pecific qualities about the user agent that can affect content processing and display, such as physical location. See Figure 7.20. CC/PP is designed to work with a wide variety of web-enabled devices, such as PDAs, desktop machines, laptops, WAP phones, phone browsers, web television units and spe- cialized browsers for users with disabilities. Proxies may also be used to provide markup transformation, transmission or caching services for CC/PP-enabled clients and servers. 7.7 IMPLEMENTATION 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 r