ITT300 Chapter 4 Data Encoding Part 2

Digital-to-Analog Conversion

• Converts digital data (bits) to analog signals for transmission.
• At sender's end, digital data encoded into analog signal; at receiver's end, analog signal decoded back to digital data.

Key Terminology

• Data Element: Smallest unit of information exchanged, typically a bit.
• Signal Element: Smallest unit of a signal that remains constant.
• Bit Rate (N): Number of data elements transmitted per second (bps).
• Baud Rate (S): Number of signal elements transmitted per second (baud).

Relationship Between Data Rate and Signal Rate

• Formula: S = N x 1/r (where r is the number of data elements in one signal element).
• In analog transmission, baud rate is less than or equal to bit rate, indicating efficiency.

Bandwidth and Transmission

• Bandwidth required for analog transmission is proportional to baud rate rather than bit rate; higher baud rate necessitates higher bandwidth.

Examples of Data Rate and Baud Rate

• If an analog signal carries 4 bits per signal unit and sends 1000 units per second:

  • Baud rate = 1000 baud/s
  • Bit rate = 4000 bps (1000 x 4).

• For a signal with a bit rate of 3000 and each signal unit carries 6 bits:

  • Baud rate = 500 baud/s (3000 x 1/6).

Constellation Diagrams

• Visual representation for modulation schemes like ASK (Amplitude Shift Keying), BPSK (Binary Phase Shift Keying), and QPSK (Quadrature Phase Shift Keying).

Digital-to-Digital Conversion Techniques

• Involves three techniques:
  • Line Coding: Essential for converting digital data into digital signals.
  • Block Coding: Optional, adds redundancy for error correction.
  • Scrambling: Optional, ensures a more random signal pattern.

Data Rate vs Signal Rate

• Increase in data rate enhances transmission speed but may increase bandwidth needs.
• Formula for relationship: S = c × N × 1/r, where c is the case factor.

Practical Examples

• If one data element is encoded as one signal element (r=1) with a bit rate of 100 kbps:

  • Average baud rate can vary between 0 and 100,000 baud depending on c (case factor).

• For an analog signal with a 250 kbps bit rate and r=1:

  • Baud rate needs calculation based on the defined variables to understand the transmission capacity.

Understanding Signal and Data Elements

• One signal element can carry multiple data elements, establishing data efficiency in communications.
• Values of r (number of data elements per signal element) directly impact baud and bit rates.

Summary

• Digital-to-analog and digital-to-digital conversions are essential for efficient data communication.
• Understanding the relationship between bit rate, baud rate, and bandwidth is vital for optimizing performance in networking contexts.

Digital Transmission Basics

• Bit Rate and Baud Rate: In modulation, bit rate equals baud rate when each symbol represents one bit; this occurs in protocols like Amplitude Shift Keying (ASK).
• Calculating 'r': Using the formula r = log2(L), where L represents the number of levels in modulation (L = 256 in the provided example).

Amplitude Shift Keying (ASK)

• Definition: ASK varies the amplitude of a carrier signal to represent binary data.
• Baud Rate Calculation: For ASK, baud rate equals bit rate when modulation is carried out without additional phases.
• Bandwidth Center: When locating carrier frequencies, the center frequency for ASK is calculated as half the bandwidth.

Full-Duplex ASK

• Bandwidth Allocation: Each direction in full-duplex ASK uses half of the available bandwidth.
• Carrier Frequencies: Calculated based on the bandwidth; e.g., fc1 (forward) and fc2 (backward) determined from the given frequency range.
• Bit Rate: For d = 0, the bit rate equates to the baud rate, reflecting that each signal represents a single bit.

Frequency Shift Keying (FSK)

• Carrier Frequencies: In FSK, different frequencies represent different binary values. The relationship is linear, as shown in given examples.

Phase Shift Keying (PSK)

• PSK Overview: Phase modulation techniques change the phase of the carrier signal while keeping amplitude and frequency constant.
• Types of PSK: 2-PSK involves two phases (0 and 180 degrees), while 4-PSK utilizes four phases (0, 90, 180, 270 degrees).

Constellation Diagrams

• Purpose: Visual representation of signal phase and amplitude, aiding in understanding potential signal combinations.

