The new transmission media used to transport Internet traffic present different characteristics from the network TCP is tuned to. This results in a degradation in the performance of the protocol in terms of resource utlization and transfer delay. Many works have studied the performance of the protocol over these new transmission media. The majority of these works were interested in a particular environment such as a satellite network or a mobile network. A large number of solutions have been proposed to improve TCP performance. In this paper, we summarize the main problems of TCP and the proposed solutions. The originality of this work is that we conduct the study independently of the network type. Instead of talking about particular transmission supports, we consider the different possible characteristics of the connection path. We study then the effect of these characteristics on TCP mechanisms. This analysis permits us to present an understanding of TCP problems, the limitations of the actual solutions and the required modifications to let TCP cope with an heterogeneous Internet on an end-to-end basis.