说明：  After the successful global introduction during the past decade of the second generation (2G) digital mobile communications systems, it seems that the third generation (3G) Universal Mobile Communication System (UMTS) has finally taken off, at least in some regions. The plethora of new services that are expected to be offered by this system requires the development of new paradigms in the way scarce radio resources should be managed. The Quality of Service (QoS) concept, which introduces in a natural way the service differentiation and the possibility of adapting the resource consumption to the specific service requirements, will open the door for the provision of advanced wireless services to the mass market.