Open Systems Interconnection model (OSI model)

The OSI model divides the complex task of computer-to-computer communications into a series of stages known as layers. Layers in the OSI model are ordered from ​the lowest level to highest. Together, these layers comprise the OSI stack. The stack contains seven layers in two groups:

Upper layers:

• Application
• Presentation
• Session

Lower layers:

• Transport
• Network
• Data link
• Physical