12.3. Domain Hierarchies

We have seen that (topological) hierarchies are used with various routing protocols (OSPF, IS-IS, and ATM's PNNI routing) to enhance scalability. In transport networks and other types of circuit switched networks (e.g., the telephone network), hierarchies are also used to demarcate specific boundaries of networks (from the policy perspective). This is particularly the case when networks cross geopolitical boundaries. For example, a transport network may be composed of metropolitan networks interconnected by a state (or province)-wide core network. These state-wide core networks may be interconnected by a regional core network. These regional networks might then be interconnected by a country or continent-wide core network. ...

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