Layered Architecture Overview

Layered Architecture

• In layered architecture, each layer provides services to the layer above it without disclosing implementation details, ensuring independence between layers.
• Layered architecture offers modularity, making design and implementation easier to manage.
• The number of layers, their functions, and contents can vary for each network.
• Each layer uses protocols to communicate with its peer entity on other machines, following specific rules for message content and order.
• Interfaces define how between messages are transferred between layers.
• Example of a five-layer architecture: Data is passed from layer n on one machine down through lower layers until it reaches the physical medium. This approach divides complex tasks into manageable sub-tasks.
• A network architecture comprises a set of layers and protocols.

Advantages of Layered Architecture

• Divide-and-conquer approach: Unmanageable tasks are broken down into smaller, easier-to-manage tasks, simplifying design.
• Modularity: Each layer operates independently, making understanding and implementation more straightforward.
• Easy to modify: Changes in one layer do not affect other layers, enabling easier modification and updates.
• Easy to test: Each layer can be analyzed and tested separately.

OSI Model

• Open System Interconnection (OSI): A reference model explaining how data travels from one computer's application to another through a physical medium.
• Structure: The OSI model has seven layers, each performing a specific network function.
• Development: Created by the International Organization for Standardization (ISO) in 1984, serving as an architectural foundation for inter-computer communication.
• Purpose: Breaks down the complex communication process into seven manageable tasks, assigning a specific function to each layer.
• Characteristics: Each layer is self-contained, enabling independent task execution.
• Two main layer classifications:
  • Upper layers (Application, Presentation, Session): Deal with application-related issues, implemented in software, and closest to the end user.
  • Lower layers (Transport, Network, Data Link, Physical): Manage data transport, implemented in hardware and software, closest to the physical medium.

OSI Layers and Functions

• 1. Physical Layer*

• Function: Transmits individual bits between network nodes.

• Location: Lowest layer in the OSI model.

• Responsibilities:

  • Establishing, maintaining, and deactivating physical connections.
  • Specifying mechanical, electrical, and procedural network interface specifications.
  • Defines line configuration, data transmission mode (simplex, half-duplex, full-duplex), network topology, and signal types.

• 2. Data-Link Layer*

• Function: Ensures error-free transfer of data frames.

• Responsibilities:

  • Defines data format on the network.
  • Provides reliable and efficient communication between devices.
  • Uniquely identifies each device on a local network.

• Sub-layers:

  • Logical Link Control (LLC): Transmits packets to the receiver's network layer, identifies network layer protocols based on headers, and implements flow control.
  • Media Access Control (MAC): Connects the LLC to the physical layer, responsible for transferring packets over the network.

• 3. Network Layer*

• Function: Manages addressing, tracks device locations, and determines the best data path between source and destination.

• Responsibilities:

  • Routing and forwarding packets.
  • Employing routers (layer 3 devices) to provide routing services within an internetwork.
  • Utilizing network layer protocols (e.g., IP, IPv6) for routing network traffic.

• 4. Transport Layer*

• Function: Ensures reliable data delivery, flow control, and error correction.

• Protocols:

  • User Datagram Protocol (UDP): Provides connectionless, end-to-end delivery, but is unreliable as errors are only discovered, not corrected. Offers limited error detection through checksums.
  • Transmission Control Protocol (TCP): Provides full transport layer services, establishing virtual circuits between sender and receiver, offering reliable delivery with error detection and retransmission.
  • UDP: Discovers errors but doesn't identify lost packets.
  • TCP: Detects errors and retransmits damaged frames, requiring acknowledgment of all segments before completing transmission.

This quiz covers the fundamentals of layered architecture in network design. Learn how different layers provide services, maintain independence, and communicate through protocols. Understand the advantages of this modular approach and how it simplifies complex tasks.