Description
The Radio Resource Control (RRC) protocol is a critical component of the control plane in 3GPP radio access networks (UTRAN, E-UTRAN, NG-RAN). It operates between the User Equipment (UE) and the radio access network node (Node B, eNodeB, or gNodeB). The RRC layer is responsible for the establishment, configuration, maintenance, and release of Signaling Radio Bearers (SRBs) and Data Radio Bearers (DRBs), which carry control and user plane data respectively. It manages the connection states of the UE, primarily the IDLE and CONNECTED states (with sub-states like RRC_IDLE, RRC_INACTIVE, and RRC_CONNECTED in 5G NR), dictating the level of network awareness and resource allocation for the device.
RRC functions through a series of procedures initiated by either the network or the UE. Key procedures include RRC Connection Establishment, Security Activation, Radio Bearer Setup/Reconfiguration, Handover, Measurement Configuration and Reporting, and System Information Broadcast. The protocol conveys critical configuration messages that define the operation of the lower layers (PDCP, RLC, MAC, and PHY). For instance, an RRC Reconfiguration message can instruct the UE to apply new ciphering algorithms, modify logical channel priorities, add or remove carrier aggregation components, or prepare for a handover to a new cell.
Architecturally, RRC messages are carried over Signaling Radio Bearers (SRBs). In LTE and NR, SRB0 is used for contention-based initial access (using the CCCH logical channel), SRB1 is for RRC messages (and optionally NAS messages) before the establishment of SRB2, and SRB2 is dedicated for NAS messages. The protocol is inherently asymmetric, with the network possessing the controlling role. It ensures the UE operates within the network's configured parameters for radio resource efficiency, interference management, mobility robustness, and quality of service fulfillment. Its design is highly parameterized to support a vast range of services, from massive IoT to ultra-reliable low-latency communications.
Purpose & Motivation
The RRC protocol was created to provide a centralized, robust, and flexible mechanism for controlling all radio-specific functions of a mobile device's connection to the network. Prior to its standardization in 3GPP, control signaling was less structured. RRC provides a unified framework for connection management, mobility, and radio bearer control, which is essential for efficient spectrum utilization and service delivery in cellular networks. It solves the problem of how to dynamically manage a shared, interference-prone radio resource among millions of devices with varying service requirements.
Its creation was motivated by the need for a sophisticated control plane to support packet-switched services and advanced features introduced in 3G UMTS and beyond, such as variable data rates, quality of service differentiation, and seamless mobility. RRC abstracts the complexity of the physical and link layers, providing the network with a direct means to command and configure the UE's radio behavior. This allows for optimized network performance, rapid adaptation to changing radio conditions, and the introduction of new features through software upgrades to the RRC protocol specification without overhauling the entire radio interface architecture.
Protocol Stack
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (321 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the RRC function introduced specific procedures and corrections for new capabilities like the RRC_INACTIVE state, Early Data Transmission (EDT), and optimizations for NB-IoT and URLLC. This included clarifications and corrections for RRC connection resume and establishment procedures, handling of the UE context during re-establishment, and paging monitoring in RRC_CONNECTED for BL UEs. The release also provided specific corrections for mobility, such as inter-RAT cell reselection in RRC_INACTIVE and RRC redirection involving 5GC.
- RRC version handling TS 38.473CR0105
- Introduction of support for MAC PDU containing UE contention resolution identity MAC control element without RRC response message in NB-IoT TS 36.306CR1570
- CR on wait timer in RRC release TS 38.331CR0660
- Correction for the RRC Resume procedure TS 24.301CR3083
- EDT-CP - CPSR provided at time of RRC connection establishment TS 24.301CR3144
- Data forwarding for Retrieve UE Context in case of RRC connection re-establishment TS 36.300CR1189
+ 76 more changes
In Release 16, key RRC enhancements included the introduction of downlink RRC message segmentation, an on-demand system information procedure for UEs in RRC_CONNECTED state, and specific support for NR operation with shared spectrum access. The release also introduced early security re-activation during the RRC Connection Resume procedure and defined new RRC parameters and UE capabilities for enhanced high-speed scenarios. Furthermore, it standardized RRC configuration for uplink transmission switching and added specific processing delay requirements for the RRC resume process.
- Introduction of RACS and DL RRC segmentation TS 36.300CR1258
- Early security re-activation at RRC Connection Resume TS 36.306CR1723
- Introduction of DL RRC segmentation TS 36.306CR1732
- Introduction of RRC parameters and UE capabilities for enhanced high speed scenario TS 36.331CR4095
- Early security re-activation at RRC Connection Resume TS 36.331CR4167
- Introduction of DL RRC segmentation TS 36.331CR4200
+ 62 more changes
In Release 17, the RRC function introduced new signaling and configuration support for several key enhancements, including positioning, NR sidelink, uplink transmission switching, measurement gaps, Multi-USIM (MUSIM) operation, and RAN-based network slicing. It also added specific capabilities such as uplink RRC segmentation and new configurations for Integrated Access and Backhaul (IAB) nodes. Furthermore, the release included corrections and refinements for operations in RRC_INACTIVE state and for Non-Terrestrial Networks (NTN) and IoT.
