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Network+ Training Guide by Mike Harwood, Drew Bird

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OSI Reference Model 101

  • Identify the seven layers of the OSI model and their functions.

The OSI model consists of seven layers, which is why it is sometimes called the OSI seven-layer model. In diagram form, as shown in Figure 4.1, the model is drawn from bottom to top in the following order: physical, data-link, network, transport, session, presentation, and application layers. The physical layer is classified as Layer 1, and the application layer is classified as Layer 7. In many cases, devices are referred to in relationship to the numbered layers at which they operate. For example, a router is said to be a Layer 3 (network layer) device.

Figure 4.1. The OSI reference model.

The model is used to relate the transport of data from one host to ...

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