Download T215A Communication and information technologies

Block 1
Storing and sharing
Arab Open University - Spring 2013
T215A
Communication and
information technologies
1
[1]
• Digital communication and information
technologies have become fundamental to the
operation of modern societies
• New products and services are rapidly
transforming our lives, both at work and at play
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Why T215?
2
[2]
• This course will help you to learn about these
developments, and will equip you with the
understanding and skills to continue learning
about new developments in the future
• We will study the core principles on which the
technologies are built and, through a range of
online and offline activities, investigate new
topics and technologies
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Why T215?
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Aims and Learning Outcomes
To increase the knowledge of the basic
principles of communication and information
systems and technologies, and the issues relating
to their use
• To develop your ability to apply your
understanding of communication and
information technologies to learn about new or
unfamiliar systems and technologies
• To enable you to develop a variety of skills
appropriate to a practitioner in communication
and information technologies
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•
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Knowledge and Understanding [1]
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LANs
WLANs
mobile communication networks
Encoding
Modulation
Multiplexing
Routing
Switching
Protocols
standards
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• Understand key principles and concepts of digital
communication and information systems and their
component devices
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Knowledge and Understanding [2]
• Storage
• Manipulation and transmission of digital data
• Associated privacy and security issues
• Being aware of major trends in communication and
information technologies
• Understand key concepts, issues and technologies
associated with online communication and collaboration
• Critically analyse documents
• Perform calculations using simple equations
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• Understand key principles and concepts relating to digital
data
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Assessment
• Midterm Examination (MTA)  30%
• Final Examination  50%
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• Tutor-marked assignment (TMA)  20%
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Session Outline
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Information
Communication and information technologies
Electronic data
Studying this block
• Part 2: Data storage
• Introduction
• Data coding
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• Part 1: Introduction to the block
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Information
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Part 1:
Introduction to the block
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Information [1]
• Text
• Pictures
• Sounds
• Can consume enormous resources, both financial
and personal
• Repressive governments seek to control it,
commercial organisations may sell it, and numerous
industries are devoted to creating, managing and
organising it
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• In its broadest interpretation, information is
something a human is capable of perceiving and
making sense of
• It takes many forms
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• A standard English dictionary is likely to define
information as  “knowledge acquired or
something told.”
• Information theorists concern themselves with
• Coding
• Transmitting
• Storing
• retrieving and decoding of information
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Information [2]
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Information [3]
• Computer scientists make a distinction between data and
information
• This course will take the more general approach
• Data will be used to refer to information associated with
computer processing
• Database will most likely refer to a collection of data stored
electronically
• Data processing will refer to the manipulation of data by a
computer and data protection to legal control of or access to
electronic data
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• Data: refer to information that is in a suitable form for processing
and manipulation using a computer
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Communication and
information technologies [1]
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The Gutenberg printing press in 15th century
The electric telegraph
Telephone and phonograph in the 19th century
Mobile communication systems
Satellites in the 20th century
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• Major new phase in communication technology:
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• Maybe it was even said when Chinese calligraphers
began to use pens around 1000 BC or when paper mills
first began to appear in Europe in the 14th century
• It’s tempting to think of information technology only in
the context of computer processing
 this is not the case!
• Information technologies have been around for centuries
and many of the older ones are still in daily use.
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Communication and
information technologies [2]
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Storing information [1]
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Notebook computer
Notepad
Printed diary
File of papers
Printed books
CDROMs
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• Examples of a number of different information
storage devices
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DVDs
USB flash drives printed calendar
Production schedules
Metal filing cabinets with printed papers and
notes
• Newspaper
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Storing information [2]
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• Could we instead simply store all the information
on the computer hard disk (if it were big enough)
and clear our offices (homes) of the other items.
 Why don’t We?
• It is because each different information storage
medium has particular characteristics that make
it more suitable for us to use in a particular
situation.
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Storing information [3]
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Storing information [4]
• Data entry is quicker in situations where we don’t
have access to a full keyboard
• It provides with instant access (no need to switch
anything on or log on!)
• It’s cheap!
