Physical Layer in the OSI Model: It’s Functions, component and Protocols.

7-layer-of-osi-model

Physical Layer in the OSI Model: Functions, component and Protocols

In an OSI (Open Systems Intercommunication) model, the physical layer (Layer 1) is the lowest or bottom most layers of OSI model, which standardizes the functions of a telecommunication or computing system. The primary responsibility of the Physical Layer is to transmit raw bitstreams coming from upper layer (Data link layer) over a physical medium. Physical layer establishes, maintains and deactivates the physical connection.

Learn more about OSI model Click here

What Is computer Network?

Data rate also maintained by the function of the Physical Layer. It defines how two or more devices are connected to a link by line configuration. Physical layer also maintain the Synchronization between sender and receiver. This layer also provide functionality to its upper layer called Data Link Layer (DLL). Physical layer pick data from data link layer and encode it at the sender side and decode data at the receiver side.

Physical layer In OSI model

Physical Layer in the OSI Model: Its Functions

Physical Layer in the OSI Model

Functions of the Physical Layer

The key responsibility of physical layer is sending bits from one node to another node along the network. Its role is determining how physical connections to the network are set up, as well as how bits are represented into signals — as they are transmitted either in the form of electrical signal, optical signal or by radio waves.

To do all this, the physical layer performs a different functions, that are given below:

  1. Bit Transmission: The Physical Layer is responsible for transmitting raw bits (0s and 1s) from one node to another over a physical medium, such as cables, fiber optics, or radio waves.
  2. Signal Encoding: It converts the data bits into signals that can be transmitted over the physical medium. This include encoding bits into electrical, optical, or radio signals depending on the medium used.
  3. Data Rate Control: It determines the rate at which data is transmitted over a physical medium, which is usually measured in bits per second (bps). This data rate can vary depending on the transmission medium and the technologies used.
  4. Topologies: It defines how two or more devices physically and logically connect to make a network. There are six types of topologies such as bus topology, star topology, ring topology, and mesh topology, tree topology and hybrid topologies.

5. Transmission Modes: It describes the direction of the data flow. Transmission modes are classified into three types: Simplex, Half-Duplex, and Full-Duplex.

6. Interfaces and Standards: The Physical Layer defines the hardware specifications and interfaces, including pin layouts, voltage levels, cable types, connectors, and other physical attributes. Examples include RS-232, RJ45, and V.35.

7. Multiplexing: Multiplexing is the process of combining multiple data streams and send it through a single stream for transmission over a communication channel.  It uses different methods like Frequency Division Multiplexing (FDM) or Time Division Multiplexing (TDM) to allow multiple signals to share the same physical medium. Multiplexing is done at the sender side and demultiplexing is done at receiver side.

Components of the Physical Layer

  1. Cables and Connectors: Physical layer use physical media such as twisted pair cables, coaxial cables, optical fiber cables, and wireless media (radio waves, microwaves).
  2. Network Interface Cards (NICs): It is a hardware device that connects a computer to a network.
  3. Repeaters and Hubs: These are the devices that is use to extend the range of a network by amplifying the signals.
  4. Modems: It is a devices that modulate and demodulate signals for transmission over telephone lines or cable systems.

Physical layer Standards and Protocols

  1. Ethernet (IEEE 802.3): It specifies the physical and data link layer’s operation in wired Ethernet networks.
  2. Wi-Fi (IEEE 802.11 ): It governs wireless networking.
  3. Optical Transport Network (ITU-T G.709): it defines the standard for optical fiber networks.
  4. SONET/SDH: It is a standards for synchronous optical networking.

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Examples of physical layer technologies

  1. Ethernet: The most widely used LAN technology that operates at both the data link and physical layers. Uses various media like twisted pair (Cat5e, Cat6) and fiber optics.
  2. Fiber Optics: It uses light signals for high-speed data transmission over long distances with minimal loss.
  3. DSL (Digital Subscriber Line): It uses existing telephone lines to provide high-speed internet access.
  4. Wi-Fi: Wireless technology that provides high-speed internet and network connections.

What is the Physical Layer in the OSI Model?

The Physical Layer is the first and lowest layer of the OSI (Open Systems Interconnection) model. It is responsible for the transmission and reception of raw bit streams over a physical medium, such as cables, optical fibers, or radio waves.

What are the main functions of the Physical Layer?

1. Bit Transmission: Transmits raw bits from one device to another.
2. Signal Encoding: Converts bits into signals suitable for the transmission medium.
3. Data Rate Control: Manages the speed at which data is transmitted.
4. Physical Topologies: Defines the physical layout of network devices.
5. Transmission Modes: Supports simplex, half-duplex, and full-duplex modes.
6. Synchronization: Ensures sender and receiver are synchronized.
7. Multiplexing: Allows multiple signals to share the same medium.
8. Physical Interfaces and Standards: Specifies hardware details like pin layouts and voltage levels.

What are some common physical media used in the Physical Layer?

1. Twisted Pair Cables: Commonly used for Ethernet connections.
2. Coaxial Cables: Used for cable TV and internet.
3. Fiber Optic Cables: Provides high-speed data transmission over long distances.
4. Radio Waves: Used for wireless communications like Wi-Fi and Bluetooth.

What are some devices associated with the Physical Layer?

1. Network Interface Cards (NICs): Connect computers to networks.
2. Repeaters: Amplify signals to extend the range of a network.
3. Hubs: Basic devices that connect multiple Ethernet devices.
4Modems: Modulate and demodulate signals for transmission over telephone lines or cable systems.

Full Adder : It’s Truth table, Circuit Diagram

Full adder is a combinational logic circuit perform addition of three single bit number. It is a digital circuit has three inputs A, B and Cin , where Cin is the previous carry and two output sum (S), carry (Cout). Here sum is the least significant bit (LSB) and carry is the most significant bit (MSB). Full adder circuit is used in computer ALU (Arithmetic and Logic Unit ) to perform arithmetic operation.

Full Adder Block Diagram

Truth Table of Full Adder

The full adder circuit perform OR (addition) operation between two single bit binary number A,B and previous carry Cin. Basically, a full adder is a three input and two output combinational circuit. Three inputs A,B and Cin having eight input combinations. After addition of three single bit binary number this circuit produces two outputs Sum (S) and carry (Cout).

Truth table explain the relationship between inputs and outputs.

Full Adder Truth Table

In the above table,

  1. A and B are the two single bit inputs and Cin is the previous carry. So, three inputs having 23 = 8 Possible combination.
  2. When we perform OR operation between three inputs, it produces two output sum (s) and carry (c).
  3. Here sum is the least significant bit (LSB) and carry is the most significant bit (MSB).
  4. Carry output is “1” only when the sum of inputs are greater then “1”.
  5. The least significant bit of the addition is defined by the ‘sum’ bit.

Now, To find the Boolean logical expression from truth table make a k-map for outputs Sum (S) and carry (Cout) and get Boolean expression in SOP form.

If you want to know more on how to design full adder using half adder click here

Know more about Half Adder click here

K-Map for the Sum Output

k-map for Sum (S)

Expression for sum after solving k-map

Sum =A xor B xor Cin

K-Map for Cout

K-Map for cout

Expression for Cout after solving k-map

Co = AB + ACin +BCin

Now draw the logic diagram of Full adder

A Logic Diagram For Full Adder

full adder Circuit

For more detail watch my video

Q1: What is a full adder?

A full adder is a combinational logic circuit that adds three input bits: A, B, and a carry input (C_in). It produces a sum (S) output and a carry output (C_out). The carry input (C_in) represents the carry bit from the previous stage of addition.

Q2: How does a full adder differ from a half adder?

While a half adder adds two input bits, a full adder takes into account an additional carry input. This allows the full adder to handle the carry bit from the previous stage, enabling the addition of multiple bits in cascaded adders.

Q3: What is the truth table of a full adder?

The truth table for a full adder consists of the input bits (A, B, C_in) and the corresponding outputs (S, C_out). The table defines all possible input combinations and their resulting outputs.

Q4: What is the circuit diagram of a full adder?

A full adder can be implemented using logic gates such as XOR, AND, and OR gates. The circuit diagram typically includes two XOR gates, two AND gates, and an OR gate, along with the input and output connections.

