This paper deals with both enforcing and charging end-to-end Quality of Service (QoS) and differentiated services in the Internet. Today, much work for optimizing QoS and defining charging mechanisms accordingly is related to low network layer (up to IP), and the current proposals under the spotlights are VPN, CDN, (over)-provisioning, and of course DiffServ. However, the service an user can get can be quite different from the one provided by the network layer (IP in the Internet). Transport protocols (TCP most of the time) induce oscillations (often seen as self-similarity) in the traffic, in particular because of their congestion control mechanisms. Based on this result, it is obvious that it is impossible to coherently charge such kinds of services at layer 3. QoS has also to be managed and enforced by transport protocols, that also have to strongly impact the way pricing is done. As a consequence, a new approach for services differentiation and charging (in addition to existing layer 3 approaches) at transport level is proposed. This approach relies on the aggressiveness of congestion control mechanisms because the more aggressive a protocol, the better the QoS it provides in case of a well provisioned network. And of course charging has to evolve accordingly. This idea is demonstrated by taking examples as UDP and several versions of TCP. In particular it is proved that service differentiation can be made that way in the Internet. This paper also gives a quantitative study of the QoS got by users depending on the amount of resources consumed, and it is observed that this function is linear. The charging of each service can then be quantified that way.