Open Systems Interconnection Reference Model (OSI Reference Model)
OSI reference model invented as a result of providing a global standard for computer networking and networking devices. Previously each vendor has their own manufacturing standards. This forced the user to stuck with single vendor for all his/her networking needs. Devices from different vendors were not compatible at that time.To overcome this issue International Organization for Standardization (ISO) introduced the seven layer OSI architecture. Generally OSI model divides network architecture into seven layers.
The seven layers of OSI reference model are:
1. Physical layer
2. Data link layer
3. Network layer
4. Transport layer
5. Session layer
6. Presentation layer
7. Application layer
Each layer has its own protocols and the total network communication is happening through the different layers by processes called encapsulation and de-encapsulation. In brief encapsulation is the flow of data from the top layer to the physical layer by adding control information to the data in each layer. De-encapsulation is the reverse process.