Modern Three-Layer Hierarchical Network Architecture
Having understood networking topologies, routers and switches, and so on, we take a quick look at Fig. 1.2, which represents a typical, modern three-layer Ethernet network architecture, mainly popularized by Cisco. It also includes a connection to the Internet. The basic purposes of the three layers can be summarized as follows.
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FIGURE 1.2   Hierarchical three-layer network architecture (and where PoE fits in).
Core Layer
This is the high-speed “backbone” of the “inter-network.” The core ...

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