Open Systems Interconnection

The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard protocols. The model partitions a communication system into abstraction layers. The original version of the model defined seven layers.


Prior to OSI, networking was largely either government-sponsored (ARPANET in the US, CYCLADES in France) or vendor-developed and proprietary standards (such as the System network architecture (SNA) of IBM and DECnet of Digital Equipment Corporation). An Experimental Packet Switched system in the UK circa 1973, also identified the need to define higher level protocols. The NCC (UK) publication 'Why Distributed Computing' which came 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.[1]

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 very defined in raw form in Washington, DC in February 1978 by Hubert Zimmermann of France and the refined standard was published by the ISO in 1984.[1]


The OSI protocol suite that was specified as part of the project was considered by many, such as computer scientist Andrew S. Tanenbaum, to be too complicated and inefficient, and to a large extent unimplementable.[2] 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 vendors' implementations were not interoperable.[2]

Although the OSI model is often still referred to, the Internet's TCP/IP protocol suite is used in lieu of the OSI protocols. TCP/IP's pragmatic approach to computer networking and two independent implementations of simplified protocols made it a practical standard.[2] Some protocols and specifications in the OSI stack remain in use, one example being IS-IS, which was specified for OSI as ISO/IEC 10589:2002 and adapted for Internet use (with TCP/IP) as RFC 1142.

ISO/IEC 7498

The standard ISO/IEC 7498 consists of the following parts:

  • ISO/IEC 7498-1 The Basic Model
  • ISO 7498-2 Security Architecture
  • ISO/IEC 7498-3 Naming and addressing
  • ISO/IEC 7498-4 Management framework

See also


  1. ^ a b, March 2017, IEEE Spectrum.
  2. ^ a b c Andrew S. Tanenbaum, Computer Networks, § 1.4.4.

Further reading

  • John Day, "Patterns in Network Architecture: A Return to Fundamentals" (Prentice Hall 2007, ISBN 978-0-13-225242-3)
  • Marshall 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, Computer Networks, 4th Edition, (Prentice-Hall, 2002) ISBN 0-13-066102-3
  • Gary Dickson; Alan Lloyd (July 1992). Open Systems Interconnection/Computer Communications Standards and Gossip Explained. Prentice-Hall. ISBN 978-0136401117.

External links

Common Management Information Service

The Common Management Information Service (CMIS) is the service interface specified in ITU-T Recommendation X.710, ISO/IEC International Standard 9595 that is employed by OSI network elements for network management. It defines the service interface that is implemented by the Common Management Information Protocol (CMIP) as specified in ITU-T Recommendation X.711, ISO/IEC International Standard 9596-1. CMIS is part of the Open Systems Interconnection (OSI) body of international network standards.

Note the term CMIP is sometimes used erroneously when CMIS is intended. CMIS/CMIP is most often used in telecommunication applications, in other areas SNMP has become more popular.

Connection-Oriented Network Service

Connection-Oriented Network Service (CONS) is one of the two Open Systems Interconnection (OSI) network layer protocols, the other being Connectionless-mode Network Service (CLNS). It is basically X.25, with a few adjustments.


DIXIE is an obsolete protocol for accessing X.500 directory services. DIXIE was intended to provide a lightweight

means for clients to access X.500 directory services. DIXIE allowed TCP/IP clients to connect a DIXIE-to-DAP gateway which would provide access to the X.500 Directory Service. This design allows the client to access the directory without requiring it to support the cumbersome Open Systems Interconnection protocol stack.

DIXIE was created in 1990 at the University of Michigan by Tim Howes, Mark Smith, and Bryan Beecher. DIXIE was formally specified in RFC 1249, published in 1991. The university offered a completed UNIX implementation of the protocol, including a DIXIE server, an application development library, and DIXIE clients. A DIXIE client for Apple Macintosh was also provided.

These efforts led to the development of the Lightweight Directory Access Protocol. LDAP replaced DIXIE.When created, the acronym DIXIE did not stand for anything, however later it become known to stand for Directory Interface to X.500 Implemented Efficiently.


DO-212 is a performance standard published by RTCA, Incorporated. It contains Minimum Operational Performance Standards (MOPS) for aircraft equipment required for the Automatic Dependent Surveillance (ADS) function (ADSF). The supporting hardware can be a stand-alone ADS unit (ADSU) or alternatively, the ADS function may be installed within other on-board equipment.


