Transcript Slide 1

Standard Grade Computing
Communications and Networks
What is a Network?
A series of computers linked together
so can send and receive data.
 They are divided into two types:
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Local Area Network
(LAN)
Wide Area Network
(WAN)
Local Area Networks
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Local Area Networks (LANs) operate in
one area, such as an office block, a
factory a school a bank or even a home
The computers are joined together using
cables or wireless transmitters
Advantages of LANs
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users can share peripherals such as hard
drives, printers, and web cameras
users can share data files such as
database files, standard letters and
multimedia presentations
they make it easy to communicate by
sending e-mails
Copper Cabling
Coaxial cabling
 The central cable that
transmits the data is
surrounded by a shield
of copper braiding.
This protects it from
interference and so is
found in in places such
as factories where
there could be a lot of
interference
Copper Cabling
Twisted-pair cabling
 This is a simple type of
cabling made up of
two copper cables. It
is relatively cheap and
can support quite high
transmission speeds,
for example over 100
Mbits per second
Fibre-optic Cables
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Fibre-optic cable is made up of
fine strands of glass that carry
pulses of light
These pulses of light represent
data being transmitted
More difficult to break into the
cable and is more secure
Does not suffer from electromagnetic interference
Transmits data at high speed
Costs more to buy and install
than other types of cabling
Wireless Networking
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Wireless networking transmits data
through the air using radio waves and
microwave frequency radiation
a wireless network is relatively easy to
install, all you need is a
transmitter/receiver and a wireless
Network Interface Card on each
computer on the network
there is no need for any wiring
transmission speeds are very fast
security is a problem, wireless networks
are easy to hack into
Wireless Protocols
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Infrared
communication
 Like
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the TV controls
Bluetooth
 Range
of about 10
metres
 WIFI (Wireless Fidelity
Alliance)
 Range
metres
of about 12-50
Network Interface Card
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A NIC takes the data sent by your
computer on to the network, stores it
in its own memory locations and then
adapts it to make sure that it follows
the communication rules that govern
the network
It takes data coming in from the
network to your computer and passes
it on to the processor
Every device that is connected to the
LAN will need a NIC, e.g.. computer,
printer and scanner
Clients and Servers
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A client is a workstation
on the network
A server is a computer
that has a fast processor
and lots of memory and
is used to
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hold all the data files or the
applications software
organise the clients’ access
to the internet
control the resources the
client workstations can use.
For example printing,
internet access etc
Wide Area Networks
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Wide Area Networks (WANs) connect
computers across large distances
WANs stretch across towns, link up cities
and countries using telecommunications
links
Wide Area Networks
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people can communicate instantly worldwide
they can be used to
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send e-mail
send data files
carry out financial transactions
work from home and still be in contact with the
central office
access information
carry out research
WANs are central to the success of large
businesses
Wide Area Networks
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Telecommunications links
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The communication of information over a
distance using:
 Microwave transmission
 Satellite links
 Optical Fibre
Multi-access Computers
These are powerful computer systems that
enable many users to
access the system at the same time
share the processing power of the system
share the available memory
share the data on the backing storage
Multi-access Computers
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Multi-access computers have many terminals
attached to them
These terminals are made up of keyboards and
monitors that people use to
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interact with the main processor
load data to and from backing storage
display data held on the system
The key point about these terminals is that they
have little or no local processing or memory
How does multi-access work?
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It gives each terminal a slice of the processor’s
time. It goes round the users very quickly, so
quickly that they are not aware that they are
sharing the system with lots of other people
Large organisations such as banks, insurance
companies and mail-order companies as well as
colleges and universities use them to store and
process their data
Security on Networks
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All networks need to have security
measures in place
If they do not then the network can be
hacked into, data deleted, copied or
changed
Physical Security Measures
Physical security measures can prevent
unauthorised people accessing the network
Network
computers with a physical lock
Security locks on the computer rooms
Computers without floppy or CD drives
Software Security Measures
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Authorised users are issued with IDs and
passwords to gain entry to the network
When users log on, the computer system checks
their IDs and passwords with those that it keeps
on file
Some systems use biometric systems to ID
authorised users. They store data about
fingerprints, voices or eyes
Encryption encodes the data held on the system.
This means that if the network is hacked into
then the data is meaningless to the hacker
Text Messaging
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Instant messaging allows you
to send text messages to
people on their PCs
Short text messages can be
sent to and from pagers,
mobile phones, and palmtop
computers
Electronic-mail (e-mail)
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E-mails can be sent anywhere in the world
Mail delivery is very fast
It costs a lot less than surface mail
Web-based e-mail allows you to check your
inbox anywhere there is an internet connection
Multiple copies of a message can be sent easily
E-mail is secure as an ID and password is
needed to access it
Electronic-mail (e-mail)
E-mail problems
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Viruses can be hidden in e-mail
attachments
Lots of spam arrives by e-mail. Spam is
unwanted adverts, special offers and
general junk mail
Netiquette
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Netiquette is a set of rules that govern the
way people behave when using email, or a
network
Netiquette
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DON’T TYPE IN CAPS!
Don’t leave the Subject Field blank
Do not start flame wars
Do not use bad language, always be polite
Use proper English in e-mails.
Do not post unwanted mail or use e-mail
to spam
Email Task
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Set your groupwise password
Send an email to someone in the class saying
hello and giving some information about what
you did at the weekend.
