Communication is the transfer of data from
one location to another
– 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.
MAS - 12 IPT 2
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
equipment should be reliable
data should be secure, available only to
MAS - 12 IPT 3
Elements of a Comms System
Every comms system has these common
Activity: Write a deﬁnition for each
element, including an example.
MAS - 12 IPT 4
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
Cable links include twisted pair, coaxial and
Non-cable links include satellites, satellite
dishes, ground stations and infrared.
MAS - 12 IPT 5
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.
MAS - 12 IPT 6
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.
MAS - 12 IPT 7
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
The concentric layers of an optical ﬁbre
include the light-carrying core, the cladding
and the protective buffer.
MAS - 12 IPT 8
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
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
4. Very durable 3. Complex to layout and
NOTE: Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI)
MAS - 12 IPT 9
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.
MAS - 12 IPT 10
Microwave Research Activity
Try to ﬁnd answers to the following
– what is the difference between microwaves and
– what materials can microwaves bounce off?
– what materials are satellite/microwave dishes
MAS - 12 IPT 11
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.
MAS - 12 IPT 12
Infrared light beams are used to transmit data
between devices that are in the same general
An example is between
computer devices. This
method is good because it
doesn’t require cables,
however, it is slower and
more susceptible to
MAS - 12 IPT 13
In order to transmit data many different
input/output devices are used, including:
– acoustic couplers
– facsimile transceiver
– point of sale terminal (POST)
– automatic teller machine
– teletext keypad
MAS - 12 IPT 14
Modem is short for modulator-
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
MAS - 12 IPT 15
Modem Communication Process
Picture of a typical looking
1 1 1 1 1 1 1 1
0 0 00 0 0 00
Digital data Analog data Digital data
MAS - 12 IPT 16
An acoustic coupler is a cheaper type of
modem that has a cradle for a telephone
They are not as good at coding and
decoding signals, and the rate of transfer is
The advantage is the ability to use any
phone handset around the world.
MAS - 12 IPT 17
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
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
MAS - 12 IPT 18
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
MAS - 12 IPT 19
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
MAS - 12 IPT 20
Research one of the following on the
internet and answer the questions below:
Real-time auctions (start with www.internet
Global Positioning Systems
MAS - 12 IPT 21
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
– communication software
MAS - 12 IPT 22
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?
– Has the use of computer communication
systems enhanced human communication?
Be sure to include adequate detail. WP your
MAS - 12 IPT 23
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
» communications servers, used share
MAS - 12 IPT 24
When computers are connected directly, the
transfer of data is very fast.
MAS - 12 IPT 25
Other hardware is required where
computers aren’t directly connected. Most
common transmission media is telephone
Medium of Transmission
1 1 1 1 1 1 1 1
0 0 00 0 0 00
Digital data Digital data
MAS - 12 IPT 26
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.
MAS - 12 IPT 27
An intelligent network connecting device
that sends (routes) communications trafﬁc
directly to the appropriate network; used
when several networks are connected
MAS - 12 IPT 28
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.
MAS - 12 IPT 29
The most widely used network protocol for
LAN networks; can transmit data at 10 or
MAS - 12 IPT 30