OSI

OSI stands for Open Systems Interconnection. It is a conceptual framework and standard for network communications developed by the International Organization for Standardization (ISO) during the 1980s. The OSI model provides a universal reference for describing and designing network interactions, aiming to enable interoperability among diverse systems and vendors. It is formalized in ISO/IEC 7498, with Part 1 defining the basic reference model and additional parts detailing services, interfaces, and protocols for the layers.

The OSI model comprises seven layers, from bottom to top: Physical, Data Link, Network, Transport, Session, Presentation, and Application. The Physical layer covers hardware transmission of raw bit streams. The Data Link layer handles node-to-node data transfer and framing. The Network layer manages routing and logical addressing. The Transport layer provides end-to-end communication control, reliability, and flow control. The Session layer manages sessions between applications. The Presentation layer handles data representation, encryption, and compression. The Application layer provides end-user services and interfaces, such as file transfer, messaging, and remote access.

In practice, OSI is a reference model rather than a deployed protocol stack. The Internet largely relies on the TCP/IP protocol suite, which maps to parts of the OSI layers but does not implement the OSI model in full. Nevertheless, OSI has had a lasting influence as an educational tool and as a framework for network architecture, standardization practices, and the analysis of interoperability between different systems.