The current best-effort infrastructure in the Internet lacks key characteristics in terms of delay, jitter, and loss, which are required for multimedia applications (voice, video, and data). Recently, significant progress has been made toward specifying the service differentiation to be provided in the Internet for supporting multimedia applications. In this paper, we identify the main traffic types, discuss their characteristics and requirements, and give recommendations on the treatment of the different types in network queues. Simulation and measurement results are used to assess the benefits of service differentiation on the performance of applications.