Q5: How can I cascade multiple full adders to create larger adders?

Multiple full adders can be cascaded by connecting the carry output (C_out) of one full adder to the carry input (C_in) of the next full adder. This allows for the addition of multiple bits, creating n-bit adders.

Q6: What are the practical applications of full adders?

Full adders are fundamental building blocks used in various digital systems. They find applications in arithmetic operations, microprocessors, calculators, memory addressing, and digital signal processing. Full adders are crucial for binary addition and are extensively used in data processing and arithmetic units.

Q7: Can a full adder be implemented using other logic gates?

Yes, a full adder can be implemented using different combinations of logic gates. While the traditional implementation involves XOR, AND, and OR gates, other gate combinations, such as NAND or NOR gates, can also be used to achieve the same functionality.

Q8: What are the considerations for signal propagation and timing?

Propagation delay, signal integrity, and timing are important considerations when working with full adders. Propagation delay refers to the time it takes for signals to propagate through the circuit. Signal integrity ensures accurate and reliable data transmission. Timing considerations involve meeting setup and hold time requirements to avoid timing violations.

Wiki link for adder here

Most Important MCq on Power Electronics | Electrical Engineering

Question 1 A forward-biased PN junction acts as a/an

  1. Thyristor
  2. Closed switch
  3. Amplifier
  4. Chopper
Answer : Closed switch

Question 2 Leakage current flows through the thyristor in

  1. Forward conduction mode
  2. Reverse blocking mode
  3. Forward blocking mode
  4. Both forward and reverse blocking mode
Answer : Both forward and reverse blocking mode

Question 3 A step up chopper has input voltage 110 V and output voltage 150 V. The value of duty cycle is

  1. 0.32.
  2. 0.67.
  3. 0.45.
  4. 0.27.
Answer : 0.27

Question 4 A single phase full bridge inverter can operated in load commutation mode in case load consist of

  1. RL.
  2.  RLC underdamped.
  3.  RLC overdamped.
  4.  RLC critically damped.
Answer : RLC underdamped.

Question 5 A freewheeling diode is phase-controlled rectifiers.

  1. Stops rectifier operations
  2. Improves line power factor
  3. Is the reason for additional harmonics
  4. Is the reason for the sudden breakdown
Answer : Improves line power factor

Question 6 Find the average output of a semi-converter connected to a 220 V, 50 Hz power supply, and firing angle is  𝝅/𝟑

  1. 178.52
  2. 248.05
  3. 148.55
  4. 198.49
Answer : 148.55

Question 7 Which triggering is the most reliable?

  1. Forward voltage triggering.
  2. Gate triggering.
  3. dV / dt triggering.
  4. Thermal triggering.
Answer : Gate triggering.

Question 8 In a 3-∅ controlled bridge rectifier, the frequency of ripple in the output voltage depends on

  1. Power factor
  2. Supply frequency
  3. Voltage source
  4. Firing angle
Answer : Supply frequency

Question 9 Which semiconductor power device out of the following, is not a current triggering device?

  1. Thyristor
  2. Triac
  3. G.T.O
  4. MOSFET
Answer :MOSFET

Question 10 Which of the given device is the most suitable power device for a higher frequency (above 100 kHz) switching application

  1. SCR
  2. Power MOSFET
  3. GTO
  4. BJT
Answer : Power MOSFET

Question 11 A half-wave rectifier circuit using an ideal diode has an input voltage of 10 sin ?t V; find the average and RMS value of output voltage?

  1. 3.18 V, 5V
  2. 3.68 V, 8V
  3. 4.18 V, 5V
  4. 4.68 V, 8V
Answer : 3.18 V, 5V

Question 12 A three phase full controlled converter can operate as a

  1. Converter for α = 0 to 1200
  2. Converter for α = 0 to 900
  3. Converter for α = 0 to 1800
  4. Converter for α = 0 to 600
Answer : Converter for α = 0 to 180 degree

Question 13 The advantages of SCS over SCR is

  1. Slow switching time and large VH
  2. Slow switching time and smaller VH
  3. Faster switching time and smaller VH
  4. Faster switching time and large VH
Answer : Faster switching time and smaller VH

Question 14 Leakage current flows through the thyristor in

  1. forward blocking mode.
  2.  reverse blocking mode.
  3.  both forward and reverse blocking mode.
  4.  forward conduction mode.
Answer : both forward and reverse blocking mode.

Question 15 The minimum duration of the pulse in a pulse triggering system for thyristors should be at

  1. 10 μs
  2. 10 ms
  3. 30 ms
  4. 1 sec
Answer : 10 μs

Question 16 The triple frequency of a six-phase half wave rectifier for 220 V, 60 Hz input will be

  1. 2160 Hz
  2. 720 Hz
  3. 360 Hz
  4. 60 Hz
Answer : 360 Hz

Question 17 In a three-phase bridge rectifier, the maximum conduction of each thyristor is

  1. 1200
  2. 900
  3. 300
  4. 600
Answer : 1200

Question 18 Which of the given regulator provide output voltage polarity reversal without the involvement of a transformer.

  1. Linear voltage regulator
  2. Shunt voltage regulator
  3. Buck-Boost regulator
  4. Series voltage regulator
Answer : Buck-Boost regulator

Question 19 A chopper converts

  1. AC to DC
  2. AC to AC
  3. DC to AC
  4. DC to DC
Answer : DC to DC

Question 20 PWM switching is used in voltage source inverters for the purpose of

  1. Controlling output current
  2. Controlling input voltage
  3. Controlling input power
  4. Controlling output harmonics and output voltage
Answer : Controlling output harmonics and output voltage

Question 21 Which of the given configurations is used for both regenerative and motoring breaking?

  1. First quadrant chopper
  2. Fourth quadrant chopper
  3. Third quadrant chopper
  4. Two quadrant chopper
Answer : Two quadrant chopper

Question 22 Power diode is

  1. Two terminal semiconductor device
  2. Three terminal semiconductor device
  3. Four terminal semiconductor device
  4. None of these
Answer : Two terminal semiconductor device

Question 23 The V-I characteristics of diode lie in the

  1. First quadrant
  2. Fourth quadrant
  3. The third and second quadrant
  4. The first and third quadrant
Answer : The first and third quadrant

Question 24 If a firing angle α of a single phase fully controlled rectifier feeding a constant DC current into the load is 600, Find the displacement factor of the rectifier

  1. 0
  2. 0.5
  3. 1
  4. 1.5
Answer : 0.5

Question 25 For a specific transistor, if the value of beta is equal to 400 and the Base current is 8mA, Find the value of Emitter current?

  1. 4.308
  2. 3.208 A
  3. 7.808 A
  4. 9.276 A
Answer : 3.208 A

[Download pdf] Top 20 PLC MCQ – Part -3

Hi All, In this series I explained top 20 objective questions and answer. For more questions of PLC and SCADA MCQ series. Please checkout my all MCQ series on PLC and SCADA. I have created MCQ series on Basic Electronics, Power Electronics, 8051 Microcontroller, 8086 Microprocessor.

#1 PLC and SCADA MCQ Series click here

#2 PLC and SCADA MCQ Series click here

#4 PLC and SCADA MCQ Series click here

If you are going to attempt any competitive exam then check your skills here. This is mock test questions which is asked in previous year paper in UPPCL, RSEB, Metro rail corporation and SSC JE.

[ays_quiz id=”2″]

Question 1 Which of the following statements about RLL is NOT true?

  • NO contact symbol has two parallel lines to indicate an open contact.
  • RLL stands for Relay Ladder Logic.
  • NC contact symbol has the same two parallel lines with a line across them to indicate closed contacts.
  • The right power rail is positive or the high side of the source, and the left power rail is the power return or ground.

Answer : The right power rail is positive or the high side of the source, and the left power rail is the power return or ground.

Question 2 _____ is a method of entering ladder logic representation.

  • Segment programming
  • TINT
  • Boolean mnemonics
  • All of the above

Answer : Boolean mnemonics

Question 3 When a relay is NOT energized

  • There is an electrical path through the NO contacts
  • There is an electrical path through the NC contacts
  • Neither the NO or the NC contacts have an electrical path
  • Both the NO and the NC contacts have an electrical path

Answer : There is an electrical path through the NC contacts

Question 4 In a current sinking DC input module _____

  • The current flows out of the input field device
  • Requires that a AC sources be used with mechanical switches
  • The current flows out of the input module
  • Currents can flow in either direction at the input module

Answer : The current flows out of the input field device.

Question 5 How is the speed of operation of conventional relay system as compared to digital controllers?

  • Very slow
  • Very fast
  • Same
  • Almost similar

Answer : Very slow.

Question 6 The type of memory which is fast and temporarily stores the data which are immediately required for use is called as______.

  • HDD
  • ROM
  • RAM
  • SSD

Answer : RAM.

Question 7 _____ of PLCs can be done in very little time.

  • Programming
  • Installation
  • Commissioning
  • All of the above

Answer : All of the above

Question 8 How is the noise immunity of PLCs to electrical noises as compared to that of conventional relay controllers?

  • Poor
  • Excellent
  • As good as noise immunity of conventional relay controllers
  • Unpredictable

Answer : Poor

Question 9 _____ of PLCs can be done in very little time

  • Programming
  • Installation
  • Maintenance
  • All of the above

Answer : All of the above

Question 10 Which of the following statements is correct?

  • Ladder logic is a PLC graphical programming technique introduced in the last 10 years.
  • Ladder logic program is hard to analyze because it is totally different when compared with the equivalent relay logic solution.
  • The number of ladder logic virtual relays and input and output instructions is limited only by memory size.
  • The number of contacts for a mechanical relay is limited to number of coils on the relay.

Answer : The number of ladder logic virtual relays and input and output instructions is limited only by memory size.

Question 11 PLC can be _____ in plant to change the sequence of operation.

  • Only programmed
  • Only reprogrammed
  • Programmed and reprogrammed
  • Able to give a set point

Answer : Programmed and reprogrammed.

Question 12 The PLC is used in _______.

  • Machine tools
  • Automated assembly equipment
  • Molding and extrusion machines
  • All of the above

Answer : All of the above.

Question 13 Which of the following can be the output of PLC?

  1. Relay coils
  2. Solenoids
  3. Indicators
  4. Motors
  5. Lamps
  6. Alarms

Select correct option

  • Only (1), (2), (3) and (4)
  • Only (3), (4), (5) and (6)
  • Only (1), (2), (3) and (5)
  • All the (1), (2), (3), (4), (5), and (6)

Answer : All the (1), (2), (3), (4), (5), and (6)

Question14 Instructions available in PLCs can be grouped in two categories: ________and ________ instructions.

  • basic ladder _ enhanced ladder
  • basic ladder and simple ladder
  • Enhanced ladder _relational ladder

Answer : basic ladder _ enhanced ladder

Question15 What one item in the output module circuit above should be changed to make it correct.

  • The battery polarity
  • Output module should be sourcing
  • Field device should be sinking
  • Current flow direction

Answer : Current flow direction

Question 16 Which of the following cannot be an input that is given to the PLC?

  • Manual switches
  • Relays
  • Sensors
  • None of the above

Answer : None of the above

Question 17 An AND function implemented in ladder logic uses

  • Normally-closed contacts in series
  • Normally-open contacts in series
  • A single normally-closed contact
  • Normally-open contacts in parallel

Answer : Normally-open contacts in series

Question 18 Ladder contacts can be programmed in

  • series-parallel
  • series or parallel
  • a and b both true
  • All of the above

Answer : a and b both true

Question 19 PLC instructions ___________.

  • Uses the same symbols as relay logic.
  • were copied using the original relay instructions
  • Were added to the original relay instructions to make PLCs more powerful.

Answer : Were added to the original relay instructions to make PLCs more powerful.

Question 20 The L2 rail side of an electromechanical circuit is represented by _____________.

  • The left side of the rail
  • The right side of the ladder rung.
  • sub-script lettering with arrows

Answer : The right side of the ladder rung.


Download pdf here for above questions


Check all explanations of above questions in below Hindi video

Top 10 PLC MCQ questions asked in previous year paper

Programmable Logic controller Multiple Choice Question

Top 10 PLC Programmable logic controller questions asked in various competitive exam. Please give this exam. This is free mock test and check your score.

First give this exam. If your answer is wrong then check below video for detail description of question

[ays_quiz id=”7″]

Series#1 ( Top 10 Questions )

Question 1 The acronym PLC stands for:

  1. Pressure Load Control
  2. Programmable Logic Controller
  3. Pneumatic Logic Capstan
  4. PID Loop Controller
  5. Pressure Loss Chamber

Answer: Programmable Logic Controller

Question 2 Ladder logic programming consists primarily of:

  1. Virtual relay contacts and coils
  2. Logic gate symbols with connecting lines
  3. Function blocks with connecting lines
  4. Text-based code
  5. Hieroglyphics

Answer: Virtual relay contacts and coils

Question 3 In a PLC, the scan time refers to the amount of time in which …..

  1. The technician enters the program
  2. Timers and counters are indexed by
  3. One “rung” of ladder logic takes to complete
  4. The entire program takes to execute
  5. Transmitted data communications must finish

Answer: The entire program takes to execute

Question 4 Identify the problem in this motor control PLC program:

  1. Coil
  2. Start contact
  3. Seal-in contact
  4. Stop contact
  5. Power source

Answer: Seal-in contact

Question 5 The Boolean representation of this PLC program is:

  1. ABC + D
  2. C + (A + B)D
  3. C + D(A + B)
  4. ABC + BD
  5. C(AB + D)

Answer: C(AB + D)

Question 6 The difference between online and offline PLC programming is . . .

  1. Whether the PLC is running or stopped
  2. Whether the programming PC has internet connectivity
  3. The type of programming cable used
  4. Where the edited program resides
  5. The type of programmer used

Answer: Where the edited program resides

Question 7 In PLC programming, a retentive function is one that:

  1. Defaults to the “on” state
  2. Comes last in the program
  3. Defaults to the “off” state
  4. Cannot be edited or deleted
  5. Is not reset after a power cycle

Answer: Is not reset after a power cycle

Question 8 Normally open contacts are open when:

  1. When Input is not energized
  2. When the input is energized
  3. When input is higher than 20 volts
  4. None of these

Answer: When Input is not energized

Question 9 An OR function implemented in ladder logic uses:

  1. Normally-closed contacts in series
  2. Normally-open contacts in series
  3. A single normally-closed contact
  4. Normally-open contacts in parallel
  5. Normally-closed contacts in parallel

Answer: Normally-open contacts in parallel

Question 10 A good application for a timed interrupt in a PLC program would be:

  1. A communications function block
  2. A PID function block
  3. A math function block
  4. A motor start/stop rung
  5. A “watchdog” timer

Answer: A PID function block

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FAQ’s

1. What is PLC ?

PLC stand for “Programmable Logic Controller”. It is a general purpose computer modified specifically to perform control task . It is a hardware device having microprocessor based control system. It is used in industrial automation.

2. What do you mean by PLC scan time?

PLC Scan Time is the time taken by the PLC to read the inputs, solve the Logic, and update the output is called a PLC Scan Time. This time is measured in millisecond .

3. Which is the most popular language in plc programming ?

The most popular language in plc programming is Ladder Logic Diagram.

4. What are the applications of PLC ?

PLC is used in industrial automation. These controllers can automate a specific process, machine function, or even an entire production line.

5. What are components of PLC system ?

There are major 6 components of PLC:
•Processor (CPU)
•Rack/Mounting
•Input Module
•Output Module
•Power Supply
•Programming Device/Unit

6. What is ladder diagram ?

Ladder diagram is the most popular programming language used in Plc programming. Ladder diagrams expresses a program as a series of “coils” and “contacts”, simulating the operation of electromechanical relays.
The advantage of ladder diagram is the familiarity many electricians have with the simple operation of relays.


Topics

The OSI Model: Understanding the 7 Layers of Networking

The OSI (Open Systems Interconnection) model was developed by the International Organization for Standardization (ISO) in 1978 and adopted by all major computer and telecommunication companies since in 1984.

The OSI model is a reference model it is not practically implemented.