The EnOcean technology is an energy harvesting wireless technology used primarily in building automation systems, and is also applied to other applications in industry, transportation, logistics and smart homes. Modules based on EnOcean technology combine micro energy converters with ultra low power electronics, and enable wireless communications between batteryless wireless sensors, switches, controllers and gateways.

In March 2012, the EnOcean wireless standard was ratified as the international standard ISO/IEC 14543-3-10. The standard covers the OSI (Open Systems Interconnection) layers 1-3 which are the physical, data link and networking layers.

The energy harvesting wireless modules are manufactured and marketed by the company EnOcean which is based in Oberhaching, Germany. EnOcean offers its technology and licenses for the patented features within the EnOcean Alliance framework.

Gateway (telecommunications)

A gateway is a piece of networking hardware used in telecommunications for telecommunications networks that allows data to flow from one discrete network to another. Gateways are distinct from routers or switches in that they communicate using more than one protocol and can operate at any of the seven layers of the open systems interconnection model (OSI).

The term gateway can also loosely refer to a computer or computer program configured to perform the tasks of a gateway, such as a default gateway or router.

Government Open Systems Interconnection Profile

The Government Open Systems Interconnection Profile (GOSIP) was a specification that profiled open networking products for procurement by governments in the late 1980s and early 1990s.

Hubert Zimmermann

Hubert Zimmermann (1941 – November 9, 2012) was a French software engineer and a pioneer of computer networking.

Zimmermann was educated at École Polytechnique and Ecole Nationale Supérieure des Telecom.

His career began at Institut National de Recherche en Informatique et Automatique (INRIA) in Rocquencourt from 1972 through 1979, where he led research into what became ChorusOS series of distributed operating systems.

In 1977, he was an early member of the International Organization for Standardization as it developed the Open Systems Interconnection protocols.

He then worked for France Télécom in 1980 through 1986.

He developed and promoted the OSI reference model which became a popular way to describe network protocols, and published a paper on the model in 1980 and one with John Day in 1983.

He founded Chorus systems in 1987, purchased by Sun Microsystems in 1997, where he was director of telecom software engineering for 5 years. Then he invested in entrepreneurial high-tech companies such as Arbor Venture Management, Boost Your StartUp, Gingko Networks and UDcast.In 1991, Zimmermann was awarded the SIGCOMM Award for "20 years of leadership in the development of computer networking and the advancement of international standardization".A 2011 article in the Anecdotes section of IEEE Annals of the History of Computing documents his view of the early history of the Internet protocol suite.On 9 November 2012, Zimmermann died in France.


Intermediate System to Intermediate System (IS-IS, also written ISIS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices.

It accomplishes this by determining the best route for data through a packet-switched network.

The IS-IS protocol is defined in ISO/IEC 10589:2002 as an international standard within the Open Systems Interconnection (OSI) reference design. The Internet Engineering Task Force (IETF) republished IS-IS in RFC 1142, but that RFC was later marked as "historic" by RFC 7142 because it republished a draft rather than a final version of the ISO standard, causing confusion.

IS-IS has been called "the de facto standard for large service provider network backbones."


ISO/IEC JTC 1/SC 6 Telecommunications and information exchange between systems is a standardization subcommittee of the Joint Technical Committee ISO/IEC JTC 1 of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC), that develops and facilitates standards within the field of telecommunications and information exchange between systems. ISO/IEC JTC 1/SC 6 was established in 1964, following the creation of a Special Working Group under ISO/TC 97 on Data Link Control Procedures and Modem Interfaces. The international secretariat of ISO/IEC JTC 1/SC 6 is the Korean Agency for Technology and Standards (KATS), located in the Republic of Korea.

Internet protocol suite

The Internet protocol suite is the conceptual model and set of communications protocols used in the Internet and similar computer networks. It is commonly known as TCP/IP because the foundational protocols in the suite are the Transmission Control Protocol (TCP) and the Internet Protocol (IP). It is occasionally known as the Department of Defense (DoD) model because the development of the networking method was funded by the United States Department of Defense through DARPA.

The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, addressed, transmitted, routed, and received. This functionality is organized into four abstraction layers, which classify all related protocols according to the scope of networking involved. From lowest to highest, the layers are the link layer, containing communication methods for data that remains within a single network segment (link); the internet layer, providing internetworking between independent networks; the transport layer, handling host-to-host communication; and the application layer, providing process-to-process data exchange for applications.

