In this paper we consider a network implementing congestion pricing. For general user utility functions, and in a regime where user peak rates are small compared to network link capacities, we establish optimality of the considered pricing scheme. The corresponding optimal user policies are perhaps contrary to what one would expect: file transfers must either be done at maximal speed, or have access denied, whereas real time applications will display elasticity in their choice of sending rates. We also discuss how the optimality property is affected by price encoding mechanisms implemented in the network, and the resulting effect on user policies.