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 & NetworksFace to Face

Visuals & Signals / Writing / Speech

Around year 1700

Directly

Communication & NetworksNot Face to Face

Visuals & Signals

Around year 1700

Waiving a flag

Communication & NetworksNot Face to Face

Visuals & Signals

Around year 1750

Giving smoke signals

Communication & NetworksNot Face to Face

Writing

Around year 1700

Pigeon Flight

Communication & NetworksNot Face to Face

Writing

Around year 1750

Communication & NetworksNot Face to Face

Speech

Around year 1700 or 1750

Shouting or Howling

Communication & NetworksNot 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

Voltage

Time

5

10

Direct Current Behavior

1 inch

5V

1 km

5V

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

5V

Michael Faraday

N

S

EW

Magnetic Field

There is some relation between electric and magnetic energies.Conclusion:

MagneticCompass

Communication & NetworksMichael Faraday

Click here Click here

Conclusion:

Nature of current is Alternating.

This is called:Alternating Current(AC)

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

Step-Down TransformerRectifier

Transformer (Step-Up / Step-Down)

Power Plant

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

Carrier

Information

Put (Encode) the information on the carrier so that information can travel across.

MODULATION Kite Example

Data Communication Networks

Encoding /Modulation

Decoding /De-Modulation

Electromagnetic wave carrying information

Medium

Is physical medium really necessary?

Encoding /Modulation

Decoding /De-ModulationAir is the medium

Electromagnetic wave (not Sound wave) carrying information

No physical medium

No. If Sound waves can travel without any physical medium, why not Electromagnetic waves?

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

Voltage

Time

Continuous Comparison (Analogy)with Input at all Times.

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

Comparison (Analogy & Not measurement) with the position of hands of the clock.

Continuously with Time.

Hour hand is on second ‘1’ of ’11’,Minute hand has touched ‘1’,Second hand is on 5, no about to leave 5.

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.

Not an Analogy (Comparison).

It is measurement in Digits.

Analog Digital

Comparison (Analogy & Not measurement) with the size of laptop.

Continuously with Time. Discontinuous / Discrete with Time.

Data Communication Networks

How many marbles have you collected?

It’s 25 marbles.

Not an Analogy.

It is measurement in Digits.

DigitalAnalog

Comparison (Analogy & Not measurement) with the number of marbles.

Continuously with Time.Discontinuous / Discrete with Time.

Data Communication Networks

Tell the time

- Hour hand is on second ‘1’ of ’11’,- Minute hand has touched ‘1’,- Second hand is one 5, no about to leave 5.

It’s 5 past 11.

DigitalAnalog

Comparison (Analogy & Not measurement) with the position of hands of the clock.

Continuously with Time.

Data Communication Networks

Voltage

Time

Voltage

Time

After every 5/10 sec, just measure the voltage.

1

2

Everything is stored inthe form of digits at

discontinuous (discrete) portion of 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

1 Bulb Off

On

2 Bulbs

Number of Bulbs Possible Combinations

Off Off

Off OnOn 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

1 Digit 0

1

2 Digits

Number of Digits Possible Combinations

0 0

0 11 0

1 1

3 Digits

0 0 00 0 10 1 00 1 11 0 01 0 11 1 01 1 1

(2)

(4)

(8)

= 21

= 22

= 23

4 Digits 24 16 possible combinations5 Digits 25 32 possible combinationsn Digits 2n possible combinations