In this chapter we shall have a look at the functionalities of different RRC States.
There are 3 RRC states in 5G NR.
1. RRC Connected
2. RRC Inactive
3. RRC Idle
RRC Connected State:
1. Initially UE will be in RRC Idle mode and it will move from RRC Idle to RRC COnnected state by completing RRC Setup Procedure.
2. In this state UE will be allocated C-RNTI. One C-RNTI will be allocated if it is connected to single BS, 2 C-RNTI will be allocated with UE is connected to Multi-RAT Dual COnnectivity.
3. UE will be in CM-Connected mode.
4. UE stores access stratum context.
5. AMF will have NG signalling connection with BS.
6. UPF will have GTP-U tunnels with BS.
7. Transfer of Uplink and Downlink data.
8. Configuration of COnnected Mode DRX.
9. UE will monitor PDCCH DCI using P-RNTI.
RRC Inactive State:
1. UE will move from RRC Connected to RRC Inactive by sending RRC Release Procedure.
2. “suspendConfig” parameter is used to indicate that RRC is moving to RRC Inactive instead of RRC Idle state.
3. UE will be moved to RRC Inactive state to reduce the signalling load.
4. UE will be in CM-Connected mode.
5. UE will have access stratum context.
6. UE will do RNA update.
7. UE will apply DRX for paging.
8. UE monitors PDCCH DCI using P-RNTI.
RRC Idle
1. UE will move to RRC Idle by completing the RRC Connection Release Procedure.
2. UE will release C-RNTI along with all radio bearers and radio resources.
3. UE will be in CM-IDLE state.
4. UE will read system information for RRC Setup.