Pricing is one of the biggest challenges of the next generation of the Internet. Even if flat rate pricing is probably one of the main reasons of the Internet success, the only way to prevent from network congestion and to differentiate services is by means of usage-based pricing schemes. We review in this paper, from a mathematical modeling point of view, the pricing schemes without resource reservation that have been developed in the litterature. Indeed, an advantage of the absence of reservation in the Internet is that network management is cheap. Even if accounting and billing will increase this cost, we believe that pricing without resource reservation is the lesser of two evils with respect to applying some costly bandwidth reservation procedures.