Traditionally, switches were organized into a tree structure or hierarchy, and additional high-usage trunks were added to connect exchanges with high volumes of traffic between them. This approach was static. Now, a dynamic approach is used. Routing decisions are influenced by current traffic conditions. Circuit-switching nodes have a peer relationship with each other rather than a hierarchical one.
All nodes can perform the same function.
More complex, but more flexible, because more alternative routes are available. Alternate routing - the possible routes to be used between two end offices are predefined. Each originating switch selects the appropriate route for each call. Each switch is given a set of preplanned routes for each destination, in order of preference. Dynamic alternate routing scheme - a different set of preplanned routes is used for different time periods.