Abbreviation for Open Systems Interconnect Reference Model. An international standard for conceptualizing the architecture of computer networks, established by the International Organization for Standardization (ISO) and the Institute of Electrical and Electronics Engineers (IEEE), that improves network flexibility. The employs a divide-and-conquer approach, in which network functions are divided into seven categories, called layers, and communication standards are established to handle the transfer of data from one layer to another. Within each layer, protocols are developed that focus on those layers functions, and no others.
Within a network-connected computer, outgoing messages move down a protocol stack, successively transforming until the data is ready to be sent out via the physical network. At the receiving end, the data moves up the stack, undergoing the mirror image of the transformation process until the data is ready to be displayed by an application — the calls for a total of seven layers. From the top of the stack to the bottom, they are: application layer, presentation layer, session layer, transport layer, network layer, data link layer, and physical layer. See the application layer, data link layer, network layer, physical layer, presentation layer, session layer, transport layer.