Open Systems Interconnection (OSI) is an effort to standardize networking that was started in 1977 by the International Organization for Standardization (ISO), along with the ITU-T.
Prior to OSI, networking was largely either government-sponsored (ARPANET, CYCLADES) or vendor-developed and proprietary, the latter effort consisting of protocol standards such as SNA, Appletalk, NetWare and DECnet. In the UK work on the Experimental Packet Switched system circa 1973, the need to define so called higher level protocols above the HDLC link level communications protocol and the content of an NCC (UK) publication ‘Why Distributed Computing’ resulting from considerable research into future configurations for computer systems resulted in the UK presenting the case for an International Standards Committee to cover this area at the ISO meeting in Sydney in March 1977. OSI was hence an industry effort, attempting to get industry participants to agree on common network standards to provide multi-vendor interoperability. It was common for large networks to support multiple network protocol suites, with many devices unable to interoperate with other devices because of a lack of common protocols. However, while OSI developed its networking standards, TCP/IP came into widespread use on multivendor networks for internetworking, while on the local network level both Ethernet and token ring gained prominence.
The OSI reference model was a major advance in the teaching of network concepts. It promoted the idea of a consistent model of protocol layers, defining interoperability between network devices and software. The OSI model was defined in raw form in Washington DC in February 1978 by Hubert Zimmerman of France and the refined standard was published by the ISO in 1984.
The OSI protocol suite that was specified as part of the project was considered by many to be too complicated and inefficient, and to a large extent unimplementable.
Taking the “forklift upgrade” approach to networking, it specified eliminating all existing protocols and replacing them with new ones at all layers of the stack. This made implementation difficult, and was resisted by many vendors and users with significant investments in other network technologies. In addition, the OSI protocols were specified by committees filled with differing and sometimes conflicting feature requests, leading to numerous optional features; because so much was optional, many vendors’ implementations simply could not interoperate, negating the whole effort. Even demands by the USA for OSI support on all government purchased hardware did not save the effort.
Beyond their objections to the protocol suite itself, OSI opponents generally contended that the very OSI standardization process represented little more than institutional unwillingness on the part of the ISO and ITU-T to admit that vendor-neutral standards might exist that had not been developed and ratified by their own particular processes (an example of the “Not Invented Here” phenomenon). Much bad blood arose between these standards organizations and the IETF, the Internet standards body, as a result of this dispute. The most vitriolic opponents of the OSI suite at times made the further claim that, far from being a “vendor neutral” standard, OSI represented an attempt by minor, or diminishing, players in the networking and computer industries to recover by government fiat market share that they were rapidly losing to the proponents of TCP/IP through fair competition.