a pipe Advanced value added platforms (e.g. WAP, IS, location services, unified messaging, etc.) Standard interface to phone display Power efficient handsets Dynamic management control points Effective yet very light device OSs New and flexible billing systems Text speech Perception of market needs Speech Personalization Intelligent voice recognition Addressing all user segments Multi-band terminals exploiting software radio New data processing and management Synchronization techniques Cost efficient terminals and devices Pragmatic user interfaces (e.g. efficient portals) Clearly, the challenges cover all main areas of SW/HW and management technology. In the forthcoming sections we will see how UMTS addresses these needs and outline the main approaches and requirements to meet the challenges. THE UMTS BEARER ARCHITECTURE As illustrated in Figure 6.1 after [1], UMTS proposes a layered bearer service architec- ture, where each bearer service on a specific layer offers its individual services based on lower layers. Thus, the UMTS bearer service architecture serves as an ideal platform for end-to-end services providing key features in preceding layers. END TO END SERVICE TE/MT local UMTS BEARER SERVICE External Bearer Service Bearer Service RADIO ACCESS Core Network BEARER SERVICE Bearer Service Radio Bearer Iu Bearer Backbone Service Service Net Service Physical FDD/TDD Bearer Service Service CN Iu Figure 6.1 UMTS bearer service architecture. Service Components in UMTS Because of its layered-bearer service architecture UMTS permits users or applications to negotiate, re-negotiate or change appropriate bearer characteristics to carry their in- formation. Negotiations take place based on application needs, network resource avail- ability, and demands of quality of service (QoS). QUALITY OF SERVICE IN 3RD GENERATION NETWORKS The main four classes of UMTS traffic differentiated by their delay sensitivity are con- versational, streaming, interactive, and background. Conversational classes have higher delay sensitivity th