Open Systems Interconnection
Open Systems Interconnection (OSI) is an effort to standardize networking
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

 that was started in 1977 by the International Organization for Standardization
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 (ISO), along with the ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....



Prior to OSI, networking was largely either government-sponsored (ARPANET
The Advanced Research Projects Agency Network , was the world's first operational packet switching network and the core network of a set that came to compose the global Internet...

The CYCLADES packet switching network was a French research network created in the early 1970s. It was developed to explore alternatives to the ARPANET design and to support network research generally...

) or vendor-developed and proprietary standards such as SNA and DECnet
DECnet is a suite of network protocols created by Digital Equipment Corporation, originally released in 1975 in order to connect two PDP-11 minicomputers. It evolved into one of the first peer-to-peer network architectures, thus transforming DEC into a networking powerhouse in the 1980s...

. 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
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....

 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, such as computer scientist Andrew S. Tanenbaum
Andrew S. Tanenbaum
Andrew Stuart "Andy" Tanenbaum is a professor of computer science at the Vrije Universiteit, Amsterdam in the Netherlands. He is best known as the author of MINIX, a free Unix-like operating system for teaching purposes, and for his computer science textbooks, regarded as standard texts in the...

, 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 protocols included so many optional features that many vendor's implementations were not interoperable.

The OSI approach was eventually replaced by the Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

Internet protocol suite
The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...

 protocol suite. TCP/IP's pragmatic approach to computer networking and two independent implementations of simplified protocols made it a practical standard. Some protocols and specifications in the OSI stack remain in use in legacy systems.

See also

  • OSI model
    OSI model
    The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...

  • OSI protocols
    OSI protocols
    The Open Systems Interconnection protocols are a family of information exchange standards developed jointly by the ISO and the ITU-T starting in 1977....

  • Common management information service
    Common management information service
    The Common Management Information Service is the service interface specified in that is employed by OSI network elements for network management. It defines the service interface that is implemented by the Common Management Information Protocol as specified in...

  • GOSIP, the (U.S.) Government Open Systems Interconnection Profile

Further reading

  • Marshall T. Rose, The Open Book (Prentice-Hall, Englewood Cliffs, 1990)
  • David M. Piscitello, A. Lyman Chapin, Open Systems Networking (Addison-Wesley, Reading, 1993)
  • Andrew S. Tanenbaum
    Andrew S. Tanenbaum
    Andrew Stuart "Andy" Tanenbaum is a professor of computer science at the Vrije Universiteit, Amsterdam in the Netherlands. He is best known as the author of MINIX, a free Unix-like operating system for teaching purposes, and for his computer science textbooks, regarded as standard texts in the...

    , Computer Networks, 4th Edition, (Prentice-Hall, 2002) ISBN 0-13-066102-3

External links

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