T175: Networked living: Exploring Information and Communication technologies
Block (1): Living in a networked world.
Part (1): ICTs in ever day life.
Study session (1): The Network Society.
What is the different between data and information?
Data: Are the row material of any ICT system.
Information: Are the meaningful output from an ICT system that resulted from
Input ICTs System Output
ICTs system: are the technologies used in the conveying, manipulation and storage of data
by electronic means.
Example of ICTs:
Landline telephone system.
Mobile phone system.
Transmitter network receiver
User1 Receives from user 1 Conveys Receives user 2
Manipulates Manipulates Manipulates
Sends Selects route Sends to user 2
Stores/Retrieves Stores/Retrieves Stores/Retrieves
Information society and network society are term that has been used to analyze the
social and economic changes that are taking place in conjunction with technology
Technology push is a commercial term which means that sometimes we have no
influence or control over how intrudes into our life.
Market pull is a commercial term which means the opposite of “Technology push”.
What are the factors that affect ICTs?
Society and consumer’s behavior: can influence the development of technology due
the ultimate control over whether they buy it or not or how frequently they use its
Developers and Designers: Technologies are shaped by the people who design and
Political power (governments): can influence the growth of technology by funding or
Study session (2): You’re Network Life
ICT System in everyday life:
Example of communication using Device or systems used
Reading train information at station Electronic notice board to display information
Getting into my office building Bar code on swipe card, card reader at the
Emailing colleague from my work Network linking my computer to my
computer colleague’s computers.
Sending a text message on my mobile Wireless connection into mobile phone
Finding out my bank balance from ATM ATM machine
ICTs impact on Finance:
Using credit card while shopping online or over the phone.
Some types of businesses have disappeared completely, ex you rarely see door-to-door
salesmen these days.
New types of business appeared such as auctions like eBay.
Existing business types have been transformed through the use of ICT systems, ex. The
development of online booksellers such as Amazon.
The internet impact on all areas of life:
Online information’s resources.
New ways of communicating.
New online communities.
New technologies have engendered new types of crime.
ICTs impacts on entertainment:
Image production using digital cameras, printers and scanners.
Graphical interfaces to support the development of computer games.
Music’s development and distributions.
ICTs impact on public services:
In the health area:
Sharing the electronic patient records easily between departments within the
hospital and may be transferable across the whole health service.
In remote rural areas, doctor may be able to make use of computer network to
make a diagnosis if they are unable to see the patient in person.
In the transportation area:
Real-time information over the internet is available for passengers.
Controlling transport system such as traffic lights using network communication
In the online government service area:
You can renew or apply for a passport.
Book a driving test, claim benefits.
Fill in your tax returns.
Learn online as you are doing now with The AOU.
ICT systems at home (Smart Homes):
Most homes contain a variety of systems for entertainment, lighting, security, heating
and so on.
The idea of a Smart Home is to integrate the control of these systems.
Part (2): Introducing ICT Systems.
Study session (1): describing an ICT system.
A system is a set of components which are put together in a certain way to perform a
certain function in some context.
Examples of systems:
Personal filing system.
Central heating system.
A System Map: Is a graphical representation that describes the systems in order to explain
it and analyze it.
Draw each component inside a closed curve.
Draw a think closed curve to represent a system boundary which separates the system
from the rest of the world. System boundary shows what to include and exclude. This
often depends on the perspective of the person viewing the system.
System Environment: Is the area outside the system.
If a component is a subsystem then you can draw a system map in its place.
System map is very flexible since it can be used to represent different perspectives.
Sample of system map:
Why using system map:
It’s important to realize that systems are composed of subsystems and that these
subsystems are often themselves composed of subsystems. This idea will help us in
exploring ICT systems.
We may draw the system boundary in different places at different times For example, if
we want to discuss the social or economic impact of a particular ICT system, we will be
drawing the boundary very widely indeed but if we want to look at how some
subsystem in an ICT system works, then we will be drawing the boundary very tightly
around the subsystem.
Block Diagram: which another graphical way to represent a system. Each block represents
something in the real world, and the labels in the black tell you what that something
Types Of Blocks:
The oval shapes represent the users of the communication system.
The rectangular blocks represent inanimate objects in the communication system.
The lines between blocks represent the flow of something.
Sender means of conveying recipient
User1 messages user2
More detail model of a communication system:
User 1 Transmitte Network Receiver User2
In a mobile system, the transmitter, which is user 1’s mobile phone?
Receives a message from user 1 in the form of sound.
It manipulates the incoming sound into a data format suitable for sending into the
mobile phone network.
Even basic models of mobile phone handsets can store names and telephone
numbers, so in this example the transmitter is also storing and retrieving data.
The network: It’s a communication channel.
It’s conveys data from the transmitter to the receiver.
Network also manipulates data in some way.
Network may also store or retrieve data.
A network can be very complex, so a call does not usually go directly from one caller
to another in a single step. It will select the rout for conveying a call through the
network from the transmitter to the receiver.
The receiver receives data from the network.
The receiver manipulates the data into a message to send it to user 2.
Sometime the receiver may also store or retrieve data.
The processes: are those that will always be carried out and they are shown in bold; the
other process may or may not performed.
A model of communication system showing the processes involved:
User1 Transmitter Network Receiver user2
Receives from user1. Conveys Receives
Manipulate Manipulate Manipulate
Sends Selects rout Sends to user2
Links can be cables or wireless
Physical cables can provide a path for conveying data between points.
A common example is the telephone wires that are used to connect the landline in
people homes to the nearest exchange.
Cables are also used to carry television and often radio signal to homes of cable TV
Fiber-optic cables are also used to interconnect telephone exchanges.
Cables are also used to connect computers to gather into various kinds of
- Wireless link:
Bluetooth is used for short-range wireless links between devices, for example to
connect a computer and printer.
A Wi-Fi link, with its slightly longer range, might be used to connect a Wi-Fi-
enabled notebook computer to a Wi-Fi hotspot (in a café or other public place),
which provide a link to the internet.
While using the remote control for your television set.
Provide a communication between computers and devices such as printers.
Different between wireless links and infrared is that infrared link must be along a
line of sight, whereas radio link need not to be.
Some ICTs important expressions:
- Capacity: ability of communication link to convey data. It’s measured by bandwidth.
- Bandwidth: It’s the maximum data rate that a communication link can support.
- Bits: Is an abbreviation for “Binary Digit”.
A binary digit can have just one two values: it cans either 1 or 0.
Pulses can be represented by 1s and 0s.
- Data rate, Bit rate: Is the rate at which the 1s and 0s are conveyed.
- Bit per second (Bps): is used to measure data rate and bandwidth.
- Prefix of data rates:
Prefix In figures this is In words this is Symbol
Kilo 1000 A thousand K
Mega 1000 000 A million M
Giga 1000 000 000 A billion ( thousand million) g
Study session (2): Computers.
A stand alone computers:
Types of standalone computers:
- Microcomputer (personal computer).
Notebook computer: are designed to be small and light in order to be portable, so
the screen and keyboard are part of the one unit and run on an internal battery as
well as from an electronic socket.
A standalone computer is a computer is not connected to a network.
- The key processes are the manipulate and storage of data.
- Standalone computer components:
Computer receives data from user via input device.
Computer sends data to user via output device.
Computer manipulates data using the processor and RAM.
Computer stores and retrieve data using storage devices.
Receives from user
Sends to user
Sending and receiving data:
- Scanner: converts images and text into a format can be processed by computer and
displayed on screen.
- Touch screens and graphics tablets: convert the pressure from stylus or finger strokes
- Digital cameras and camcorders.
- Monitor (screen).
- On the outside of a case there are a number of connection points that look like
- Ports control the flow of data between the computer and other devices, ensuring that
data is sent and receive quickly and reliable.
- Serial ports which was often used for a modem.
- Parallel port, use to connect the computer to a printer.
- Tow high-speed ports:
Firewire: can provide a fast connection at a rate up to 800 megabits per second
Universal serial bus (USB): come into two versions: USB 1.1 and the more recent
used USB 2.0. The latter is faster, at about 480 Mbps, while USB 1.1 is only 12
A computer needs two main components to manipulate data: a processer and a working
- A processer is contained on a single microchip or (chip).
- A chip is a small, thin slice of silicon, which might measure a centimeter across but can
contain a hundred of millions of transistors, the transistors joined together into
circuits by tiny wires which can be more than hundred times thinner than a human
hair. These tinny circuits enable the processer to carry out calculations and other
manipulations of data.
- Processor speed influence how quickly the computer can carry out its operations.
- Types off processors currently available:
Memory / Random Access Memory:
- The computer’s working memory in which programs and data are stored so that they
can be accessed very quickly by the processer.
- The processor stores data in RAM and retrieves data from it as it carries out
manipulations. (Temporal Storage).
- The more RAM the computer has, the faster the computer programs will run.
- RAM memory is used and reused and any data in RAM is normally lost when the
computer is turned off.
Hard Disk (Hard Drive): store data permanently.
Booting process: part of the starting-up process of a computer is to copy start-up
programs and data from hard disk into RAM, and all important data in the RAM is
copied to hard disk during the closing-down process.
- Hardware: the electronic components and other equipments that make up your
- Software: computer program and have such types:
A computer program is written in a programming language and contains the
instructions that tell the computer what to do.
Computer program (source code) is converted into low-level instructions
understood by the processor.
Each programming language suit different type of task.
Java, C++, Visual Basic, COBOL, FORTRAN …. Etc is types of programming
Handles communication with other software on the computer and with
hardware resources of the machine, such as the processor and memory.
The operating system provides a means of running the computer’s application
It also provides a standard user interface with windows, buttons and menus so
that user can interact with the computer.
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Operating systems are usually commercial products and protected by copyright
like Microsoft Windows, Apple Macintosh OS.
Open source programming: programs which are available free. Anyone can
make improvements to them, provided they make the details of the programs
available to other programmers such as Linux.
Applications: programs that end user buy the computer to run, it have these types:
Such as Microsoft Word.
Allow you create, edit and store documents.
Different typefaces (known as ‘fonts’).
Incorporating graphics such as drawing and photographs.
Such as Excel.
Allow you to perform calculation based on the numbers and formulae that
You can keep track of a household budget on a spreadsheet, but what’s
make spreadsheets a powerful tools is its modeling ability.
Depended on how spreadsheet has been setup, when new values entered,
the whole spreadsheet can be automatically updated.
Spreadsheets are often used in business organizations to model financial
Such as Microsoft Access.
Store information in a form that can be organized and searched.
Database range is size and complexity. An example of a small database
might be an address book that you keep on your own computer to store the
names and contact details of friends and family. There are much larger
database in use by institutions containing specify types of information, such
as library catalogues, banks records of customer accounts, and hospital
Graphic and image editing software:
Allow you to create and edit drawings and images.
Digital photography has become very popular and image-editing software
allows you to crop and resize your photos, touch-up blemishes and then
print the results.
Education and training software:
Intended to help children’s and adults learn.
There are a number of programs intended to teach children basic
mathematics and English skills, program designed to train people in
computer skills or to help them learn new languages.
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Represent a large sector in the computer software market. While many run
on dedicated game consoles rather than PCs, some make use of the PCs
computing power to achieve high-quality graphics and complex game play.
Technical developments for games have resulted in improvements for
personal computers. You can play games alone on your PC, but other
provide multi-player environment via internet.
Allow you to compose, send, read and delete messages.
Often include tools such as a filling system for storing messages, a calendar
and address book.
Such as Microsoft internet explorer and Mozilla Firefox.
Allow you to view web pages.
Use the links in them to ‘jump’ from one page to another and from on part
of a page to another.
Screen readers: ‘read’ the accessible text aloud.
Speech recognition software: enable the computer to respond the human
Storing data: (permanent storage):
Data stores in files.
Why the need of external or portable storage media? To move files from one
computer/device to another.
Storage capacity and file sixe measurement units:
- Bit (b): (binary digit) can have one of two values wither 0 or 1.
- Byte (B):
A group of 8 bits which can represent:
A text character like “a” or “A”.
Ex: how many bytes of storage space would the phrase ‘storage technology”
17 letters + 1 space = 18 bytes = 144 bit.
- Kilobyte (KB) = 210 byte = 1024 bytes.
- Megabyte (MB) = 220 byte = 1048576 bytes.
- Gigabyte (GB) = 230 byte = 1073741824 bytes.
Types of storage devices:
- Magnetic storage:
Provide a Permanente storage area for the computer programs and the files you
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An example of magnetic storage is your computer hard disk.
Data stored in magnetic form can be changed once it has been stored.
Examples on magnetic storage:
At the time of writing, a medium price computer has a hard disk storage
capacity of up to 100 GB.
A floppy disk can store about 1.44 MB.
A zip disk is high capacity form of magnetic storage which is portable. Zip disks
are available in capacities of 100 MB, 240 MB, and 750 MB.
- Optical storage:
A CD-ROM (Compact Disk Read Only Memory):
Uses a laser-based optical form of storage.
Used for many years to distribute music and computer software.
A CD-ROM Drive is needed to read the disks.
Data is locked into the disk during manufacture, and cannot afterward be
Can store up to 800 MB of data, 90 minutes of audio or 60 minutes of video.
With the rights sort of CD drive in your computer, you can “burn” data (that is,
write data) to either type.
Data written to CD-R disk cannot be changed afterward, although further data
can be added.
Vary in their capacity, but typically it is in the region of 700 MB.
This kind of disk, allows users to erase data from it, and reused.
Vary in capacity, but typically it is in the region of 700 MB.
DVD(Digital Versatile Disk):
Works in a similar way to CDs, but data is held in a more compact format.
Can have more than one layer of data. A single data layer can hold about 4.4
In a higher quality, roughly two hours of video can be held in a layer.
As with CDs, there are “R” and “WR” version to which the user can write data.
“Blue Ray system, using blue laser (instead of a red one), stores data even more
compactly. This system promises to increase the capacity of a layer to 27 GB.
Is an electronic form of memory which can be used, erased and reused?
A flash memory card is a small storage device used to store data such as text,
picture, sound and video. These cards are used in portable devices such as
digital cameras and in small portable computer, such as Personal Digital
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A USB Flash Memory, sometimes called a ‘memory stick’, Is a small storage
device which is completely external and connects to the computer via a USB
port, this portable memory comes in different capacities, e.g. 256 MB, 512 MB,
1 GB, and 2 GB.
Networked computers (what happens when stand alone computers are linked):
Figure 11 is a block diagram which models the situation when a computer user browses
a web site.
In the block diagram, the computer receives data from user and sends it into network. It
will manipulate and also store and retrieve data.
If you send a message to a LMS/ACES forum, the computer receives the message from
you as data from the keyboard.
The computer manipulates the data into a form (packets) that can be sent into the
Your computer will also store or retrieve relevant data, such as details of the LMS/ACES
computer’s (server) internet address.
This network conveys the data to the receiver (Your AOU branch server that has the
LMS/ACES), selecting the most appropriate rout for it travel.
In order to do this, the network may need to manipulate and store or retrieve data.
Second computer (the LMS/ACES server):
A server is a computer whose hardware and software is dedicated to making data
available to other computers.
The LMS/ACES server receives data from the network and stores it.
It carries out the manipulations necessary to add your message to those already in the
conference, retrieving other details about the conference as it does so.
It’s also sends data back to you, showing you that your message is now in the
Personal digital assistance:
Personal digital assistance (PDAs), or handheld computers are small, portable
computers, they each contain a small processer and have specially written operating
Two popular types of PDA:
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- Those running the Palm OS operating system.
-Those using windows mobile operating system, (also called Pocket PC).
- There is a range of applications purposely written for PDAs.
- But many also use special version of popular applications like Microsoft word, Excel,
Input data: some PDAs have very small keyboards to input data, whilst others use touch
screens which can tapped with a finger or a stylus.
Many can accommodate flash memory cards to increase space for data storage. Many
PDAs can be used to view digital photographs or sometimes video, and can be used to
play music in MP3 format. Some PDAs have integral digital cameras.
PDA are designed:
- To connect with personal computers.
- Other PDAs used to transfer data between them using a range of communication links,
such as Bluetooth and Infrared.
- At more expensive end of the range, some PDAs have built-in mobile phones and can
connect to the internet to send and receive e-mails.