Signal Elements vs Data Elements

• Definitions: Signal elements are the basic units of a digital signal, used to transmit data. The ratio of data elements to signal elements (r) indicates efficiency.
• Data Rate vs Signal Rate: Data rate refers to the number of data bits transmitted per second, while signal rate (baud rate) shows the number of signal changes per second.

DC Component Issues

• Effects: A remaining DC component in signals can cause distortion and limit transmission integrity.
• Avoidance Methods: Techniques such as Manchester encoding and 4B/5B encoding are used to reduce or eliminate unwanted DC components.

Self-Synchronization

• Importance: Synchronization between sender and receiver’s bit intervals is crucial for accurate data interpretation. Mismatched timings can lead to errors.

Line Coding Schemes

• Unipolar and Polar Encoding: Unipolar uses single polarity signals, while polar encoding utilizes both positive and negative voltage levels to convey data.

Practical Example Calculations

• Bandwidth Calculations: When given specific parameters, calculations can yield baud rates and carrier frequencies necessary for effective communication strategies.

Lesson Outcomes

• Understand the main functions of each layer in the OSI model.
• Explain the specific responsibilities for each OSI layer.
• Differentiate the OSI model from the TCP/IP model.
• Identify different types of addressing used in networks.

OSI Model

• Open Systems Interconnection (OSI) model is an ISO standard for network communication, introduced in the late 1970s.
• Comprises seven layers, facilitating communication between different systems regardless of operational architecture.
• Layers communicate through peer-to-peer processes, using specific protocols for each layer.

Layered Architecture

• Communication within a machine follows a downward path through layers, while between machines, layer x on one communicates with layer x on another.
• Each layer adds headers or trailers for data unit management, except for layer 2, which may add trailers.
• The physical layer converts data into electromagnetic signals for transmission and reverts it back at the destination.

Organization of the Layers

• Network support layers: Layer 1 (Physical), Layer 2 (Data Link), Layer 3 (Network) manage data transmission between devices.
• Transport layer: Layer 4 ensures data from lower layers is available for upper layers' processes.
• User support layers: Layers 5 (Session), 6 (Presentation), 7 (Application) provide interoperability for unrelated software systems.

Physical Layer Responsibilities

• Transmits individual bits between nodes and coordinates functions necessary for bit stream transmission.
• Defines mechanical/electrical specifications and encoding procedures for signals.
• Manages data rate, synchronization, physical topology (mesh, star, ring), and transmission modes (simplex, half-duplex, full-duplex).

Data Link Layer Responsibilities

• Ensures error-free node-to-node delivery of data frames.
• Accepts data units from Layer 3, adding headers and trailers for addressing and control.
• Framing: Divides data into frames, enforces flow and error control, and manages access control over shared links.

Network Layer Responsibilities

• Delivers packets from source to destination across multiple network links.
• Provides switching and routing services to optimize data paths.
• Implements logical addressing to identify source and destination systems.

Transport Layer Responsibilities

• Facilitates end-to-end delivery, ensuring data arrives intact and in order.
• Service-point addressing directs messages to specific applications on hosts.
• Handles segmentation/reassembly of messages, connection and flow control, and error checking.

Session Layer Responsibilities

• Manages dialog control and synchronization between systems.
• Establishes and maintains communication sessions, providing half-duplex or full-duplex options.

Presentation Layer Responsibilities

• Translates, compresses, and encrypts data for transmission.
• Ensures interoperability between different encoding methods.

Application Layer Responsibilities

• Provides user interfaces for network access, allowing both humans and software to interface with the network.

Addressing in TCP/IP

• Four levels of addresses: physical (link), logical (IP), port, and specific addresses, each linked to TCP/IP architecture layers.
• Physical Addresses: Unique MAC address for devices, defined by the network interface card.
• Logical Addresses: Universally identifying IP addresses, currently 32-bit, allowing host identification regardless of physical network topology.
• Port Addresses: TCP/IP 16-bit identifiers used to connect processes on hosts.
• Specific Addresses: Customized addresses for particular applications, offering user-friendly access to underlying network addresses.

Explore the principles of data encoding in this quiz based on ITT300 Chapter 4. Learn about the transition between digital and analog signals, data rate versus signal rate, and modulation techniques including ASK, FSK, and PSK. Test your understanding of constellation diagrams and data representation.