The OSI model full form is Open Systems Interconnection define how to transfer data between two systems having different hardware and software across the globe. For example, if two computer having different operating system so, how they communicate with each other, to solve this issue and for successful communication 7 layer OSI model will help.

The OSI mode is a 7 layer architecture, where every layer having his own specific functionality. Here each or every layers interact and help to its lower and upper layer.

Read more What Is Computer Network?

7 Layers of OSI Model

OSI model 7 layers is divided into 3 parts. The upper three layer (Application layer, Presentation layer and Session layer) is called software layers, the lower three layer (Network layer, Datalink layer and Physical layer ) is called hardware layers and the middle layer (Transport layer) is called the heart of the OSI model.

Here’s a detailed explanation of each layer:

Application Layer

The Application Layer (also known as End User layer or desk top layer) is the top most layer of OSI model. It is closest to the end user. It interacts with software applications to implement a communicating component and provides services such as email, file transfer, and network management.

Functions:

  1. It act as an interface between system and the user.
  2. It provide interface through which we ca send data easily.
  3. it Facilitates various protocols and services (e.g., HTTP, FTP, SMTP, Telnet, DNS).

Examples: HTTP (Hyper Text Transfer Protocol), FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), DNS (Domain Name System).

Presentation Layer

The presentation layer is also known as Translation layer. On the sender’s end, the presentation layer translates the data from a user-dependent format to the common binary format. On the receiver’s end, their presentation layer translates it to another, receiver-dependent format.

After translation, presentation layer compress data bit by the process known as data compression and then Encryption and decryption are carried out by the presentation layer to secure data over the computer network. It ensures that only the communicating devices can understand pertinent data.

Functions of the presentation layer

3 main function perform by presentation layer

  1. Data translation and encoding (e.g., ASCII, EBCDIC, Unicode).
  2. Data compression and decompression.
  3. Data encryption and decryption.

Translation : On the sender’s end, the presentation layer translates the data from a user-dependent format to the common binary format. On the receiver’s end, their presentation layer translates it to another, receiver-dependent format.

Data Compression: Data compression is the process of encoding, restructuring or otherwise modifying data to reduce its size. Compression is often used to maximize the use of bandwidth across a network. Data compression id done at sender side and decompression is perform at receiver end.

Encryption/Decryption : Encryption and decryption are carried out by the presentation layer to secure data over the network. It ensures that only the communicating devices can understand pertinent data.

                                                                       OR

Encryption is the process by which a readable message is converted to an unreadable form to prevent unauthorized parties from reading it. Decryption is the process of converting an encrypted message back to its original (readable) format. The original message is called the plaintext message.

 Protocol Use:  JPEG, MPEG, GIF

Session layer

The session layer establish, controls and maintains connections between two systems to share data. It establishes, maintains, and ends sessions across all channels. In case of a network error, it checks the authenticity and provides recovery options for active sessions.

Functions of the session layer

  1. Session establishment, maintenance, and termination: This layer allows to establish, use, and terminate a connection between the two processes.
  2. Dialog control: Session layer acts as a dialog controller that creates a dialog between two processes or we can say that it allows the communication between two processes which can be either be in half-duplex or full-duplex.
  3. Synchronization: Session layer adds some checkpoints when transmitting the data in a sequence. If some error occurs in the middle of the transmission of data, then the transmission will take place again from the checkpoint. This process is known as Synchronization and recovery.

Protocol use: SQL (Structured Query Language) sessions, NetBIOS (Network Basic Input/Output System) sessions.

Transport layer

The transport layer layer is the heart of OSI model. It provides services to the application layer and takes services from the network layer. It receives the data from the session layer (upper layer) and converts them into small-small units known as segments.

This layer provide end-to-end communication and ensures complete data transfer. It manages error detection, data flow control, and retransmission of lost data packets.

Functions of Transport layer

1.Segmentation : Transport layer receives the data from the upper layer (session layer), it divides the data unit into multiple segments, and each segment is assigned with a sequence number that uniquely identifies each segment. When the message has arrived at the destination, then the transport layer reassembles the message based on their sequence numbers.

2.Flow Control: The transport layer also responsible for flow control end to end. Flow control define amount of data to be send.

3.Error Control: The transport layer is also responsible for Error control. Error control is performed end-to-end rather than across the single link. The sender transport layer ensures that message reach at the destination without any error. For error control transport layer use ARQ Algorithm (Automatic Repeat Request ) and check Sum.

4.Connection-oriented and connection less transmission: A connectionless service treats each segment as an individual packet, and they all travel in different routes to reach the destination. A connection-oriented service makes a connection with the transport layer at the destination machine before delivering the packets. In connection-oriented service, all the packets travel in the single route.

Protocols Use: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).

Network Layer

The Network Layer is responsible for determining the best physical path for data to travel from the source to the destination. It manages packet routing, addressing, and forwarding.

Functions of Network layer

  1. Logical Addressing: To identify each and every device in a networks uniquely, the network layer defines an addressing scheme known as logical address or IP addressing. The sender & receiver’s IP addresses are placed in the header by the network layer. Such an IP address distinguishes each and every device uniquely.
  2. Path Determination and Routing: Out of so many paths in inter-network network layer find the best path to reach the destination.
  3. Packetizing: A Network Layer receives the segments from the upper layer (transport layer) and add source and destination IP address to each segment so this segment converts into packets. This process is known as Packetizing. It is achieved by internet protocol (IP).

Protocol Use: IP (Internet Protocol), ICMP (Internet Control Message Protocol), and routers.

The data link layer is responsible for the node-to-node delivery of the data. 

The Data Link Layer ensures reliable data transfer between two physically connected devices. It manages error detection and correction, frame synchronization, and flow control. When a packet arrives in a network, it is the responsibility of the DLL to transmit it to the Host using its MAC address.

  1. Framing: Data Packet coming from upper layer (network layer), data link layer add physical address ( known as MAC address ) of source and destination in header and a tailer in each packet to make a frame.
  2. Physical Addressing: DLL (data link layer) uses MAC (Media Access Control) addresses also known as physical address to ensure that data is sent to the correct destination within the same network segment. MAC addresses is a physical addresses that uniquely identify devices on a local network, enabling proper routing of frames to their intended recipients.
  3. Error Detection and Correction: This layer includes mechanisms to detect and correct errors that may occur during data transmission. A method of detecting errors in transmitted messages by using a checksum. These techniques ensure data integrity by allowing the receiver to detect errors and request retransmission if necessary.
  4. Flow Control: Flow control manage the rate of data transmission between two devices to prevent a fast sender from overwhelming a slow receiver. The technique use for flow control is Stop-and-Wait Protocol and Sliding Window Protocol.
  5. Access Control: These mechanisms ensure that only one device transmits data at a time, reducing the chances of collision and ensuring efficient use of the network medium. Techniques use for access control is Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).

Protocol use: Ethernet (MAC addresses), PPP (Point-to-Point Protocol), and switches.

Physical Layer

This is the lowest layer of the OSI model. This layer is responsible for the physical connection between devices via physical medium. It handles the transmission of raw binary data over a physical medium, such as cables, radio frequencies, or optical fibers.

The function of the physical layer

Line configuration: It defines how two or more devices are connected to a link.

Representation of Bits: It encodes the bit stream into electrical and optical signals. 

Establishment of Physical Connections:

Transmission media: Wired or wireless

Data Rate: How many bits send per second?

Synchronization: The sender and receiver must be synchronized.

Transmission mode: It describes the direction of the data flow.

Topology: the physical and logical arrangement of nodes and connections in a network.

Read more: 8051 Microcontroller

8086 Microprocessor

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What is the OSI model?

The OSI (Open Systems Interconnection) model is a conceptual framework used to understand and standardize the functions of a telecommunication or computing system. It divides the communication process into seven distinct layers

What are the seven layers of the OSI model?

The seven layers of the OSI model are:
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer

What is the function of Physical Layer?

The main functions of physical layer are:
Line configuration: It defines how two or more devices are connected to a link.
Representation of Bits: It encodes the bit stream into electrical and optical signals. 
Establishment of Physical Connections:
Transmission media: Wired or wireless
Data Rate: How many bits send per second?
Synchronization: The sender and receiver must be synchronized.
Transmission mode: It describes the direction of the data flow.
Topology: the physical and logical arrangement of nodes and connections in a network.

