Source
OSI model
Description of levels, purpose and historical context.
The OSI model is a networking reference diagram that describes communication in seven layers. It is convenient for teaching and discussing architectural decisions, but in practice the protocol stack is different.
Layers of the OSI Model
The layers are ordered from top to bottom: from application protocols to physical signaling.
OSI model layers
Select a layer to see its role and protocol examples
Active layer
Layer 7: Application
Application-level interfaces and protocols.
Examples
Theory vs practice
Excellent theoretical model
Clear layers and interfaces between them allow you to share responsibilities, discuss problems at the right layer, and not confuse the roles of network components.
The Internet is based on TCP/IP
The Internet protocol suite became the foundation for the development of the Internet and real networking stacks.
The model remains useful
OSI is useful as a model for discussing and teaching networking concepts.
How the OSI model was useful
OSI provided a common “map” of the network: clear layers and interfaces between them simplified the division of responsibilities, standardization of terms and diagnostics. It was possible to isolate the problem to a specific level without affecting the entire system.