Abstract : This thesis presents three main contributions that aim to improve the transport layer of the current networking architecture. The transport layer is nowadays overruled by the use of TCP and its congestion control. Recently new congestion control mechanisms have been proposed. Among them, TCP Friendly Rate Control (TFRC) appears to be one of the most complete. Nevertheless this congestion control mechanism, as TCP, does not take into account either the evolution of the network in terms of Quality of Service and mobility or the evolution of the applications. The first contribution of this thesis is a specialisation TFRC congestion control to propose a QoS-aware Transport Protocol specifically designed to operate over QoS-enabled networks with bandwidth guarantee mechanisms. This protocol combines a QoS-aware congestion control, which takes into account networklevel bandwidth reservations, with full reliability in order mechanism to provide a transport service similar to TCP. As a result, we obtain the guaranteed throughput at the application level where TCP fails. This protocol is the first transport protocol compliant with bandwidth guaranteed networks. At the same time the set of network services expands, new technologies have been proposed and deployed at the physical layer. These new technologies are mainly characterised by communications done without wire constraint and the mobility of the end-systems. Furthermore, these technologies are usually deployed on entities where the CPU power and memory storage are limited. The second contribution of this thesis is therefore to propose an adaptation of TFRC to these entities. This is accomplished with the proposition of a new sender-based version of TFRC. This version has been implemented, evaluated and its numerous contributions and advantages compare to usual TFRC version have been demonstrated. Finally, we proposed an optimisation of actual implementations of TFRC. This optimisation first consists in the proposition of an algorithm based on a numerical analysis of the equation used in TFRC and the use of the Newton's algorithm. We furthermore give a first step, with the introduction of a new framework for TFRC, in order to better understand TFRC behaviour and to optimise the computation of the packet loss rate according to loss probability distributions.