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OSI - Open System Interconnection

(1) (pronounced as separate letters) Short for Open System Interconnection, an ISO standard for worldwide communications that defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.

Recommended Reading: The 7 Layers of the OSI Model

At one time, most vendors agreed to support OSI in one form or another, but OSI was too loosely defined and proprietary standards were too entrenched. Except for the OSI-compliant X.400 and X.500 e-mail and directory standards, which are widely used, what was once thought to become the universal communications standard now serves as the teaching model for all other protocols.

Most of the functionality in the OSI model exists in all communications systems, although two or three OSI layers may be incorporated into one.

OSI is also referred to as the OSI Reference Model or just the OSI Model.

See a breakdown of the seven OSI layers in the Quick Reference section of Webopedia.
Also see "The OSI Reference Model - Understanding Layers" in Webopedia's "Did You Know..." section.

(2) Abbreviation for the Open Source Initiative.

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