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Study session (3): Computer and Communications System working to gather:
System Map For Supermarket Checkout System:
Block Diagram For Checkout System:
Receiving data: (the checkout terminal receives data from barcode scanner.).
- Input device: barcode reader, keyboard for entering data.
- Checkout operator uses barcode reader to scan the barcode printed on the label of
each purchase item.
- A barcode is pattern of narrow and wide stripes which can be read barcode by a
- A barcode reader is a device which optically scans the barcode and converts the
stripes into numerical data which can be automatically input to the checkout
Storing and retrieving data:
- As each item is scanned, the checkout computer looks up its price from the database
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- The running total for each customer’s purchases is stored temporally in the checkout
- Other data may also be stored, such as the amount of money that has been taken at
the checkout during the day.
- The checkout terminal manipulates the data to obtain the total cost.
- The checkout terminal manipulates the data to obtain by subtraction the amount of
- Output device: computer monitor, small display for the customer, beep when
scanning item, receipt printers.
The system from the engineers point of view:
- Networks are dividing according to the area they cover into:
A network belonging to a single organization, where the computers are closed to
each other on a single site is known as a Local Area Network or LAN.
In a Wide Area Network, or Wan, the computers may be spread over a large
- Positive of network:
Shared access to network resource such as printers and software.
Shared access to data and possibly storage space on other computers.
A network also can support email, internet connection and other communication
service for its users.
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- A database server:
A database server is used to make data in databases available to other computers
on the network, and therefore to user.
Database server holds number of different database.
Identity of ICT system:
Barcodes give identity to products.
People are usually identified by their Personal Identification Numbers (PIN).
Radio Frequency Identity (RFID): technology provides a means of RFID Indentifying
- An RFID tag works in conjunction with a device called RFID reader. In response to a
signal from the reader, the tag transmits data (identification number) to the reader
using radio link.
Block diagram for supermarket with one checkout terminal and a database server.
Block diagram representing a more comprehensive view of supermarket ICT System.
E-commerce: buying and selling things using the internet is as ‘electronic commerce’:
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- Shopping can be done from home.
- You can probably find out what you need without trudging from one shop to another
and waiting in queues.
- You can also purchase goods 24 hours a day, every day.
- Wide customer base.
- Setting up a website and using it to do business can be more cost effective than using
a conventional shop.
- There are fewer overheads in terms of, for example heating, lighting and staffing.
- The costs of delivering goods are relatively low compared with those of running a
- Businesses can use the web to reach customers on a national or even international
bases rather than being confined to a shop’s geographic location.
-The web creates a more level playing-field in that smaller companies compete against
What businesses need to work will in e-commerce?
- Has a good warehouse system.
- Access to an effective distribution system.
- The company must have the goods can be conveyed to the customer as quickly as
possible, which may involve using couriers and other special delivery service.
The ICT Consist of the following components:
- User’s computers.
- Database server.
- Web servers: computers that hold web pages and make them available to users over
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Block (2): Communication and identity.
Part (3): Device to Device Communication
Study session (1): Communication between devices.
Communication system can be categorized according to the nature of the communication
People: Are the main players – either communicating with each other, or retrieve
information from computer system.
Devices: Are the main players, passing information to and from each other and possibly
acting on that information to produce some kind of outcome.
Example on communicating devices IC system:
Computer and printer while printing a file:
- Computer and printer are point to point connection.
- Process initiated by the user when clicking the print icon.
- In order to talk to each other, the computer and printer need:
A communication link between them.
Protocols (Rules): which are used to establish a common language and to control
the exchange of data (what to say and what to speak)?
Some way of storing data (for example (printer queue)).
Some way of recognizing and coping with error.
- What really happens:
The computer receives the print command from the user and sends data over the
communication link to the printer.
The communication is point-to-point so there is no requirement for network
routing, or for storing or manipulating the data as it travels through the
communication link. (Conveys).
Printer stores data in buffer which is a portion of printer memory - before being
The paper copy produced by the printer is an output to the user.
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Two computers sharing printers via network:
- What really happens:
There may be now a need for routing (Network), storing and manipulating data as
it travels through the communication links.
We need a way to identify each device so that data can be correctly directed to the
Protocols are needed:
To establish a common language.
To establish how the printer will be shared so that one user doesn’t hog the
To establish some way of sharing the communication link (Network) so that
data from different devices doesn’t become jumbled.
Sales busy office with printers, PCs, and print servers:
- A printer server may be used to handle data flows between the printers and the user’s
- Problem that could happened:
Printer or print server breaks down.
Network breaks down.
Network is congested that it can no longer cope with the volume of data being
Provide more than one printer.
A stand by server.
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Alternative way of routing data to the printers (when network down).
Developing skimming and active reading:
Why skimming a document (taking a quick overview)?
- An overview enable you to assess whether the document contains anything is of use
- If it does, you might choose to concentrate only on the section that is of interest to
- Overview gives you a familiarity with the document before you engage with it in
- An overview will help you to identify particular parts you may really need to focus on.
A will structured document usually contains a number of clues about contents.
Skimming is the practice of finding and using these clues.
- Clues are:
Visual clues such as:
A document title.
Figures and figure captions.
Words and boldface and italics.
Numbers and bulleted lists.
Verbal clues such as:
Conclusion or summary.
The first (or sometimes the last) sentence in each paragraph.
Abstract summarize the main points of the text.
- Abstract is usually presented before the main text.
- Followed, in some cases, by a list of keywords or phrases.
- Numbers included in the text.
- Some are shown a subscripts (small figures or characters raised above the normal line
of text) and others in square brackets.
- Each subscript gives a cross-reference to an endnote listed at the end of article.
- Each number in square brackets gives and index to a reference list at the end of the
- Passive reading
- Active reading.
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Study session (2): Signals
- Any number can be expressed in scientific notation. For example:
5 000 = 5 × 10 × 10 × 10 = 5 × 103.
72 000 = 7.2 × 10 × 10 × 10 × 10 = 7.2 × 104.
82 600 = 8.26 × 10 × 10 × 10 × 10 = 8.62 × 10 4
- In the first example 10 is called the base and 3 is exponent/power/index.
- To get scientific notation for a number:
Divide it successively by 10 until it is reduce to a number that is less than 10.
This will result a number that includes a decimal fraction.
Indicate how many times the number would have to be multiplied by 10 in
order it to its original value by raising 10 to number of multiplication times
Join to gather the result from the two earlier stages using a multiplication sign.
Imagine there is a decimal point at the right hand end of the number.
7 390 000 = 7 390 000.0
Move the decimal point one place at the time until it sits after the left-most
number, and count the number of places the decimal point has been moved.
7 390 000.0 = 7.397 000 0 dismal point moved 6 places to the left.
Remove all the 0s at the right-hand end after the decimal point and multiply
what is left by 10 raised to the power of the number of places the decimal point
has been moved.
7.397 000 0 = 7.397 × 106.
Round 3482 to 3 significant figures 3480 (we chose to round down since 3482 is
closer to 3480 than 3490).
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Round 3482 to 2 significant figures 3500 (we chose to round up since 3482 is
closer to 3500 than 3400).
Round 2.14565879 x 108 to 4 significant figures 2.145 x 108.
Round 2.14565879 x 108 to 3 significant figures 2.15 x 108.
Round 299 792 458 m/s to 4 significant figures 299 800 000.
Round 299 792 458 m/s to 3 significant figures 300 000 000.
Signal: is a deliberate variation in some property of the medium used to convey the
Signals example are:
- An electrical voltage traveling along copper wires between telephone and the local
- Pulses of lights in a fiber-optic cable.
- The radio emissions that picked up by mobile telephone or radio receiver.
- Electromagnetic radiation:
Electromagnetic radiation is caused by the change in electrical and magnetic fields.
Electromagnetic radiation can support signals even with there is no physical
medium such as a cable involved. Such as a pulses of lights and the radio emission.
Ripples on a pond example to illustrate nature electromagnetic radiation.
Electromagnetic waves are:
- Sinusoidal (that is, having the shape of the sign wave).
- A signal full oscillation is known as a wave cycle.
- The frequency of the wave is the number of waves completes in a signal second.
- Units of measuring frequency are:
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Hertz (Hz): a wave that completes one wave cycle every second has a frequency of
Kilo Hertz (kHz): 100 wave cycles every second.
Mega Hertz (MHz): 1000,000 wave cycles per second.
Giga Hertz (GHz): 1000,000,000 wave cycles per second.
- Electromagnetic waves are characterized by their wave frequency.
- Example of electromagnetic waves:
- Electromagnetic spectrum refers to the entire range of frequency electromagnetic
Modifying the medium to carry the message:
A signal as a deliberate variation in some property of the medium used to convey the
data. Variation need to be done in a meaningful way.
For example, to convey Morse code the light could be switched on and off so that a
short light pulse could represent a dot and a lounger pulse a dash.
With an electrical voltage applied to a copper wire, the sequence of on and off periods
could be used to represent data, say, a stream of 1s and 0s.\
In radio signals, frequency which is a property of the electromagnetic waves could be
varied in a meaningful way – as show in Figure 7. In intervals 1,5,6 and 8 it complete 3
cycles and intervals 1,3,4,7,9 and 10 it complete one and half cycle. That cab used to
represent 1 and 0.
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Carrier: something that carries the data such as the electromagnetic wave.
Modulation: the process of modifying the carrier property in order to represent the
A transmitter: takes the data from the sender, modify the carrier, and then send the
resulting signal through the communication link.
A receiver: takes the signal, and extract the data by a process known as demodulation,
then passes the data to recipients.
Demodulation: process of extracting data from signal at the receiving end.
The figure 8 description:
- Both sender and receipt could be computer or printer or any other device.
- Users are no longer shown but they can be adding before sender and after the
- A cloud represents the network to indicate that is something going there but does not
give any details of what it is.
- Communication show in one direction from left to write. Transmitter only receives
data from the sender and sends it to receiver.
The figure 9 description:
- Transceivers: perform both the sending and receiving of signals, so they could replace
both the transmitter and receiver.
- Communication in both directions since we used transceiver device.
- The end points both become sender/recipient because both can be send and receive.
- The transceiver could be a modem and both sender and receiver could be a computer.
Propagation delay: the time taken for a signal to travel from its source to its destination.
The propagation delay depends on a number of factors:
- The distance the signal has to travel.
- The signals speed.
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- The process required to manipulate and manage the signals on their journey from
sender to receiver.
- Contemporary physics states that nothing can travel faster than the speed of light (or
any electromagnetic wave) in a vacuum which, to the nearest meter, is 299 792 458
meters per second.
- You are more likely to see the speed of light given as ‘approximately 3 x 108 m/s’ (that
is 300 000 000 meters per second).
- Not all carriers are able to achieve the speed of light. A voltage pulse travelling in a
copper cable has a speed of approximately 2 x 108 m/s.
Problem when signals travels from one device to another:
- Attenuation: a signal weaker the farther it travels, because some of energy is
absorbed by the transmission medium.
- Solutions: an amplifier can be used to boost the signal power at the transmitter and
receiver, and if necessary at various points in the transmission link, so that signal
power can maintained at usable level.
- Distortion: the signal can become distorted by external influence as it travels along
the communication path.
- Distortion can be caused by:
Other signal travelling in the vicinity.
By wave of energy such as solar energy, lighting, and pulses of energy from
- Example of everyday life on distortions:
Power on a TV and when use hairdryer nearby you can see spots and lines on TV
screens that are caused by the electromagnetic energy generated by the motor in
Place a mobile phone next to a radio you often hear beeps on the radio as the
phone sends signal to phone network.
- Distortion may be removed from the signal at the receiving end then
- Any amplification to overcome the problems of attenuation will also amplify any
distortion in the received signal.
- Binary signals are quite resistant to distortion because they represent only two states
that can usually be distinguished quite easily from any unwanted effects.
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Study session (3): a weird network
A network: is a set of nodes with communication paths among them.
A node: is any device (for example, computer, printer, and server) connected to the
network, either as end point (that is, a point where the communication link terminates)
or some intermediary point (that is, a point which lies between end points in the
Network classification according to the communication nature:
Wired network: network that use a physical communication link where nodes are
physically linked to each other by a cable – for example, copper or fiber optic.
Wireless: have no physical connection between the nodes.
Network classification according to geographical spread:
Personal Area Network (PANs): cover small area such as a home, a single room within a
home or even a car. A PAN is a type of LAN.
Local Area Network (LANs): connect together a number of nodes within a single building
or group of buildings situated close to each other. A LAN can connect together as few as
two or three nodes or hundreds of nodes.
Wide Area Network (WANs): connect together two or more LANs that are geographically
separated. This is done by using links between. A WAN could connect together all the
LANs in offices of a national company and could even cross international boundaries.
Weird network principles of operation:
Each node identified by MAC address and has its own NIC to handle physical connection
A Network Interface Card (NIC): provides the interface between the node and the
communication link. In order to enable the physical connection to the network. It carries
out process to control the flow of data over the network.
Media Access Control (MAC) address: each node is assign an identified number known as
MAC address to distinguish it from all the other nodes on the network. It used by other
nodes when they want to send data to a particular destination.
Frames: messages between nodes are broken up into small chunks called frames which
are sent one at time.
- Each frame includes some information which enables it to be routed through the
network and delivered to the intended destination.
- All frames include the MAC Address of both the destination and the sending node.
- In some networks. Each node reads the destination address and picks out those
frames where the destination address matches its own.
A repeater: increases the practical distance between nodes by regenerating the signals
and passing it on.
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Weird network configuration:
Network Topology: arrangement in which nodes are connected.
- Network topology Types:
Bus Topology: all nodes connect to a signal network cable and communicate with
every other attached node by placing a message onto the cable.
How it works?
Each node connects to the same cable, so frame sent by one node will arrive
at every other node.
Each node must read the distention MAC address in the frame to decide
whether or not accept it.
If any nodes become inoperable, all other nodes are still able to communicate
with each others.
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Any cable failure will result in the loss of communication between nodes on
opposite sides of the failure point.
Star topology: each node has its own cabled link to a central point called a hub.
How it works?
All messages all conveyed through the hub and, like the bus topology, will
arrive to each node.
Any single cable failure will affects only one node.
A hub failure would make the entire network inoperable.
Typically, the maximum number of nodes that can be connected to gather in
the star topology is 24.
Extended start topology: hubs are joined to gather so that nodes connected to one
hub can communicate with nodes connected to another hub.
Full mesh: has a web-like structure in which each node has a point-to-point with
every other node.
Partial mesh: has a web like structure in which some nodes have connections to a
numbers of nodes, but some may connected to only one other nod e.
Data between two nodes may have to travel through intermediary nodes
before reaching its destination.
Nodes must have some knowledge of the network layout so that message can
be routed correctly.
If the node or the communication link fails it is possible to find another path to
the destination. So mesh-type networks have high reliability.
Protocols and standards:
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- Protocols: rules to govern how information is sent, transmitted and received.
- A number of organization have taken responsibility for insuring the particular
communication protocols are clearly stated, recorded and made available to others.
- These organizations agree on and produce the necessary standard, which are a kind of
- A standard document is drawn up with the involvement and agreement of all
interested parties, for example representative of users, manufactures and
- The dominate standard of weird LANs is one that is commonly known as Ethernet.
Establish Ethernet standards:
- When: the first Ethernet network was developed in the early 1970, long before the
World Wide Web and personal computers.
- Where: Ethernet was designed by researchers at the Xerox Palo Alto Research Center
in California, USA to connect the Center ‘Alto’ computers to office printers.
- Why succeeded: one of the main reasons for its success lies with decision to publish
the standard (used open standard).
Open standard: are published and available to everyone.
Availability of open standard helps to establish related product in the market place:
Many different manufacturing are able to produce products that are
This increases competition and drives down the costs to consumer.
It increases manufacturers’ confidence in the market and so encourages them
to invest in and develop products.
This in turn is likely to lead to great reliability.
The Institute of Electrical and electronic Engineers (IEEE):
- The IEEE was formed from two earlier organization:
AIEE: The American Institute of Electrical Engineers.
IRE: The Institute of Radio Engineers.
