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Network OSI Model, A Quick Guide

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A Quick Guide on the OSI Layers

  1. Physical Layer (Layer 1):

    • Deals with the physical connection between devices.
    • Defines characteristics like voltage levels, data rates, and physical connectors.
    • Ensures reliable point-to-point and point-to-multipoint communication.
    • Responsible for node-to-node communication.
  2. Data Link Layer (Layer 2):

    • Divided into two sublayers: MAC (Media Access Control) and LLC (Logical Link Control).
    • MAC addresses, unique hardware addresses, are managed here.
    • Responsible for framing, addressing, and error detection at the data link level.
  3. Network Layer (Layer 3):

    • Focuses on logical addressing (IP addresses) and routing.
    • Routers operate at this layer, making decisions on the best path for data packets to reach their destination.
    • Examples of protocols: IP (Internet Protocol), ICMP (Internet Control Message Protocol).
  4. Transport Layer (Layer 4):

    • Manages end-to-end communication between devices.
    • Handles error detection, correction, and flow control.
    • TCP provides reliable, connection-oriented communication with features like acknowledgment and retransmission.
    • UDP offers faster, connectionless communication suitable for real-time applications.
  5. Session Layer (Layer 5):

    • Establishes, maintains, and terminates sessions (dialogue) between applications.
    • Responsible for synchronization, allowing data exchange between applications on different devices.
  6. Presentation Layer (Layer 6):

    • Translates data between the application layer and the lower layers.
    • Handles data format conversions, encryption, and compression to ensure compatibility between different systems.
  7. Application Layer (Layer 7):

    • Provides network services directly to end-users and applications.
    • Houses various protocols like HTTP (Hypertext Transfer Protocol), SMTP (Simple Mail Transfer Protocol), and FTP (File Transfer Protocol).
    • Allows user interfaces, network virtual terminal, and file access.

Remember the acronym "Please Do Not Throw Sausage Pizza Away" to recall the seven layers in order. Each layer adds specific functionality to the communication process, and this model helps in understanding and designing network architectures.