Data & Communication Networks
•Data:
–Collection of raw facts and figures represented in
the form of,
•Text,
•Audio,
•Video etc.
•Communication:
–Giving/Exchanging of Data/Information/News OR
–Activity of conveying information by,
•Visuals & Signals,
•Writing,
•Speech etc.
•Network:
–Infrastructure / Setup that allows entities to,
•Communicate / Exchange Data.
Data & Communication Networks
•Data Communication Networks:
–So what is Data & Communication
Networks?
•Actually it is supposed to be,
–Data Communication Networks
–Data Communication & Networks
–Networks that allow (facilitate),
•The communication of,
•Data between various entities.
Communication & Networks
Face to Face
Visuals & Signals / Writing / Speech
Directly
Around year 1700
Communication & Networks
Not Face to Face
Visuals & Signals
Waiving a flag
Around year 1700
Communication & Networks
Not Face to Face
Visuals & Signals
Giving smoke signals
Around year 1750
Communication & Networks
Not Face to Face
Writing
Pigeon Flight
Around year 1700
Communication & Networks
Not Face to Face
Writing
Around year 1750
Communication & Networks
Not Face to Face
Speech
Shouting or Howling
Around year 1700 or 1750
Communication & Networks
Not Face to Face
Signal / Text / Speech
Around year 1700 or 1750
Data Communication Networks
•Communication & Networks:
–At the other end,
•Scientist by the name of ‘Benjamin Franklin’
was busy doing his experiments.
•In one of his famous experiment, he found out
something revolutionary.
Communication & Networks
Benjamin Franklin’s
Kite Experiment
Reference: http://www.codecheck.com/cc/BenAndTheKite.html
Data Communication Networks
•Communication & Networks:
–Electrical Energy & Direct Current (DC):
•Later on,
–Scientists found out that due to a reaction between various
chemicals such as,
»Zinc & Carbon,
»Nickel & Cadmium etc,
–Some kind of energy is produced.
•This energy is called:
–Electrical Energy
•Reaction that happens between chemicals is called:
–Electrochemical Reaction
–Conclusion:
•Scientists were successful in converting,
–‘Chemical’ energy into ‘Electrical’ energy.
•Current that was generated out of it was called:
–Direct Current (DC)
Direct Current
Direct Current Graph
10
Voltage
5
Time
Direct Current Behavior
5V
1 inch
5V
1 km
Data Communication Networks
•Direct Current Behavior:
–To operate or function, most devices
require,
•High DC voltage.
–However,
•It is very difficult to generate high DC voltage.
•Moreover during transmission, so much power
is lost in the form of heat due to,
–Resistance of the wire (path).
–Conclusion:
•It was virtually impossible to transmit DC
voltage directly to the homes of the consumers.
Communication & Networks
Michael Faraday
Magnetic Field
N
5V
E
W
S
Magnetic
Compass
Conclusion: There is some relation between electric and magnetic energies.
Communication & Networks
Michael Faraday
Conclusion:
Nature of current is
Alternating.
This is called:
Alternating Current
(AC)
Click here
Click here
Alternating Current (AC)
Alternating Current Graph
ElectroMagnetic Waves / Radiation
Data Communication Networks
•Alternating Current Behavior:
–If magnet is moved (by reversing the directions),
•Electric current is produced.
•Conclusion:
–‘Mechanical’ energy could be converted into ‘Electrical’
energy.
•Led to the invention of a device called:
–Electric Generator.
–If electric current is produced and alternated,
•Magnet / Iron can be moved.
•Conclusion:
–‘Electrical’ energy could be converted into ‘Mechanical’
energy.
•Led to the invention of a device called:
–Electric Motor.
Data Communication Networks
•Alternating Current Behavior:
–It is easy to generate,
•High AC voltage compared to high DC voltage.
–Need at that time was:
•For transmission to consumers’ homes,
–High voltage is required.
»Step-Up Transformer
•Once it reaches to/near consumers’ homes,
–Voltage should be reduced.
»Step-Down Transformer
•Moreover most of the devices of the consumers work on
DC voltage and not AC voltage.
–So facility should be there to convert AC voltage to DC
voltage.
»Rectifier
Electric Power Transmission
Step-Up Transformer
Power Plant
Step-Down Transformer
Rectifier
Transformer (Step-Up / Step-Down)
Electric Power Transmission
Data Communication Networks
•Communication v/s Electricity:
–Communication:
•It could not go beyond oceans.
–Electricity:
•It could travel across oceans now in the form of,
–Alternating Voltage or Alternating Current OR
–Electromagnetic Waves
–Important question was:
•How can communication travel across oceans?
Data Communication Networks
Information
Carrier
Put (Encode) the information on the carrier so that information can travel across.
MODULATION
Kite Example
Data Communication Networks
Electromagnetic wave carrying information
Encoding /
Modulation
Medium
Decoding /
De-Modulation
Is physical medium really necessary?
No. If Sound waves can travel without any physical medium,
why not Electromagnetic waves?
Electromagnetic wave (not Sound wave) carrying information
Encoding /
Modulation
No physical medium
Air is the medium
Decoding /
De-Modulation
Data Communication Networks
•Data Communication Networks:
–Based on this principle of electromagnetic
waves,
•Several devices were invented such as:
–Microphone, Telephone, Radio, Television etc.