- The IEEE 802.3 standard specifies a total data rate of 10 Mbps, but subsequent
developments in technology enable faster data rates to be achieved and so new 802.3
standards have been defined, providing data rates of 100 Mbps, 1 Gbps (gigabits per
second) or 10 Gbps. These new standards are identified by adding a suffix to the
standard number so, for example, the 10 Gbps Ethernet standards are known as IEEE
Magnitude and estimate:
Comparisons and estimates are two very useful tools.
A comparison with something you are already familiar with can help you to get a feel for
new ideas or concepts. (For example, I can get a feel for the size of a hectare once I
know it is about the same size as a soccer pitch of international standard.).
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As well as providing a quick way of making comparisons, estimates can also be useful in
checking that the answers you come up with for calculations are sensible.
- Example: Estimate how many times faster the data rate of the original Ethernet
standard (10 Mbps) is, compared to the data rate of a modern standard dial-up
modem of 56 kbps. (Hint: round down the dial-up modem rate to 50 kbps.).
- 10 Mbps = 10 000 000 bps
- 50 kbps = 50 000 bp
- 10 000 000 = 200
- 50 000
- So the first commercial Ethernet network was about 200 times faster than a modern
56 kbps modem dial-up connection.
A router: One type of network device which generally works at the edge of a LAN rather
than within it.
A router holds information about the structure of a network.
A router can make decisions about how data should be routed through it.
A router used to:
- Connect together different types of LAN, for example used to join an Ethernet LAN
with a LAN that uses different protocols.
- Connect different types of network. For example a router would be used to connect a
LAN to a WAN.
Study session (4): a wireless network
Wireless networks –, networks that transmit data through the air (or space) using radio
The principles of transmitting information using radio waves were discovered over a
Using radio waves to provide the transmission links in a network is a relatively new and
It enables us to connect into networks in public places like airports and city centers
without needing a wired link.
Basic principle of wireless transmission:
Aerial / Antenna: a special electrical conductor that picks up the radio signals.
an antenna can be used to both receive and send radio signals :
- Receives radio signals:
Radio signals arrive through the air as fluctuations ( )تقلباتin the electromagnetic
field of a radio wave.
This induces ( )يستحثa fluctuating electrical current to flow in the antenna.
These fluctuations are detected and translated into data.
- Send Radio Signals: Fluctuations in electrical current flowing in an antenna can also
emit a radio signal, Most devices operating in radio networks are transceivers (that is,
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they can both send and receive radio signals) and will use the same antenna when
sending and receiving.
- When signals are travelling in cables, they follow the path of the cable, even though
this may twist and turn. For this reason, cables are described as ‘guided’ media.
- Radio signals are not guided in this way.
- The electromagnetic waves carrying the signal can propagate in all directions, and may
spread out in a spherical pattern as shown in Figure 12.
- The wave fronts refers to all points on a wave that are equidistant from its source.
- In figure wave fronts are represented by the concentric circles in both figures.
- The circles become fainter with distance from the centre, representing the way the
- Figure 12(a) shows a representation of a side view of an antenna. Figure 12(b) is a
representation looking down onto the antenna.
- Antennas can be designed to be directional so that the signal power is directed into a
beam (Figure 13). This allows the signal to travel further for the same power.
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- In general, the attenuation of a radio signal is greater than the attenuation of a signal
travelling an equivalent distance via a cable.
- Factors which influence the maximum practical distance that a signal can be
The signal frequency and strength.
the physical environment.
the design of the antenna.
- Low-frequency waves:
Low-frequency waves can travel further than high-frequency waves.
Low-frequency waves are also more efficient at penetrating physical barriers such
as walls and floors – something that high-frequency waves, like visible light, can’t
So it is the waves at the lower frequency end of the electromagnetic spectrum that
are used for over-the-air communications. These include the radio and microwave
the approximate frequency range of radio waves is the difference between the
highest and lowest frequencies is somewhere around 1010 Hz minus 103 Hz (10 000
000 000 Hz minus 1 000 Hz) which is 9 999 999 000 Hz or approximately 10 10 Hz.
(notice than 1KHz is insignificant compared to 1010 Hz).
Increasing demand for wireless technology means that the radio frequencies must be
carefully managed and allocated by governments to satisfy all the different users and to
prevent interference between them.
Before transmitting radio signals, organizations must usually obtain a license permitting
them to use a specified frequency or band of frequencies.
The industrial, scientific and medical (ISM) radio band: Band of radio frequencies which
is available internationally for unlicensed users and lying between 2.4000 GHz and
2.4835 GHz. Also referred to simply as the 2.4 GHz frequency band – (Some countries
also allocate additional frequencies for unlicensed users.)
Two wireless standards designed to operate within the ISM band of radio frequencies.
- WiFi developed by the IEEE and covered by the IEEE 802.11 families of wireless LAN
- Bluetooth developed by the Bluetooth Special Interest Group (SIG) and covered by the
IEEE 802.15 families of wireless PAN standards.
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- Bluetooth, developed by the Bluetooth Special Interest Group (SIG) and covered by
the IEEE 802.15 families of wireless PAN standards.
Ad hoc mod.
- ‘ad hoc’ meaning from the dictionary means ‘for a specific purpose, impromptu, not
- In an ad hoc network, stations communicate with each other directly, without the
need for any intermediary or central control.
- how it is established?
When one WiFi device comes within range of another, a direct communication
channel can be set up between them. This is known as peer-to-peer
Additional devices can join the network, all communicating with each other in a
In this context, ‘broadcast’ means that a message sent by one node will arrive at
every other node in the network, regardless of the destination address.
- An ad hoc network is independent of, and isolated from, any other network.
- In Figure 14:
The dark circles represent WiFi stations.
The concentric circles around them show that the communication channel is radio
In this case, the diagram indicates non-directional antennas.
- Where it can be used:
a network set up for a business meeting where people want to share information
stored on portable devices like lap-top computers and personal digital assistants
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- ‘infrastructure’ from the dictionary means ‘underlying foundation, basic structure, and
- Stations communicate with each other via a wireless access point (AP) which also acts
as a connector between a wired network and the wireless network.
- The access point is effectively a base station that controls the communication
between the other stations.
- Access points form part of a wired network infrastructure and are not mobile.
How WIFI stations find each other:
- A WiFi station determines whether it is in range of an AP by transmitting an enquiry,
known as a probe request frame, and waiting for a response.
- If more than one AP responds, the station will choose to communicate with the one
that has the strongest signal.
- A probe request frame initiates the WiFi connection and is an example of a
management frame – a type of frame that does not carry any message data.
- Just like the nodes on an Ethernet network, each station must have a means of being
uniquely identified by a MAC address.
- Every message data frame sent must contain the MAC address of the source,
destination and access point, as well as other management data that enables the
frames to be correctly sequenced and errors to be detected.
Sharing the medium:
- All the stations in a WiFi network share the same communication channel only one
station at a time can be allowed to send data.
- A station waits until it detects a period of inactivity and then uses a special protocol
which prevents two or more stations sending data at exactly the same time.
- The exchanges involved in these protocols are another example of management data.
- The first WiFi standard was developed in 1997.
- At the time of writing, the latest WiFi standard to be published – IEEE 802.11g –
defines a data rate of 54 Mbps.
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- Rate for transmitting messages between stations is affected by:
The management information that is included with each frame.
the protocols used to enable multiple stations to share the communication
channel; both points 1 & 2 impose an overhead that uses up some of the capacity
of the communication channel reduces the capacity available for sending
message data (as compared to management data) -> effective data rate will be
lower than the value quoted.
Multiple users on a WiFi network As the number of user’s increases, the data rate
available to each individual user decreases.
- throughput : The practical message data rate that can be achieved in a wireless
- Even in ideal operating conditions, the throughput may be only 50% to 75% of the
maximum data rate.
- For WiFi, throughput is generally about half the maximum data rate possible on the
communication channel, giving about 30 Mbps for 802.11g networks, and this has to
be shared between all the stations on the network.
Operating range is affected by:
- Distance from the AP (or in the case of an ad hoc network, with distance from other
stations) will reduce as the distance increases.
Maximum data rates can be achieved only within about 30 m of an AP, tailing off at
distances greater than this.
For 802.11g networks the data rate drops to as low as 1 or 2 Mbps at 100 m.
- Physical barriers such as partitions and walls will further reduce the maximum rate
possible at a given distance from the AP.
- Number of stations ( no limit but in practical manufacture may put one to prevent
- The WiFi standards do not define any upper limit on the number of stations that can
join a network.
- As the number of communicating stations increases, the channel capacity available for
each station decreases.
- A point will eventually be reached when the network becomes too congested to
provide an adequate service.
Why it was developed? ( the need for it)?
- to eliminate the need for connecting wires between local ICT devices such as
keyboards, monitors, printers, PDAs (Personal Digital Assistants), cell phones and
Infrared would solve the problem so why Bluetooth?
- The requirement for line-of-sight positioning between the communicating interfaces
limits infrared’s usefulness. Because Bluetooth uses radio waves, Bluetooth devices
can communicate with each other without line-of-sight.
The Bluetooth standard: (when developed and the parties involved)?
- Is part of the IEEE 802.15 family of standards for wireless PANs. It was developed by a
group of five interested parties who, in 1998, formed the Bluetooth Special Interest
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Group (SIG) and founded the Bluetooth consortium. Now the consortium has over
Frequency used: Like WiFi, Bluetooth uses the 2.4 GHz ISM frequency band.
Microchip instead of wireless NIC: instead of using a wireless NIC like in WiFi networks,
the Bluetooth wireless transceiver and control functions are embedded in a small, low-
cost microchip that is more suitable for incorporation into small devices like a mouse or
a headset, and has a much lower power requirement than a WiFi NIC.
How devices found each other in a Bluetooth network?
- When switched on, Bluetooth devices find each other by transmitting a message
which alerts other Bluetooth devices in the vicinity.
Bluetooth network structure:
- Any two Bluetooth-enabled devices can form an ad hoc connection and establish a
personal area network (PAN) known as a Pico net.
- One device in the Pico net becomes the master unit and the others act as slaves,
responding to ‘commands’ from the master.
- Pico net which can connect together up to eight communicating devices, each being
identified by its MAC address.
Sharing the medium: The master unit controls all aspects of the communication within
the Pico net, designating dedicated time slots when each slave can communicate. This
prevents slaves from sending data simultaneously.
Number of stations:
- Eight active devices form a Pico net.
- When need for more than eight active devices two or more Pico nets can be
connected together into what is known as a scatter net.
- In scatter net, every Pico net must have one master, but a device could be a slave in
one Pico net and a master in another.
- Information can then be passed from Pico net to Pico net under the control of the Pico
nets’ master units.
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- Distance: Because of the low power output of a Bluetooth transmitter,
communication is limited to a range of approximately 10 m but this distance may be
reduced by physical obstructions.
- Bluetooth’s maximum data rate is 1 Mbps but management overhead reduce this to
an effective throughput of around 75% – usually quoted as 721 kbps depending on the
mode of operation.
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Study session (5): Comparisons
Comparing WiFi And Bluetooth:
Characteristic WiFi Bluetooth
How transmitted Wireless In ISM Band Wireless In ISM Band
Equipment Needed NIC And Possibly Access Point Bluetooth Enabled-Microchip
Maximum Data Rate 54 Mbps 1 Mbps
Approximate Data Rate 30 Mbps 721 kbps
Method For Sharing the Medium Protocols For Sharing Controlled By Master Unit
Optimum Operating Range Up To 30 M Less Than 10 M
Standards Family IEEE 802.11 IEEE 802.15
Network Structure Ad hoc or Infrastructure Pico Net Or Scatter Net
Number of node supported Depends on equipments 8 Per Pico Net But More When Pico
manufacturing but limited practical Net Connected Into A Scatter Net
A range of issue for competing technology:
- Power requirement:
Wireless devices still need a power source to provide them with the energy to
operate. The power can be provided by:
A cable connection to an electrical power socket.
A battery power in laptop and PDAs.
WiFi is more ‘Power Hungry’ than Bluetooth and so will drain the a battery much
- Wireless signal are insecure, because they travel in free space, they can picked up by
any device in range equipped with a suitable radio receiver.
- Security solution for WiFi and Bluetooth:
Authentication: is a method of controlling access to the network so that only
recognized device are accepted. This can be done using a password or the MAC
address of the device.
Encryption: involve scrambling the data in such a way becomes extremely difficult
for any unauthenticated device to unscramble it.
- Bluetooth and the 802.11g WiFi standard provide a good but not perfect data security.
- Reliability is the ability of technology to perform its intended function, without failure,
under stated conditions, and for a stated period of time.
- Issues to be raised when discussing reliability:
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What is the likelihood of data errors being introduced during transmission?
How will the technology recover from such errors?
What is the likelihood of system failure?
How does the technology perform in terms of availability of service?
Set-up and maintenance:
- Issues for set-up and maintenance:
Availability of component.
Interoperability (will device from deferent vendors work together).
Continuity of supply.
- Comparing WiFi And Bluetooth according to set-up and maintenance:
Because of its greater range and complexity, a WiFi network is more expensive to
setup and maintenance than a Bluetooth network.
WiFi and Bluetooth standard are both open, so all devices that follow the standard
The open standard is likely to have positive influence on the take-up of the
- Issue about usability include question such as:
How easy to install, setup and maintain the technology?
How easy is it to use?
What is the quality of product support?
Structuring information ( reading and writing skills):
A good structure will help the reader to follow the points the author is making and grasp
the contents of a document more easily.
Points to concern when structuring a documents:
- Headings, sub-headings.
- Grouping of points into paragraphs.
- Appropriate ordering of points.
- Use tables.
- Use numbered or bulleted list.
- Where the position any figured used.
Structuring information using headings and sub-headings give strong visual cues of what
you are going to read and helpful when you come back searching for information.
Structuring information using paragraphs is less helpful but for short sections.
- Sometimes a paragraph may contain a sentence which does not seem to fit
comfortably with others.
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Study session (6): Smart home
Smart home / automated home / networked home: where all the important electrical
device and services are linked together by a communication network so that they can be
monitored and controlled automatically or remotely.
Network home: is more likely to refer to a home with a network that connects
together entertainment devices such as television and DVD players with computers, and
often include internet connection.
Device in the home:
Events and activities involved electrical devices in a normal day:
- Domestic heating system comes on.
- Alarm clock switches on the radio.
- If it’s winter times switch on bedroom light.
- The bathroom, take a shower (adjusting the temperature to my own preferences).
- Make coffee.
- Burn the toast and the smoke alarm sounds.
- Use a remote control to switch on the TV for the morning news.
- Dry hair.
- Run the vacuum cleaner over the carpets.
- Load and switch on the washing machine.
-Preset the oven so that the casserole cooked and ready to eat on my return.
Monitoring and controlling:
- The devices that control central heating monitor the temperature of the air and hot
water and control the boiler accordingly.
- Alarm clock monitors the time and control switching on and off the radio.
- The smoke alarm monitors certain chemicals in the air and activities an alarm when
these rise above a critical level.
- If I have one of the more expensive models of toasters, it might monitor the dryness
of the beard and control the toasting time to prevent burning.
- TV can be controlled with a remote device.
- The washing machine and the oven are both operated by some kind of program
Devices for automatic control:
Sensors: are device that measure some physical property and provide an output in a
form that can be interpreted and communicated , such as
- Electrical resistance.
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Actuators: are device that take some kind of actions in response to a signal.
Examples of devices for automatic control:
- Examples of sensors:
PIR (Passive Infrared): Detector used to trigger a security light outside the house.
The smoke detectors imbedded in smoke alarms.
The temperature sensors in central heating and hot water system.
The device in the electric kettle that sense when the water is boiling.
- Example of actuator:
The electrically operated valves that control flow of water into the washing
machine and dishwasher.
The release mechanism on the washing machine door.
The loudspeaker on the audio system.
Physical property like time, temperature, and water level are changing continuously in
small time events.
- We need to capture, store and manipulate data about these kinds of data this requires
periodic sampling and the converting the sampled value into digital information.
- The amount of digital information required to represent the original analogue signal
depends on how close the representation needs to be. (More bits more accurate).
This will determine the number of samples needed and the number of quantization
Many control and monitoring applications don’t require high degree accuracy.
Smart home network:
Devices in smart home need to communicate to:
- Communicate information about the environment for examples:
Information about light.