What is the function of the Data Link Layer?

The Data Link Layer ensures reliable data transfer across a physical link, do framing, error detection and correction, flow control, and physical addressing (using MAC addresses).

How does the Network Layer differ from the Data Link Layer?

The Network Layer is responsible for determining the best path for data to travel across networks (routing) and logical addressing (using IP addresses), while the Data Link Layer focuses on reliable data transfer between two directly connected devices within the same network segment.

What role does the Transport Layer play?

The Transport Layer provides end-to-end communication services, ensuring complete data transfer with error detection, data flow control, and retransmission of lost packets. It establishes, maintains, and terminates connections between devices.

What is the purpose of the Presentation Layer?

The Presentation Layer translates data between the application layer and the network format, ensuring that data is in a usable format. It handles data encryption, compression, and translation.

What functions are performed by the Application Layer?

The Application Layer provides network services directly to end-users and interfaces with application software. It facilitates various protocols and services like HTTP, FTP, and SMTP.

Quantization and its Types

Looking for what is Quantization and its types?

In this article, we explained all the important points regarding quantization in detail.

let’s understand the topic:

Quantization is a process of converting discrete time continuous valued signal (discrete time signal) into discrete time discrete valued signal (digital signal). Other definition of quantization, It is the process of mapping the infinite range of continuous values signal to a finite set of discrete values signal or levels.

The device that performs quantization is called Quantizer. Quantifying an continuous analog signal is done by discretizing the signal with a number of quantization levels.

In quantization, the amplitude of sampled signal is round off to the nearest quantized level. This rounding off is known as quantization error. By increasing the numbers of quantization levels we can reduce the quantization error.

Quantization of an Analog Signal

Quantization is a process of ” Rounding off the sampled value to the nearest quantization level”.

Here I explain the step-by-step quantization process of an continuous analog signal.

Steps of quantization

  1. Divide the sampled signal amplitude (voltage range) into L different level.
  2. The number of level or value of L is depend upon “number of bit that encoder can encode” L is given by L= 2n where n is the
  3. The number of level or value of L is depend upon “number of bit that encoder can encode” L is given by L= 2n where n is the number of bit that encoder can encode. If we have 4-bit encoder it means the value of n=4 so we divide the signal amplitude into L=24=8 level.
  4. If the number of level is more the quantization error is less and vice-versa.
  5. The space between two interval is called step size (Δ or S). Step-size (Δ or S )= VH-VL / L where VH is max and VL is lowest value of sampled voltage.
  6. Now, draw mid line at S/2, representing quantization levels.
  7. Now, assign binary codes to each quantization level.

8. Now, calculate the quantization error, which is the difference between the original sampled value and the quantized value. This error represents the loss of information due to quantization.

The figure given below shows how an continuous analog signal gets quantized. Here, the blue line represents continuous analog signal and the brown one represents the quantized signal.

This figure shows the resultant quantized signal which is the digital form for the given analog signal.

This is also called as Stair-case waveform, in accordance with its shape.

Types of Quantization

There are basically two type of quantization

Delta Modulation (∆-modulation)-Digital Communication

Looking for delta modulation (DM or ∆-modulation)?

In this article we explained all main and important points regarding Delta Modulation (DM) in detail.

let’s understand the topic:

like PCM (Pulse Code Modulation) and DPCM (Differential Pulse Code Modulation), Delta modulation (DM or Δ-modulation) is also a analog-to-digital modulation technique used for converting analog signals into digital format. It’s particularly suitable for signals with relatively slow variations.

In PCM , N-number of bit are transmitted per sample. Therefore, bandwidth requirement is very large. To overcome this problem we use delta modulation. In this scheme, only 1 bit is used to encode 1 voltage level thus, the technique allows to transmission only one bit per sample.

Read more: DPCM (Differential Pulse Code Modulation)

PCM (Pulse Code Modulation)

Sampling Theorem

Characteristics of delta modulation

It reduces the delivered data to a 1-bit data stream. It has the following characteristics:

  1. It is a simplified form of DPCM technique also known as 1-bit DPCM scheme.
  2. Here two sample values are compared, and result of this comparison is transmitted.
  3. Here input sequence is much higher than the Nyquist rate.
  4. It is simple to implement in both hardware and software compare other modulation scheme.
  5. Here quantization is simple, encoded signals which are over-sampled.
  6. Here, step-size is very small and fixed, i.e. Δ delta.
  7.  It provides a staircase approximation of over-sampled base-band signal.
  8. Here bit rate can be decided by the user.

Operating Principle of delta modulation

In delta modulation, present sample value X(nTs) is compared with previous approximated sampled value  x^(nTs), and the result of this comparison is encoded and transmitted.

The compared value is called delta (Δ) value. The delta value is then compared to a predefined threshold or step size.

If present sample value X(nTs) is greater than previous approximated sampled value  x^(nTs) then the step of the signal denoted by Δ is increased by 1.  If present sample value X(nTs) is smaller than previous approximated sampled value  x^(nTs) then step of the signal is decreased by 1 i.e., reduction in Δ.

mathematically,

X(nTs) > x^(nTs) +Δ i.e., increase in step size, then 1 is transmitted.

X(nTs) < x^(nTs) –Δ i.e., decrease in step size, 0 is transmitted.

Hence, delta modulation transmitted only one bit per sample.

Delta Modulation

Block Diagram of Delta Modulation

Let’s understand first the generation and detection of delta modulated signal.

Generation of delta modulated signal

The block diagram given bellow shows the generation of delta modulated signal:

Delta Modulator consist of a 1-bit quantizer and a delay circuit along with two comparator circuits.

Block diagram of delta modulation

The sampled signal x(nTs) and previous approximated sampled value  x^(nTs) generated by accumulator circuit, is given to comparator circuit. The output of comparator circuit is an error signal ep(nTs) given by.

ep(nTs)=x(nTs)−xˆ(nTs)

This error signal ep(nTs) is given to the quantizer circuit. The quantizer quantizes the error signal ep(nTs). The quantizer generates the output in the form of steps. If positive magnitude pulse is provided to the quantizer as its input then quantizer performs increment by 1 step size, Δ.

It means that positive pulse at the output of the comparator circuit shows that message signal is greater than the arbitrary signal. Thus quantizer increases Δ by 1.

Similarly, If negative magnitude pulse is provided to the quantizer as its input then quantizer performs decrement by 1 step size, Δ. Thus, quantizer decreases Δ by 1.

The output of the quantizer at the same time, through a feedback path, is provided to the accumulator. An accumulator is nothing but a device that stores the signal for further operation. Thus, output of the accumulator is behaves like the second input of the comparator. 

Finally,  depending on the staircase signal if the step size is +Δ then binary 1 is transmitted and if it is –Δ then binary 0 is transmitted.

Detection of delta modulated signal

Detection of a delta modulated signal is very easy and is somewhat reverse of generation of a delta modulated signal.

It is a process of decoding the binary output of the delta modulator to reconstruct an approximation of the original analog signal. The goal is to reverse the encoding process and recover an estimate of the continuous analog signal from the binary data.

The block diagram given bellow shows the detection of delta modulated signal:

It consist of a accumulator circuit and LPF (low pass filter).

The accumulator consists of a comparator circuit and a delay unit. The transmitted signal along with the delayed signal is added at the comparator circuit.

If here the input is binary 1 then after a delay the output increased step size +Δ noticed. However, in the case of binary 0 as input, a decrease in step size is noticed. This generates the staircase signal equivalent to the message signal.

The output of the accumulator circuit is given to the LPF that smoothens the staircase signal to regenerate the original message signal.

Advantages of delta modulation

  1. It is relatively simple to implement.
  2. It has less components and computational requirements compared to Pulse Code Modulation (PCM).
  3. It has lower bit rate compared to PCM.
  4. It is particularly useful in telecommunications.
  5. It is well-suited for real-time applications, such as audio and video streaming.
  6. It permits low channel bandwidth as well as signaling rate due to transmission of 1 bit per sample.

Disadvantages of delta modulation

The main disadvantages of DM are

  1. Slope Over load distortion [occur when step size (Δ) is small]
  2. Granular noise [occur when step size (Δ) is large]

What is delta modulation?

