What is the OSI model in networking?

The OSI model is a conceptual framework that standardises the functions of a communication system into seven distinct categories or layers.

The Open Systems Interconnection (OSI) model is a theoretical construct that helps us understand and describe how different network protocols interact and work together to provide network services. It was developed by the International Organisation for Standardisation (ISO) to promote interoperability and standardisation among different network technologies.

The OSI model is divided into seven layers, each representing a specific network function. These layers are, from top to bottom: the Application, Presentation, Session, Transport, Network, Data Link, and Physical layers. Each layer provides a set of functions that are necessary for the transmission of data over a network, and each layer communicates with the layer directly above and below it.

The topmost layer, the Application layer, is where network applications and their related protocols reside. This layer is closest to the end user and provides services such as email, file transfer, and web browsing. The Presentation layer is responsible for data translation, encryption, and compression. The Session layer establishes, manages, and terminates connections between applications.

The Transport layer provides reliable data transfer services to the upper layers. It is responsible for end-to-end error recovery and flow control. The Network layer is responsible for routing and transferring data between different networks. It manages network congestion and determines the best path for data transfer.

The Data Link layer provides reliable transit of data across a physical link. It is concerned with physical addressing, network topology, and error notification. The bottommost layer, the Physical layer, is responsible for the transmission and reception of raw bit streams over a physical medium. It defines the electrical and physical specifications for devices.

In essence, the OSI model provides a standard for different computer systems to communicate with each other. It allows for the design and description of network communication protocols in a layered manner, promoting interoperability and standardisation. Understanding the OSI model is fundamental to grasping how networks operate and interact.