In the early years of networking, several large companies, including IBM, Honeywell, and Digital Equipment Corporation (DEC™), each had its own standard for how computers could be connected together. These standards described the mechanisms necessary to move data from one computer to another. These early standards, however, were not entirely compatible. Networks adhering to IBM Systems Network Architecture (SNA) could not communicate directly with networks using DEC Digital Network Architecture (DNA), for example.
In later years, standards organizations, including the International Standards Organization (ISO) and the Institute of Electrical and Electronic Engineers (IEEE), developed models that became globally recognized and accepted as the standards for designing any computer network. Both models describe networking in terms of functional layers.