Communications systems was a topic I taught in senior high school and this presentation collected several definitions and examples of networking concepts.

1. Communication Systems
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2. Introduction
Communication is the transfer of data from
one location to another
Examples include:
– computer to printer
– computer to comp. on a network
– terminals to M’frame comp.
– comp. to server
– comp. to dish to satellite to dish to comp.
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3. Requirements of a
Good Comms System
message must arrive accurately
message arrives as quickly as possible
cost should be less (in time, money and
quality(more)) than other methods of
communicating data.
equipment should be reliable
data should be secure, available only to
authorised people
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4. Elements of a Comms System
Every comms system has these common
elements:
– sender
– receiver
– message
– medium
Activity: Write a definition for each
element, including an example.
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5. Medium - Links
A link is a connection between computer
devices. In the past, data communication
used cables only. New technology has
meant that non-cable links are commonly
used today.
Cable links include twisted pair, coaxial and
fibre optics.
Non-cable links include satellites, satellite
dishes, ground stations and infrared.
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6. Twisted Pair
Communications cable
consisting of pairs of plastic-
coated copper wires that are
twisted together. A thin layer
of coloured plastic insulates
and identifies each wire; the
wires are then twisted to
reduce electrical interference.
Most commonly used in telephone cables.
Susceptible to interference.
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7. Coaxial Cable
Coaxial cable is a combination of two or
more insulated wires that run inside one
another. It is protected well from
interference and is faster than twisted pair.
However, it is a heavier cable than twisted
pair and more expensive to install.
Shield
Conductor
Insulation
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8. Fibre Optics
Fibre optics is a technology in which signals
are converted from electrical into optical
signals, transmitted through a thin glass
fibre, and re-converted into electrical
signals.
The concentric layers of an optical fibre
include the light-carrying core, the cladding
and the protective buffer.
Buffer
Cladding
Core
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9. Comparison of Cable Links
TYPE OF CABLE ADVANTAGES DISADVANTAGES
Twisted Pair 1. Inexpensive 1. Susceptible to RFI
Cable 2. Often available in and EMI
existing phone system 2. Not as durable as
3. Well tested and easy coax
to get 3. Doesn't support as
high a speed as other
media
Coaxial Cable 1. Fairly resistant to RFI 1. Can be effected by
and EMI strong interference
2. Supports faster data 2. More costly than TP
rates than twisted pair 3. Bulkier and more rigid
3. More durable than TP than TP
Fiber Optic Cable 1. Highly secure 1. Extremely costly in
2. Not affected by RFI product and service
and EMI 2. Sophisticated tools
3. Highest bandwidth and methods for
available installation
4. Very durable 3. Complex to layout and
design
NOTE: Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI)
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10. Microwave Links
Microwave links are non-cable links often
used for longer distances.
They transmit data using radio waves at a
very fast rate. Both voice communications
and digital signals can be transmitted.
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11. Microwave Research Activity
Try to find answers to the following
questions:
– what is the difference between microwaves and
radio waves?
– what materials can microwaves bounce off?
– what materials are satellite/microwave dishes
made from?
– try:
www.howstuffworks.com
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12. Because the microwave beam travels in a
straight line, hardware elements must negate
the earths’ curves and provide line-of-sight
between sender and receiver.
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13. Infrared Links
 Infrared light beams are used to transmit data
between devices that are in the same general
area.
An example is between
computer devices. This
method is good because it
doesn’t require cables,
however, it is slower and
more susceptible to
interference.
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14. Input/Output Devices
In order to transmit data many different
input/output devices are used, including:
– modems
– acoustic couplers
– facsimile transceiver
– point of sale terminal (POST)
– automatic teller machine
– teletext keypad
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15. Modems
Modem is short for modulator-
demodulator.
Modems can be fitted internally to an
expansion slot or externlly via a port.
Modems convert the computer’s digital
signal into an analog signal (called
‘modulation’) required by the telephone
lines and vice versa (called ‘demodulation’).
Both sending and receiving computers
require modems.
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16. Modem Communication Process
Picture of a typical looking
external modem
Modems
Telephone Line
1 1 1 1 1 1 1 1
0 0 00 0 0 00
Digital data Analog data Digital data
Modulation Demodulation
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17. Acoustic Couplers
An acoustic coupler is a cheaper type of
modem that has a cradle for a telephone
handset.
They are not as good at coding and
decoding signals, and the rate of transfer is
very slow.
The advantage is the ability to use any
phone handset around the world.
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18. Facsimiles
Facsimile, or fax, equipment is used to
transmit an image of a document over the
telephone lines. The document can contain
text (hand-written or typed), graphics or
even photographs.
A fax machine scans the document and
converts the image into digitised data,
which is transmitted over a telephone line.
The receiving fax converts it back into its
original image.
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19. Many PCs use fax equipment and a modem
to send documents over telephone lines.
This can be sent to a fax machine or another
PC. The person who receives the fax on a
PC can print the document to receive a hard
copy.
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20. POST
Stands for Point Of Sale Terminal
Most shops have the facilities to do
EFTPOS, which uses card scanning devices
to communicate with banks.
Once the card is scanned the user is asked
for account and PIN details. Confirmation is
sought over dedicated lines between the
shop and the bank.
Occasionally lines are down and
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21. Internet Activity
Research one of the following on the
internet and answer the questions below:
Real-time auctions (start with www.internet
auctionlist.com/New.asp)
Global Positioning Systems
Groupware
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22. Networks
A network is a system in which computers
are joined to each other in order to exchange
data or share hardware
A network may comprise some or all of the
following:
– servers
– terminals
– hubs
– routers
– communication software
– ethernet
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23. Research Activity
Use reference books and/or the internet to
answer one of the following questions:
– In what ways has the progress of
communication technology reduced the world
to a global village?
– OR
– Has the use of computer communication
systems enhanced human communication?
Be sure to include adequate detail. WP your
answer.
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24. Servers
A server is a computer that shares it’s
resources across a network.
There are four types of servers:
» file servers, used to share files
» print servers, used to share printers
» application servers, used to share application
programs
» communications servers, used share
communications devices
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25. Direct Communication
When computers are connected directly, the
transfer of data is very fast.
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26. Indirect Communication
Other hardware is required where
computers aren’t directly connected. Most
common transmission media is telephone
line.
Medium of Transmission
1 1 1 1 1 1 1 1
0 0 00 0 0 00
Digital data Digital data
MoDem MoDem
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27. Hubs
A central connecting point for devices such
as computers, printers, and storage devices
that are connected to the server; also called
concentrator, or multistation access unit.
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28. Routers
An intelligent network connecting device
that sends (routes) communications traffic
directly to the appropriate network; used
when several networks are connected
together.
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29. Communication Software
Programs that perform data
communications tasks such as dialing, file
transfer, terminal emulation, and Internet
access, allowing data to be transmitted from
one computer to another.
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30. Ethernet
The most widely used network protocol for
LAN networks; can transmit data at 10 or
100 Mbps.
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