awesome slides by sir zia.............

1. IT-162
FUNDAMENTALS OF Information
Technology
Lecture #3

2. Lecture Outline
WEEK Topic Lecture
02 Introduction to Information and
Communication Systems
Types and forms of Information
Analogue and Digital Information
Information Systems communication modes
Comments for next class
03

3. Data , Information, Messages
and Signals
It is important to distinguish between information, messages and signals:
 Data : A representation of facts, concepts, or instructions in a
formalized manner suitable for communication, interpretation, or
processing by human beings or by automatic means.
 Signal: The actual entity (electrical, mechanical, etc) that is transmitted
from sender to receiver (ex: electrical signals, sound waves, optical
pulses)
 Message: The content of the signal (ex: song, speech, binary code etc.)
 Information: The content of the message, i.e. the knowledge that is
communicated/received by the message.
Message and information are sometimes used interchangeably,
however there is a subtle difference between the two.

4. Information/Data/Signals
4
Information Data Signal
001011101

5. Properties of a Signal
Data and Information is transformed in to electromagnetic or
Optical Signal before transmission.
Three important characteristics of a signal are :
 Amplitude : The Intensity of Signal or the instantaneous value of a
signal at any time measured in volts.
 Frequency : the number of repetitions of the period per second ,it is
expressed in cycles per second or Hertz (Hz).
 Phase : a measure of the relative position in time within a single period
of a signal, measured in degrees.

6. As an example, consider the following
scenario:
Yes, Mr. Faraday
would like to meet you
at 4:00 p.m. today Sure, I’ll be there!
Electrical signal
Message (speech) Information Information

7. Analog and Digital
Information
 The term analog is used to refer to the natural world, where time
is continuous, and most parameters (like light, sound intensity,
position, etc. ) can vary smoothly and continuously over some
range, taking on an infinite number of possible values
 The term digital is used to refer to information representations
for which both time and the value being measured move in
discrete steps i.e. when there are a finite number of possible
values

8. Analog Versus Digital
DISCRETE CONTINUOU
S

9.  When each discrete information value is converted to a binary
value, the information becomes digitized.
Exists at SPECIFIC POINTS in space and
time
Variables can have ONLY SPECIFIC values
Example: Clock hand that rotates in jumps
(ticks)
Exists for ALL values of space and time
Variables can have ALL POSSIBLE
values
Example: smoothly rotating hand on a clock
Analog Versus Digital

10. The Natural World is Analog
This continuous acoustical waveform can be detected by a microphone and
converted into an analog electrical signal for transmission over a piece of wire.
Human speech is an example of analog communication.
Speech causes air to vibrate with varying amplitude (volume) and frequency (pitch).

11. The Computer World is Digital
 Digital computers communicate using 2 discrete values. In other
words, they speak in binary (0 and 1).
 Of course, 0s and 1s are not literally transmitted
 In an electrical network, variations in voltage represent one of the two
values.
 In an optical network, pulses of light provide the discrete values.
 The pulses of light or voltage variations are the “signal.”
 Two values in different combinations sufficiently encode text, numbers,
image, and sound!
 Recall that the telegraph was an early example of communications
using discrete, electrical pulse transmission.

12. Digital vs. Analog
 Analog signals are susceptible to distortion and inaccuracy due to other
signals (interference)
 Digital information can be compressed for efficient transmission and
storage
 Digital information can be encrypted for increased security and
multiplexed for increased capacity
 Digital technology is much cheaper
 Digital signals can be accurately reproduced
 Digital signals are easier to detect
 There is opportunity for error detection and correction in digital
technology

13. A Problem with Analog
Analog signal
Noise
If an analog signal provides such a close representation ofIf an analog signal provides such a close representation of
information, why do we use digital?information, why do we use digital?
 Analog signal on magnetic tape. Random fluctuations in the magnetic
tape add “noise” to the signal. The noise cannot be removed and
becomes part of the subsequent versions of the analog signal.
Distorted Signal
(unwanted electrical/
electromagnetic energy)

14.  Restoration of digital signals stored on magnetic tape. Random
fluctuations in the magnetic tape add noise to the digital signal. A device,
called a threshold detector, compares the signal to a threshold (dashed
line) and decides that the data value is a 1 if the signal lies above the
threshold, or a 0, otherwise.
Digital Signal Noise Distorted Signal
Threshold
Detector
Regenerated Digital SignalProcessor
The Digital Advantage

15. Communication Modes.
 It refers to the direction of flow of signals among linked devices.
 There are three ways for transmitting data from one point to
another
 1. Simplex
 2. Half-duplex
 3. Full Duplex

16. 1.SIMPLEX MODE :
Features:
a) Unidirectional
b) Send-only or Receive-only devices
c) Sender is unaware about the status of transmission.
d) Rarely used for data communication.
Example: Radio transmission
Sender Receiver

17. 2. HALF-DUPLEX:
Features:
a) Two-way communication but not simultaneously.
b) At a moment it is unidirectional only.
c) Can alternately send and receive data.
c) Transmission direction can be changed whenever
required.
d) Delay factor (Line Turnaround Time) is associated.
Example: i ) Wireless handsets used by military personnel
ii) Data transmission to & from hard disk.
Sender
or
Receiver
Receiver
or
Sender
OR

18. 3. FULL DUPLEX:
FEATURES:
a) Also known as Duplex Mode
b) Communicates in both directions simultaneously.
c) Line Turnaround time is eliminated.
d) Much efficient mode.
Example: Telephone line
Sender
and
Receiver
Receiver
and
Sender
AND

19. Comments for next class
 Go over today’s lecture notes
 Download next week’s lecture notes
 Finish reading chapters 1 and 3