The traffic generated by multimedia applications presents a great amount of burstiness, which can hardly be described by a static set of traffic parameters. The dynamic and efficient usage of the resources is one of the fundamental aspects of multimedia networks: the traffic specification should first reflect the real traffic demand, but optimise, at the same time, the resources requested. This chapter presents: a model for dynamically renegotiating the traffic specification (RVBR), how this can be integrated with the traffic reservation mechanism RSVP, and an example of application able to accommodate its traffic to managing QoS dynamically. The remaining of this chapter is focused on the technique used to implement RVBR) taking into account problems deriving from delay during the renegotiation phase and on the performance of the application with MPEG4 traffic.