For questions about the Open Systems Interconnect (OSI) model defined by the International Organization for Standardization (ISO).
The Open Systems Interconnect (OSI) model is one of several theoretical or conceptual models/frameworks for network communications. The OSI model defines seven layers through which a communication message passes. Each layer defines a distinct and separate function which is independent of the other layers. This allows different methods or protocols in one layer to be changed without affecting the other layers.
It should be stressed that the OSI model is an idealized concept which rarely aligns with the real world. This disparity has led to the development of other models which parallel the OSI model, but strive to more closely match network communications in the real world.