The technical standards underlying the Internet protocol suite and its constituent protocols are maintained by the Internet Engineering Task Force (IETF). The Internet protocol suite predates the OSI model, a more comprehensive reference framework for general networking systems.

List of network protocols (OSI model)

This article lists protocols, categorized by their nearest Open Systems Interconnection (OSI) model layers. This list is not exclusive to only the OSI protocol family. Many of these protocols are originally based on the Internet Protocol Suite (TCP/IP) and other models and they often do not fit neatly into OSI layers.


In telecommunication, a n-entity is an active element in the n-th layer of the Open Systems Interconnection--Reference Model (OSI-RM) that (a) interacts directly with elements, i.e., entities, of the layer immediately above or below the n-th layer, (b) is defined by a unique set of rules, i.e., syntax, and information formats, including data and control formats, and (c) performs a defined set of functions.

The n refers to any one of the 7 layers of the OSI-RM.

In an existing layered open system, the n may refer to any given layer in the system.

Layers are conventionally numbered from the lowest, i.e., the physical layer, to the highest, so that the (n + 1)-th layer is above the n-th layer and the (n − 1)-th layer is below.


NSEL may refer to:

NSEL (networking), part of a Network Service Access Point address used in Open Systems Interconnection networking

National Spot Exchange, a commodities exchange in India

NSEL case, a legal investigation

Newmark Structural Engineering Laboratory, University of Illinois at Urbana-Champaign

Network Based Application Recognition

Network Based Application Recognition (NBAR) is the mechanism used by some Cisco routers and switches to recognize a dataflow by inspecting some packets sent.

The networking equipment which uses NBAR does a deep packet inspection on some of the packets in a dataflow, to determine which traffic category the flow belongs to. Used in conjunction with other features, it may then program the internal application-specific integrated circuits (ASICs) to handle this flow appropriately. The categorization may be done with Open Systems Interconnection (OSI) layer 4 info, packet content, signaling, and so on but some new applications have made it difficult on purpose to cling to this kind of tagging.The NBAR approach is useful in dealing with malicious software using known ports to fake being "priority traffic", as well as non-standard applications using dynamic ports. That's why NBAR is also known as OSI layer 7 categorization.

On Cisco routers, NBAR is mainly used for Quality of Service and Security purposes.

OSI model

The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard protocols. The model partitions a communication system into abstraction layers. The original version of the model defined seven layers.

A layer serves the layer above it and is served by the layer below it. For example, a layer that provides error-free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that comprise the contents of that path. Two instances at the same layer are visualized as connected by a horizontal connection in that layer.

The model is a product of the Open Systems Interconnection project at the International Organization for Standardization (ISO).

Security service (telecommunication)

Security service is a service, provided by a layer of communicating open systems, which ensures adequate security of the systems or of data transfers as defined by ITU-T X.800 Recommendation.

X.800 and ISO 7498-2 (Information processing systems – Open systems interconnection – Basic Reference Model – Part 2: Security architecture) are technically aligned. This model is widely recognized A more general definition is in CNSS Instruction No. 4009 dated 26 April 2010 by Committee on National Security Systems of United States of America:

A capability that supports one, or more, of the security requirements (Confidentiality, Integrity, Availability). Examples of security services are key management, access control, and authentication.Another authoritative definition is in W3C Web service Glossary adopted by NIST SP 800-95:

A processing or communication service that is provided by a system to give a specific kind of protection to resources, where said resources may reside with said system or reside with other systems, for example, an authentication service or a PKI-based document attribution and authentication service. A security service is a superset of AAA services. Security services typically implement portions of security policies and are implemented via security mechanisms.


In telecommunication, the term sublayer has the following meanings:

In a layered open communications system, a specified subset of the services, functions, and protocols included in a given layer.

In the Open Systems Interconnection--Reference Model, a subdivision of a given layer, e.g., a conceptually complete group of the services, functions, and protocols included in the given layer.


X.500 is a series of computer networking standards covering electronic directory services. The X.500 series was developed by ITU-T, formerly known as CCITT, and first approved in 1988. The directory services were developed in order to support the requirements of X.400 electronic mail exchange and name lookup. ISO was a partner in developing the standards, incorporating them into the Open Systems Interconnection suite of protocols. ISO/IEC 9594 is the corresponding ISO identification.

ISO standards by standard number

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