OSIModell

OSIModell, commonly known as the OSI model or OSI-Modell in German, is a conceptual framework that standardizes the functions of a telecommunication or computing system independent of the underlying technology. It was developed by the International Organization for Standardization (ISO) in the 1980s as a reference model to facilitate interoperability and multilayer networking across diverse systems.

The model divides network communication into seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. The Physical layer covers the hardware transmission of raw bit streams over a physical medium. The Data Link layer provides node-to-node data transfer and framing, with addressing and access control. The Network layer handles routing and logical addressing to determine paths between hosts. The Transport layer ensures reliable or best-effort end-to-end communication and controls data flow and error handling. The Session layer manages sessions or connections between applications, including control dialogs. The Presentation layer concerns data formats, encryption, compression, and translation of data representations. The Application layer is the interface to end-user software and network services.

Although widely taught and used as a reference, the OSI model is not a protocol suite. Most modern networks use the TCP/IP protocol suite, which maps roughly to the OSI layers but blends several functions within fewer layers. The OSI model remains influential in education, standardization discussions, and in describing networking concepts and service boundaries.

See also: OSI model, TCP/IP model.