Open Systems Interconnection (OSI) is a technical network reference model created in 1984 by the International Organization for Standardization (ISO). It was the basis for international agreement and collaboration on various technologies to help establish standards for connecting computers and other devices. The OSI model divides communication processes into seven distinct layers: the Application, Presentation, Session, Transport, Network, DataLink and Physical layers.
The Application layer enables applications such as FTP client, web browsers, and email to communicate across a network. The Presentation layer describes how data is represented, encoded, and converted to meet the needs of the user. The Session layer establishes, manages, and terminates communication sessions between endpoints. The Transport layer provides end-to-end data communication services and is responsible for the end-to-end integrity of data. The Network layer is responsible for providing information required to route messages, including network addressing and network topology. The Data Link layer is the layer responsible for partitioning data into frames and providing error control for the data. Finally, the Physical layer provides the bit-level transmission.
The IPv4 protocol is the most commonly used networking protocol today, and it follows only the layers 1, 2, and 3 of the OSI model. Each layer has its own set of protocols and services designed to manage data within the layer and between the connected layers. For example, Layer 3, the Network layer, may be controlled by protocols like the Internet Protocol (IP), or the Address Resolution Protocol (ARP); layer 4, the Transport layer, by Transmission Control Protocol (TCP), or the User Datagram Protocol (UDP); and Layer 5, the Session layer, by protocols like the Session Initiation Protocol (SIP).
Overall, Open Systems Interconnection (OSI) provides a common reference for communication between computers and other devices across a network. It provides a clear definition of how each layer should function and how the layers interact with each other. As a result, data exchange can occur efficiently and reliably with greater ease, enabling better communication among network-connected devices.
