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Understanding the OSI Model Layers

Oct 24, 2024

OSI Model Lecture Notes

Introduction to OSI Model

  • OSI Model (Open System Interconnection Model) is a framework for understanding data transfer across computer networks.
  • It was introduced by the International Organization for Standardization (ISO) in 1984.
  • The model consists of 7 layers:
    1. Application Layer
    2. Presentation Layer
    3. Session Layer
    4. Transport Layer
    5. Network Layer
    6. Data Link Layer
    7. Physical Layer

Application Layer

  • Used by network applications (e.g., browsers, email clients).
  • Contains application layer protocols that enable network services.
  • Examples of protocols:
    • FTP: File Transfer Protocol
    • HTTP/HTTPS: Web surfing protocols
    • SMTP: Email transmission protocol
    • Telnet: Virtual terminal protocol
  • Provides services for network applications to perform user activities.

Presentation Layer

  • Converts data from Application Layer into a machine-readable binary format.
  • Functions include:
    • Translation: Converts characters and numbers (e.g., ASCII to FCD).
    • Data Compression: Reduces file size for faster transmission (lossy or lossless).
    • Encryption/Decryption: Enhances data security (using SSL protocol).

Session Layer

  • Manages connections between applications (similar to event helpers for a party).
  • Functions include:
    • Session Management: Establishes, maintains, and terminates connections.
    • Authentication: Verifies user identity (username and password).
    • Authorization: Checks access permissions for resources.

Transport Layer

  • Ensures reliable communication through:
    • Segmentation: Divides data into segments for transmission.
    • Flow Control: Manages data transmission rates between sender and receiver.
    • Error Control: Detects and retransmits lost/corrupted data.
  • Protocols:
    • TCP (Transmission Control Protocol): Connection-oriented, ensures complete data delivery.
    • UDP (User Datagram Protocol): Connectionless, used for faster data transfer where delivery confirmation is not critical.

Network Layer

  • Responsible for data transmission between different networks.
  • Functions include:
    • Logical Addressing: Assigns IP addresses to data packets.
    • Routing: Determines paths for data packets based on IP addressing.
    • Path Determination: Chooses the best route for data delivery (using protocols like OSPF, BGP).

Data Link Layer

  • Receives packets from Network Layer and prepares them for transmission.
  • Functions include:
    • Framing: Adds headers and trailers to create frames.
    • Media Access Control: Manages data transmission to avoid collisions on shared media.
    • Error Detection: Uses checksums to identify transmission errors.

Physical Layer

  • Converts frames into signals for transmission over physical media (copper cable, optical fiber, radio signals).
  • Responsible for the actual physical connection between devices.

Conclusion

  • The OSI Model aids in understanding how data is transferred between hosts in a network.
  • Each layer has distinct functions that contribute to the overall data communication process.
  • Encouragement to like, share, and subscribe for more learning content.

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