5G • RAN
RRC
Radio Resource Control
The 5G NR Layer 3 control plane protocol managing radio connection states, security configuration, measurement reports, and handovers.
Technical Explanation
RRC is the Layer 3 protocol terminating between the UE and gNodeB (CU-CP). In 5G NR, RRC introduces three operating states: RRC_IDLE, RRC_CONNECTED, and the new energy-saving RRC_INACTIVE state. RRC handles system information broadcasting (MIB/SIBs), connection establishment, re-establishment and release, radio bearer setup/reconfiguration (SRB and DRB), mobility procedures, paging, and measurement configuration/reporting.
Key Functions
- Management of 3 RRC states: IDLE, CONNECTED, and the new RRC_INACTIVE state
- Fast state transition from INACTIVE to CONNECTED with resume ID and stored security context
- System Information broadcast (MIB, SIB1, SIB2, SIB3, SIB4, etc.)
- Radio bearer establishment, modification, and security activation (ciphering/integrity)
Specifications
3GPP TS 38.331
Interfaces
Uu (Layer 3 Control Plane)
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