Delta modulation is a digital modulation technique used to convert analog signals into digital format by encoding the difference (delta) between consecutive samples of the analog signal.

What is the purpose of delta modulation?

The main purpose of delta modulation is to efficiently represent analog signals with low bit rates, making it suitable for applications with limited bandwidth or storage capacity.

Read more: wiki

Differential Pulse Code Modulation (DPCM)

Looking for Differential Pulse Code Modulation (DPCM)?

In this article we explained all main and important points regarding Differential Pulse Code Modulation (DPCM) in detail.

let’s understand the topic:

 In PCM (Pulse code modulation) It is observed that, the adjacent samples of a signal are highly correlated with each other. So, the adjacent sampled valued signal does not much change.  Which means , present sampled value to next sampled value does not vary by a large amount. It means, the adjacent samples of the signal carry the same information with a small difference. 

Read more: Pulse Code Modulation (PCM)

Sampling Theorem

The adjacent samples of the signal carry lots of redundant information. If these samples are encoded by a Standard PCM system, the resulting encoded signal contains some redundant bits (redundant information).

Figure 1 below shows a continuous time signal x(t) by dotted line. This signal is sampled by flat top sampling at regular time intervals T, 2T, 3T …..  nTs .

Figure 1: Redundant Information in PCM (Pulse code modulation)

Here, sampling frequency is selected in such a way, it is higher than the Nyquist rate. These samples are encoded by using 3-bit (7 levels) PCM. In figure 1, small circles shown the quantized value of samples to the nearest digital level. On the top of the each samples encoded binary value is written. Here we see in figure 1, that the samples taken at 4T, 5T and 6Tare encoded to same value of (110). This information can be carried only by one sample value. But three samples are carrying the same information means redundant.

Now, consider another example of samples taken at 9Ts and 10Ts time interval. The difference between these samples only due to last bit and first two bits are redundant, since they do not change. If this redundancy is reduced, then overall bit rate will decrease and number of bits required to transmit one sample will also be reduced. This is obtained by a digital pulse modulation technique is called as Differential PCM (DPCM) technique.

Working Principle of Differential pulse code modulation (DPCM)

DPCM works on the principle of prediction. The present sampled value is predicted from the past sampled value. The predicted value may not be exact, but it is very near to the actual sampled value.

Working of DPCM is explained with the help of block diagram of DPCM transmitter section and DPCM receiver section.

Differential pulse code modulation (DPCM) Transmitter

Figure 2 given below shows the block diagram of DPCM transmitter section.

Figure 2: Block DPCM transmitter section

The main components of DPCM transmitter are comparator, quantizer, prediction filter, and an encoder.

Let x(t) be the signal to be sampled and x(nTs) be its samples. The predicted signal is indicated by x^(nTs). Now x(nTs) sampled signal and x^(nTs) predicted signal is given to the comparator. The comparator in the transmitter, finds out the difference between the actual sample value x(nTs) and predicted sample value xˆ(nTs). The output of comparator is called error signal and it is denoted by e(nTs).

The output of comparator is given by,

e(nTs) = x(nTs) – xˆ(nTs)……………………….(1)

The predicted sample value xˆ(nTs) is produced by using a prediction filter.

Now, the output of comparator e(nTs) is given to the quantizer.

Quantizer output,

eq(nTs) = Q[e(nTs)] = e(nTs) + q(nTs) ……………………..(2)

The quantizer output signal eq(nTs) is called quantized error signal eq(nTs).

By encoding the quantizer output, in this method, we obtain a modified version of the PCM called differential pulse code modulation (DPCM).

Now, to makes the prediction more and more close to the actual sampled signal. The quantizer error signal eq(nTs) and the previous prediction is added and given as input to the prediction filter, this signal is denoted by xq(nTs). 

Predictor input is the sum of quantizer output eq(nTs) and predictor output xˆ(nTs)

xq(nTs) = xˆ(nTs) +  eq(nTs)……………………..(3)

 Now, put the value of  eq(nTs) from eq.(2)  in the above eq. (3) , we get,

xq(nTs) = xˆ(nTs) +  e(nTs) + q(nTs) ………………….(4)

So, the equation (1) is written as,

e(nTs) = x(nTs) – xˆ(nTs)

we get x(nTs) from the above equation

x(nTs) = e(nTs)  +  xˆ(nTs)

by putting the value of  e(nTs)  +  xˆ(nTs) from the above equation into equation 4, we get,

xq(nTs) = x(nTs) + q(nTs) …………………..(5)

From equation (5) we can say that, the input of the predictor xq(nTs) is the sum of original sample value x(nTs) and quantized error q(nTs). 

DPCM receiver

Figure 3 given below shows the block diagram of DPCM receiver section.

The DPCM receiver section consists of a decoder to reconstruct the quantized error signal from incoming DPCM input signal. The decoder output eq(nTs) and predictor output xˆ(nTs) are summed up to give xq(nTs) the quantized version of the original signal. Correspondingly the receive output signal differs from the input x(nts) only by the quantizing error q(nTs).

Figure 3: Block Diagram DPCM Receiver Section

Advantages of Differential pulse code modulation (DPCM)

There are three important advantages of Differential Pulse Code Modulation technique (DPCM) are given below:

  1. Reduced Bitrate: By using DPCM efficiently reduces the bitrate of digital audio signals by encoding the difference between consecutive samples. This means that instead of transmitting or storing each sample individually, DPCM only transmits the changes or variations in the signal, resulting in a lower data rate.
  2. Improved compression efficiency: DPCM reducing redundancy in the signal. It can achieve better compression ratios than PCM, by encoding the difference between two consecutive samples.
  3. Lower quantization noise: DPCM encodes the differences between two consecutive samples, it’s less sensitive to quantization errors than PCM.
  4. Simplicity of implementation: conceptually, DPCM is more simpler than other compression techniques like transform coding (used in JPEG and MP3), making it easier to implement in hardware or software.

Read more wiki

What Is DPCM?

DPCM stands for Differential Pulse Code Modulation. It is a digital signal compression technique that encodes the difference between consecutive samples in a signal or data stream.

How does DPCM differ from PCM?

In Pulse Code Modulation(PCM), each sampled signal is quantized and then encoded independently. But in DPCM, find the difference between the two consecutive sample and encode, It reduces the redundancy.

What is the main advantage of using DPCM?

By using DPCM efficiently reduces the bitrate of digital audio signals by encoding the difference between consecutive samples. This means that instead of transmitting or storing each sample individually, DPCM only transmits the changes or variations in the signal, resulting in a lower data rate.

When is DPCM commonly used?

DPCM is commonly used in telecommunications for voice and video compression, as well as in image and audio compression applications.

Pulse Code Modulation (PCM) – It’s Block Diagram

Pulse code modulation (PCM) is a digital modulation technique by which analog signal gets converted into digital form for transmission, storage, or processing. It involves sampling, quantizing, encoding, and, if needed, reconstructing the original analog signal.

Basics of Pulse Code Modulation (PCM)

Pulse Code Modulation (PCM) is a digital scheme, that digitize all forms of analog data, including video, audio, music, telemetry, etc. In PCM, the continuous analog signal is discretized into discrete values, which are then encoded into binary numbers.

This technique is widely used in various applications, such as telecommunications, audio recording, and data transmission, to convert and transmit analog information in a digital format, It allow efficient storage, transmission, and processing of signals while maintaining a high level of fidelity.

Pulse code modulation (PCM) is a digital modulation technique where as PPM (pulse position modulation), PWM (pulse width modulation) are the example of analog modulation techniques.

Read more: Block Diagram of Digital Communication

2. Sampling Theorem

Block Diagram of PCM

A communication system consist of three section a transmitter, communication channel, and receiver. A transmitter and a receiver have various components depending on the input signal and the output requirements. Transmitter perform modulation and receiver perform demodulation functions. 

In modulation process, sends the message signal with the carrier signal, which helps in enhancing the signals’ characteristics. It also removes any noise, interference, or distortion in the signal. The demodulation process recovers the original signal to make it suitable for the receiver.

