The Open Systems Interconnection (OSI) Model was developed by the International Organization for Standardization (ISO) and includes seven layers. It is used to describe a framework for connecting multiple computers to each other. Each layer is focused on a set of specific tasks or functions.
Data is packaged, or encapsulated, at each layer with additional data that the layer requires. For example, at the lowest layer (the physical layer), data arrives as bits (ones and zeros). The next layer (the data link layer) adds additional data and packages the data into frames. Figure 3-1 shows a diagram of the OSI Model identifying the layers and the data encapsulation names. The following subsections describe these different layers.