OSI model

The OSI model, short for Open Systems Interconnection, is a reference model for network communication standardised by ISO. It divides transmission into seven layers, each performing defined tasks and providing services to the layer above. The layers cover physical transmission, data link, network, transport, session, presentation and application. Typical technologies are assigned to them, such as cabling and transceivers at layer 1, Ethernet and MAC addresses at layer 2, IP and routing at layer 3, and TCP and UDP at layer 4. In practice, the model mainly serves to classify components and to support structured troubleshooting, for example when determining whether an issue lies with cabling, switching, routing or the application. Actual implementations usually follow the leaner TCP/IP model.