It was presented in 1972 by the
ISO with the target to enable the connection between networks of different manufacturers and with different topologies!
The OSI reference model (layer model) is a standard, which classifies and determines, according to which principles the communication - with application of different protocols (rules) - between the components in a network takes place.
There are seven layers: Application, Presentation, Session, Transport, Network, Data Link und Physical Layer. With the lowest layer (physical layer) the electrical and mechanical specifications of cables and line adapter cards are determined, as well as the way of how to send bits via the cable. The second layer (data link layer) summarizes the bits of the lowest layer in groups or frames and adds a control information (sender and receiver address, length of the frame, used protocols of the higher layers) at the beginning of the frame. On the next higher level (network layer) information are transmitted via the used network etc.
