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 Around year 1700 Directly

Communication & Networks Not Face to Face Visuals & Signals Around year 1700 Waiving a flag

Communication & Networks Not Face to Face Visuals & Signals Around year 1750 Giving smoke signals

Communication & Networks Not Face to Face Writing Around year 1700 Pigeon Flight

Communication & Networks Not Face to Face Writing Around year 1750

Communication & Networks Not Face to Face Speech Around year 1700 or 1750 Shouting or Howling

Communication & Networks Not Face to FaceSignal / 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:

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 E W Magnetic Field There is some relation between electric and magnetic energies. Conclusion: Magnetic Compass

Communication & Networks Michael Faraday 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 Transformer Rectifier 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-Modulation Air 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. AnalogDigital 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 in the 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

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: –1 st 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: –2 nd 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 BulbsPossible Combinations Off Off On On Off 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 Digits Number of DigitsPossible Combinations Digits (2) (4) (8) = 2 1 = 2 2 = Digits possible combinations 5 Digits possible combinations n Digits2n2n possible combinations