Admission control and congestion control can provide performance guarantees in ATM networks. However some users may not be able to describe their traffic accurately enough for the network to provide these guarantees. By sending a dynamic feedback signal about the current utilization of network resources, the network could provide some guarantees to adaptive users who respond appropriately: this is the basis of ABR service. We outline a user-oriented framework for network operation and control, explicitly defining how such feedback is generated by the network and what form it takes. We show through simulations that it is possible to simultaneously gain both network and economic efficiency by using a form of feedback we call responsive pricing, which is compatible with current ATM Forum UNI specifications.