問題文
A utility connects 40 substations to two control centers. Substation-to-substation traffic is negligible, but every substation must keep reaching a control center even if one center is unreachable. The team must minimize the number of circuits it leases. Which topology satisfies both, and what does it give up?
選択肢
- Two circuits per substation, one to each center, which is a partial mesh; it gives up any direct substation-to-substation path.
- A full mesh among all 40 substations plus the two centers, which is the only arrangement that survives the loss of a center while also keeping every possible pair of endpoints directly reachable at all times.
- A ring through all 40 substations terminating at both centers, which leases the fewest circuits and still offers each substation two directions toward a center.
- One circuit per substation to the nearer center, with a mesh between the two centers to reroute if the nearer one fails, so the loss of either center leaves every substation served.