7. Determining the Levels of Hierarchy

Most internetworks today are constructed in a layered, hierarchical fashion. Traffic at the fringes of the internetwork is concentrated into successively denser aggregates as you proceed toward the center, gaining economies of scale at each step. This concentration enables the core of the network to take advantage of economies of scale on carrier circuits and services, even when the individual access connections are not big enough to benefit from them.

Hierarchy is primarily an abstraction, an aid to description. It helps us to understand the internetwork. In addition, hierarchy can result in a more manageable and more cost-effective network. There may be further benefit in propagating the hierarchical layering ...

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