Unit II: Physical Layer | CSE306: COMPUTER NETWORKS | B.Tech CSE

Unit II: Physical Layer

⭐PHYSICAL LAYER: Signal & Media

1. Basics for Data Communications and Analog and Digital signals

• Data Communication: The transfer of data between devices through a transmission medium.

• Key Components:

• Sender: Device that sends the data (e.g., computer).
• Receiver: Device that receives the data (e.g., printer).
• Medium: Physical path between sender and receiver (e.g., cables, air).

• Types of Data Communication

• Simplex Communication: Data flows in only one direction (e.g., TV broadcasting).
• Half-Duplex Communication: Data flows in both directions, but not at the same time (e.g., walkie-talkies).
• Full-Duplex Communication: Data flows in both directions simultaneously (e.g., telephone conversation).

What are Signals?

• Signals are patterns of voltage or electromagnetic waves used to carry information. They represent data in a form that can travel over a medium.

• Analog Signals:

• Definition: Continuous signals that vary over time, representing information in a waveform.
• Continuous and vary over time. 
• They represent data as a continuous wave (e.g., sound waves, radio waves).
• Characteristics:
  • Can take on any value in a range.
  • Examples: Sound waves, radio waves.
  • More susceptible to noise and distortion.

• Digital Signals:

• Definition: Discrete signals that represent data as binary values (0s and 1s).
• Discrete and use binary (0s and 1s) to represent data. 
• Digital signals have only two levels: HIGH (1) or LOW (0).
• Characteristics:
• Limited to two values (high/low).
• Easier to process and transmit.
• Less susceptible to noise and interference.
• Examples: Computer data, digital audio signals.

2. Transmission Impairments and Performance

Transmission Impairments:

• Factors that affect the quality of signal transmission.

Types of Impairments:

1. Attenuation:

   • Reduction in signal strength as it travels through a medium.
   • More pronounced over long distances or in poor-quality media.

2. Distortion:

   • Alteration of the signal shape or waveform during transmission.
   • Can occur due to different propagation speeds of various frequency components.

3. Noise:

   • Unwanted signals that interfere with the transmission of the desired signal.
   • Types of Noise:
     • Thermal Noise: Caused by the random motion of electrons in conductors.
     • Crosstalk: Interference from adjacent wires or channels.
     • Electromagnetic Interference (EMI): External electromagnetic fields affecting the signal.

Performance Factors in Transmission:

Transmission performance refers to how effectively data is transmitted from the sender to the receiver. It is influenced by several factors:

• Bandwidth

• The range of frequencies that a transmission medium can carry. 
• It determines the amount of data that can be transmitted over the medium in a given time.
• Effect on Performance:
• Higher Bandwidth: More data can be transmitted, leading to faster communication and better performance.
• Lower Bandwidth: Slower transmission and reduced data rates.
• Example: A fiber optic cable has higher bandwidth than copper cables, making it more suitable for high-speed internet connections.

• Throughput

• The actual rate at which data is successfully transmitted from the sender to the receiver. Throughput is usually measured in bits per second (bps).
• Factors Affecting Throughput:
  • Bandwidth: Higher bandwidth increases throughput.
  • Errors and Noise: More errors mean more retransmissions, reducing throughput.
  • Network Congestion: When many devices share the same network, the throughput decreases due to competition for resources.
• Effect on Performance: Higher throughput indicates better performance, meaning more data is transmitted in less time.

• Latency (Delay)

• Definition: The time it takes for a signal to travel from the sender to the receiver. Measured in milliseconds (ms).
• Components of Latency:
• Propagation Delay: The time taken for the signal to travel through the transmission medium.
• Transmission Delay: The time needed to push all the data onto the medium.
• Processing Delay: The time taken by devices (routers, switches) to process the data.
• Queuing Delay: Time spent waiting in queues inside network devices before being transmitted.
• Effect on Performance: High latency leads to slow communication, especially in real-time applications like video calls or gaming.

• Jitter

• Jitter is the variation in packet arrival time. It refers to the inconsistency in delay times for data packets traveling through the network.
• Causes:
• Network congestion, packet queuing, and varying processing times in routers or switches.
• Effect on Performance: 
• Jitter affects real-time applications such as voice calls and video streaming, causing choppy audio or video if it exceeds acceptable limits.
• Solution: 
• Use buffers to compensate for jitter, or Quality of Service (QoS) settings in networks to prioritize certain types of traffic.

Data Rate:

• Data Rate or Bit Rate is the speed at which data is transmitted, measured in bps (bits per second).

• The data rate is affected by factors such as:
• Bandwidth (the wider the bandwidth, the higher the data rate).
• Signal-to-Noise Ratio (SNR) (a higher SNR leads to a better data rate).
• Error Rates (higher error rates reduce the effective data rate).
• Medium Type (different media have different capacities, with fiber optics providing the highest rates).

• Data rates can be improved through increasing bandwidth, reducing noise, and using compression, modulation techniques, and multiplexing.

