OSI Model
The OSI model is a seven-layer reference framework that describes how data moves through a network, from the physical cable up to the user's application.
What is OSI Model?
Published by ISO in 1984, the Open Systems Interconnection model divides networking into seven layers, each relying on the one below and serving the one above. It is mainly a teaching and design tool: real networks largely run the simpler TCP/IP suite, but engineers still describe equipment and services by OSI layer, for example a "layer 2 switch" or "layer 3 VPN".
How it works
From the bottom up the layers are: 1 Physical (bits), 2 Data Link (frames), 3 Network (packets), 4 Transport (segments or datagrams), 5 Session, 6 Presentation and 7 Application (all handling data). When data is sent, each layer adds its own header (encapsulation); the receiver removes them in reverse order.