fit l03 information_communication
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Fundamentals of Information Technology
(IT-162)
Meer Qaisar [email protected]
Lecture # 03
Department of Information Technology, University of Gujrat
Lecture Outline
WEEK Topic Lecture
02 Introduction to Information and Communication SystemsTypes and forms of InformationAnalogue and Digital InformationInformation Systems communication modesComments for next class
03
Data , Information, Messages and SignalsIt 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.
Information/Data/Signals
4
Information Data Signal
001011101
Properties of a SignalData and Information is transformed into 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.
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
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
Analog Versus Digital
DISCRETE CONTINUOUS
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
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).
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.
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
A Problem with Analog
Analog signal
Noise
If an analog signal provides such a close representation If an analog signal provides such a close representation of information, why do we use digital?of 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)
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
ThresholdDetector
Regenerated Digital SignalProcessor
The Digital Advantage
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
1.SIMPLEX MODE :
Features:a) Unidirectionalb) Send-only or Receive-only devicesc) Sender is unaware about the status of transmission.d) Rarely used for data communication.
Example: Radio transmission
Sender Receiver
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
SenderOR
3. FULL DUPLEX:
FEATURES:a) Also known as Duplex Modeb) Communicates in both directions simultaneously.c) Line Turnaround time is eliminated.d) Much efficient mode.
Example: Telephone line
Sender and
Receiver
Receiver and
SenderAND
Comments for next class
Go over today’s lecture notes Download next week’s lecture notes Finish reading chapters 1 and 3