Open Systems Interconnection (OSI)

Open Systems Interconnection (OSI) is a conceptual or theoretical model for the communication process between two endpoints on a network. It is a model used as a reference when designing methods or protocols for networking, and usually serves as a training tool for beginners in the field. It is typically used to describe the process of communication between two computers, but can also be used between larger networks.

The OSI model consists of seven layers, each with a specific purpose. The bottom layer of the model is the physical layer which is responsible for data transmission; this layer does not provide any logical connection between two endpoints. The second layer is the data link layer, responsible for providing logical and physical connections between two endpoints. The third layer is the network layer, which is responsible for establishing connections between nodes and providing services such as routing and addressing. The fourth layer is the transport layer, which acts as the link between the two endpoints and is responsible for the reliable transmission of data. The fifth layer is the session layer, which is responsible for maintaining connections between the two endpoints. The sixth layer is the presentation layer, which is responsible for encoding and formatting of data sent over the network. The top layer is the application layer, which provides access to the services available on the network.

The OSI model has been widely adopted by computer networking industries and vendors. It is used as a reference when designing or implementing protocols and applications for networking. Also, the OSI model is a crucial part of the overall structure of computer systems and networks, and is used by system administrators and network engineers as a training tool.