OSI Model

The Open Systems Interconnection model (OSI model) is a conceptual model that describes the universal standard of communication functions, without any regard to the system's underlying internal technology and specific protocol suites.

In theory, every communication between devices can be described within the OSI Model.

There are 7 layers within the OSI Model:

OSI Layer 7 - Application

Application is the software that initiated the communication.

Application is the closest layer to the user, since users typically use applications to interact with the network.

Common examples include:

  • Internet Browser (Chrome, Firefox, Brave, etc.)

  • Online Games (more specifically, the networking library used within the code)

  • Remote Applications

  • Remote File Managers

OSI Layer 6 - Presentation

Presentation layer establishes data formatting and translation into a specific format.

Common examples include:

  • HTTP / HTTPS

  • FTP

  • SSH

  • SMB

  • SMTP

OSI Layer 5 - Session

Session layer establishes, maintans, and terminates the 'connection' between 2 devices.

Common examples include:

  • Name lookups using DNS

  • Authentication

  • Session establishment

OSI Layer 4 - Transport

Transport layer provides the procedural means of transferring data.

Some parameters, such as connection reliability and packet size are considered in this layer.

This is where the data might require chunking into data segments, since the Network Layer (OSI Layer 3) imposes a maximum packet size.

Common examples include:

OSI Layer 3 - Network

Network layer provides the means of data transmission between networks, using IP Addresses.

Routers operate in this layer.

OSI Layer 1 - Physical

Physical layer provides the means of data transmission between two components, typically through conductors, such as cables or copper pins.