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A bearer service is a link between two points, which is defined by a certain set of characteristics. Whenever a UE is being provided with any service (CS/PS service), always, the service has to be associated with a Radio Bearer specifying the configuration for Layer-2 and Physical Layer in order to have its QOS clearly defined. Radio bearers are channels offered by Layer 2 to higher layers for the transfer of either user or control data. In other words Layer 2 offers to the upper layers the service of information transmission between the UE and the UTRAN by means of the Radio Bearers (RBs) and Signaling Radio Bearers (SRBs).Therefore the service access points between Layer 2 and upper layers are RBs. == Radio Access Bearers(RAB) == The purpose of a Radio Access Bearer (RAB) is to provide a connection segment using the WCDMA Radio Access Network (WCDMA RAN) for support of a UMTS bearer service. The WCDMA RAN can provide Radio Access Bearer connections with different characteristics in order to match requirements for different UMTS bearers. * The conversational speech RAB is tailored to 12.2kbit/s Adaptive Multi Rate (AMR) speech and will also be used to carry emergency calls. * Video telephony and ftp services may be offered across the Conversational 64 kbit/s Circuit Switched (CS) RAB. * The streaming 57.6 kbit/s is offered to support a specific modem. * The new PS streaming 8/54 kbit/s RAB will be implemented on DCH. This streaming RAB will be supported only in combination with PS interactive 8/8 kbit/s RB, no standalone PS streaming RAB will be supported. * The maximum data rate supported by the Interactive RAB (Packet Switched, PS) is 384 kbit/s in the downlink and 64 kbit/s in the uplink, making it ideal for email or web browsing. * It is also possible to use the speech RAB together with the interactive RAB that is usually called a MultiRAB. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Radio Bearer in UMTS」の詳細全文を読む スポンサード リンク
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