Layer 2 provides upper layers with information transmission between the UE and UTRAN by means of Radio Bearers (RBs) and Signaling Radio Bearers (SRBs).
RBs are for transmission of user data.
SRBs are for transmission of control information that can be originated either in the RRC or in upper layers.
RB specifies the configuration and the parameters of layer 2 and physical layer depending on the characteristics of the service (voice, interactive service, etc.).