Pulse code modulation my youTube video in Hindi

The block diagram of the Pulse Code Modulation (PCM) system is shown below:

1. Transmitter Section: The transmitter section consist of low pass filter, sampler, quantizer, encoder. The function of all the component explained below.

Analog Signal Input: PCM starts with an analog signal as its input. This analog signal can represent various types of data, such as audio waveforms in the case of voice or music.

Block Diagram of Pulse Code Modulation (PCM)

Image credit: tutorialspoint

LPF (low pass filter):Low Pass Filter (LPF) passes all the low frequency and rejects the higher frequencies from the input signal. It is done to avoid the problem of aliasing or distortion in the input signal.

Sampler: Sampling refers to the process of converting continuous time signal into discrete form this is done by sampler.

In this process the continuous time signal (analog signal) is sampled at regular time intervals. Each sample take the instantaneous amplitude of the analog signal at that moment. The rate at which these samples are taken is called the “sampling rate” or “sampling frequency.” According to Nyquist’s theorem, the sampling rate must be at least twice the highest frequency present in the analog signal to avoid aliasing.

The output of sampler is a discrete time signal.

Quantizer: After sampling, each sample’s amplitude is quantized using quantizer. This involves dividing the range of possible amplitudes into a finite number of discrete levels. The number of quantization levels is determined by the “bit depth” or “resolution.” Common bit depths are 8 bits, 16 bits, or 24 bits. More bits allow for finer amplitude resolution.

Encoder: The digitization of analog signal is done by the encoder. Each quantization level is assigned a unique binary code or digital word. The length of this binary code is determined by the bit depth. For example, with 8-bit PCM, there are 256 quantization levels, each represented by an 8-bit binary code.

2.Communication channel: A communication channel is a medium between the transmitter and the receiver. The PCM bitstream can be transmitted over digital communication channels. It also includes a repeater and regenerator that can regenerate the coming digital signal, increase signal strength, and reduce effect of noise.

3. Receiver section: The receiver section consist of decoder, Reconstruction Filter. The function of all the component explained below.

Decoder: Decoder perform the opposite operation of encoder placed in the transmission section. The digitally encoded signal arrives at the receiver. It first removes the noise from the signal. Then decoder circuit decodes the receive pulse coded waveform to reproduce the original signal. This circuit acts as the demodulator.

Reconstruction Filter: To smoothen the reconstructed analog signal and remove high-frequency components introduced during quantization, a reconstruction filter is often used.

Read More wiki

What is PCM, and how does it work?

PCM stands for Pulse Code Modulation. It’s a method of digitally encoding analog signals by sampling the signal’s amplitude at regular intervals, quantizing the samples into binary values, and then encoding them into a digital bitstream.

What is the purpose of sampling in PCM?

Sampling in PCM involves measuring the amplitude of an analog signal at specific time intervals. This process converts the continuous analog signal into discrete data points for digital representation.

What is quantization, and why is it necessary in PCM?

Quantization involves assigning a discrete value (usually binary) to each sampled amplitude. It’s necessary to represent the analog signal accurately in digital form. The number of quantization levels determines the bit depth, which affects the signal’s resolution.

What is the Nyquist Theorem, and how does it relate to PCM?

The Nyquist Theorem states that the sampling rate must be at least twice the highest frequency component in the analog signal to accurately reconstruct it from its samples. PCM adheres to this principle to avoid aliasing.

What are the advantages of using PCM for audio recording?

PCM offers high-fidelity audio representation, compatibility with a wide range of devices and software, robustness against noise, and flexibility in terms of adjusting audio quality.

Top Electrical Measurements and Measuring Instruments MCQ (Multiple Choice Questions)

Here I discuss Top Electrical Measurements and Measuring Instruments MCQ (Multiple Choice Questions)

Q1. which Instruments measure the total quantity of electricity delivered in a particular time. ​
a) Absolute​
b) Indicating​
c) Recording​
d) Integrating​

Answer: Integrating​

Q2. Which of the following are Integrating instruments?​
a) Ammeters​
b) Voltmeters​
c) Wattmeters​
d) Ampere-hour and Watt-hour meters​

Answer: Ampere-hour and Watt-hour meters​

Q3. Resistances can be measured with the help of​
a) Wattmeters​
b) Voltmeters​
c) Ammeters​
d) Ohmmeters and resistance bridges 

Answer: Ohmmeters and resistance bridges 

Q4. Which of the following essential features is possessed by indicating instrument?​
a) Deflecting device​
b) Controlling device​
c) Damping device​
d) All of the above

Answer: Controlling device​

Q5. The household energy meter is​
a) Absolute Instrument​
b) Indicating Instrument​
c) Recording Instrument​
d) Integrating Instrument​

Answer: Integrating Instrument​

Q6. The pointer of the indicating instrument should be​
a) Very light​
b) Very heavy​
c) Very thick and wide​
d) Neither very light nor very heavy​

Answer: Very light

Q7. A moving-coil permanent-magnet instrument can be used as  ……….  by using a low resistance shunt.​
a) Ammeter​
b) Voltmeter​
c) Flux-meter​
d) Ballistic galvanometer

Answer:  ​Ammeter​

Q8. Which of the following properties damping oil must possess?​
a) Must be a good insulator and non-evaporating​
b) Should not have corrosive action upon the metal of the vane​
c) The viscosity of the oil should not change with the temperature​
d) All of the above

Answer:  ​All of the above

Q9. A moving-coil permanent-magnet instrument can be used as flux-meter​
a) By using a low resistance shunt​
b) By using a high series resistance​
c) By eliminating the control springs​
d) By making control springs of large moment of inertia

Answer: By eliminating the control springs​

Q10. An induction meter can handle current upto​
a) 10 A​
b) 30 A​
c) 60 A​
d) 100 A​

Answer: 100A

Q11. Induction type single phase energy meters measure electric energy in​
a) KW​
b) Wh​
c) KWh​
d) VAR​

Answer: KWh

Q12. Which of the following meters are not used on DC circuits?​
a) Mercury motor meters ​
b) Commutator motor meters​
c) Induction meters​
d) None of the above ​

Answer: Induction meters​

Q13. A potentiometer may be used for​
a) Measurement of resistance​
b) Measurement of current​
c) Calibration of ammeter and voltmeter​
d) All of the above ​

Answer: All of the above ​

Q14. Which instrument is used for measuring the insulation resistance of an electric circuit relative to earth and one another?​
a) Tangent galvanometer​
b) Megger​
c) Current transformer​
d) None of the above ​

Answer: Megger​

Q15. Which of the following meters are not used on DC circuits?​
a) Mercury motor meters ​
b) Commutator motor meters​
c) Induction meters​
d) None of the above ​

Answer: Induction meters​

Read More Power Electronics MCQ

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Sampling Theorem | Sampling In PCM | Digital Communication

The sampling theorem, also known as the Nyquist-Shannon sampling theorem, is a fundamental concept in signal processing and digital communication.

Sampling is a process of converting a continuous-time analog signal into discrete-time signal. This conversion is done with the help of sampler.

Sampling is the second step in Pulse Code Modulation (PCM) technique where we convert analog signal into digital signal. In PCM after sampling amplitude of the discrete-time signal is quantized with the help of quantizer and then this quantized signal is coded to the binary sequence using encoder, allow the computer to process the signal, then transmitted to the far end receiver then it is converted back to the original signal.

Read more “Block Diagram of Digital communication”

Need for Sampling

Most of the real-life signals, such as audio, video, temperature etc., are continuous in nature and represented as analog signals. However, for efficient processing, storage, and transmission, these analog signals need to be converted into digital form. Sampling make possible this conversion by taking a limited number of discrete data points from the continuous signal.

Sampling convert continuous-time, continuous amplitude signal into discrete-time continuous amplitude signal.

Analog signals are more susceptible to noise and external interference, which can degrade signal quality. Through sampling and subsequent digital processing, noise can be filtered out or reduced, resulting in cleaner and more reliable data.

What is the Sampling Theorem?

The sampling theorem, also known as the Nyquist-Shannon theorem, it is a fundamental principle that guides the process of converting analog signals to digital form.

The sampling theorem states that “if a signal is sampled at regular time intervals (ts), then the sequence of samples can be reconstructed or recreate the original signal. when the sampling rate is at least twice the highest frequency component present in the signal.”

