OSI reference model

Open System Interconnection reference model

Open System Interconnection reference model A network architectural model developed by International Organization for Standardization (ISO) and International Telecommunication Union Telecommunication Standardization Sector (ITU-T). The model consists of seven layers, each of which specifies particular network functions such as addressing, flow control, error control, encapsulation, and reliable message transfer. The highest layer (the application layer) is closest to the user. The lowest layer (the physical layer) is closest to the media technology. The next to lowest layers are implemented in hardware and software, while the upper five layers are implemented only in software. The OSI reference model is used universally as a method for teaching and understanding network functionality. Similar in some respects to SNA. See application layer, data link layer, network layer, physical layer, presentation layer, session layer, and transport layer.