 Noll (1989). Networks in Telecommunications and providing an empirical test of whether a particular market was in fact a natural monopoly. Even after the collapse of ruinous competition as a basis for regulation, policy makers have sometimes imposed regulation even when competition is possible. The classic situation is when a change in technology or demand opens a market previously dominated by one player to competition, although such competition may take some time to emerge and the dominant player will continue to be able to exercise market power for quite some time. When this occurs, policy makers have sometimes imposed asymmetric regulation on the dominant player to prevent it either from charging supracompetitive rates or from engaging in predatory actions to protect its market position. Although somewhat inconsistent with the growing embrace of a policy of open competition, the hope was that such asymmetric regulation would protect against anticompetitive excesses by the dominant firm while simultaneously nurturing the new entrants' ability to survive. Another form of managed competition arises when new entrants struggle to put their entire networks in place before offering service. To allow competition to emerge before entrants had fully established their networks, policy makers have sometimes imposed interconnection access by requiring the incumbent network owners to provide new entrants with access to portions of their networks. This allowed a new entrant to pursue an incremental-entry strategy by using the existing network to provide any components that had not yet been deployed. In each case, the impact of attempts to manage competition would depend critically on the scope of the intervention, the prices that the existing network owner would be per- mitted to charge for the use of its facilities, and how quickly the owner of the existing network would be relieved from these regulatory obligations after effective competition had emerged. B. Basic Regulatory Instruments 1. Tariffing As noted earlier, the