Understanding the OSI Model Layers

Sep 14, 2024

OSI Model (Open System Interconnection Model)

Introduction

  • The OSI Model defines how data is transferred between computers in a network.
  • It facilitates communication between different architectures (e.g., Windows and MacOS).
  • Introduced by the International Organization for Standardization (ISO) in 1984.

Structure of the OSI Model

  • The OSI 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
  • Each layer has its own set of protocols.

Layer Descriptions

1. Application Layer

  • Used by network applications (e.g., Google Chrome, Outlook, Skype).
  • Functions include:
    • File transfer (FTP)
    • Web surfing (HTTP/HTTPS)
    • Email (SMTP)
    • Virtual terminals (Telnet)

2. Presentation Layer

  • Converts data into a machine-readable format (e.g., ASCII to FCD).
  • Functions include:
    • Translation: Converts character formats.
    • Compression: Reduces file size (lossy or lossless).
    • Encryption/Decryption: Uses SSL for secure data transmission.

3. Session Layer

  • Manages connections between applications.
  • Functions include:
    • Session Management: Tracks files being downloaded.
    • Authentication: Verifies user identity (username/password).
    • Authorization: Checks user permissions.

4. Transport Layer

  • Ensures reliable communication via:
    • Segmentation: Divides data into smaller segments.
    • Flow Control: Adjusts data transmission rate to prevent overload.
    • Error Control: Resends lost or corrupted data using checksums.
  • Protocols: TCP (Connection Oriented) and UDP (Connectionless).

5. Network Layer

  • Transmits data packets between different networks.
  • Functions include:
    • Logical Addressing: Assigns unique IP addresses.
    • Routing: Determines the best path for data packets.
    • Path Determination: Chooses optimal delivery routes.

6. Data Link Layer

  • Receives data packets and adds physical addresses (MAC addresses).
  • Functions include:
    • Framing: Converts packets to frames for transmission.
    • Media Access Control: Manages how devices access shared media.
    • Error Detection: Identifies transmission errors.

7. Physical Layer

  • Converts binary data into electrical, light, or radio signals for transmission.
  • Receives and converts signals back to bits for higher layers.

Conclusion

  • The OSI model underpins the functioning of the internet by facilitating communication between devices across different networks.
  • Each layer plays a crucial role in ensuring reliable data transmission.