RRC States – 5G

RRC – Radio Resource Control protocol exists at IP level (layer 3) between UE and gNB.

The major functions of the RRC protocol include connection establishment and release functions, broadcast of system information, radio bearer establishment, reconfiguration and release, RRC connection mobility procedures, paging notification and release and outer loop power control.

The operation of the RRC is guided by a state machine which defines certain specific states that a UE may be present in. The different states in this state machine have different amounts of radio resources associated with them and these are the resources that the UE may use when it is present in each specific state.

1.) RRC_IDLE:

• PLMN selection
• Broadcast of system information
• Cell re-selection mobility
• Paging for mobile terminated data is initiated by 5GC
• DRX for CN paging configured by NAS

2.) RRC_INACTIVE:

• PLMN selection
• Broadcast of system information
• Cell re-selection mobility
• Paging is initiated by NG-RAN (RAN paging)
• RAN-based notification area (RNA) is managed by NG- RAN
• DRX for RAN paging configured by NG-RAN
• 5GC – NG-RAN connection (both C/U-planes) is established for UE
• The UE AS context is stored in NG-RAN and the UE
• NG-RAN knows the RNA which the UE belongs to

3.) RRC_CONNECTED:

• 5GC – NG-RAN connection (both C/U-planes) is established for UE
• NG-RAN knows the cell which the UE belongs to
• Transfer of unicast data to/from the UE
• Network controlled mobility including measurements