Description
The RAN-based Notification Area Update (RNAU) is a fundamental mobility management procedure defined for the 5G New Radio (NR) system, specifically for User Equipment (UE) operating in the RRC_INACTIVE state. This state, introduced in 5G, is a low-power state where the UE's Access Stratum (AS) context is stored in both the UE and the last serving gNB (or NG-RAN node), but the UE is not actively transmitting or receiving user plane data. The UE is assigned a RAN Notification Area (RNA), which is a logical area defined by the RAN, typically comprising one or multiple cells. The purpose of the RNAU procedure is for the UE to periodically or event-triggered update the network when it moves outside its configured RNA, ensuring the network knows a paging area to locate the UE if downlink data arrives or for other network-initiated actions.
Architecturally, the RNAU procedure is initiated by the UE when a trigger condition is met, such as upon leaving the current RNA, upon expiry of a periodic RNAU timer, or upon cell reselection to a cell that is not part of the current RNA list. The UE performs the procedure by initiating a transition from RRC_INACTIVE to RRC_CONNECTED, specifically using the RRC Resume Request message. This message includes a Resume ID, which allows the receiving gNB (which may be different from the last serving gNB) to retrieve the UE's AS context from the previous gNB via the Xn interface. The procedure involves context retrieval, integrity protection verification, and security key update. Upon successful completion, the network may keep the UE in RRC_CONNECTED if there is pending data, or it may reconfigure a new RNA and move the UE back to RRC_INACTIVE.
The RNAU's role is critical for balancing mobility management efficiency with UE power saving. It decouples frequent location updates from the core network (5GC), handling them within the RAN. This reduces signaling load on the N2 and N3 interfaces towards the Access and Mobility Management Function (AMF) and User Plane Function (UPF). The RNA is managed by the RAN, allowing for more dynamic and traffic-adaptive area sizing compared to the core network's Tracking Areas (TAs). The procedure works in conjunction with RAN-based paging, where a gNB can page the UE within the last known RNA without involving the core network for initial paging, leading to faster call setup times and reduced latency for mobile terminated services.
Purpose & Motivation
RNAU was created to address the limitations of legacy mobility management, particularly for the massive number of IoT devices and smartphones with bursty data traffic expected in 5G. In 4G LTE, a UE in RRC_IDLE state would perform a Tracking Area Update (TAU) procedure with the core network (MME) whenever it moved outside its Tracking Area List. This involved always establishing an RRC connection and performing NAS signaling, which incurred significant signaling overhead, core network load, and UE battery consumption for what were often very short, infrequent data transmissions.
The introduction of the RRC_INACTIVE state in 5G NR required a corresponding RAN-centric mobility management mechanism. The purpose of RNAU is to enable efficient, lightweight location tracking for UEs that are inactive but have a valid AS context stored in the RAN. It solves the problem of frequent core network signaling by keeping location updates local to the RAN. This is motivated by the need to support enhanced Mobile Broadband (eMBB) with always-on connectivity expectations and massive Machine-Type Communications (mMTC) with a vast number of low-power devices. RNAU allows the network to maintain reachability for these UEs while optimizing the trade-off between location accuracy, signaling cost, and UE power consumption, which was not optimally balanced in previous generations.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (74 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, a correction was introduced for the RNAU (RAN-based Notification Area Update) procedure specifically for the case where it is performed without a UE context relocation. This update provided necessary clarifications and corrections to ensure the proper handling of this RAN-level mobility management function.
