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Definition: OSI

(1) See Open Source Initiative.

(2) (Open System Interconnection) An ISO standard for worldwide communications that defines a protocol framework in seven layers. OSI functionality exists in all communications systems, although two or three layers may be incorporated into one (see OSI model). Control is passed from the top application layer to the bottom layer, out over the network to the bottom layer of the receiving station and back up to the application layer.

Never Completely Defined
OSI was too loosely defined to become a single standard. Nevertheless, the model serves to teach communications, and TCP/IP, the global networking standard, embodies most of the OSI layers (for a comparison, see TCP/IP).