What is the Open Systems Interconnection (OSI) model?

The Open Systems Interconnection (OSI) model is a reference model which describes seven layers of communication between computing systems over a network.

These seven layers are as outlined:

• Layer 1 – Physical: Converts signals back into data packets.
  • example: Physical (Hardware/Cabling)
• Layer 2 – Data Link: Reassembles data packets
  • example: Frames (MAC addresses)
• Layer 3 – Network: Ensures packets arrive correctly
  • example: Packets (IP addresses)
• Layer 4 – Transport: Reorders packets if necessary
  • Example: End-to-end connections (TCP, UDP)
• Layer 5 – Session: Maintains the session until the communication is complete
  • example: Synchronization & Send to port (API’s, Sockets)
• Layer 6 – Presentation: Translates data into a format that the application layer can use
  • example: Syntax Layer (SSL, SSH, FTP, IMAP etc)
• Layer 7 – Application: Delivers the data to the client
  • example: End User Layer (HTTP, FTP, SSH)

The OSI model was developed by the International Organization for Standardization. It describes the tasks required to transmit data via radio waves, light, or electricity.

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