- Give information about their state:
- Give temporal information:
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- Instruct, interrogate or acknowledge another device.
Properties of smart home’s network:
- Data rate is low: data rate of smart home network is a fraction of the capability of the
network technologies you met earlier (Ethernet, WiFi, and Bluetooth).
- Information communicated needs few tens of bits. Voice signal, an image, or a few
seconds of video needs much more bits of data.
- Many monitoring and control devices used in the home need to be activated only for a
short periods, with relatively long period of inactivate in between.
- Duty cycle: the ratio of activity to inactivity is known as duty cycle and is generally
expressed as a percentage.
- Example: a device typically connects to a network and transmits for 15 milliseconds in
every second. ( A milliseconds is 1/1000th of a second and is indicated by the symbol
ms – m for ‘mili’ and s for second).
First express 15 milliseconds in seconds
15ms = s = 0.015s.
Next express 0.015 seconds as a percentage of 1 second.
× 100 = 1.5%.
In this particular example the device has a typical duty cycle of 1.5% which means
its active for only about 1.5% of the time.
- Monitoring and control devices used in the home to be tolerant of delays between the
sending of a message and a response.
- Devices of home network characteristic that result in very low data rate requirement:
The small quantity of data needed to represent the signal.
The low duty cycle.
To tolerance of dely.
- Bluetooth and WiFi are not suitable for smart home:
They operate for data rates far in excess in the requirement.
WiFi device need some kind of NIC which would make them bulky.
WiFi is ‘energy hungry’. For device such as the smoke alarm that rely on battery
power, this could leaded to frequent battery changing.
Bluetooth would nevertheless be significant in a multi-device installation.
Bluetooth has an operating range up to only 10 m and this is reduce in situations
where are physical barriers such as walls and windows.
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Development of ZigBee standard is the result of a group of interesting parties coming
together to form the ZigBee alliance. When approved it will an open standard sitting
with the subset of IEEE 802.15.4 low data wireless standard.
ZigBee was designed specifically setup for the purposes of monitoring and controlling.
Two of the major development aims:
- It should be low cost so it is cheap to install and maintain.
- Low power for long battery life.
- The low duty cycle characteristics.
- Low data rate requirements of device it serves.
- Enables devices to enter a sleep when they are inactive.
- In the sleep state they consume very little power and this means the batteries can
have extremely long lives.
Characteristics of ZigBee wireless system:
How transmitted Radio transmit ion in 2.4 GHz to 2.483 GHz ISM frequency band
Equipment needed Transceiver, processor, small amount of memory
Maximum data rate 250 kbps
Maximum throughput Over 200 kbps
Method of sharing the medium Managed by the network coordinator device.
Operating range Up to 70 m indoors, but increasing possible using mesh rather start topology
A network coordinator: each ZigBee network must include a device called network
coordinator which is responsible for network set-up and message routing, as well as
managing data communications.
The transceiver, processor and memory can be build together into a microchip.
Because of low energy requirements of device, quit small batteries can power it for a
convention period of time.
This mean that ZigBee can be incorporated into many of home-control and remote
sensing devices without significantly increasing their size.
A mesh structure gives more reliability to the network.
- A mesh structure implies data routing capabilities, so of a node or a link fails it could
possible to find an alternative route.
In a smart home network reliability is an important consideration. For example, you
could be depending on a signal from a smoke alarm trigger a sprinkler system.
Benefit of smart home:
Relieving user from tedium of performing a lot of routine tasks.
Saving in energy the technology could bring.
Independence provided for elderly or infirm.
Automating routine tasks.
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Devices could feed information back to monitoring system.
A user can monitor his/her home remotely.
Ask the house to report certain conditions to owner when he or she was a way.
Security: the hacker can break into the smart home network.
What happened if technology goes wrong?
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Study session (7):RFID
Radio frequency identity (RFID): a system of electronic tagging where an electronic tag is
attached to an object. For example the pin described by gates.
An RFID reader is used to interrogate the tag wireless and receive information store on
it. Where the reader send out Radio Frequency Signal and the tag response with its data
in a question-and-answer type of exchange.
Information held in the tag are:
- An identity code, which may be used as reference to information stored in a database.
RFID reader transmits the tag’s information to a host computer for processing.
- The tag could store information about the object it’s attached to.
Third party: is a term borrowed from the legal profession in the context of contracts
between two parties.
RFID has been used for many years for example:
- In a proximity card entry system in buildings.
- In pet identification where a microchip inserted just below the animal’s skin.
Barcode example: a barcode can identify an item as one of a particular of product.
Barcode limitations: (RFID capabilities):
- Barcode can’t identify an item individually and uniquely.
- Barcode cannot provide access to other information like:
The length of time was stored in the warehouse.
The name of the carriers who shipped it to supermarket.
The length of time it has displayed in the shelf.
- The scanner and barcode have to be within line-of-sight of each other, and correct
recognition is dependent on the optical clarity of both of them. But RFID tags don’t
required line-of-sight so can still read through obstruction like packaging and pallets,
and some tags can be read from tens of meters.
- Barcode may suffer damage- the check out staff making several attempts to scan a
barcode, only the end up entering the number into the checkout system. But RFID tags
can suffer some damage and still be read. They’ll work in environment that are hot
Components in an RFID technology:
- A tag (consisting of electronic circuitry and an antenna), which acts as data store and
Transponder: is a device that automatically sends a signal in response to
interrogation from another device.
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- A reader (consisting of electronic circuitry and an antenna), which acts as a controller
unit and transceiver.
- A host computer system: that process and manages the information it receives from
How data about the item using RFID tag can be followed?
- A reader can interrogate multi tags and send the data from each to a host computer.
- This in turn could be connected through a network to other computers in an RFID
- In this way, the data from a tag on an item could be recorded as travels from the
manufacturer to the warehouse, through the distribution and transport networks, to
the retailer, to the point-of-sale and even beyond.
- The data could be stored on a central database to provide a complete history of the
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An RFID tag consist of:
- Some kind of encapsulation, such as epoxy resin, to bind the two together and protect
RFID main types:
Active and Passive RFID Compression:
Attribute Tag type
Power source Internal batteries Draws power from
Typical lifespan 10 years max Unlimited
Typical capabilities Read/write Read only
Read range 100 ft 1-10 ft
Typical memory size 1 Mbyte 32 – 128 bits
Physical size > passive < active
Weight > passive < active
Cost > passive < active
Reader power < passive > active
Plagiarism: is copying some else work and passing it off as your own, and is not
acceptable. Neither is lightly paraphrasing the work of other.
Paraphrasing: is the act of restating, using different words, what someone else had said.
Light Paraphrasing: means that the original words or structure are hardly changed.
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Study session (8): Using RFID and Epilogue
The driving force for RFID development is coming from the major retails who want to
track goods as they travel through the supply chain.
Benefit of applying RFID technology in tracking goods:
- Reduce the manual checking necessary.
- Cutting down on labor cost.
- Reducing human error.
At the time of writing the cost of an RFID tag means that is the only economically viable
to tag things like pallets, cases and high-value goods.
Retail who currently are using RFID tags:
- Marks, Spencer carried out trials of individual item tagging.
- The UK supermarket giants Tesco has trailed the tagging of razor
Rewrite this chapter hos.
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Block (3): Entertainment and Information.
Part (1): Entertainments
Study session (1): Introduction.
Generic communication system:
In digital broadcasting:
- User1 might be the production company that generates and record an audio or TV
- The transmitter would be owned by a broadcasting or other company:
Take the file prepared by user1.
Manipulate it into form suitable for broadcasting.
Transmit it by terrestrial, satellite or cable mean.
- Network carries out functions that would depend on which of these mean used.
Terrestrial digital broadcasting, there may be route selection in order to send the
data to a number of different transmitter.
Satellite or cable distribution, again there would be a need to select routes at some
point of the system, possible with intermediate storage.
- The receiver:
The files are manipulated in a form suitable to be seen or heard by user2, the
viewer or listener.
For broadcast service there would be many such user, so diagram should really be
modified to reflect this. By adding additional receivers and user blocks at the right
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DVD Player Representation:
Processes carried out:
- Receives: information from the user about play, pause, fast forward, select subtitle,
etc, may store such information in internal memory.
- Retrieves: the data from disk.
- Manipulates: the data read from the disk into the appropriate audio and video signals.
- Sends: the audio and video signals via integral or separate TV or hi-fi system.
Time, Space and ICTs system:
ICTs system can recognize time and space for both entertainment and information.
- The time aspect: synchronous and asynchronous communication.
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Study session (2): Digital ICTs.
Examples where digital technology are used in entertainment activities or products:
- Digital radio and TV broadcasting.
- Digital production and recording of music and video.
- Digital control of lighting etc. for concerts and clubs.
- Computer games.
- Digital special effects and even digital actors in cinema.
- Digital cameras.
Ways of representation information (particular aspect of real like temperature) to be
stored, transmitted and manipulates:
- Analogue representation:
The representation is a direct counterpart (analogue) of the real-world aspect that
we are trying to capture.
In an analogue representation, one medium is a direct counterpart of another, a
sound signal, for example, can be converted into an electrical analogue and then
stored or transmitted. The variations of the electrical analogue show the same
pattern of variations as those in the original sound wave.
Analogue signals vary continuously over a given range.
Analogue representation can generally take on any value within the range.
Sound is rapid variation, up to about 20 000 per second in pressure, transmitted
through the air or some other medium such as water or metal.
In analogue sound recording, the variations in the air presser were converted to a
corresponding variation in a wavy groove in a vinyl record, or magnetization of a
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Until the end of twentieth century many of the technologies used to store or
transmit information where analogue in form: telephone, radio, television, venial
disc and magnetic tape.
- Digital representation:
Codes using a limited set of symbols are used to represent the original information.
A limit set of symbols is used to store, transmit, or display a coded version of the
So a digital representation can have only cretin values.
Printed text and Morse code are an example of digital representation, as the
numerical display of a digital room thermometer.
Morse code is an example of a digital coding schema. Three symbols used (dot,
dash and space) are used to code any messages.
Any analogue signal can be converted into corresponding digital one, by using code
to represent the original analogue signal.
In principle, digital codes can be used to represent any type of information.
On a computer screen, images are generated by dividing the display into a large number
of tiny units called pixels (from picture elements).
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- Each pixel can generally be displayed in a number of different colors and brightness.
- The grater the number of pixel used for a given size of display, and the greater number
of colors, then the higher the quality of the image.
The representation of black and white images: 8 rows of sixteen pixels:
- The staircase effects are important features of digital display.
- In binary representation just two symbols or states are used. The two states are
representing as 0 and 1.
Inside the computer these binary states could be two different values of an
electrical voltage or electrical charge. A low voltage could represent a binary 0, and
a high voltage represents the binary 1.
In magnetic storage media, such as hard disk, two different patterns of
magnetization are used.
For transmission over optical fiber, the two states are the presence or absence of a
short pulse of laser light.
In CDs and DVDs the two states are differently shaped microscopic indentation in
the surface of the disk.
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- And image can be converted into a set of binary ones and zeros that we could store or
transmit using any digital technology at our disposal.
- Suppose black pixel = 1, and white pixel = 0, write the binary code representation of
the triangle of figure 5.
- Once the information (image) is coded in digital form, all sort of possibility for
manipulation the information arias such as black to white or one color to another.
- By increasing the number of pixels we can improve the resolution. Get high-quality
black and white image.
- Double the number of pixels horizontally and vertically will quadruple the total
number of pixels in the screen.
- A binary digit is usually known as a bit, a bit can take only the value 0 or 1.
Example: four color image (Red, Blue, Black, And White):
- We need to allocate 2 bit for each color, two bit per pixel.
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For eight colors, we need to use three bit for each color, three bit per pixel.
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Binary word: a sit of a given number of bits used for data representation, not just for
To represent 16 different color we need 4 bit binary word.
Bitmap: coding schemes that code color and brightness values directly- normally to
computer files with the extension .bmp that can be displayed by a wide range of
JPEG: other techniques use information about human perception to reduce file size.
They still assign binary code to pixel, but in different way, and not usually called Bitmap.
Vector graphics: is a coding image technique, instead of sending or storing information
about each pixel, information about the different shapes in the image is used.
- Vector graphics are most appropriate where the image is made up of regular shapes.
As the case in many web and computer games.
- For example: a straight line can be defined simply by its starting and ending points.
- In this way, file size can be kept much smaller than a bitmap.
- It is also easy to produce animations of such shape.
- The vector graphics approached is not effective.
The binary numbers game:
The same principles apply to the representation of sound, text, and other sources of
Each time you increase the length of the word by one bit, you double the number of
different binary codes possible.
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A common bitmap format for displaying reasonable high-quality computer images, such
as those generated by digital cameras is to use 24 bit for each pixel.
- Pixels required for 1024 × 768 screen resolution:
Screen resolution 1024 × 768 = 786,432 pixels.
Each pixel needs 24 bits for the color information 786,432 × 24 = 18,874,368.
Important note: do activity no 15.
Advantages of digital technology:
The ease with which digital data can be processed.
- Changing the color of simple image, just you need to change all binary 0s with 1s and
- Easy editing.
- Generation of special effects.
Dealing with errors (the way errors can be detected and corrected).
- How errors can happened:
There is always some chance that a bit will be misinterpreted. If electrical voltage
are used, for example, interference from other electrical machinery or devices can
- How errors can be detected:
One simple way to reduce the error rate is to transmit each bit 3 times:
110101100 would be transmitted:
111 111 000 111 000 111 111 000 000.
Suppose the sequence has been received with 4 errors which underlying in the
111 101 000 111 100 111 111 001 010.
It’s still can be represented as the original sequence.
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In practical systems, the likelihood of any single error is very much lower, and such a
‘transmit three times’ scheme can be extremely reliable.
-ve of the ‘best of three’ strategy:
- increasing the number of bits used to code the information by a factor of three the
file will take three times longer to send, or the bit rate will have to be increased by a
factor of three more expensive (in time or money or both) to store or transmit the
- And there is an extra ‘overhead’ in the additional processing needed to construct the
‘triplet’ format, and then to check it for errors on decoding.
+ve by incorporating enough redundancy: transmission of information in digital form
highly reliable, giving potentially much higher-quality sound and images in
entertainment and other products than was possible in earlier, analogue systems.
Transmitting a bit stream at a higher rate can result in a greater proportion of errors.
The precise design of error correction systems therefore requires careful consideration
of a number of such ‘trade-offs’.
Transmitting a greater number of bits than is strictly necessary to code the original
information is known as ‘adding redundancy’. If there is no possibility of error, then two
out of the three bits in each triplet are redundant. Adding redundancy, however, gives
us the means to combat errors. In the triplet example we could say that there is 2/3 =
If each bit has been transmitted twice instead of 3 times then the receiver will be able to
tell that there has been an error, because the two bits will differ, but it will be
impossible to know which is correct. Transmitting each bit twice means that there is 1/2
= 50% redundancy; this compares with 67% redundancy for the triplet example.
Transmitting each bit twice is an example of an error detecting code. Error detecting
codes can be used when, for example, a receiver can request the retransmission of data
known to contain an error (in some internet applications, for example).
The triplet scheme is an error correcting code. If there is no possibility of requesting a
repeat, error correcting codes are often used (in transmitting images from deep space,
for example, when the signal may take hours or even days to reach Earth).
The type of error protection that is appropriate depends on the nature of the
information being transmitted.
- In many cases, the occasional bit in error will not detract from the value of the
information (a telephone conversation, for example).
- In other cases (a computer program, for example), even one bit in error might render
the information completely useless.
Common digital technology for all applications. Examples include audio, video, motion
picture, photography, etc., and the rise of the internet as a common delivery medium.
- Until recently text, audio, video, film were all completely separate in the technologies
For example, the sound recording system developed for film (motion pictures) in the
early part of the twentieth century used an optically recorded soundtrack placed
alongside the movie images. In this technique, illustrated in Figure 9, the sound wave of
the soundtrack is converted into a continuously varying optical pattern printed
alongside the images. A light is shone through the optical track, and a sensor converts
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the varying light intensity to an electrical signal which then feeds an amplifier and
The optical sound track is analogue. The clue is that I said the optical pattern is
‘continuously varying’ -- in effect the proportion of black to white corresponds to the
sound intensity at any given time.