Mathematically,

if a massage signal (continuous signal ) is denoted as m(t), and its highest frequency component is denoted as fm, then the sampling theorem states that to accurately reconstruct m(t) from its samples, the sampling frequency (or rate), denoted as fs, must be greater than or equal to twice the highest frequency component:

fs ≥ 2 * fm

When this condition is met, the original signal can be reconstructed from its samples using techniques like interpolation or various digital signal processing methods. The process of converting a continuous signal into discrete samples is known as “sampling” or “digitization.”

What is the Nyquist Rate?

The Nyquist rate, also known as the Nyquist frequency or Nyquist limit, is the minimum sampling rate required to accurately represent a continuous signal in a discrete form without introducing distortion or aliasing. It is a fundamental concept in signal processing and digital communication.

The Nyquist rate is defined as follows:

“The Nyquist rate is equal to twice the highest frequency component present in a continuous signal.”

Mathematically,

if the highest frequency component in a signal is denoted as fm, then the Nyquist rate, denoted as fs (the minimum sampling frequency), is given by:

fs = 2 * fm

If the sampling rate is less than the Nyquist rate, aliasing can occur, where higher-frequency components of the signal “overlap” into lower-frequency ranges, making it impossible to accurately reconstruct the original signal from the samples.

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What is sampling?

Sampling is a process of converting a continuous-time analog signal into discrete-time signal. This conversion is done with the help of sampler.

Why do we need to sample signals in digital communication?

Digital communication systems operate with discrete signals, and most information sources generate continuous analog signals. Sampling allows us to represent these analog signals in a digital format, making it easier to process, transmit, and store them.

Statement of sampling theorem

The sampling theorem states that “if a signal is sampled at regular time intervals (ts), then the sequence of samples can be reconstructed or recreate the original signal. when the sampling rate is at least twice the highest frequency component present in the signal.”
Mathematically,
if a massage signal (continuous signal ) is denoted as m(t), and its highest frequency component is denoted as fm, then the sampling theorem states that to accurately reconstruct m(t) from its samples, the sampling frequency (or rate), denoted as fs, must be greater than or equal to twice the highest frequency component:
fs ≥ 2 * fm

what is Nyquist rate?

The Nyquist-Shannon sampling theorem states that to accurately represent a continuous signal, the sampling rate must be at least twice the highest frequency component in the signal (Nyquist rate). It’s crucial to avoid aliasing and information loss during sampling.

How do I choose the right sampling rate for a signal?

Determine the highest frequency component (f_max) in your signal and choose a sampling rate (fs) that is at least twice f_max (fs ≥ 2 * f_max) to satisfy the Nyquist theorem.

IBPS Clerk Admit Card 2023: IBPS Clerk Admit Card Out, download here

IBPS Clerk Admit Card 2023: Institute of Banking Personnel Selection (IBPS) has released the IBPS Clerk Prelims Admit Card 2023 on August 16, 2023.

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IBPS Clerk Admit Card 2023 Out:

Institute of Banking Personnel Selection (IBPS) has released the IBPS Clerk Prelims Admit Card 2023 on Wednesday, August 16, 2023. Candidates who have registered for IBPS Clerk preliminary exam can download their admit card through the official website of IBPS at ibps.in.

IBPS Clerk Pre Exam Date 2023

The admit card for the candidates will be available on the official website of IBPS from August 16 to September 02, 2023. IBPS Clerk 2023 preliminary exam is scheduled for August or September.

IBPS Clerk 2023 preliminary exam is scheduled to be held on August 26, 27 and September 02, 2023. The result will be declared in September/ October 2023. The main exam will be conducted in October 2023. This recruitment drive aims to fill a total of 4045 vacancies.

Download IBPS Clerk Admit Card

  1. First of all, visit the official website of IBPS at ibps.in.
  2. Click on IBPS Clerk Prelims Admit Card 2023 link available on the home page.
  3. Enter login details and click on submit.
  4. Your call letter will be displayed on the screen.
  5. Check and Download Admit Card.
  6. Keep a hard copy of it with you for further need.

Download IBPS clerk admit card click here

Investigating Why Transmission line Voltage is in multiple of 11 

Why Transmission line Voltage is in multiple of 11

In this article we are Investigating Why Transmission line Voltage is in multiple of 11. So, you must have heard that this transmission line is of 11kV (11000V), it is 33kV, 22kV, or 33kV….etc. so friends, have you ever wondered why it is in multiple or coefficient of 11, so let’s know.

Transmission Line Voltage

First of all, let us tell you that not all the voltage of the transmission line is in multiples of 11. Transmission line voltage is 11kV, 22,kV, 33kV, 66kV and 132kV apart from 400kV, 765kV and 800kV which is not 11 multiple.

Image credit: electricalnotebook.com

Due to form factor

In many places you must have heard the answer to this question that transmission line voltage is due to the multiple form factor of 11.

Let us understand below.

The value of the form factor is 1.1. Because the Form factor is the ratio of RMS and the average value of voltage or current.

Form factor= Vr.m.s / Vavg

Vr.m.s= Vm / √2
&
Vavg= 2Vm / π

Form factor= (Vm/√2) / (2Vm/π)

Form factor= Vmπ / √22Vm

Form factor= 1.11

Now if we multiply this 1.11 with the line voltage then below are some conclusions-

10kV x 1.11 = 11.1kV
20kV x 1.11 = 22.2kV
30kV x 1.11 = 33.3kV
60kV x 1.11 = 66.6kV
120kV x 1.11 = 133.2kV

But the transmission line voltage is not 133.2kV ​​but 132kV.

Therefore, there is no multiple of 11 in transmission line voltage due to form factor.

Due to voltage drop in transmission line

Let us tell you that when Thomas Edison did electricity transmission for the first time in the history of electricity, he had to transmit more than 100V to get exactly 100V.

This happens because the transmission line has some losses of its own, due to which the voltage we receive is always less than the transmit voltage.

Engineers studied this and told that the voltage loss in the transmission line is about 10%. Perhaps 10% would have been done to make the calculation easier, the exact value could be 12 or even 8.

10% of Transmit Voltage

10kV x 10% = 1kV
transmit voltage = 10+1 = 11kV

20kV x 10% = 2kV
transmit voltage = 20+2= 22kV

30kV x 10% = 3kV
transmit voltage = 30+3 = 33kV

60kV x 10% = 6kV
transmit voltage = 60+6 = 66kV

120kV x 10% = 12kV
transmit voltage = 120+12 = 132kV

200kV x 10% = 20kV
transmit voltage = 200+20 = 22

Higher Transmission Line Voltage – 400kV, 765kv and 800kV

10% line loss is not taken for transmission voltage higher than this because the higher the line voltage, the less the losses keep on decreasing.

That’s why Transmission voltage 400kV, 765kV or 800kV is not in multiples or multiples of 11.

So friends, now you must have understood why Transmission line voltage is in multiple of 11, so it is taken because of the loss in Transmission line.

Read more wiki

What is a transmission line?

A transmission line is a specialized cable or conductor used to transfer electrical energy or signals from one location to another, typically over long distances. It is an essential component of power distribution and telecommunication networks.

What are the main types of transmission lines?

The two main types of transmission lines are:
a. Power Transmission Lines: These lines carry high-voltage electrical power from power plants to substations and from substations to distribution networks.
b. Communication Transmission Lines: These lines carry signals for data and communication, including telephone, internet, and television signals.

How are transmission lines different from distribution lines?

Transmission lines are used to transmit power or signals over long distances at higher voltages, while distribution lines distribute power or signals at lower voltages to end-users in local areas.

What are the factors that determine the efficiency of a transmission line?

The efficiency of a transmission line is influenced by factors such as line length, conductor material, insulation, and the quality of insulators used.

How are power transmission lines insulated?

Power transmission lines are insulated with materials such as glass, porcelain, or composite insulators. These insulators prevent electricity from leaking to the ground and help maintain the safety and reliability of the transmission system.

What is the significance of the voltage level in power transmission lines?

Higher voltage levels are used in power transmission lines to reduce power losses during transmission. Increasing the voltage allows for the same power to be transmitted with lower current, reducing resistive losses in the conductor.