Read any emails you receive.
Forward one of your messages to someone else
in the class.
Customise the party invitation and save.
Send your invitation as an attachment to five
people in the class using BCC
Internet
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A Wide Area Network across the world
The network of networks
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Lots of smaller networks joined together
Accessing the Internet
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To access the internet an internet-ready
computer system is required as follows
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Desktop, laptop and palmtop computers are
suitable
A modem
Telecommunications connection either dialup
or broadband
A browser
An internet service provider
Modem
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It is a device that changes your
computer’s signals into a form that can be
sent down the phone system
Dialup Connection
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It uses a modem and an ordinary phone
line to dial up the number of your ISP that
connects you to the internet
Data is transmitted at a speed of 56
Kilobits per second
Broadband Connection
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A broadband connection is a high-speed
telecommunications link
BT digital subscriber line (ADSL) gives speeds of
maximum 512 Kbps download and 128 Kbps
upload
Cable modems can reach speeds up to 10
Megabits per second
Actual speeds are slower because the cable
bandwidth often has to be shared with other
users
Browser
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A browser is the software that fetches and
displays web pages e.g. Microsoft Explorer
Type in the page address in the address bar
Click on a hyperlink
Favourites remembers where web pages are
You jump back and forward between viewed
pages
History shows which pages that have been
visited
Online / Offline
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Once your computer is connected up and
ready to send and receive information it is
said to be online
When your computer is not ready to send
and receive information it is offline
Internet Service Providers (ISPs)
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To access the internet you need to have an
agreement with an internet service provider
You have to log on to your ISP’s computer to
access the internet
Your ISP
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helps your browser find web pages
gives access to web-based e-mail
provides access to newsgroups and chat rooms.
provide space on their servers to store your own web
pages
How to choose a ISP?
Points to consider
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how
how
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how
much they charge per month
reliable the service is
long you can stay online
efficient the service is
Mobile Internet Technology
This technology uses devices that let you
access the internet while on the move
All of the devices have
mobile phone technology
a mini-browser
internal memory
a processor
Mobile Internet Technology Devices
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Some are phones with a browser – smartphones
Some are palmtops with phone technology built in
They often have features such as
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touch screens
WIMP HCI
mini browser
calendar
a database
a calculator
mobile phone connection to access the internet as well as make
phone calls and send text messages
Services on the Internet
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World Wide Web (WWW) is made up of web
pages that are stored on servers worldwide
E-mail
Newsgroups and take part in discussions on a
whole range of topics
Chat rooms are electronic groups that are less
structured than newsgroups
Search engines look for web pages
Software on the Internet
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There is a wide range of software that you
can download from the internet
They all have different agreements
attached to them
Freeware
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Free software but the author holds the copyright
You can use the software and even make copies
of it and give them away to people
You must not change the software or to sell it
Device drivers for printers and CD-writers are
examples of freeware as are some games
Shareware
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Shareware software comes with a free 30day trial period
After the 30 days you should register and
pay a fee or delete it from your computer
You can make copies of the software and
distribute them to other people
The disadvantage of this system is that it
relies on people’s honesty
Commercial software
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Commercial software is bought across the
counter in shops such as PC World or
through the internet
You are often limited to making one
backup copy or simply are allowed to copy
the software once on to your hard disk
and keep the CD as a backup
Videoconferencing
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Videoconferencing is using a computer network to send
audio and visual data to enable people in distant
locations to have face-to-face meetings
A point-to-point conference connects two people at two
different locations using simple webcams, microphones
and speakers attached to their computers
Multipoint conferencing links several people in distant
locations
Sounds and images are captured by the microphone and
camera. They are then transmitted across the network,
which can either be a LAN, a WAN or even the internet
Advantages of Videoconferencing?
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People who are located in different countries can
have face-to-face meetings where they can
discuss and make decisions
This avoids travelling and staying in hotels,
saving time and money
Teams of workers can be brought together
quickly no matter where they are located
Social Issues
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The internet is a rich source of information
on almost any subject
This information can help you find work,
be successful in school, business and
leisure
Not everyone has access to this
information
Some people are at a disadvantage
Isolation
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People could isolate themselves from
others and spend most of their time
communicating using computers
Over use could lead to people becoming
detached from the world around them.
We should keep a balance between using
networks and keeping in touch with
people face to face
Legal Issues
People sadly use networks to commit crime
 hack into networks and steal or corrupt data
 hack into networks and cause damage by
leaving viruses
 commit fraud such as stealing money from bank
accounts
 break copyright law by illegally transferring
software, data or other files
Privacy
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Some people disregard others’ right to
privacy and use networks to send
unwanted e-mails, chain-mail, adverts,
junk e-mail or spam
Ethical issues
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When we are looking at ethical issues we are
basically looking at right ways and wrong ways
to use networks
Networks are very powerful communication tools
and, used properly, they can bring great benefits
to people and society in general
Used irresponsibly, and for the wrong purposes,
they can spread bad feelings and disinformation,
stir up hatred, be a source of crime and
corruption and generally undermine the bonds
that hold society together
Codes of conduct
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Businesses and organisations have set out
codes of conduct for network users
These codes are called ‘Acceptable Use
Policies’
They are based on the need to
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respect other people, their rights and property
adhere to the law