OSI Model

The application of a layered framework to networking allows individual layers to be modified, without affecting the layers above or below. The OSI model can be thought of as the networking community's application of the concept of interchangeable parts.

Figure 1-1 illustrates the seven layers of the OSI model. Each layer is tasked with specific functions that allow for the eventual communication of network devices. Note that the model is divided into upper layers and lower layers, which are described in the next sections.

Figure 1-1. OSI Layers

OSI Upper Layers

The upper OSI layers provide application level support such as the user ...

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