The sound system of the cinema was completely different in character from other audio
recording systems such as vinyl disc or magnetic tape.
Factors in the rise of ICT,
- Increasing commonality in digital techniques.
The coding schemes developed for movies, digital photography and MP3 music files
have a great deal in common.
All such files can be processed and recorded in a similar way -- basically by
means of computer hardware and software -- something that brings about
significant commercial advantages.
The enormous expansion of the internet in the 1990s, particularly since the
development of the Web. As a universal digital network became available to an
increasing number of people, the advantages of storing, processing and transmitting
information in digital form became ever clearer.
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Problems of digital recording, processing and transmission with the huge amounts of
data generated in for example, moving pictures:
Revolution or evolution?
One useful distinction to make in technological change is between substitution
technologies and supplementary technologies.
A substitution technology is one that completely replaces another.
- Example: the way the internal combustion engine rapidly replaced other early
automobile designs such as that using steam power.
A supplementary technology is one that continues to coexist alongside an earlier
technology for a considerable time.
- An example is the way analogue magnetic tape recordings in the form of
audiocassettes continued alongside vinyl records for many years. Both have now been
substantially replaced by the digital techniques such as in CD, DVD or MP3 players,
etc., at least for most commercial recordings.
Examples of substitution and supplementary technologies in the ICT field, particularly
for information and entertainment purposes:
- Fax continues to exist alongside the supplementary technology of email (although
computer-generated faxes quickly took off in the 1990s and are widely used).
- DVD appears to be substituting videotape cassettes, at least for pre-recorded movies -
- and writable DVDs or hard-disk video recorders are rapidly increasing their market
share for home off-air recording, for example.
- Video-on-demand narrowcasting has not substituted the video shop/library/postal
service (narrowcasting means the targeting of a programmed to individual listeners or
viewers, rather than broadcasting it to everyone within a certain area).
- The telephone did not replace the telegraph and, later, telex (a commercial system
similar to the telegraph) until the end of the twentieth century.
- Digital radio and TV broadcasting continues alongside analogue broadcasting
(replacement will be due as much to political decisions as technological
- Television and home video have not replaced cinema.
- Mobile telephony has not yet replaced land lines (in the UK and many industrialized
countries most people have both).
Factors that are important in technological change include:
- Accessibility (to all).
- Standardization because technologies that conform to commonly accepted standards
can be used much more widely than those that do not
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Example on standardization importance:
- One of the drivers of digital mobile telephony within Europe was to develop a
technology with a common standard in different countries. Compare this with fixed-
line telephony which, although operating to a common standard in many ways (so
users can talk across national boundaries), uses a variety of plugs and sockets in
different countries (Figure 10).
Aspects of standardization of two entertainment technologies --cinema and audio CD:
- Width of film strip (8, 16, 35 mm are/were all standards)
- Aspect ratio (the ratio of the width and height of the image) which determines the
general rectangular shape of the projected image
- Speed of projection (24 frames per second for cinema) was standardised in 1927. Note
that this is not quite the same as video/ television which is 25 frames per second in
Europe and 30 frames per second in the USA.
- Optical sound recording system (recall Figure 9). Audio CD:
Size of disk
Recording technique for the digital data, including the way the data is represented
as microscopic indentations on the disk.
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Others such as electrical standards for power supplies and plugs and sockets
Example on standards importance, CD players from various manufacturers have to
be compatible, as do the projection systems in cinemas nationally, and even
internationally. Similar considerations apply to video, CD-ROM, DVD, radio,
television, email, computers, and so on
When an agreed standard format does not exist, there are often ‘format wars’
between competing technologies. The way a particular standard ‘wins out’ is often
a result of a complex mix of technological, social and political effects, as you will
see from the following section.
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Study session (3): A socio-technology case study: video recording
Replacement of valves with transistor:
The chronology of some of the major technical developments in video recording and
tape and digital disk:
Year Main technical information
1956 First video recorder, standing nearly 2 m high, recording 15 minutes at 20-inch
reel tape, required air condition because of the heat generated by the
electronic circuit of the time.
1957 More compact machine approx 1 × 1 × 1.5 m, no air condition needed
1967 First Japanese transistor, color, real to real video recorder, retail price around
€500, price for a small car.
1974 Philips (VCR) Video Cassette Recorder introduced
1977 Philips home machine on sale for €600 in UK, one hour cassette tape about
€20, tape heads have to be replaced every 1000 hours at a cost €50
1978 Large-format laser disc introduced, but never achieve huge market success
1982 VHS standard emerges as clear winner, three-hour cassette down to €10.
1995 Philips/Sony and Toshiba/Warner announced and demonstrate rival digital disc
Agreement reached on a common standard for DVD
1996 First DVD sold in Japan (November)
1997 DVD Forum established to promote collaboration on future standard
Notes from the time table:
- Valves and transistors can both used in electronic circuits for amplification and other
purposes, but there are a key different.
Are known as thermionic devices; rather like miniature light bulbs.
Operates by heating a wire filament to a high temperature.
- Transistors: perform a similar function to valves:
Operates at room temperature.
Based upon solid materials such as silicon – hence the term ‘solid state’.
Was invented in 1947, but early products using transistors were not particularly
successful, or reliable.
Because of the transistor’s enormous potential to replace the valves in many
applications (with the advantages of reduce size, power consumption, and heat
generation), huge efforts were devoted over the following decades to improve the
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Particularly important was the invention of the integrated circuit, in which many
transistors and other components were fabricated on a single silicon chip, rather
than as individual devices that then had to be interconnected.
- In 1982, VHS was predominate: which have many features :
Timer that allowed several episodes to be recorded automatically.
The long play option.
Machines come available with two tape drives, to enable the user to copy tapes.
- Why VHS was better than Betamax:
Whole product model includes a lot more than technology.
To the average viewer, Betamax did not offer better quality.
VHS offered longer tapes to record, which was the consumers wanted.
In the early days expense was not a key issue.
To start with Betamax offered a wide range of rental cassette, but later VHS had a
much grate range.
Functions like long play were more interest to consumer than higher picture
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Study session (4): Dealing with the data mountain: compression
Common Compression Techniques:
Problem of data mountain: the inability to process and transmit large data files,
produced by the digital encoding of sound, images, and -- in particular -- moving
pictures, fast enough for digital television or cinema -- or even to store the information
in an easily accessible form.
Solution: data compression techniques.
Data compression: taking the original digital file (representing audio, video, text, etc.)
and converting it into a new file that uses considerably fewer bits without significantly
degrading the quality.
compression technique as shown in figure 11:
- First the source data is analyzed, to determine its properties, and how these can be
exploited to reduce the size of the file.
- Following such compression the file is stored or transmitted.
- Finally, when we want to recover the data, there is a decompression process, which
reverses the compression.
Runlength encoding, exploits situations like these by transmitting or storing information
about the length of ‘runs’ of ones and zeros, rather than each bit.
The first runlegth scheme:
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- Figure 12 is transmitted to the following binary representation
- It can be rewritten as a continuous string of binary digits, reading horizontally from
top left to bottom right, we have:
- In other words, the sequence
- So, for example, we might transmit or store a binary coded representation of:
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- Where 80(1) means a run of 80 ones, 28(0) means a run of 28 zeros, and so on.
The second runlegth scheme:
- The above scheme could be made more efficient by beginning with a code (a ‘header’)
to specify whether to start with binary ones or zeros, and then just listing the numbers
of ones and zeros
Two common applications of runlength encoding are:
- Fax machines. Runlength encoding is ideal, because a typical printed text contains
long runs of both white and black pixels. Both black and white pixels are runlength
encoded where appropriate, using special codes for the various runs.
- The JPEG standard for digitizing images, widely used in digital still and video cameras.
The data is first processed in a way that results in a data file containing a lot of zeros
(a result of suppressing information that is unimportant for human perception). This
file is then compressed using a version of runlength encoding that codes non-zero
values directly, but looks for runs of zeros.
The third runlength scheme:
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- The first runlength scheme will lead to Far from
compressing the original data, this scheme would mean several bits being transmitted
for each original single bit!
- The second runlength scheme would lead to which
would increase the file size by a small amount depending on the nature of the header.
- So a modified coding scheme scanning from top left to bottom right would simply
be which is potentially a huge compression.
- A fourth possible runlength scheme might be scanning in a different way -- a vertical
scanning scheme would pick up runs of ones and zeros, in contrast to a horizontal
technique. But then extra information would have to be included about which way to
scan something that would also add an overhead.
The important point to note here is that the characteristics of the original data source
are vital in deciding exactly what sort of compression to use. In the compression
schemes used in current audio, image and video encoding, the original data is analyzed
in various ways in order to code the data most efficiently.
- Lossless compression: none of the original information is lost: it is possible to
reconstruct the original data file perfectly, bit by bit. The runlength coding and
dictionary-based coding are lossless compressions.
- Lossy compression: the original file is processed in a way that preserves the important
information, but discards other information that is less important for the particular
application. The original data file cannot be reconstructed perfectly, but if the
compression is done appropriately, the reconstructed version will be fit for purpose.
The first stage of JPEG, which results in a data file containing a lot of zeros, is lossy
compression, but still leads to a final image of acceptable quality. also perceptual
coding techniques are lossy compression.
- a very powerful form of lossless coding
- an example is the widely used ‘Lempel-Zev- Welch’, or LZW algorithm, found in the
popular Winzip compression software, and also in the GIF format used for images in
The LZW format operates on binary codes of any type of source file. In essence, the
- Look for repeated binary patterns
- Build up a ‘dictionary’ of codes that represent the original, longer repeating binary
patterns using fewer bits
- Update and modify this ‘dictionary’ as the file is processed
- Select the dictionary codes in a way that makes the compression efficient -- for
example, the most commonly occurring patterns are allocated shorter binary codes.
- Note: In the coding of text we need to include things like upper- and lower-case
letters, spaces, punctuation marks, fonts, etc. When the compression algorithm
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operates on binary files, all these aspects are represented in the binary code, and are
taken into account in the selection of recurring binary patterns.
- Read the following and find out repeated words:
Looking for repeated patterns in the first sentence, we could begin to build up a
dictionary as follows:
Now replace some of the words by the codes (numbers) that represent them, so
the first sentence is encoded as:
Moving on now to the rest of the extract, we could extend our dictionary:
The whole extract can then be represented as:
Sending the dictionary: When we store or transmit this coded form, we also have to
store or transmit the dictionary along with the code.
- In short texts, this does not result in a significant compression, since the need to send
the dictionary adds a significant overhead.
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- In longer texts, we tend to find many more repeated words (or letter groupings), and
the compression can be much greater, so the need to send the dictionary is not a
Perceptual coding schemes:
- Lossy coding ones
- Use the power of digital processing to exploit the nature of human hearing and vision.
In this way, enormous compression can be achieved in comparison with the sort of
digital coding that does not take perception into account.
- In contrast to the LZW algorithm, which treats all binary files identically, in perceptual
coding the nature of the source information is very important in the way the binary
code is created.
- Found in the MPEG set of standards,
Developed by the Motion Picture Experts Group.
These have become some of the most important standards in the entertainment
They cover both audio (including the MP3 format used in digital players) and video
(digital television as well as movies).
The nature of human hearing has always been an important factor in the technologies of
sound recording and reproduction.
The range of frequencies (high and low notes) that humans can hear is restricted So
in any audio recording technique there is no point trying to record sounds outside this
Analogue audio recording and transmission techniques have always restricted the
frequency range to one that is considered to be ‘good enough’.
‘Good enough’ is an important criterion, and differs between applications.
- The quality of sound on a telephone is good enough for understanding voices easily,
but is not considered adequate for music.
- The quality of mobile telephony is sometimes significantly worse than that of land
lines, but is acceptable because of the convenience of a mobile.
- Decisions on what exactly is ‘good enough’ and ‘acceptable’ for a given application are
taken with the aid of panels of users, who grade the different possibilities during the
development of the technologies.
- Humans are much more sensitive to sounds at some frequencies than others.
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Figure 14 is a graph showing how loud a sound has to be at a particular frequency in order
for it to be perceived by a human.
The frequency axis of Figure 14 shows in numerical terms of hertz (Hz), the unit of
The loudness axis was not labeled with numerical values -- it’s not worth going into
details here of how the loudness of a sound can be quantified.
The threshold line represents the border between audibility and inaudibility -- where
the threshold line is lower, the ear is most sensitive.
Most people can hear only sounds louder than the threshold line shown in Figure 14 for
a given frequency.
In the MPEG-1 and MPEG-2 standards, designed to be used with multimedia CD-ROMs
and digital television, the audio signal is analyzed and compared with a graph similar to
that shown in Figure 14. Audio content that falls below the threshold for a particular
frequency is not coded, since it will not be audible to most listeners.
Look again at Figure 14. According to this figure, to what frequencies in the range 1 kHz
to 10 kHz is the average human (a) most, and (b) least sensitive?
The threshold line indicates the quietest sound that can be heard. So the ear is most
sensitive where the threshold is lowest, at about 3500 Hz or 3.5 kHz. Similarly, it is least
sensitive where the threshold is highest within this range, at about 9 kHz.
A further complication of human perception is that a loud sound at a particular instant
in time affects the shape of Figure 14. A loud sound at one particular frequency
decreases the sensitivity of the listener temporarily to other nearby frequencies -- so if a
particularly loud sound occurs, even more of the rest of the audio signal can be ignored
by a recording system (for a short time), because it will not be perceived by the listener.
The MP3 standard can reproduce music that most people find equivalent to CD quality,
but using only a fraction of the standard CD bit rate.
In any compression technique there is always a price to be paid.
- The MPEG audio coding schemes demand highly complex analysis of the audio signal
at the recording/transmitting end in order to obtain the desired compression.
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- Players using an MPEG standard also need to process the information quickly in order
to reproduce a high-quality version of the original.
This requires suitably fast processors at a price consumers are willing to pay.
One reason that manufacturers have been willing to invest in the mass production of
such complex hardware is market confidence in the MPEG formats.
Image and video coding
Digital image and video coding also exploits aspects of human perception.
Techniques used in MPEG coding schemes related to human perception:
- Human perception is less sensitive to color than it is to brightness. Information about
color and brightness can be coded and recorded separately use fewer bits to code
color information than are used to code the brightness
- In motion pictures (cinema) or video, there is often very little change between one
frame and the next, at least during a particular scene. So, for example, lips might
move slightly, but the head stay still; or a background is the same, while the
characters move only the changes are important, so information about changes
could be recorded/ transmitted, rather than a whole image.
'Motion compensation’ in the MPEG standards:
There are three types of individual video frame:
- Some frames are coded completely independently -- so-called I-pictures. I-pictures are
used, for example, for the first scene in a video clip, or when a completely new image
- Some frames are coded by predicting the movement of a particular object in a scene.
These are called P-pictures. For example, if an object is moving smoothly between one
frame and the next, it is only necessary to transmit information about the motion,
rather than coding that small section of the image each time it reaches a new position.
If the motion is regular, prediction can be used for several frames ahead with
- Some frames, called B-pictures (the B stands for ‘bidirectional’), are obtained from the
coded data by interpolation -- for example, by taking an I-picture and a P-picture and
generating an intermediate picture by averaging the characteristics of the two.
Interpolated frames are constructed at the receiving end on the basis of I and P
frames, which means that there is no need to transmit any data for B frames.
The sequence of decoded frame types when all is going well is, in the European
In other words, two B-pictures between consecutive I- or P-pictures, and 12 frames
between each I-picture.
If, for some reason, this approach does not give good enough quality, then a new I-
picture is introduced to start the sequence again.
As with other types of compression, there is additional processing involved at the
receiver to ‘undo’ the compression. In the case of motion compensation this can result
in a significant delay between the reception and the display of the moving image. Such a
delay can be important in live TV using MPEG coding, such as interviews, when any
delay longer than a fraction of a second can result in practical problems of maintaining a
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Joint Photographic Experts Group -- JPEG.
One of the most important standards for still photo image coding (also used as part of
JPEG files (file extension .jpg).
Processes images and remove or reduce some components because they’re not
important for human vision.
