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### Summary: Physical Layer (S305)

The physical layer is the first layer in the Internet model, responsible for the transmission of raw data over physical circuits. This lecture covers different aspects of data transmission, including circuit types, data flow, coding schemes, transmission modes, multiplexing, media types, and both digital and analog data transmission.

#### Key Topics:

1. Circuits & Configuration

- Physical Circuits: The actual wires connecting devices.

- Logical Circuits: Transmission characteristics of the connection.

- Point-to-Point vs. Multipoint Circuits: Wired networks often use point-to-point; wireless networks use multipoint.

2. Data Flow & Transmission Modes

- Simplex: One-way communication.

- Half-Duplex: Two-way, but only one direction at a time.

- Full-Duplex: Simultaneous two-way communication.

- Serial Transmission: Bits sent one at a time.

- Parallel Transmission: Multiple bits sent simultaneously.

3. Coding & Multiplexing

- ASCII & Unicode: Standardized ways to represent characters.

- Multiplexing (MUX): Combining multiple low-speed circuits into one high-speed circuit.

- Types: Time-Division (TDM), Frequency-Division (FDM), Wavelength-Division (WDM), Inverse Multiplexing (IMUX).

4. Media Types

- Guided (Wired): Twisted-pair, coaxial, fiber-optic.

- Wireless: Radio/WiFi.

- Factors for Selection: Cost, distance, speed, security, error rates.

5. Digital & Analog Transmission

- Digital Transmission of Digital Data: Uses encoding (e.g., ASCII, Unicode).

- Analog Transmission of Digital Data: Requires modulation (AM, FM, PM) for transmission over analog networks.

- Digital Transmission of Analog Data: Uses Codecs and Pulse-Code Modulation (PCM) for conversion.

6. Modulation Techniques

- Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM).

- Combining Modulations: 64-QAM, 256-QAM used in cable modems.

7. Data Rate Calculation

- Symbol Rate x Bits per Symbol = Data Rate.

- Quantizing Error: Reduced by increasing sampling frequency and amplitude levels.

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### Flashcards

(You can print these or use an app like Anki to review.)

#### 1. What is the role of the Physical Layer?

- It focuses on the transmission of raw data over physical circuits.

#### 2. What are the types of circuits?

- Physical Circuit: Actual wires connecting devices.

- Logical Circuit: Transmission characteristics of a connection.

#### 3. What are the types of circuit configurations?

- Point-to-Point: Direct connection between two devices.

- Multipoint: Shared connection among multiple devices.

#### 4. What are the three types of data flow?

- Simplex: One-way transmission.

- Half-Duplex: Two-way, but only one direction at a time.

- Full-Duplex: Simultaneous two-way transmission.

#### 5. What are the differences between Serial and Parallel Transmission?

- Serial: One bit at a time, slower but used in long distances.

- Parallel: Multiple bits at once, faster but prone to interference.

#### 6. What is Multiplexing (MUX)?

- It divides one high-speed circuit into multiple low-speed circuits.

#### 7. What are the three types of Multiplexing?

- TDM (Time-Division): Divides transmission into time slots.

- FDM (Frequency-Division): Uses different frequency bands.

- WDM (Wavelength-Division): Uses different light wavelengths in fiber optics.

#### 8. What are the three types of guided media (wired)?

- Twisted-pair (TP): Used in LANs, inexpensive.

- Coaxial cable: Used in cable TV, better shielding.

- Fiber-optic: High speed, long distances.

#### 9. What are the three types of wireless media?

- Radio/WiFi: Wireless LANs.

- Microwave: Long-distance communication.

- Satellite: Global communication.

#### 10. What is the difference between Digital and Analog Transmission?

- Digital: Uses discrete binary signals (0s and 1s).

- Analog: Uses continuous waves.

#### 11. What are the three main modulation techniques?

- AM (Amplitude Modulation): Varies the height of the wave.

- FM (Frequency Modulation): Varies the number of waves per second.

- PM (Phase Modulation): Varies the starting point of the wave.

#### 12. What is Pulse-Code Modulation (PCM)?

- A technique that converts analog signals into digital by sampling and quantizing.

#### 13. What is Quantizing Error?

- The difference between the original analog signal and the digital approximation.

- Reduced by increasing sampling frequency and amplitude levels.

#### 14. What is 64-QAM and 256-QAM?

- 64-QAM: Uses AM + PM with 6 bits per symbol.

- 256-QAM: Uses AM + PM with 8 bits per symbol, higher data rate.

#### 15. How is Data Rate calculated?

- Data Rate = Symbol Rate × Bits per Symbol.

- Example: If Symbol Rate = 16,000 symbols/sec and Bits per Symbol = 4, then:

Data Rate = 16,000 × 4 = 64,000 bits/sec (64 Kbps).

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