Open Systems Interconnection (OSI) Model

Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different merchants. It is now considered the primary architectural model for inter-computing and inter-networking communications. There are seven layers within the OSI model that serve to differentiate the various hardware and software functions that a network provides. Each layer depends on the proper functioning of the layer immediately below it to provide its raw functionality, which is enhanced and then passed to the next higher layer. Status messages may be communicated up or down the various layers, although each layer only communicates with its immediate neighbors. As each layer is solely dependent on the layer below it for lower-level services, higher layers are shielded from system, hardware, and software implementation details. This leads to the independence from specific systems and interoperability with many vendors’ offerings.

The Open Systems Interconnection (OSI) model is very useful for developing and understanding a big picture views of network processes because it provides this independence. However, the model doesn’t claim to exactly match any specific network technology. Each layer must encapsulate the data it receives into a standard format for the next higher layer, thus incurring an overhead, and in the name of efficiency, the lines between one or more layers can be blurred. Some layers may not specifically have counterparts in an actual network implementation. However, as a tool for understanding the considerations involved in networking, the OSI model is unparalleled.

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