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Overview of Digital Transmission

• Digital transmission uses discrete, digital data format to encode and transmit data.
• It differs from analog transmission which uses continuous signals.
• Digital transmission boasts advantages like enhanced noise immunity, improved security, and support for diverse data types.
• Digital signals consist of discrete values, principally binary (0s and 1s).

Encoding Techniques

• Converting digital data into electrical signals for physical media transmission is done through encoding techniques.
• Encoding dictates binary data mapping to electrical signals.
• Common encoding schemes:
  • Non-return-to-zero (NRZ): Signal level remains constant for a bit duration. Variations include NRZ-L (level), NRZ-I (inversion), and Manchester encoding.
  • Manchester encoding: Signal level changes mid-bit, providing a clocking signal and improved noise immunity.
  • Differential Manchester encoding: Signal level change signifies the bit value. A change at bit beginning or middle indicates different binary values.
  • Return-to-Zero (RZ): Signal returns to zero voltage level between bits.
  • Bipolar-AMI (Alternate Mark Inversion): Signal polarity alternates for each transmitted 1; no signal represents 0.

Transmission Media

• Digital signal transmission media types include wired and wireless.
• Wired media (twisted-pair cable, coaxial cable, fiber optic cable) uses electrical or optical signals for data transmission.
• Wireless media (radio waves, microwaves, infrared) transmit data without physical connections.

Modulation Methods

• Modulation is vital for wireless transmission, converting digital signals into analog signals suitable for the medium.
• Various modulation techniques exist with varying bandwidth efficiency and noise immunity tradeoffs.
• Examples include:
  • Amplitude Shift Keying (ASK)
  • Frequency Shift Keying (FSK)
  • Phase Shift Keying (PSK)

Multiplexing

• Multiplexing lets multiple signals share a transmission medium, boosting throughput and efficiency.
• Types include:
  • Time Division Multiplexing (TDM): Signals are interleaved in time slots on the shared medium, each signal gets a dedicated time slot.
  • Frequency Division Multiplexing (FDM): Signals are separated into distinct frequency bands, each signal occupying a specific frequency range.

Error Detection and Correction

• Transmission errors due to noise or disturbances are common.
• Techniques ensure data integrity:
  • Parity bits: Adding extra bits to detect errors.
  • Cyclic Redundancy Checks (CRCs): Using polynomial calculations to check for errors.

Digital Signal Characteristics

• Digital signals have quantifiable characteristics influencing transmission performance:
  • Bit rate: Bit transmission speed.
  • Baud rate: Signal changes per second.
  • Bandwidth: Transmission frequency range.

Transmission Standards

• Numerous standards govern digital transmission in various network technologies.
• Examples include Ethernet standards (10Base-T, 100Base-TX) for wired networks, and Wi-Fi standards for wireless networking.
• Defining physical layer protocols and related parameters for reliable transmission.

Noise and Interference

• Noise and interference significantly impact digital transmissions.
• Common causes: electromagnetic interference, crosstalk, and atmospheric conditions.
• Techniques like signal amplification and error correction protocols mitigate these issues.

Line Coding

• Line coding schemes convert digital bits into voltage levels suitable for the transmission medium.
• These schemes influence bandwidth requirements and noise immunity.

Digital Transmission in Networks

• Digital transmission is fundamental to network architectures (LANs, WANs, internet).
• Transmission medium, encoding scheme, and related factors are paramount for optimal network performance.

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