3. Transmission Media like Guided and Unguided media

Guided Media (Wired)

1. Twisted Pair Cable:

   • Structure: Pairs of insulated copper wires twisted together.
   • Types:
     • Unshielded Twisted Pair (UTP): Common in local area networks; inexpensive but vulnerable to interference.
     • Shielded Twisted Pair (STP): Offers shielding against interference; used in environments with high electromagnetic noise.

2. Coaxial Cable:

   • Structure: Central copper conductor surrounded by insulation and a conductive shield.
   • Uses: Cable television, internet connections.
   • Advantages: Better resistance to interference than twisted pair cables.

3. Fiber Optic Cable:

   • Structure: Consists of thin strands of glass or plastic that transmit data using light.
   • Advantages:
     • Extremely high bandwidth.
     • Long-distance transmission without loss.
     • Immune to electromagnetic interference.

Unguided Media (Wireless)

1. Radio Waves:

   • Used for long-range communication.
   • Applications: Wi-Fi, cellular networks.
   • Characteristics: Propagate through the air; require less infrastructure.

2. Microwaves:

   • High-frequency radio waves used for point-to-point communication.
   • Characteristics: Requires line-of-sight; can transmit data over long distances.

3. Infrared:

   • Used for short-range communication (e.g., remote controls, IR data transfer).
   • Characteristics: Requires a direct line-of-sight and has limited range.

Feature	Guided Media	Unguided Media
Physical Conductor	Requires physical cables (e.g., copper, fiber)	No physical cables, data sent via air or space
Distance	Effective for short to long distances, depending on the medium	Radio waves can travel long distances; microwaves and infrared are more short-range
Bandwidth	High bandwidth (especially in fiber optics)	Generally lower bandwidth than fiber optics
Interference	Less prone to interference (especially fiber optics)	More prone to interference (e.g., from weather, obstacles)
Installation Cost	Higher installation costs, especially for fiber optics	Generally lower costs, especially for wireless
Mobility	Limited mobility (requires physical connections)	High mobility (no physical connections needed)
Usage	Used in wired networks (e.g., LANs, Internet backbone)	Used in wireless networks (e.g., Wi-Fi, cellular)

4. Cabling Standards

Cabling standards apply to various types of cables used in networking:

• Twisted Pair Cables
• Coaxial Cables
• Fiber Optic Cables

4.1. Twisted Pair Cable Standards

Twisted pair cables are widely used in local area networks (LANs) and telecommunications. The standards include:

Category (Cat) Standards

• Cat5:

  • Maximum Data Rate: 100 Mbps
  • Maximum Bandwidth: 100 MHz
  • Use Case: Basic networking, voice, and video applications.

• Cat5e (Enhanced):

  • Maximum Data Rate: 1 Gbps (Gigabit Ethernet)
  • Maximum Bandwidth: 100 MHz
  • Use Case: Improved performance and reduced crosstalk compared to Cat5.

• Cat6:

  • Maximum Data Rate: 1 Gbps (up to 100 meters), 10 Gbps (up to 55 meters)
  • Maximum Bandwidth: 250 MHz
  • Use Case: Supports high-speed applications, such as streaming and gaming.

• Cat6a (Augmented):

  • Maximum Data Rate: 10 Gbps
  • Maximum Bandwidth: 500 MHz
  • Use Case: Enhanced performance for data centers and enterprise networks.

• Cat7:

  • Maximum Data Rate: 10 Gbps
  • Maximum Bandwidth: 600 MHz
  • Use Case: Shielded cables for reduced interference and longer distances.

• Cat8:

  • Maximum Data Rate: 25-40 Gbps
  • Maximum Bandwidth: 2000 MHz
  • Use Case: Designed for high-speed data centers and short-distance applications.

Wiring Standards

• T568A:

  • One of the wiring schemes for terminating twisted pair cables.
  • Pins are arranged in a specific order (used mainly in residential installations).

• T568B:

  • Another wiring scheme similar to T568A but with a different pin order.
  • More common in commercial installations.

• Crossover Cables:

  • A type of twisted pair cable where the transmit and receive pairs are swapped, used to connect similar devices (e.g., switch to switch).

4.2. Coaxial Cable Standards

Coaxial cables are often used in cable television, internet, and broadband connections. Key standards include:

• RG-6:

  • Commonly used for cable TV and broadband internet.
  • Has better shielding than RG-59, making it suitable for longer distances.

• RG-59:

  • Older standard, used for shorter cable runs (e.g., CCTV).
  • Lower bandwidth capacity compared to RG-6.

4.3. Fiber Optic Cable Standards

Fiber optic cables are used for high-speed data transmission over long distances. Key standards include:

Fiber Types

• Single-Mode Fiber (SMF):

  • Core Diameter: ~9 micrometers.
  • Supports long-distance communication (up to 100 km).
  • Used in telecommunications and internet backbone connections.

