Radio Bearer Setup is allways initiated by network s it involves radio resources.
If UE requires with particular conf. RB it should send through RRC.
There are 4 ways.
1) Radio Bearer setup with dedicated channel activation - A straight forward procedure
-> UTRAN RRC configures Physical Layers in Both RNC and NodeB
-> After the above RB Setup msg send to UE
-> Once UE receives the above message, it configures its RRC with receied parameters and try
to do L1 Synchronization (UL and DL)
-> UE sends Radio Bearer Setup Complete to UTRAN
2) Radio Bearer Setup with unsynchronized channel modification
-> This is like modify current physical channel to meet new bearer requirements.
-> Unsynchronized implies: Both old and new RBs can co-exists. Such that UTRAN can use one and UE can use another
-> But while modifying L1 similary through Comm.Phy.RL.Modify.Req, if any error occurs this will be acknowledged to RRC as error as Negative.
3) Radio Bearer Setup with Synchronized Channel Modification:
-> This is when physical channels can't be reconfigured as per the need
-> So the old and new RBs can't co-exists and only new RB only exists.
-> Before modifying RRC queries NodeB whether Node B Supports this configuration
-> While Modifying after if no error from Nodeb:
RRC includes activation time in RB Setup message and signal to UE. UE intern informs the same to lower layers. At activation time all entitles starts with new configuration. At end UE responds with RB Setup Complete to Network.
4) Radio Bearer Setup without dedicated channel
-> Here new bearer does not need a permanent DCH
-> So this does not involve any physical channel modifications. But just RLC and MAC configuration.