videoconferencing, faxes and voice applications.
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ASYMMETRIC DIGITAL SUBSCRIBER
LINE
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ADSL for short.
Usually referred to as ‘Broadband.’
Is permanently switched on, no need for dial up to get a
connection. Uses telephone lines to transmit data at very
fast speeds (512,000 bits per second)
ADSL modem and splitters required to separate telephone
signal from the ADSL signal
Has a high bandwidth.
You can still make telephone calls when surfing the web!
CONNECTING TO THE INTERNET
Single users can connect to the Internet. Special
Hardware and Software is required to allow people
to access the Internet. As well as an electronic
device (PC, Tablet etc.) you need:
 Internet Service Provider.
 Browser Software.
 Telecommunications line e.g. ISDN, ADSL.
 Modem/Broadband Modem/ISDN adapter.
NETWORK SECURITY
GCSE ICT
LEARNING OUTCOMES:
 Understand
how to secure a network.
 Understand Dangers posed to networks.
 Identify different types of security.
THE BASICS
There are many ways to secure a network ranging from complicated
around the clock security services to a simple lock and key.
Security is now a major item in every network it can mean the difference
between life and death for some businesses.
Example: The play station network, was taken down by hackers and
some of their customers credit card details stolen. This was all because
the security on this network was weak or unprotected.
NETWORK SECURITY
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Physical security means that the hardware of
the network is protected from theft and kept safe.
Access security means that there is a limit to
the amount of access a user has to the
information held on the network.
Data security means that there are measures
taken to prevent the loss of data held on the
system.
WAYS OF PROTECTING YOU AND YOUR
COMPUTER AND NETWORK
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There are now many company's offering users different
packages to protect and prevent your computer and or
network.
Most of theses packages detect, quarantine and delete
infected files And some monitor the websites accessed and
links to other servers and or networks.
TYPES OF VIRUS
There are many types of virus for example there are:
 Worm virus
 Trojan houses virus
 Boot sector virus
 Macro virus
 Root kit virus
 Time bomb virus
 Memory resistant virus
 Polymeric virus
PHYSICAL SECURITY FOR A NETWORK
As well as security software you will need to protect
your network in more conventional ways i.e. lock and
key.
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Fire protection- fire doors, smoke doors, fire proof safes est.
Alarms-rooms containing the server should be alarmed
Locks-all rooms with services inside and have limited
recorded access to them
Visibility-avoid putting computers on ground flour and where
they are visible to passes bye
DATA SECURITY
There are many ways to prevent loss of your data:
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Password protecting your data.
You can also set the information as read only so it can not be
tampered with.
You can also back up data either as a hard copy of saved
digitally.
You will also need to keep a log on access to your server, so
that if the worst happens you can trace the perpetrator.