- Introduction of DEFLATE based UDC Solution TS 36.300CR1090
- Enabling MBMS Bearer Event Notification TS 36.300CR1138
- Implementing network-based CRS interference mitigation TS 36.304CR0729
- Introduction of DEFLATE based UDC Solution TS 36.331CR3211
- Implementing network-based CRS interference mitigation TS 36.331CR3408
- Stage 2 Changes based on CN type indication for Redirection from ng-eNB to E-UTRA TS 36.300CR1185
+ 15 more changes
In Release 16, the RNAU procedure was enhanced with specific clarifications on its initiation criteria and improved support for system information change notifications for UEs in RRC_INACTIVE state. These updates provided greater precision in managing mobility and state transitions for inactive UEs. Furthermore, corrections were applied to related procedures like autonomous gap-based CGI acquisition for FR2 to ensure consistent RNAU behavior.
- Introduction of LTE-based 5G terrestrial broadcast TS 36.331CR4190
- Update on V2X UE capability TS 36.331CR4449
- Introduction of Inter-gNB CSI-RS Based Mobility TS 38.300CR0249
- Stage-2 updates for IIOT (36.300) TS 36.300CR1280
- Removal of RSS based RSRQ measurements TS 36.304CR0835
- Updates for R16 LTE Mobility Enhancements and LTE updates for R16 NR Mobility Enhancements TS 36.331CR4290
+ 10 more changes
In Release 17, the RNAU function was enhanced with a correction to the UE's behavior for the NAS-based busy indication while in the RRC_INACTIVE state. This update ensures proper handling of the busy indication during the notification area update procedure. Additionally, there were small corrections made to the mechanisms for coverage-based paging, which is related to the RNAU process.
- Introduction of new bands and bandwidth allocation for LTE-based 5G terrestrial broadcast TS 36.300CR1360
- Introduction of event-based trigger for LTE MDT logging [LTE-Event-MDT] TS 36.304CR0834
- Introduction of mobility-state-based cell reselection for NR HSDN [NR_HSDN] TS 36.331CR4730
- Introduction of new bands and bandwidth allocation for LTE-based 5G terrestrial broadcast TS 36.331CR4750
- Introduction of event-based trigger for LTE MDT logging [LTE-Event-MDT] TS 36.331CR4752
- UE capabilities for new bands and bandwidth allocation for LTE-based 5G terrestrial broadcast TS 36.331CR4780
+ 12 more changes
In Release 18, the RNAU function saw no new, forward-looking enhancements described in the provided materials. The listed Change Requests for this release focus exclusively on corrections and updates for other areas, such as timer-based conditional handover and location-based measurements for IoT NTN and NR NTN. Therefore, the technical evolution of RNAU itself was not a primary subject of innovation in this particular release cycle.
- Correction of timer-based conditional handover for IoT NTN TS 36.300CR1399
- Corrections to location-based measurement TS 36.300CR1417
- Corrections on distance-based measurements during T-Service for IoT NTN TS 36.304CR0876
- Corrections on location based measurements and need code for IoT NTN TS 36.331CR5052
- Correction of timer-based conditional handover for NR NTN TS 38.300CR0822
- Correction on DL PSI based discard TS 38.300CR0874
+ 4 more changes
In Release 19, the RNAU function was enhanced with a clarification on Notification Configuration. This update provided specific details on the procedures and parameters for managing RAN-based notification areas.
- Introduction of LTE-based 5G Broadcast Phase 2 TS 36.300CR1428
- Introduction of CAS muting in LTE-based 5G broadcast [5GB_CASMuting] TS 36.331CR5139
- Introduction of LTE-based 5G Broadcast Phase 2 TS 36.331CR5143
- Rapporteur correction on CAS muting for LTE based 5G broadcast [5GB_CASMuting] TS 36.331CR5162
- Corrections to LTE-based 5G Broadcast Phase 2 after ASN.1 review TS 36.331CR5168
- Clarification on Notification Configuration TS 36.331CR5186
+ 3 more changes
Explore further
Broader topics and technologies where RNAU plays a role.
Defining Specifications
3GPP specifications that define or reference RNAU, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.304 vj00 | UE Idle Mode Procedures in E-UTRA | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.304 vj00 | UE RRC_IDLE and RRC_INACTIVE Procedures | Rel-19 |