hannels Virtual Channel Identifier Visitor Location Register Voice over Internet Protocol Virtual Path Virtual Path Identifier WCDMA Wideband Code Division Multiple Access Weighted Fair Queuing WiMAX Worldwide Interoperability for Microwave Access Weighted Random Early Detection 1 Introduction 1.1 Motivation The Universal Mobile Telecommunication System (UMTS) is one of the most important and popular standards of the third generation (3G) mobile communication system specified by the 3rd Generation Partnership Project (3GPP). It provides global high-speed mobile access for a great variety of services including voice, Internet access, video conferencing, and general multimedia applications. Each service has its own particular traffic characteristics and specific Quality of Service (QoS) requirements to be met by the network, for example end-to- end delay, jitter, packet loss and blocking ratio. In the public multi-service UMTS networks, the key objective is to support the required QoS for various services to deliver an improved end-user experience for mobile data applications while minimizing the network costs to attain efficient resource utilization. Over the past few years UMTS has experienced an unprecedented development. Since the first UMTS networks were launched in 2002, there has been an intensive growth of the subscriber population and the number of operative networks all over the world. By the end of 2006, there were around 140 UMTS networks operational in more than 50 countries, and the worldwide subscriptions to UMTS networks reached 100 million, with more than 3 million new customers each month [UMTS06]. At present the number of UMTS subscribers and operative networks are still growing rapidly. On the technology evolution path, UMTS has unequivocally delivered on its promise to provide a compelling mobile multimedia experience with a wide range of new services. The evolved wireless technologies of UMTS have significantly increased the network capacity and throughput to improve the end-user experience. A