(1) (Open System Interconnection) An ISO standard for worldwide communications that defines a 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. Never Completely Defined 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. A Reference Model The OSI serves as a reference model for all network protocols because its functionality exists in all communications systems, although two or three OSI layers may be incorporated into one. For details of the layers, see OSI model. For comparisons between the OSI model and other protocol stacks, see TCP/IP, NetWare, ATM, SNA and SS7.
(2) (Open Source Initiative) A non-profit corporation dedicated to promoting open source software. The OSI logo on software certifies that it is distributed under one of several approved licenses. For more information, visit www.opensource.org. See open source.