retail access influence on, 162-163. See also design access, 220-228 of networks, optimal physical vs. nonpossessory takings, 210-220 design of networks, optimal, 41-50, 182 regulatory takings, 212-214 configuration choice, 41-42 regulatory takings and confiscatory ratemaking cost-affecting factors, 42 doctrine synthesis, 217-219 configurations with economies of scale in links, shift importance to access regulation, 219-220 45-47 constrained revenue-maximizing price, 81, 82f cost-minimizing design, 43-45 consumption externalities, 139n23 minimum spanning tree, 43, 43f, 44, 44f content delivery networks, 426-427 spanning tree, 43, 43f, 44 content layer, 379 tree graph, 43-44 contestability theory, 136-137, 202-203 max-flow/min-cut theorem and, 47, 48f, 48n6, 49f, cooperative game theory, 16-17 50, 363, 368 cost allocation networks, 5 detariffing, 129-130 cost-based approach, problems with, 4 digital broadcast satellite (DBS), 195, 281, 349-350, cost functions of networks, 60-68 354, 388-389 derivation of cost function, 61-63 digital loop carriers (DLCs), 339, 340f, 355 access regulation impact on costs, 63 digital subscriber line access multiplexer (DSLAM), cost/production function relation, 61-62 339, 340f, 342 inputs, 62-63 digital subscriber lines (DSL), 130, 339-343 total cost function formula, 61 unbundled network element (UNE), 341-342. See traffic flows and, 62, 62f also last-mile broadband regulation economies of scale, 64-66 digital technology, 137 concentration of traffic as source of, 64-65 vertical exclusion and, 247 joint and common fixed costs in, 65-66 direct costs, pricing, 205-207 volume-surface relationships in, 66 effect of platform competition, 207 economies of scope, sources of, 66-68 fair value principle, 205-206 incremental cost of product, 66 historical cost, 206 multiproduct cost functions, 66-68 replacement cost, 206 nonseparable cost function, 66 directed graph, 20-21 stand-alone cost of product, 66 direct electric current, example of, 21, 22f cost-minimizing design of cycle network, 44-