• It’s small and lightweight  easy to transport
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• For example, we choose to use a paper-based
diary in preference to an electronic one, for a
number of reasons:
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Storing information [5]
• However, there are some drawbacks to the
paper-based diary system:
• if we should lose it we would lose all the diary records
• It only covers a limited time period
• It isn’t easy to share with other people
• Entering recurring events (birthdays of family and
friends, and regular appointments) is quite labour
intensive
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• It would be labour intensive to make a back-up copy so
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Storing information [6]
• Accessibility
• Durability
• Portability
• Reuse
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• To conclude: the necessary characteristics
needed for efficient and effective storing
of information:
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• An obvious example of an information
sharing network is the internet, but
information-sharing networks take many
different forms and have varying sizes
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Sharing information [1]
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• Activity 1.2: Identify one or two examples of
large (national or global) information sharing
networks that you use, other than the internet,
and one or two examples of small (local)
networks.
• Identify some of their key features
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Scalability
Accessibility
who controls them
how well they support the sharing of information
how information gets to the required destination.
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Sharing information [2]
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• Answer: For large networks  telephone network and
the postal network
• No single organisation (or country) having control over
the whole network
• Both the telephone network and the postal network are
scalable
• The postal network is very accessible
• The telephone network is slightly less accessible
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Sharing information [3]
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Sharing information [4]
• both provide a point-to-point service with each
point being identified by an addressing system
(telephone numbers or postal addresses).
• users are charged for the service in their country
of origin and don’t have to pay a separate fee for
each leg of the information journey
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• (Answer cont.) Features:
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Sharing information [5]
• Radio and TV broadcast networks
• News networks that use a variety of media including
radio, TV and newspapers to deliver their information
 These networks deliver the same information to
multiple destinations
• Specialist equipment is needed to receive the TV and
radio broadcasts but this equipment is widely available
and (for radio at least) relatively inexpensive
• No specialist equipment is needed to access
information through newspapers, but it does need
literacy skills.
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• More networks??
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• For smaller networks  information screens
situated at strategic points within the workplace or
campus
• Any other Different features of networks??
• whether they were public or private
• whether they were point-to-point or multicast (one to
many)
• whether they facilitate two-way information exchange (like
the phone networks) or one-way (like the broadcast
networks)
• how accessible they are
• how successful they are at reaching the intended audience
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Sharing information [6]
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• Computer technologies have led to a sea of
information that washes over us on a daily basis
and can threaten to submerge us unless we find
ways of managing and controlling it.
• In October 2007 Internet World Stats gave the total
global number of internet users as
 1 173 109 925 !!
• In June 2008 the same organisation reported an
increase of some 290 million users
 1 463 632 361, but still representing only 21.9% of
the total world population.
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Electronic data [1]
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• Cisco reported 75 exabytes (An exabyte is equal to 1
billion billion bytes) of data in June 2008
• In May 2008, The Economist reported an expectation of
15.8 million servers in the USA alone by 2010
• In December of the same year there were said to be
some 25.16 billion indexed web pages!!
• In 2012, Cisco reported a total internet traffic would
reach 522 exabytes per year (so that’s 522 billion billion)
• Cisco suggested that the next milestone to look out for after
2012 would be 1 zettabyte (1000 exabytes) before 2014 of
information shared
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Electronic data [2]
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• Add to this the data stored on millions of
desktop computers sitting in millions of offices
worldwide computer hard disks
• Also, many of us have mobile phones with
memory capability, digital cameras, memory
cards, external hard disks, shelves of CDs and
DVDs and use online storage for blogs, social
networking sites and emails
• Also, the storage requirements of commercial,
social and government organisations is huge!
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Electronic data [3]
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• How can information be stored so that it can be accessed
conveniently?
• What are the best ways of finding relevant, reliable
information from the sources available to us online?
• How do networks support the sharing of information and
allow us access to it from different locations?
• What are their key components and architectures?
• How do messages get to the right destinations?
• And how can so many people use the same
communications network simultaneously for so many
different purposes?
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So, why are we studying this
block?
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Part 2: Data Storage
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Introduction
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Introduction [1]
• cave walls as a very early data storage medium
• Around 5000 years ago, the ancient Egyptians
invented one of the first known systems of
writing.
• They inscribed symbols in the form of hieroglyphs
on stone walls and monuments
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• The earliest known European cave paintings are
over 30 000 years old  Used to pass on
information!
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• Hieroglyphs remained indecipherable to modern-day
scholars until after the “Rosetta” stone had been
discovered in 1799
• Inscribed on this stone were three forms of the same
text:
• In Egyptian written in hieroglyphs
• In Egyptian written in a simpler form of script called
demotic
• and in classical Greek
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Introduction [2]
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Introduction [3]
• First, given a suitable medium, data can be
preserved for a very long time
• Second, if the data is to convey information there
has to be means of deciphering it.