• Multi-Mode Fiber (MMF):

  • Core Diameter: ~50 or 62.5 micrometers.
  • Suitable for short-distance applications (up to 2 km).
  • Used in data centers and local area networks.

Connector Standards

• SC (Subscriber Connector):

  • Square shape, used for high-density applications.

• LC (Lucent Connector):

  • Smaller size, used for high-density patch panels.

• ST (Straight Tip Connector):

  • Bayonet-style connector, commonly used in older installations.

• MTP/MPO (Multi-fiber Termination Push-on):

• Used for high-density fiber applications, connecting multiple fibers in one connector.

⭐PHYSICAL LAYER: Modulation & Multiplexing

1. Modulation

• Definition: The process of varying a carrier signal to encode information for transmission.
• Purpose: To facilitate the transmission of data over a medium and to match the characteristics of the communication channel.

Types of Modulation

1. Digital to Digital Conversion:

   • Encoding: Mapping digital data (binary) to digital signals.
   • Techniques:
     • Non-Return to Zero (NRZ): Represents binary 1s and 0s as two different voltage levels without returning to a neutral state.
     • Manchester Encoding: Each bit is represented by a transition; a 0 is a high-to-low transition, and a 1 is a low-to-high transition.
     • Differential Manchester Encoding: Similar to Manchester but uses changes in signal for encoding.

2. Analog to Digital Conversion:

   • Sampling: Taking discrete samples of an analog signal at regular intervals.
   • Quantization: Assigning finite values to the sampled signals.
   • Techniques:
     • Pulse Code Modulation (PCM): Converts analog signals into a digital format by sampling and quantizing the amplitude.

3. Analog to Analog Conversion:

   • Definition: Modulating an analog signal to carry information.
   • Techniques:
     • Amplitude Modulation (AM): Varies the amplitude of the carrier wave according to the message signal.
     • Frequency Modulation (FM): Varies the frequency of the carrier wave according to the message signal.
     • Phase Modulation (PM): Varies the phase of the carrier wave according to the message signal.

4. Digital to Analog Conversion:

   • Definition: Converting digital data into an analog signal for transmission.
   • Techniques:
     • Amplitude Shift Keying (ASK): Represents binary data by varying the amplitude of the carrier wave.
     • Frequency Shift Keying (FSK): Represents binary data by varying the frequency of the carrier wave.
     • Phase Shift Keying (PSK): Represents binary data by varying the phase of the carrier wave.
       • Quadrature Phase Shift Keying (QPSK): Uses four different phase shifts to represent two bits per symbol.

2. Multiplexing

• The technique of combining multiple signals into a single transmission medium to optimize the use of available bandwidth.

Types of Multiplexing

1. Time Division Multiplexing (TDM):

   • Definition: Divides time into fixed segments, allowing multiple signals to share the same channel by taking turns.
   • Types:
     • Synchronous TDM: Each signal is assigned a fixed time slot in each cycle.
     • Asynchronous TDM (Statistical TDM): Time slots are dynamically allocated based on demand, allowing for more efficient use of bandwidth.

2. Frequency Division Multiplexing (FDM):

   • Definition: Divides the available bandwidth into separate frequency bands, each carrying a different signal.
   • Applications: Commonly used in radio broadcasting and cable television.
   • Characteristics: Each signal is modulated to a different frequency, allowing simultaneous transmission.

3. Wavelength Division Multiplexing (WDM):

   • Definition: Similar to FDM, but used in fiber optic communication; divides light into different wavelengths (colors).
   • Types:
     • Dense Wavelength Division Multiplexing (DWDM): Allows for many closely spaced wavelengths, increasing capacity.
     • Coarse Wavelength Division Multiplexing (CWDM): Fewer wavelengths spaced further apart.

4. Code Division Multiplexing (CDM):

• Definition: Assigns unique codes to each signal, allowing multiple signals to occupy the same frequency band simultaneously.
• Characteristics:
• Used in cellular communications (e.g., CDMA).
• Allows for robust communication even in the presence of noise.

Applications of Multiplexing

• Telecommunications: To combine multiple voice or data calls over a single communication line.
• Broadcasting: To transmit multiple radio or television channels over a single frequency band.
• Data Communication: To allow multiple data streams to share the same network infrastructure.
• Fiber Optic Communications: To increase the capacity of fiber optic cables by transmitting multiple signals at different wavelengths.
• Satellite Communication: To send multiple channels of data simultaneously, improving efficiency and reducing costs.

---

Download Notes (PDF)

Download PYQ (PDF)

---

🚨Thanks for visiting classpdfindia✨

Welcome to a hub for 😇Nerds and knowledge seekers! Here, you'll find everything you need to stay updated on education, notes, books, and daily trends.

💗 Bookmark our site to stay connected and never miss an update!

💌 Have suggestions or need more content? Drop a comment below, and let us know what topics you'd like to see next! Your support means the world to us. 😍