NTATION OF QOS IN UMTS UMTS is targeted for multimedia traffic with different QoS requirements. Attributes that define the characteristics of the transfer may include throughput, transfer delay and data error rate. This section covers two main ways to manage QoS in UMTS: RAB (radio access bearer) mapping for the access network and QoS handling. 7.7.1 RAB MAPPING The composite system contains many layers of bearers. Many layers are stratified on top of each other. From a QoS point of view the RAB plays an important role, since UMTS allows negotiation of the choice and attributes of the radio bearer. An RAB offers circuit (initially) or packet mode and a number of bandwidths. The bearer class, bearer parameters and parameter values are directly related to an application as well as to the networks that lie between the sender and the receiver. Bearer negotiation is normally initiated by an application, while renegotiation may be initiated either by the network (for example in a handover situation) or by an application. An application-initiated negotiation is basically similar to a negotiation that occurs in the bearer establishment phase: the application requests a bearer depending on its needs and Quality of Service QoS parameters in UMTS: Maximum bit rate (kbit/s) Guaranteed bit rate(Kbit/s) Allowed transfer delay (ms) UTRAN Is QoS class negotiable? UMTS end-to end service UMTS bearer service: request for UMTS QoS class RAB assignment request -Admission control QoS negotiation Radio bearer and radio link establishment RAB assignment response UMTS bearer service with negotiated QoS RAB = Radio access bearer, RRM = Radio resource management Figure 7.21 RAB negotiation for the UMTS access network the network checks the available resources and the user type of subscription and then responds. The user either accepts or rejects the offer. The properties of a bearer service affect the price of a service. See Figure 7.21. At the start of UMTS service not all of the QoS functions will be implemented, and therefore delay-cri