What is the difference between the RRC IDLE and the RRC inactive state?

Radio Resource Control ( RRC ) is a layer within the 5G NR protocol stack . It exists only in the control plane, in the UE and in the gNB . The behaviour and functions of RRC are governed by the current state of RRC . In 5G NR , RRC has three distinct states: RRC_IDLE, RRC_CONNECTED and RRC_INACTIVE.6 Mar 2021

Differences between LTE RRC states and UMTS RRC States In LTE there is only 2 RRC states i.e. RRC_IDLE and RRC_CONNECTED whereas in UMTS system RRC has a 5 state i.e. IDLE, CELL_FACH, CELL_DCH, CELL_PCH and URA_PCH.

The UE is notified about the 5G bearer via the RRC Connection Reconfiguration message. The UE then connects to the 5G network while maintaining the connectivity to the 4G network .