• And third, even 5000 years ago the recording of
information was so important
• We need to have techniques for management
and safeguarding of this ever-growing data
mountain!
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• Some important points arise from the above
introduction:
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Data Coding [1]
• Other groups use different writing systems – that is, they use
other code systems.
• As humans, we deal with the coding and decoding of data as
a normal process of our lives
• It’s only when we meet an unusual code that we stop and
think about the process of decoding
• In most cases clues about the intended meaning of the symbol
can be derived from the context in which the symbol is used.
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• People who speak another language use a different code
• Similarly, writing is a code that a certain group of people use
to represent words.
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Data Coding [2]
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• A simple example of a binary code is the use of 1 and 0 to represent
‘on’ and ‘off’ on the power switches of many electronic devices
• Using a single binary digit (or bit), one of two possible pieces of
information can be represented (in this case whether the switch is
on or off)
• Binary codes are used to represent data electronically within the
circuitry of a computer and to transmit data electronically between
computers.
• It is relatively simple to design electronic circuits whose state can be
switched between either of two voltage levels
• Similarly, it is relatively simple to transmit data at just two different
voltage levels  In both cases, one voltage level can be thought of
as representing 0 and the other as representing 1
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Binary Coding [1]
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• Depending on the length of binary code used, many
different states can be coded
• For example, if two ‘binary circuits’ are used it’s possible
to store binary code words consisting of two bits. One bit
is supplied by the first circuit, and the other bit by the
second.
• The following four binary code words are available with
this system, depending on the state of the two circuits:
00 or 01 or 10 or 11
• These four code words could represent any four things
that need to be labelled or coded, for example: hot, cold,
wet, dry.
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Binary Coding [2]
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Binary Coding [3]
• Eight binary code words are available with 3-bit code
words. The code words are:
• 000, 001, 010, 011, 100, 101, 110, 111
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• Activity 2.2: How many binary code words can
be represented if the number of bits is three?
What are the code words?
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Binary Coding [4]
•
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• A binary number consists of a string of binary digits. For example,
1100 and 1010 are each binary numbers
• Whereas the weightings which apply to the digits in denary numbers
are powers of ten, with binary numbers the weightings applied to
the digits are powers of two
• So the 4-bit binary number 1101 is interpreted in denary as follows:
23 22 21 20
8 4 2 1
1 1 0 1
• This can be written as
(1 × 23 ) + (1 × 22 ) + (0 × 21 ) + (1 × 20 )
which works out as
8 + 4 + 1 = 13 in denary.
• The leftmost bit is called the most-significant bit and the rightmost
bit is called the least-significant bit.
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Binary Coding [5]
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• Exactly the same principles can be applied to larger
binary numbers
• For example, in an 8-bit word the most-significant bit has
a weighting of 27 , which is 128. So the binary number
1011 0110 is interpreted as weightings
27 26 25 24 23 22 21 20
128 64 32 16 8 4 2 1
1
0 1 1 0 1 1 0
and equals 128+32+16+4+2 = 182 in denary
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Binary Coding [6]
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Binary Coding [7]
• For example, a common 8-bit code used for the letter
A is 0100 0001.
• They can also be used to represent sounds,
colours, movements, even smells.
• Binary data in computers has historically been
manipulated in groups of eight bits, known as a
byte
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• Binary codes have a much wider use than simply
representing numbers
• They can be used to represent text
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• Data that has been coded in binary form is often
referred to as digital data
• Digital data is data that can be represented by a
limited set of discrete values
• Since binary data can only take one of two
discrete values, all binary data falls into the
category of digital data
• It’s important to appreciate, however, that the
reverse is not true: not all digital data is binary
data!
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Binary Coding [8]
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Decoding Binary Data [1]
0100 0001  How is this byte to be interpreted?
• Could it be the letter “A”?
• Could it represent two 4-bit binary numbers equivalent to 4 and 1
in denary,
• or an 8-bit binary number equivalent to the denary value of 65?
• Or could it be a fragment of digitally encoded audio data, or a
small part of a picture?
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• Given that the “1” and “0” have so many roles to fulfil in
terms of data representation, how might a string of them
be decoded?
 The fact is, there’s no way of telling without some
additional information!
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• The solution is to follow a recognised convention
when storing and transmitting data – a
convention that can be understood and
interpreted by different systems.
 This idea is discussed further in next session!
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Decoding Binary Data [2]
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