holarship on telecommunications. Our approach offers a general framework for examining internal and external network connections that models the impact of access regulation. The graph theory approach shows that mandatory access can significantly change a network's costs, traffic patterns, reliability, and quality of service. Regulated access necessarily affects market behavior, which in turn gives firms the incentive to change the configuration of their networks to compensate for the effects of mandatory access on how the networks function. The result is to force firms to deviate from the most efficient network configuration. We also introduce a classification system that distinguishes among different types of access that all too often are simply treated as if they were the same. Retail access refers to transactions between network firms and retail customers. Whole- sale access refers to transactions between network firms and resellers. Interconnec- tion access refers to transactions between network firms for the origination, termi- nation, and transit of traffic. Platform access refers to the set of transactions between network firms and suppliers of complementary services, such as programming on cable networks or Internet content provision. Finally, unbundled access refers to transactions between network firms for leasing network elements such as lines and switches. We show how each of these types of access has a different impact on the network's optimal configuration, capacity, and transaction costs. For example, retail access alters the network owner's design decisions by preventing him or her from responding to unexpected increases in demand either by refusing to add additional customers or by allowing higher prices to allocate bandwidth when expanding capacity is impossible in the short run. The only way to restore equilibrium is to allow congestion to degrade the quality of service provided until the demand curve Conclusion shifts backward SO that demand once again equals the existing capacity. Network own