–Question is:
•How every device/equipment (Microphone, TV,
Radio etc.)
–Generates, understands and reproduces the electric
signal?
Data Communication Networks
Voltage
Time
Continuous Comparison (Analogy)
with Input at all Times.
Voltage
Time
Data Communication Networks
Size of your laptop?
Comparison (Analogy & Not measurement)
with the size of laptop.
Continuously with Time.
Data Communication Networks
How many marbles have you collected?
Comparison (Analogy & Not measurement)
with the number of marbles.
Continuously with Time.
Data Communication Networks
Tell the time
Hour hand is on second ‘1’ of ’11’,
Minute hand has touched ‘1’,
Second hand is on 5, no about to leave 5.
Comparison (Analogy & Not measurement)
with the position of hands of the clock.
Continuously with Time.
Data Communication Networks
•Data Communication Networks:
–Scientists found out that to generate or
reproduce something,
•It is not necessary to continuously monitor it
with respect to time.
–Moreover it could be expressed in some
other way,
•Rather than ‘Comparison’ or ‘Analogy’.
Data Communication Networks
Measure my laptop
It’s 25 inches.
Comparison (Analogy & Not measurement)
with the size of laptop.
Continuously with Time.
Analog
Not an Analogy (Comparison).
It is measurement in Digits.
Discontinuous / Discrete with Time.
Digital
Data Communication Networks
How many marbles have you collected?
It’s 25 marbles.
Comparison (Analogy & Not measurement)
with the number of marbles.
Continuously with Time.
Analog
Not an Analogy.
It is measurement in Digits.
Discontinuous / Discrete with Time.
Digital
Data Communication Networks
Tell the time
It’s 5 past 11.
- Hour hand is on second ‘1’ of ’11’,
- Minute hand has touched ‘1’,
- Second hand is one 5, no about to
leave 5.
Comparison (Analogy & Not measurement)
with the position of hands of the clock.
Continuously with Time.
Analog
Digital
Data Communication Networks
Voltage
Time
After every 5/10 sec,
just measure the voltage.
Voltage
Everything is stored in
the form of digits at
discontinuous (discrete)
portion of time.
2
1
Time
Data Communication Networks
•Analog v/s Digital Communication:
–Analog:
•Works on the basis of comparison or analogy.
•It is continuous with time.
•Problems:
–Continuously monitor with respect to time.
»Wastage of bandwidth.
–Prone to noise.
–Digital:
•Works on the basis of digits or measurement.
•It is discontinuous (discrete) with time.
•Most popular digital device today is:
–Computer.
»Which in fact uses only 2 unique digits/states to
represent everything.
»0 or 1.
Analog v/s Digital
Analog v/s Digital
Data Communication Networks
•Digital (Computer) Communication:
–Computer represents everything in the
form of:
•Digits (Digital)
–Number of unique digits/states used by a
computer to represent everything is:
•2, ie.
–0 and 1
»True/False, On/Off etc.
–It definitely gives rise to some questions.
Data Communication Networks
•Digital (Computer) Communication:
–1st Question is:
•If computer wanted to be digital,
–Why did it select only 2 unique states (Binary Digits 0/1)?
–It could have selected 10 unique states (Decimal Digits 0 to
9)?
–Answer is:
•Just like a human being,
–It is also very easy for a circuit to make a decision based
on,
»Either/Or, True/False, Yes/No, On/Off,
Presence/Absence etc.
•So the size and complexity of the circuit is reduced to a
greater extent.
Data Communication Networks
•Digital (Computer) Communication:
–2nd Question is:
•Using just or only 2 unique digits/states,
–How is it possible to represent so many alphabets,
numbers, states etc.?
–On top of that, how can the computer distinguish alphabets
from all languages also such as English, Hindi, Gujarati etc?
–This Question is similar to:
•If there is a bulb recognizing only 2 states, ‘On’ and ‘Off’,
–Can it be used on different occasions to convey different
meaning?
•If there is a whistle having only 2 states, ‘Presence’ and
‘Absence’ of sound,
–How can it be used to convey different meanings to players
on the field regarding?
»Start the game, Foul, Stop the game etc?
Digital Communication
Number of Bulbs
1 Bulb
Possible Combinations
Off
On
2 Bulbs
Off Off
Off On
On Off
On On
Data Communication Networks
•Digital (Computer) Communication:
–Answer is:
•1 bulb can convey only 2 messages,
–On or Off.
–However,
»A series (collection) of such bulbs can be used to
create so many effects and combinations.
•1 whistle can convey only 2 messages,
–Presence of sound / Absence of sound.
–However,
»Collection (Repetition) of same sound from
whistle can convey different meaning to the
players on the field.
Digital Communication
Number of Digits
Possible Combinations
0
1 Digit
(2) = 21
1
00
01
10
11
2 Digits
3 Digits
4 Digits
5 Digits
n Digits
24
25
2n
16 possible combinations
32 possible combinations
possible combinations
000
001
010
011
100
101
110
111
(4) = 22
(8) = 23