Files in JPEG format can often be a small fraction (just a few per cent) of the directly
encoded bitmap file without appreciable loss of quality as perceived by most people, as
will be clear from the computer activities.
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Study Session (5): The influence of computer game technology
Why we study the effect of computer games development?
- Computer games have had a major effect on the development of ICTs for
entertainment, and many of the techniques developed initially for games have been
applied elsewhere in the ICT sector -- in scientific visualization and modeling, for
Read the extract of"The Wizardry of Id" article.
It is about half of an article describing the contribution of one innovative games
company, Id Software.
The extract describes and explains some of the ways computer games were influenced
by, and influenced, PC development.
The journal it’s taken from, IEEE Spectrum. So readers are expected to be professional
engineers with at least some background in electronics, but not necessarily ICT
Hints for extracting other articles:
The three dots are called ‘ellipsis’, and used when you deleted parts of the original
article that are not particularly helpful for your study.
The square brackets are used to indicate any change from the original when you quote
Strategies to cope with material you don’t fully understand
Pose yourself one or two questions, rather like the questions I asked in Activities 31--33,
and bear these questions in mind as you read.
Highlight important sentences or passages, or make marginal notes as you go along.
Write short summaries in response to your own questions.
If you don’t understand a section, try to decide whether it is important. If it is, go back
to it; but if it is not important for the task in hand, just accept that you do not (fully)
Notes on the article ( from the activities):
How John Carmack managed to speed up the scrolling:
- Carmack exploited the increased memory of the new EGA video cards. He used the
memory to hold several low-resolution images, rather than the single high-resolution
one for which the card had been designed. These low-resolution images could be sent
to the screen very quickly, resulting in smooth animation.
- Carmack wrote some graphics software that enabled rapid scrolling. The screen
background, plus an extra ‘border’ area, was held in the graphics card memory. When
a player moved, the area actually displayed on screen was just adjusted slightly. Most
of the time there was no need to draw any new background.
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What is raycasting? How did Carmack simplify the technique?
- Raycasting is a technique for identifying which parts of a three-dimensional scene can
be viewed by an observer at a particular point. Imaginary rays are ‘drawn’ from the
observer to the scene. Only the surfaces that are visible to the observer are drawn on
the screen, reducing the load on the computer.
- Carmack simplified this technique by using a 3-D environment in which all the walls
were of the same height. This meant that the number of rays required could be
How did Carmack obtain sufficient shades to produce an adequate display of the gaming
- Carmack restricted the number of colors to 16 (the VGA allowed 256), but each of
those was available in 16 shades, using up the 16 ·16 = 256 possibilities. So although
the color variation was limited, there was a wide range of shades available to simulate
depth in the image.
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Study Session (6): Bringing the news on the back of a horse
Before the industrial revolution, news was transmitted by a messenger called 'Pistol' on
the horse back.
An example of how it was slow for news to reach people is the comic scene from
Shakespeare’s Henry IV Part 2 in which Falstaff hears the news that his former friend and
drinking partner, Prince Hal, is now King Henry V, following the death of Henry IV. It is a
scene set in Gloucestershire, 200 km from the royal court in London, and it is clear that
before the messenger arrived on horseback Falstaff did not even know that Henry IV had
Think for a moment about the following aspects of news dissemination during the time of
Henry IV and V (15th century), or any time before the Industrial Revolution.
(a) What determined how fast the news could get from one place to another?
The fastest means of transport on land would have been a galloping horse, so we can
think of news travelling at up to a few tens of kilometers an hour.
(b) What determined how much information you could get about an event?
If a messenger is bringing the news, then perhaps the amount of information they can
carry is determined by how good their memory is. They might also, or instead, have
something in writing (exploiting technology) and the text could supplement their
memory. Either way, a messenger can bring quite a lot of information.
(c) What determined how many people could find out about an event?
If the spread of news is relying on word of mouth, then we can imagine news spreading
in the way of the ‘office grapevine’ today, where one person tells two or three others
who each tell another two or three people and so on. The total number of people who
know the news rises rapidly in this way. Alternatively, if the news is written down, the
written text can be passed around and read by more than one person (assuming
widespread literacy). Even better, once printing has been invented, large numbers of
copies can be produced and many people can read it at the same time
(d) How far could news travel?
In principle there is no limit to how far news can travel -- it just might take a long time,
since the speed at which it travels is limited to that of a galloping horse. In practice,
only the most important news items are likely to get very far
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Study Session (7): From newsreels to real news
Development on the news idea after the industrial revolution.
People kept up to date with the news through various sources
We have the businesses of newsgathering and dissemination ( )نشرof news.
In this session you will study the development of the technologies used for news-
gathering and dissemination by reading extracts from a paper written by one of the
leading experts in the field, E. V. Taylor. Taylor presented the introductory talk of the
colloquium entitled Capturing the Action: Changes in Newsgathering which was held by
IEE in 1995, UK.
A colloquium ( )حلقة دراسية دis a meeting at which specialists give talks on a topic or on
related topics and then lead a discussion about them.
There are two factors which you should bear in mind as you read the paper.
The audience was already familiar with many of the concepts and the specialist
language (‘jargon’) that he used because they were people working in the field or with
specific interest in newsgathering
The informal style he uses because this is essentially a script for a talk to a colloquium.
Although the colloquium digest is available as an IEE publication, its primary distribution
was to delegates who attended the colloquium (it would have been given to them when
they arrived on the day). It would be used as a reminder of the talk and to fill in some of
the factual details that the audience might have missed. It was not produced as a stand-
alone document in the form you would find in a journal. There are no section headings,
for example, and it is written using language similar to the language Taylor would have
used when speaking.
Following is a list of news related terms:
- ITN (from 1955) stands for Independent Television News. To quote from the ITN
website (ITN, 2005), ‘ITN is one of the largest news organizations in the world,
producing news and factual programmers for television, radio and new media
platforms, both in Britain and overseas. ITN was founded in 1955, as an independent
organization owned by ITV companies producing news programmers for national
broadcast on ITV.’
ENG (late 70s and early 80s) is an abbreviation of Electronic News Gathering. It is the
process of recording sound and images electronically, originally as analogue signals on
magnetic tapes (video and audio tapes), and conveying them back to the newsrooms in
an electronic format; this could be done by physically transporting the tapes or sending
the electronic signals over a communications network. ENG is here contrasted with the
previous use of film.
Video servers, digital compression and digital tapeless integrated newsrooms. Video
servers are computers with large storage capacity (large hard disks or sets of hard
disks) used to store and retrieve compressed digital video files. News editors in the
‘digital tapeless newsroom’ will be working on computers that interface with the
Early information and communication technologies and the extent to which they had an
impact upon newspapers:
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- the development of the telegraph by William Cooke in 1837
- the telephone by Alexander Graham Bell in 1876
- Not until the 20th Century that lines infrastructures were developed sufficiently for
newspapers to be in a position to report the remoter national events in the same
week that they occurred.
- Photography had been invented in the 1830s but even by the 1900s newspaper
photographs were a rarity and stories were frequently illustrated by sketches,
diagrams and cartoons
- Development of the wire picture by Reuters in the early part of the 20th century
This development enabled pictures to accompany the telegraphed or telephoned
reports from many major cities in Europe and the US.
- Taylor highlights the development of the lines infrastructure and invention of the wire
picture as being developments that enabled telephony and telegraphy to be exploited
by the news industry.
Taylor compares the merits of radio and newsreels, as sources of news, with those of
- The value of radio as a communications medium had proved itself during the 1914—
- at the time radio broadcasting began, the newspaper industry did not regard radio as
a threat but more as a useful advertising medium to alert the public to the fact that
something interesting or dramatic had happened causing them to dash out to buy a
newspaper to get the details and all important pictures to fill in the gaps in the radio
- During the 1930s the ability to add live action sound onto film (there was no sound on
early film) caused the cinema industry to explode onto the mass entertainment
scene ‘newsreels’, which were a compilation of the week’s best visual stories shot
and made on high quality 35 mm film(width of the film. The wider a film,
- The bigger the picture and the higher the quality of the projected image), were
- So it had taken around 100 years to develop a means and organization from the
original enabling telegraphic and photo graphics technologies to deliver moving news
images to the public albeit somewhat later than the actual event.
- During the 1920s and 1930s.
ewspaper. Merits: (still) pictures, details of news stories, and you can choose when
and at what pace to read. Limitations: delay (not live), no moving images, no
adio. Merits: live reports, sound. Limitations: no images.
ewsreels. Merits: moving images sound. Limitations: delay (not live).
- Today’s television has the merits of radio and newsreels -- live reports with sound and
moving images -- but often not as much depth and analysis as you can get in
newspapers, nor does it have the time flexibility of newspapers.
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The early days of television
- Restarted TV ... reborn. The BBC started a TV service in 1936, but it was suspended at
the outbreak of the Second World War in 1939. It was restarted after the end of the
- In 1955, ITN started. Recent improvements had been made to the quality of film stock
and ITN took the then controversial decision to adopt 16mm film. Compared with
35mm equipment, the 16mm camera was very light, more manageable and much
more affordable to purchase and operate. It was therefore more suitable for volume
- By the end of the 1960s, color introduced.
- In the latter half of the 1960s the development of the communications satellite, which
was to have a major impact on the immediacy of TV news.
- By the early 1970s the satellite networks had become global and TV news companies
were regularly including illustrated stories from around the world into their evening
news programmers despite the very high price tag of $2,000 for a 10 minute slot.
- The newspaper industry was now beginning to worry -- television news was able to
include stories in late evening bulletins which the dailies did not have for their next
- Communications satellites. Orbit the Earth and allow communications by microwave
links between terrestrial locations that are a long way apart (Figure 1). They can be
used for communications between fixed locations on the Earth or else to provide a
wide coverage for mobile users. The original use was only for fixed locations, because
the ground stations (the transmitting and receiving aerials and associated equipment
on the Earth) needed for the users on the Earth were too large to be mobile.
- Satellites have to be orbiting in order to stay at a fixed height above the Earth, and the
speed at which they orbit is related to their height. The higher they are, the longer
they take to go once around the Earth. At one particular height -- about 36 000 km
above the ground -- the orbit time is 24 hours. If a satellite’s orbit is a ring directly
above the equator at this height, the satellite will remain over the same spot on Earth.
Such an orbit is known as a geostationary orbit, and a satellite in a geostationary orbit
is called a geostationary satellite.
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Telstar I was the first communications satellite that allowed television signals to be
sent across the Atlantic, in 1962. Telstar I was not in a geostationary orbit and as a
consequence was only in the right position to allow transatlantic communications for
30 minutes at a time, three or four times a day.
The era when film was replaced with analogue electrical video.
- newsgathering was still all film based
In 1976 RCA (which originally stood for Radio Corporation of America) is the company
that manufactured the equipment it called ‘Hawkeye’, which was one of the first
examples of what we now call a ‘camcorder’ -- combined video camera and recorder
and replaced news film.
the disadvantages of film were that:
- there were processing delays
- the equipment needed to convert from film to electronic video for broadcasting (the
telecine equipment) was expensive and bulky
- It could not be used for live coverage.
By 1979 the ENG revolution was gathering momentum and it soon became
In 1980 ITN became the first UK broadcaster to introduce large scale ENG operations.
By 1982 film as a newsgathering medium was dead.
TV news was now moving into the position of being the public’s primary source of
news, with newspapers accepting that they had lost the battle.
It had taken TV news just 30 years from its inception to reach this dominant position.
The news reels of the 1930s, 1940s and 1950s were long gone and the demand for real
up to the minute news was growing even stronger.
Well, there were still large areas of the world which did not have a wideband cable
infrastructure or possess large expensive satellite ground stations and these became
the next technological battleground.
These communication dead spots provided the challenge to fire the development of
transportable ground stations.
In 1985 ITN formed an alliance with the IBA and McMichael Electronics to develop the
world’s first SNG uplinks -- the News hawk -- which we first used in 1986.
Into the digital era
By the mid-1990s therefore one could be forgiven for thinking that news
providers had all the technology they needed to deliver real news from more or less
anywhere in the world.
Benefits of digital techniques are attractive to news companies
- opened the way for video signal processing to be carried out on economically priced
standard computer platform
- The potential for digital computer based solutions to deliver high quality news
programmers free from the multigeneration limitations of analogue VTRs
- the editorial inflexibility of tape based production where stories cannot easily be
altered or updated and at the same time achieve substantial operational cost savings.
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the digital newsgathering promise:
- More efficient newsgathering.
- More options for getting the story back.
- Faster post production.
- Greater editorial freedom.
- Broad multiskilling opportunities.
- Easier automation.
- Improved technical quality.
- Lower operating costs.
Important dates in the development of newsgathering and news broadcasts.
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When considering the relationship between technology and society it is often helpful
to consider influences in two directions: (Thinking in terms of the user as the news
industry (journalists, and newspaper, radio or TV businesses in general)
- Technology push. Newly developed technology creates a need that wasn’t there
before. For example: the use of cinema for newsreels. The evidence is the following
extract from the article.
- Demand (or market) pull. Users have a need, and technology is deliberately developed
to satisfy that need. for example: the development of the News hawk for satellite
newsgathering. The evidence is the following extract from the article
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Introduce ‘beginning professionals in satellite and electronic newsgathering an
introduction to the technologies and processes involved in covering an event’
3.1 Introduction to SNG and ENG microwave
Taylor’s paper, From Newsreels To Real News, provided a historical overview of
newsgathering up to the time the paper was written in 1995.
This session uses an extract titles "Introduction to SNG and ENG Microwave" from a book
(Higgins, 2004) which introduces the principal elements used by a TV station to get a
report for broadcast.
The extract is divides into many sections using headings.
Basic Overview of the Role of ENG/SNG
Television newsgathering is the process by which materials, i.e. pictures and sound, that
help tell a story about a particular event are acquired and sent back to the studio. On
arrival, they may be either relayed directly live to the viewer, or edited (packaged) for
The process of newsgathering involves:
1. a cameraman
2. a reporter
3. A means of delivering the story back to the studio.
a) Recording the coverage onto tape, and then taking it back to the studio.
b) For immediacy send the coverage back by using a satellite or terrestrial
microwave link, or via a fiber optic connection provided by, the telephone
4. For live coverage, voice communication from the studio back to the reporter at the
scene of the story.
In the coverage of a sports event instead of a single reporter you would have a number of
commentators, and instead of a single cameraman, you might have up to thirty or forty
cameras covering a major international golf tournament.
Principal Elements in Covering an Event. From where it happens on location to its
transmission from the TV studio.
Suppose the story is the shooting of a police officer during a car chase following an armed
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1) Camera and sound: cameraman for shooting pictures and sound and a report for
gathering information and interviews.
2) Editing: The ‘cutting together’ of the pictures and sound to form a ‘cut-piece’ or
‘package’ used to be carried out mostly back at the studio.
1. In the later part of the 90's, the laptop editor has been introduced by digital
manufacturers. it has both a tape player and a recorder integrated into one unit,
with two small TV screens and a control panel. These units, which are slightly larger
and heavier than a laptop computer, can be used either by a picture editor, or more
commonly nowadays, by the cameraman deliver ‘faster post-production’ and
‘greater editorial freedom’.
2. A video journalist or VJ: a cameraman who can record sound and edit tape; a
reporter who can also edit tape and/ or shoot video and record sound.
(multiskilling,)lower operating costs
3) Getting the story back
1. taken back in person by the reporter and/or the cameraman
2. Sent back via motorbike dispatch rider
3. Transmitted from an ENG microwave or SNG microwave truck which finds a suitable
position, and establishes a link back to the studio, with both program and technical
communications in place.
4) Going live. The reporter may actually have to do a ‘live’ report back to the studio
during the news bulletin, and this is accomplished by connecting the camera to the
microwave link truck (along with sound signal from the reporter’s microphone) either
via a cable, a fiber optic connection or using a short-range microwave link
5) Typical transmission chain.
1. The transmission chain is between the location and the studio
2. Signals are sent back via terrestrial microwave or via satellite in either direction
Please read the extract pp 91-93, there is no need to copy it here, and follow the steps
beginning from the newsgathering from the location until it is broadcasted.
3.2 ICT processes in newsgathering
using the following extract
We find that the generic block diagram of a communication system is applicable for
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Components' processes description:
Receives from User 1 This is done by the camera and microphone,
which convert the image and sound to electrical signals.
