The Open Systems Interconnection Reference Model has been an essential part of computer network design since its ratification in 1984. The OSI is an abstract model of how network protocols and devices should communicate and interoperate.

The OSI model is a technology standard maintained by the International Organization for Standardization (ISO). Although many current technologies do not fully conform to the standard, it remains a useful introduction to the study of network architecture.

The OSI model divides the complex task of computer-to-computer communications, traditionally called internetworking, into a series of stages called layers.

Layers in the OSI model are ordered from the lowest layer to the highest. Together, these layers form the OSI stack. The stack contains seven layers in two groups: