Open Systems Interconnection

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Open Systems Interconnection (OSI) is an effort to standardize networking that was started in 1977[1] by the International Organization for Standardization (ISO), along with the ITU-T.

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[edit] History

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. OSI was 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.

[edit] Criticism

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.[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.[citation needed] This made implementation difficult, and was resisted by many vendors and users with significant investments in other network technologies.[2] 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.[citation needed]ooooooooooo Even demands by the USA for OSI support on all government purchased hardware did not save the effort.[citation needed]

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).[citation needed] Much bad blood arose between these standards organizations and the IETF, the Internet standards body, as a result of this dispute.[citation needed] 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.[citation needed]

The OSI approach was eventually eclipsed by the Internet's TCP/IP protocol suite.[2] TCP/IP's pragmatic approach to computer networking and two independent implementations of simplified protocols made it a practical standard.[2] For example, the definition for OSI's X.400 e-mail standards took up several large books, while the Internet e-mail (SMTP) definition took only a few dozen pages in RFC 821. It should be noted, however, that over time there have been numerous RFCs which extended the original SMTP definition, so that its complete documentation finally took up several large books as well. Furthermore, the X.400 standard contained so many optional format choices that early implementations in France and Germany were unable to parse each other's messages.[citation needed]

Many of the protocols and specifications in the OSI stack are long-gone or have been superseded,[citation needed] such as token-bus media, CLNP packet delivery, FTAM file transfer, and X.400 e-mail. Some still survive, often in significantly simplified forms.[citation needed] The X.500 directory structure still remains with significant usage, mainly because the original unwieldy protocol has been stripped away and effectively replaced with LDAP.[citation needed] IS-IS also continues as a network routing protocol used by larger telecommunications companies, having been adapted for use with the Internet Protocol. Many legacy SONET systems still use Terminal Identifier - Address Resolution Protocol (TARP) - utilizes CLNP and IS-IS) to translate Target Identifier of a SONET node. Often protocols and specifications in the OSI stack remain in use in legacy systems, unless or until such legacy systems are eventually upgraded, replaced or decommissioned.[citation needed]

[edit] See also

[edit] References

  1. ^ OSI Reference Model, Hubert Zimmermann, IEEE Transactions on Communications, Vol. COMM-28(4), p425, April 1980.
  2. ^ a b c d Andrew S. Tanenbaum, Computer Networks, § 1.4.4.

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

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Open_Systems_Interconnection"