Manipulates. Editing on site is an example of manipulation.
Send. The transmitter on the truck sends the signals via microwave.
Stores/retrieves. Higgins describes the material being recorded to tape
(remember that the unedited recorded tapes are referred to as
‘rushes’), and then retrieved (either the rushes or edited) to send back
to the studio.
Conveying. The main focus of Higgins’s description involves conveying
via microwave, but he also makes reference to taking the story on
tapes back in person or using a motorbike dispatch rider.
o Receiver (Equipment at the TV studio, including video servers and the
computers used by the editors, constitute the receiver)
Receives from network. the microwave signal (or the tapes) is received
Manipulates. Signals manipulated if any further editing is required.
Stores/retrieves. If the item is not being broadcast live then it will be
stored and subsequently retrieved at the time of broadcast --
presumably it is in any case stored for archive purposes.
In session 4 you will look in more detail at some of the technology used in the field.
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4 Anatomy of a digital camcorder
main component of a camcorder and their processes
o Lenses subsystem
o microphone subsystem
Storage used in Camcorders and their properties:
Batteries (electricity supply for many portable ICT devices)
o current, resistance, capacity, voltage
A video camera alone might not record (store) the image. It might only convert the
image to an electrical signal for display remotely on a TV monitor.
Example: video cameras for domestic security which allow you to view outside
your house by displaying the output of a camera on your television. If you connect
one of these cameras to a video recorder you can record what you see, but the
video camera does not itself contain storage
A film camera always stores an image (on film),
‘Camcorder’ is a contraction of ‘(video) camera and recorder’. Camcorder is a
combination of a video camera and a film camera: the camera which converts the
image to an electrical signal and a video recorder which records the electrical
From figure 4 we can deduce that a camcorder is different from a stand-alone PC
in that the camcorder has light and sound as additional inputs.
A camcorder contains a computer which, because it is hidden from the user and it
takes inputs from other sources as well as the user, is called an embedded
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Abstraction: The approach to understanding a device or system by focusing on
particular aspects and neglecting details is a common tool of technology.
To analyze a device or system you start at a high level of abstraction, where you
consider only very broad features, then move to a lower level of abstraction
where you look at more details.
4.1 Sound and light input
Figure 5 shows a model of a camcorder at a lower level of abstraction than Figure 4,
concentrating on the input of light and sound and the other features would be a
distraction for the moment. This is an important feature of abstraction: selecting what
A microphone converts sound in the air to an electrical signal. It converts energy or
information from one medium to another so it is a transducer.
How a microphone works? A microphone converts the pressure waves in the air to the
same pattern of voltage waves on a wire. If this pattern of voltage variation is applied
to a loudspeaker, the speaker converts the electrical signal back to pressure waves in
the air, reproducing the sound.
Microphone input subsystem
Microphone input subsystem functions
o Convert the analogue audio signal to a digital signal.
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o may digital audio signal might also be compressed, and put into a standard
The digital audio signal might also be compressed, and put into a standard format. A
well-designed system ensures that the image is sharp and bright.
Brightness of the image depends upon the size of the lens. The bigger the lens
o the brighter the image
o more difficult to make
o more expensive
o Bigger and heavier cameras.
In technology there are trade-offs between several factors. for example brightness of
the image (and therefore the ability of the camera to operate in low light levels)
interacts with cost, size, and weight and image quality.
CCD light sensor
The CCD light sensor is a transducer that converts light to an electrical signal.
CCD stands for ‘charge coupled device’,
Physically a CCD light sensor is an integrated circuit with a transparent cover.
Under the cover is a rectangular array of light-sensitive electronic components called
Each photo site provides an analogue electrical output that measures how bright the
light is on that site. Each photo site can therefore contribute one pixel to the detected
Important parameters of a CCD light sensor are
o The size of the light-sensitive area
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o The number of photo sites -- and hence the number of pixels in the image it
The size of the device is usually expressed in terms of the length of a diagonal line
from one corner of the rectangle to the other.
In ICT, advances in the technology lead to a reduction in the size, with the same or
better performance and maybe lower cost. CCD sensors are an example of this.
The output from one photo site on a CCD is a measure of how bright the light is at that
site. It contains no information about the color of the light.
To get color information, colored filters are placed in front of the CCD so that separate
photo sites measure the brightness in each of the three primary colors of light: red,
blue and green.
Some cameras use separate CCDs for each of the three colors whereas others use a
single CCD with different colored filters interleaved over individual sites.
Instead of using CCDs for light sensors, some cameras use CMOS (complementary
metal oxide semiconductor) sensors. CCD sensors provide better image quality but
cameras using CMOS sensors can be smaller -- but they essentially perform the same
Back to lens system: Focusing
Focusing is done by adjusting the size of the gap between the lens and the light
sensor. To get distant objects in focus, the gap needs to be smaller than that required
for close objects (see Figure 7).
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Focusing in a camcorder is invariably done with an electric motor moving a lens, and
there will be a facility to focus automatically (autofocus). Auto focusing is either
passive or active.
Passive auto focusing works by a computer embedded in the camera examining the
image (from the light sensor) to determine whether it is in focus or not.
You can tell whether an image is in focus by seeing how ‘sharp’ it is. The camera’s
computer looks for sharp edges -- sudden changes in color or brightness. These abrupt
changes will be present only if the image is in focus.
Active auto focusing works by the camera measuring the distance to the object
viewed, and using that to calculate the gap needed between lens and light sensor. It
measures the distance by sending out pulses of infrared light towards the object being
filmed, and measuring how long it takes the reflected light to get back to the camera.
During this time, between sending the pulse and detecting the reflected pulse, the
light does a round trip -- it travels out and back again. The time the light takes to go
one way is therefore half the measured interval. I’ll call this time –
The transit time is half the time between sending and receiving the pulse.
The speed of light is known, so the transit time can be used to calculate the distance
between the camera and the object.
Distance to the object = transit time ·speed of light
This can be written much more concisely using
d for the distance to the object
t for the transit time
c for the speed of light.
d = t x c Or d = t c
Figure 8 shows the quantities that are multiplied together go in the bottom two
corners (it doesn’t matter which way around), and the thing they calculate goes in the
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The speed of light in terms of how far it travels in one nanosecond (ns), which is
one thousand-millionth of a second:
t represents a time in nanoseconds and d represents a distance in meters.
d = 0.3 t
For example, if the transit time is 20 ns, the distance in meters is given by:
d = 0.3 t = 0.3 x 20 = 6
So the distance is 6 m.
Active auto focusing involves another output from and input to the camcorder
(sending and receiving the infrared pulse) to measure the distance to and object by
sending and detecting an infrared pulse.
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In figure 10 the details of the sound system has been removed to concentrate on the
light and focusing system.
Figure 10 new components' processes:
o The infrared transmitter/receiver:
Receives a digital signal from the rest of the camcorder which instructs
it to generate and transmit a pulse of infrared light.
Detects the reflected pulse of infrared light which it reports back to
the rest of the camcorder in the form of a digital signal.
o The motor output subsystem:
Receives a digital signal from the rest of the camcorder which it
converts to the appropriate analogue electrical signal that drives the
o The focusing motor:
Changes the position of the lenses so that light is focused in the light
It is controlled by the electrical signal it receives from the motor
Storage media used in news gathering:
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3. memory cards
o Is a magnetic storage medium
Data is stored by the orientation of the magnetic field in microscopic
particles on the tape.
The orientation is set when writing to the tape and detected when
reading from it.
o Can store large amounts of data,
It can only be written to and read from sequentially. It is not possible
to jump to somewhere in the middle of the tape; you have to run
through it to get there – this is called sequential access.
Compared with DVDs and memory cards, tape is less robust. It can be
quite easily damaged and wears out after repeated use.
o An optical storage medium.
Data is written to it by putting microscopic marks on the surface of the
Data is read from it by detecting the presence of the marks, which is
done by shining a laser onto the surface and measuring the amount of
o Depending on the type of disk, writing to the disk may be permanent or
reversible (for a DVD-RW, rewritable, disk). DVDs are now cheap and robust.
o Certainly data can be read from the disk any number of times with no
significant degradation to the disk,
o RW disks can be rewritten many times.
o DVDs do not need to be read serially like tape because it is possible to jump
straight to anywhere on the disk -- they are random access.
Memory cards use flash memory,
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oAn electrical storage medium
oUsed in an increasing range of applications including digital (still) cameras.
oMicroscopic cells in an integrated circuit can be set to a voltage and they
remain at that voltage by holding electrical charge even when the power is
disconnected, until deliberately changed.
o Some types of flash memory are random access, but others require sequential
o Writing to and reading from memory cards is faster than with a DVD.
o Whereas a tape has to be moved physically through a VTR, and a DVD is spun
around as the read/write ‘head’ moves across the disk, there are no moving
parts involved in using a memory card this is called solid state.
o Generally speaking, moving parts are more prone to wear and tear and failure,
so solid state components tend to be more reliable and last for longer.
o The equipment for reading and writing to flash memory is therefore more
rugged than that for tapes and DVDs.
o Example 1:
Taylor says that the 27 GB (gigabyte) capacity of the blue disk DVD provides
about 2 and half hours of recording at 25 Mbps (mega bits per second). A
gigabyte is about 1 074 000 000 bytes and there are eight bits in a byte, so 27
GB is about:
(to three significant figures). At 25 Mbps this is enough storage for:
Dividing by 60 for the number of seconds in a minute gives 155 minutes, which
is indeed ‘about two and a half hours’.
o Example 2:
If an SD card stores 16 GB, then a P2 card (which holds four SD cards) can store
4 ·16 GB = 64 GB. Using Taylor’s claim that 20 GB is enough for about 90
minutes, 64 GB should be enough for about:
Dividing by 60 for the number of minutes in an hour, that is 4.8 hours, which is
‘nearly five hours’, as Taylor says.
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Basic ideas about electricity:
Voltage (or, more correctly, electromotive force, emf): is a measure of the force with
which electricity is ‘pushed’.
Nothing happens, however, unless there is an electric circuit, which is a path from one
terminal of a voltage source (the battery, in this case) to the other, along which the
electricity can flow (Figure 12).
How much the circuit allows or resists the flow of electricity, and this is determined by
a measure known as resistance.
If a circuit has a high resistance, little electricity flows for a given voltage. If it has a
low resistance, a lot of electricity flows.
Resistance is measured in units called ohms
Current is the rate of electricity flow, which we call the electric current
Current is measured in amps.
Current is calculated by dividing the battery voltage in volts by the circuit resistance in
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For example, if a battery voltage is 3 volts and the circuit resistance is 10 ohms the
current flowing is:
o amps is a capital A.
o volts is a capital
o ohms is the capital Greek letter omega, .
o 1 milliamp, written as 1 m A. One amp is a fairly large current flow for
electronic equipment, and quite often it is easier to work in units of 1/1000 of
o Units of kilohms, k. a resistance of 1 ohm is very small for electronic
equipment and often resistance will be expressed in units of kilohms, kW
The important characteristics of a battery for a portable ICT device such as a
camcorder or a mobile telephone:
o Weight: if the device is to be portable it must not be too heavy
o Size: for a portable device it needs to be kept small
o Running time: the user does not want to have to replace or recharge the
battery too frequently
o Cost: it should not be too expensive.
Two different sizes:
1. AA size
Used in portable radios and CD players.
LR6 and MN1500 batteries are the same size as AAs.
2. C size
Used for torches, bicycle lights and portable stereo.
R14 and MN1400 are the same size as Cs
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Two battery technologies:
1. Nickel--cadmium (abbreviated to the chemical symbols NiCd, or called
2. Nickel--metal hydride (abbreviated to NiMH).
Batteries produce electricity by a chemical reaction, and nickel-- cadmium or nickel--
metal hydride refer to the chemicals used in the battery.
All four batteries in Table 1 provide 1.2 volts. This is a consequence of the chemistry
used, and the fact that each one is a single ‘cell’.
The cell is the basic building block of the battery.
Connecting in series: The way of connecting cells or batteries, with the positive
terminal of one connected to the negative terminal of the next and results in an
output voltage that is the sum of the voltages of the individual batteries. (Figure 14)
this is used in connecting batteries in radios or torches.
Batteries using a different chemistry produce different voltages from a single cell.
o A single cell of an alkaline battery (the technology used for the most common
non-rechargeable batteries) for example, produces 1.5 volts.
o The chemistry of NiCd and NiMH is similar, so they produce the same voltage
as each other.
The battery size, AA or C, characterizes the dimensions, expressed as the battery
height and diameter.
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There is a significant difference between the NiCd and the NiMH batteries in the
capacity and the price.
o The NiMH batteries are more expensive but have a greater capacity.
o The units of capacity, Ah, are ‘amp-hours’, amps multiplied by hours. (you
can’t specify a single value for the length of time a battery can be used
because it depends upon the current being drawn from it.)
o If you draw a lower current the battery will last longer. However if you
multiply the value of the current being drawn by the length of time it can be
used, you get a constant value: the battery capacity.
o For example, a battery with a capacity of 1 Ah could supply 1 A for 1 hour, or
else it could supply 2 A for half an hour or 0.5 A for 2 hours.
o If you know the capacity of a battery and want to know how long it can be
used to supply a given current, then you divide the capacity by the current.
o The relationship between capacity, running time (t) and current (i) can be
represented by a formula triangle
Example: In a test, it is found that a battery can be used for 10 hours supplying a
current of 0.4 A.
(a) What is the capacity of the battery in Ah?
capacity = i x t = 0.4 x 10 Ah = 4 Ah
(b) If a current of 0.3 A is flowing from the battery, how long can it be used for?
Time battery can be used at 0.3 A:
t= capacity / i= 4 /0.3= 13.33 hours (to two decimal places)
This is 13 hours and 20 minutes
The capacity and the length of time a battery can be used depend very strongly on the
way it is being used and the temperature.
A battery does not just suddenly run out of electricity -- it is not like a car running out
of petrol where suddenly there is no more and it stops.
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While a battery is being used the voltage falls and as the battery runs out (goes ‘flat’)
its voltage drops more quickly. When specifying a battery’s capacity a lower limit to
the acceptable voltage is specified, and the battery is defined as flat when that lower
limit is reached.
With rechargeable batteries these there are issues as:
1) To how easy they are to recharge and how many times they can be recharged.
NiMH batteries come out better than NiCd batteries.
2) Cadmium is highly toxic (poisonous) and so NiCd batteries should be handled
carefully and should not be disposed of with other waste, but should be
recycled so that the cadmium is extracted safely. For all these reasons, NiCd
batteries are falling out of favor.
Another important type of battery is based on chemical reactions involving lithium.
‘Lithium Ion’ (Li-ion) batteries are commonly used in laptop computers and other
portable ICT equipment.
A complication when comparing Li-ion batteries with NiCd and NiMH batteries is that
the voltage delivered by a Li-ion cell is around 3.6 volts, compared with the 1.2 volts of
NiCd and NiMH cells. To make fair comparisons of capacity you need to be looking at
supplies at the same voltage
If some equipment requires a 3.6 volt power supply it can use a single Li-ion cell. How
many NiCd or NiMH cells would it need, and how should they be connected?
To get 3.6 volts from NiCd or NiMH cells, which are each 1.2 volts, three cells, would
need to be connected in series, as shown in Figure 30.
5 Signal Transmissions
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Transmission of electrical signals on wires
o electrical circuit graphical representation
o Attenuation, distortion and regeneration
Transmission using microwaves
Transmission using optical fibers
Signal speeds, propagation times and distance: the formula triangle
5.1 Transmission of electrical signals on wires
To transmit a signal on wire, you operate a switch at one place and observe the effect
somewhere else. In Figure 15 this was shown as a light coming on at a remote location.
In figure 15 the standard symbols:
o For a battery two parallel lines, one shorter than the other
o For a light bulb a circle with a cross in it.
o For a switch that can be ‘open’ or ‘closed’ two dots and a line which either connects
the dots (when the switch is closed as in Figure 15b) or misses one of the dots (when
the switch is open, as in Figure 15a).
When you switch a light on, the light appears to come on immediately. In reality there is a
delay -- it is just very short indeed.
