OSIModells

OSIModells, commonly referred to as the OSI-modellen, is the Open Systems Interconnection model. It is a conceptual framework for understanding and describing how different networking protocols and devices communicate. Developed by the International Organization for Standardization (ISO) in the 1980s, the model defines seven abstraction layers that partition the functions involved in network communications.

From bottom to top, the layers are: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer offers services to the layer above and relies on the layer below to provide the necessary functionality. The model helps designers, engineers, and educators explain complex interactions, diagnose problems, and design interoperable systems.

Purpose and usage: OSIModells aims to standardize interfaces and responsibilities between network components, promoting modular design and interoperability among equipment from different vendors. Today, it is primarily used as a teaching tool and a reference framework. In practice, the TCP/IP protocol suite dominates real-world networks, and many implementations span multiple layers or map loosely to the OSI model.

Criticism and status: The model has been criticized for its rigidity and for not perfectly matching real protocols, which often cross layer boundaries. Nevertheless, it remains a foundational concept in networking education and documentation, helping professionals discuss functions, troubleshoot issues, and compare architectural approaches. ISO continues to publish documentation related to the OSI framework, though it is rarely adopted as a strict architectural standard in new deployments.