Open Systems Interconnection — a conceptual framework that standardises the functions of a networking system into seven distinct layers.
The OSI (Open Systems Interconnection) model is a reference model that describes how data travels from an application on one device to an application on another device over a network.
Data is passed down the layers at the sender side (encapsulation) and up the layers at the receiver side (de-encapsulation).
Select any layer from the stack to see its role, functions, and examples.
The Application layer is the closest to the end-user. It provides network services directly to applications, enabling user communication and data exchange.
The Presentation layer translates data between the application and the network. It ensures that data is readable by the receiving system.
The Session layer establishes, manages, and terminates communication sessions between two devices.
The Transport layer ensures complete data transfer with error recovery and flow control. It segments data and reassembles it at the destination.
The Network layer is responsible for logical addressing and routing data across multiple networks.
The Data Link layer handles the transmission of data between adjacent network nodes. It frames packets and manages error detection.
The Physical layer is the lowest layer. It transmits raw bits over a physical medium — cables, radio waves, or optical fibres.
Each layer adds a header (Layer 2 also adds a trailer) — this is encapsulation.
Each layer removes its corresponding header (and trailer) — this is decapsulation.