Voltmeter: a device used to measure the voltage between the wires. It has two wires and
a display. When you touch the ends of the wires to the terminals of a power source like a
battery, the display on the meter tells you what the voltage is between the terminals.
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Use the voltmeter to measure the voltage between the two wires at some point between
the switch and the light, as in Figure 17.
o When the switch is open (off) the reading on the meter will be zero.
o When the switch is closed (on), the reading will (ideally) be equal to the voltage of
the battery -- which is 1.2 volts.
o When the voltmeter is touching the wires while the switch is changed from open
to close. In this case you will see the voltage change from 0 to 1.2 V.
o Now, if the voltmeter is touching the wires right next to the switch, you would see
the voltage rise from 0 to 1.2 V at the same instant as the switch is closed.
o If the voltmeter is touching the wires further away from the switch there will be a
delay between the switch closing and the voltage rising. this is shown in Figure 18.
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Comments on Figure 18:
o The time axis is labeled in units of microseconds, where one microsecond is one-
millionth of a second. Notice also that the time axis is relative to sometime origin
which is labeled 0. The actual time corresponding to 0 as shown on the axis might
have been, say, Thursday 20 May 2004, 2.17 pm and 35.031233 seconds, but
labeling the axis with that level of detail would be confusing and irrelevant.
o When connected to the wires 200 m along towards the light bulb. The switch was
closed at time 1, on this scale, so the voltage measured next to the switch rises at
time 1. There is a one-microsecond delay between the switch being closed and the
voltage changing 200 m along the wire.
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Comments on Figure 19:
o Figure 19 shows changes on voltage when turning the light on and then off again
o The switch is closed at time 1 microsecond and opened again at time 3
microseconds. We now have a voltage pulse.
o Looking at the voltage across the wires 200 m from the switch, both the rise and
fall in voltage happen 1 microsecond later, and the voltage pulse has taken 1
microsecond to travel the 200 m along the wires.
o How fast is the pulse travelling, measured in meters per second? The pulse travels
200 meters in 1 microsecond. 1 microsecond is one millionth of a second, so in 1
second it would travel 200 x 1 million meters = 200 million meters or 2 x 108
meters. The speed is therefore 2 x 108 m/s.
Attenuation and distortion:
o Figure 20 shows the sort of effects that attenuation and distortion might have on a
o Attenuation reduces the height of the pulse, so that it does not reach 1.2 volts any
more. Some of the voltage has been ‘lost’ as it travels the 200 meters because
some energy from the electricity is absorbed by (very slightly) heating the wires
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and some energy is radiated into the air as the wires act as a (very inefficient)
o Distortion alters the pulse, rounding the corners and generally changing the
Qualitatively, the smoothing of the corners is because the wires do not
allow the voltage to change instantaneously -- there is a sort of electrical
drag as the pulse travels along the wires.
More random distortion effects are caused by what is referred to as noise.
Noise is the unavoidable effect where signals develop unwanted,
o Attenuation and distortion become worse as the pulse travels further.
o Amplifiers can be used to compensate for attenuation, but that still leaves
distortion, which ultimately limits how far signals can be transmitted along a wire
-- or indeed any transmission medium.
o With digital signals, however, regenerators can be used instead of (or as well as)
amplifiers to overcome both attenuation and distortion.
o Regeneration is that when a pulse has become badly attenuated or distorted, it
can be regenerated to produce a new, perfect pulse for onward transmission.
o Regeneration is illustrated in Figure 21.
To simplify the diagram a single line is used to represent a pair of wires.
The pulses drawn next to the line represent pulses across the pair of wires
at that location.
o Regeneration with digital signals:
With a binary signal, 1s and 0s might be transmitted on wire by using, say,
5 V to represent a 1 and 0 V to represent a 0.
The regenerator ‘knows’ that the only signal it is expecting is something
which started out either as a pulse of 5 V or as 0 V.
The regenerator decides which of the two possibilities is most likely, and
produces a new 5 V pulse or 0 V accordingly.
Although there are practical complications, in principle this decision can
be very simple. An electrical circuit compares the received voltage with a
threshold value (say 2.5 V) and if the received voltage is greater than the
threshold the output is a new 5 V pulse, otherwise the output is 0 V.
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Regeneration can be repeated indefinitely allowing transmission over
unlimited distances (Figure 22).
The boxes labeled ‘regenerator’ in Figure 22 are electronic circuits, but
interestingly the very first ‘regenerators’ were human beings! as in the
early electric telegraph.
5.2 Other transmission media
Wires are still used to carry electrical signals over short distances.
o most connections between telephones in private houses and the local
telephone exchange still use wires.
o The telephone networks within office buildings are mostly connected with
o many computer networks (local area networks, LANs) within single buildings.
All longer-distance communication, between towns, cities or countries, uses either
optical fiber or microwave systems.
Increasingly, even shorter distances use either optical fibers or wireless links of one
sort or another.
Wireless systems (such as microwave) or optical fibers pulses also suffer attenuated
microwave transmission is important for newsgathering
The term ‘microwave’ identifies a particular range of frequencies used for radio
The range of frequencies that are referred to as ‘microwave’ is from about 200 MHz to
on-off keying : to transmit digital signals over microwave by using pulses of microwave
power to represent 1s, and the absence of microwave power to represent 0s.
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o is used in microwave transmission systems, but surprisingly long distances are
possible without regeneration.
o In satellite communications the satellite performs regeneration (as well as
some other functions), but that still means that the signal has to travel the
distance from the ground to the satellite in one go (and the same distance
back). For geostationary satellites this is 36 000 km each way.
Even more remarkable is the microwave transmission that was used to send data back
from the Cassini--Huygens space exploration mission to Saturn and its moon, Titan, in
2004/05. The distance between the Earth and Saturn was at that time 1 517 000 000
km! The reduction in the signal strength over that distance is very great, so the power
of the signal received back on the Earth is small. In practice this means that the data
rate (bandwidth) is small, because there is a trade-off between signal power and data
rate. For high data rates higher power is needed. If the power is low, only low data
rates are possible.
Optical fiber (the transmission medium to use for high data rates over long distances)
In all developed countries, long-distance communication links (which used to be called
‘trunks’, by analogy to ‘trunk road’) nearly always use optical fiber.
problems in laying optical fibers:
o Where the terrain ( )التضااتسيmakes it difficult to lay a cable (such as in
mountains or, sometimes, between islands)
o When a new link is needed quickly and there isn’t time to lay a cable that
microwave links are used instead.
An optical fiber is a strand of glass or plastic, not much thicker than a human hair,
which guides light from one end to the other (Figure 23).
The guidance comes about because of an effect known as total internal reflection. This
means that light shone in one end of the fiber doesn’t come out from the sides of the
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fiber even if the fiber is bent around corners. The light just travels inside the fiber until
it comes to the far end.
Because the fiber is so thin it is flexible and, from the outside of a cable with
protective plastic coverings, looks and feels much the same as an electrical wire.
Signals are conveyed by changing the ‘brightness’ of the light injected into the fiber
and measuring it at the far end.
Bits are sent by ‘on-off keying’: 1s are represented by light on and 0s by light off.
The attraction (distinguished characteristic) of optical fiber is that it can be used for
very high data rates over long distances.
When electrical signals are transmitted over wires the attenuation increases with
increasing data rate, so the higher the data rate, the greater the attenuation and
therefore the shorter the distance that can be used.
So, optical fiber properties:
o used for high data rates over longs distances
o flexible and can bend in corners
o has the total internal reflection property
o the attenuation is not dependent on the data rate,
o the attenuation is very low
o Higher data rates require higher power (which is the case whatever the
medium used to carry the signal).
o optical fiber is generally more expensive to use than wires
More recently Optical Fiber has been used for shorter distances, including
o many new local area networks (LANs) within office buildings.
o in the links between private homes and the local telephone exchange.
1. In recent years the data rates required of many communication links have
been increasing. Since the attenuation of wires increases with increasing data
rates, many links which previously could use wires cannot do so anymore,
because the data rates are too high. Where data rates have got too high to use
wires, optical fiber is often used instead.
2. The equipment needed for optical fiber transmission has been getting
cheaper, making its use more economical in a variety of applications.
Satellites are frequently used for transatlantic ( )عبةردسطللية دcommunication, but the
alternative is to use undersea cables.
These days’ undersea cables would invariably use optical fiber.
Light in fiber travels at about 2/3 of the speed of light in the air (light travels more
slowly in glass than in the air) and therefore the signal speed is about 2 x 108 m/s.
5.3 Signal speeds, propagation times and distance: the formula triangle
When signals travel along a wire or optical fiber, or through space, the relationship
between the speed, propagation time and distance can be written in three ways,
depending upon which one you want to calculate
1. If distance is unknown
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2. If propagation time is unknown
3. If speed is unknown
the relationship between distance, time and speed is used for doing the calculations
1. for auto focusing in a camcorder
2. For the journey time driving along a motorway or cycling to work, assuming
constant speed (or using average speed in the calculation).
3. and now for signals travelling in some transmission medium.
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o One way of ensuring that you are working with consistent units is to use the
international standard units known as ‘SI’ units, where SI stands for the French
words System’s International.
o The SI unit for length is the meter and for time is the second, speed is
expressed as meters per second.
o But you don’t have to, so long as the units are consistent. For example, if you
have speed in kilometers per hour and time in hours, then distance will be in
Delay in transmission:
o Note: A delay of 0.24 seconds for example is quite noticeable if you are
chatting with someone which may stop you to wait for reply.
o Delay when using optical fiber is very much less than when using a
o There may be further delays when signals are manipulated (which can happen
both with satellites and optical fiber links), but nevertheless it remains true
that in speech telephony there is a noticeable delay when the communication
uses a geostationary satellite, but not, usually, when it uses a fiber link.
o Delays used to be commonly encountered when you telephoned the USA from
the UK, but that is rare these days because most transatlantic calls are via
optical fiber links.
o The large delay when using geostationary satellites comes about because
geostationary satellites are so far from the Earth.
o Other satellites are also used whose orbits are much closer to the Earth.
1. Communication via these non-geostationary satellites can have a
2. but there are other complications because the satellite is moving
relative to the Earth’s surface.
o News broadcasts often use geostationary satellites and therefore suffer from
the larger delay. The processing (manipulation) used in MPEG encoding,
especially motion compensation, adds yet more delay. The combined delays of
transmission and processing can cause problems for live news broadcasts.
Do Activities 33 and 34
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Authority of information sources: newspapers, TV, Radio and the Internet
Authentication of letters, emails, phone calls and web site.
authentication of pictures and effect of digital techniques on photography,
Information is worthless if you have no trust in it.
This has always been the case, but there are issues of trust that arise specifically in the
context of modern information and communication technologies. Think about the
o You do a search on the Web and get results from several different sites. Do you trust
the information in them all? How do you decide which are the most trustworthy?
o You get an email, a letter or a phone call purporting to come from your bank,
recommending a change to your account. Do you follow the advice that you are given?
o You read a story in a newspaper, hear it on the radio or see it on TV. Do you believe it?
Does it make any difference if it is accompanied by a photograph?
o In each of these cases there are two elements to your trust:
1. The authority of the information source. Do you trust the BBC, ITN or someone
you’ve never met writing a weblog? The Guardian or the Daily Mail? Your bank?
2. Authentication of the message -- does it really come from whom you think it
does? Is it really the BBC’s website you are looking at? Does this person writing a
weblog really live in Iraq? Is the email, phone call or letter really from your bank?
6.1 Authority and the variety of information sources
o printed books
o Digital techniques have increased the number of broadcast radio and TV
channels that we can get.
o the Web we have access to online versions of many of the above sources
Newspapers authority ( how they maintain standards
o Rely to some extent on their reputation. This may be damaged -- they might
lose readers -- if their stories are found to be wrong or misleading, so it is in
their own interests to maintain standards.
o In the UK, newspapers and magazines are regulated by the Press Complaints
Commission, the PCC.
There are similar considerations that apply to radio and TV to maintain standards.
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In all these cases there will be some degree of editorial control over the content, and
one of the responsibilities of the editors is to maintain standards of honesty
appropriate to their publication or channel.
The Internet: (issues that arise from the development of the Web)
o There are sources of news and information that are completely unregulated.
o The technology is such that with a minimum of knowledge and little expense,
virtually anyone (in the developed world anyway) can say almost anything
they like on a personal web page or a weblog, and, in principle at least, their
words are instantly available to millions of people all over the world.
o The absence of any regulation or external editorial control might be thought
to devalue personal web pages or weblogs as sources of news. ( no central
control is a property the Internet gained during its development)
o To what extent do websites gain authority by the number of other sites that
link to them, and by who links to them?
o Can personal recommendations replace recognized authorization?
o And anyway, perhaps regulation sometimes becomes censorship ()الرقتبة
o Who has the right to determine the editorial ‘line’?
One particular example where a weblog was able to provide news that was simply not
available through any other source is the article written by the ‘Baghdad Blogger’,
Salam Pax, who was posting reports from Baghdad in the run-up to, and all through,
the 2003 war in Iraq. As the US and British troops advanced on Iraq, news was coming
from several sources, most of which might be suspected to be censored in some way.
Salam was a resident of Baghdad who did not set out to be a reporter, but whose
interest in the Web led him to create a weblog that became seen by many as providing
a valuable insight into life in Baghdad at this time.The article (itself taken from one of
the traditional news sources: the Guardian newspaper)
6.2 Authentication of information
When you watch TV news, listen to the radio or buy a newspaper I never think to
question whether I really am watching ITV, listening to Radio Five-Live or getting the
Guardian. In each of these cases it is theoretically possible that they are not who they
say they are, but the practicalities of performing the masquerade are so complicated
that the possibility can be discarded.
With emails and websites it is a very different matter. You may receive ones from
organizations, such as Microsoft and NatWest bank which look entirely authentic,
with the correct graphics. These are scams.
The authentic appearance of the emails is meaningless, since it is almost trivially easy
to copy images from websites and paste them elsewhere, such as into emails.
Incoming telephone calls are equally suspect, and again there have been cases of
scams whereby a caller claims to be from somewhere they are not.
Letters with official documents have in the past been more reliable, since it was
difficult to reproduce headed notepaper accurately. It is still possible to generate
official documents that are hard to imitate (through the use of watermarks or
embossing, for example) but the availability of high-quality color printers has made it
easier to produce official looking documents.
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Suppose you are contacted by email, telephone or letter and you want to check
whether the communication is authentic. What could you do?
o If you already have a contact number for the organization that has contacted
you, you could call them and ask about it. This only works, of course, if you
already have the number which you know is correct.
o Email scams often contain a phone number, but that number is, of course,
A personal signature is the authentication of the letter, provided you know the
signature, can recognize it and it isn’t a photocopy.
Recognizing the voice of someone on the telephone authenticates the call.
A digital signature is a special piece of data which is added to a message.
o Authentication of emails is possible by the use of digital signatures.
o Software on the recipient’s computer can analyze the message and the
signature and determine whether the message is authentic.
o Digital signatures only work if your computer already ‘knows’ about the
o The technology of digital signatures can be used to authenticate websites. In
this case, your web browser checks the certificate of the site. This is usually
done automatically, with your browser reporting to you if there is a problem.
It used to be thought that a photograph could provide proof of an event -- someone
could be caught red-handed by a photograph, as proof of their guilt. ‘The camera
never lies’, it was said.
If you have a digital camera and have been ‘touching up’ photographs on your home
computer you will know that this is far from true now. It is easy to lie with a digital
The idea that the camera never lies has always been a myth.
As far back as 1917 the photographs of the Cottingley fairies ‘proved’ the existence of
fairies ( .)جنياتTwo girls, Elsie Wright (age 16) and Frances Griffiths (age 9), took
photographs of themselves apparently in the company of fairies (Figure 27).
Eventually, in 1981, the girls admitted that they had faked most of the pictures --
although they always maintained that one of them was genuine (.)أصلي
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One of the benefits that Taylor claimed for digital techniques is the improved options
for editing, and he contrasted digital techniques with analogue techniques where
‘stories cannot easily be altered’. The counterpoint to this is that digital stories can be
easily altered – which makes them all the more unreliable.
The artist David Hockney, who has used photography in his work, has argued that the
ease of editing digital images has made photography a dying art.
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