5G • RAN
RRC_INACTIVE
RRC Inactive State in 5G NR
A hybrid 5G radio state where the device sleeps like in IDLE to save battery, but the core network connection (N2/N3) remains active for instant wake-up.
Technical Explanation
In 4G LTE, switching from IDLE to CONNECTED requires extensive NAS and RRC signaling exchanges (taking 50–100 ms). 5G NR introduces RRC_INACTIVE state: to the 5G Core (AMF/UPF), the UE appears as CM-CONNECTED with active N2 and N3 tunnels, while the radio link is suspended. When new uplink or downlink traffic arrives, the UE resumes the RRC connection in under 10 ms using a lightweight RRCResumeRequest message and stored Access Stratum (AS) context.
Key Functions
- Near-instantaneous transition from sleep to active data transmission (<10 ms latency)
- Substantial reduction in core network signaling traffic during bursty IoT/app sessions
- Cell-level paging managed by the RAN (RAN-based Notification Area - RNA) instead of Core paging
- Significant battery power savings for smartphones and connected IoT
Specifications
3GPP TS 38.331, TS 38.300
Interfaces
Uu InterfaceXn Interface
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