The Radio Access Bearer (RAB) is a UMTS service for quality of service
(QoS) compliance. This radio access channel is used to ensure quality of service for communication at subscriber level between the subscriber equipment (UE) and the core network. The radio access bearer service checks the UMTS Terrestrial Radio Access Network (UTRAN) to determine whether it has the resources required to implement the requested quality of service. For this purpose, it also checks whether free channels are still available.