Face to the complexity involved in the wide deployment of QoS network services as well as the reduced set of services offered by existing transport protocols, this paper proposes a QoS-oriented transport protocol (QoSTP) as the adequate solution for providing soft QoS guarantees to common Internet users for next few years. The design of this QoSTP is based on a set of fundamental principles aimed at assuring the feasibly and efficient deployment of adequate mechanisms intended to satisfy different applications requirements. Moreover, this new protocol has to be designed within an extensible and compositional architectural aimed at integrating further mechanisms intended to satisfy new requirements and to operate under heterogeneous network environments. This paper presents the UML 2.0 specification model of this advanced architecture as well as experimental results intended to demonstrate the feasibility and the advantages of this approach.