- Introduction of R17 PositioningEnh in LTE RRC spec TS 36.331CR4762
- RRC CR for NR Sidelink enhancement TS 38.331CR2902
- RRC configuration for R17 UL Tx switching enhancement TS 38.331CR2909
- Introduction of RRC signaling for measurement gap enhancement TS 38.331CR2913
- Introduction of NR RRC support for MUSIM TS 38.331CR2919
- NR RRC CR for RAN slicing TS 38.331CR2921
+ 68 more changes
In Release 18, the RRC function introduced support for R18 positioning in RRC_IDLE and RRC_INACTIVE states and integrated Network Controlled Repeaters into the specification. It also added new RRC signalling for an advanced receiver, introduced parameters for HARQ-ACK multiplexing on PUSCH, and enhanced procedures for SDT (Small Data Transmission) including release with resume indication and switching to a connected state. Furthermore, the release included new timers for the inactive state, alignment of access causes, and various corrections and enhancements for coverage, energy savings, sidelink relay, and multi-carrier operation.
- Introduction of R18 positioning to RRC_IDLE mode and RRC inactive state TS 38.304CR0358
- Introduction of Network Controlled Repeaters in RRC spec TS 38.331CR4162
- Introduction of Further NR coverage enhancements in RRC TS 38.331CR4433
- Introduction of network RRC signalling for advanced receiver TS 38.331CR4488
- Introduction of eMBS to RRC TS 38.331CR4490
- Introduction of RRC parameters for HARQ multiplexing [HARQ-ACK MUX on PUSCH] TS 38.331CR4597
+ 77 more changes
In Release 19, the RRC function introduced specific enhancements for Extended Reality (XR) services and for devices using Low-Power Wake-Up Signal/Wake-Up Receiver (LP-WUS/WUR) mechanisms. It also defined new RRC procedures for Mobility Enhancements Phase 4, including the addition of a Mobility State parameter for UEs in RRC_CONNECTED, and introduced a new RRC establishment cause for delay-tolerant services. Furthermore, the release included corrections and support for mobility between terrestrial and non-terrestrial networks (TN-NTN), particularly for IoT redirection scenarios.
- Introduction of R19 XR enhancements for RRC spec TS 38.331CR5395
- Introduction of LP-WUS/WUR in RRC TS 38.331CR5416
- Introduction of RRC changes for mobility enhancements phase 4 TS 38.331CR5443
- Adding Mobility State in RRC_CONNECTED [SpeedStatePars] TS 38.331CR5615
- NAS overhead reduction for CP CIoT data transport, RRC establishment cause TS 24.301CR4465
- RRC establishment cause for delay tolerant service TS 24.301CR4576
+ 8 more changes
Explore further
Broader topics and technologies where RRC plays a role.
Defining Specifications
3GPP specifications that define or reference RRC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 21.810 v1300 | Multi-mode UE Issues - Categories, principles and procedures | Rel-4 |
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TR 21.910 v1300 | Multi-mode UE Operation Principles | Rel-4 |
| TS 23.050 v1100 | UMTS Network Principles and Architecture | R99 |
| TS 23.060 vj00 | GPRS Service Description Stage 2 | Rel-19 |
| TS 23.221 vj00 | 3GPP System Architectural Requirements | Rel-19 |
| TS 23.851 v1600 | Network Sharing Architecture for 3G Systems | Rel-6 |
| TR 23.979 vj00 | PoC over 3GPP Systems Architectural Requirements | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 25.123 vj00 | Radio Resource Management for TDD | Rel-19 |
| TS 25.133 vj00 | UTRAN RRM Requirements for FDD | Rel-19 |
| TS 25.142 vj00 | UTRA TDD Base Station RF Test Methods | Rel-19 |
| TS 25.171 vj00 | A-GPS Minimum Performance Requirements for UTRA FDD UE | Rel-19 |
| TS 25.172 vj00 | A-GANSS UE Minimum Performance Requirements (FDD) | Rel-19 |
| TS 25.173 vj00 | A-GANSS Performance Requirements (TDD) | Rel-19 |
| TS 25.201 vj00 | UTRA Physical Layer General Description | Rel-19 |
| TS 25.222 vj00 | UTRA TDD Multiplexing & Channel Coding | Rel-19 |
| TS 25.224 vj00 | UTRA TDD Physical Layer Procedures | Rel-19 |
| TS 25.301 vj00 | UE-UTRAN Radio Interface Protocol Architecture | Rel-19 |
| TS 25.302 vj00 | UTRA Physical Layer Services | Rel-19 |
| TS 25.304 vj00 | UTRA Idle Mode Procedures Specification | Rel-19 |
| TS 25.307 vj00 | UE Requirements for Release-Independent Frequency Bands | Rel-19 |
| TS 25.321 vj00 | MAC Protocol Specification for UTRAN | Rel-19 |
| TS 25.322 vj00 | RLC Protocol Specification | Rel-19 |
| TS 25.323 vj00 | Packet Data Convergence Protocol (PDCP) Specification | Rel-19 |
| TS 25.324 vj00 | Broadcast/Multicast Control Protocol | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.367 vj00 | Home NodeB Mobility Procedures | Rel-19 |
| TS 25.402 vj00 | UTRAN Synchronisation Mechanisms | Rel-19 |
| TS 25.410 vj00 | Iu Interface Introduction for UTRAN | Rel-19 |
| TS 25.413 vj00 | Radio Access Network Application Part (RANAP) | Rel-19 |
| TS 25.420 vj00 | Iur Interface Introduction for UTRAN | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TS 25.433 vj00 | Node B Application Part (NBAP) Protocol | Rel-19 |
| TS 25.453 vj00 | PCAP Protocol Specification | Rel-19 |
| TR 25.912 vj00 | Evolved UTRA and UTRAN Technical Report | Rel-19 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TR 25.967 vj00 | Home NodeB RF Requirements Technical Report | Rel-19 |
| TS 26.247 vj00 | 3GPP Progressive Download & DASH over HTTP | Rel-19 |
| TS 26.849 vc10 | MBMS Operation on Demand (MooD) | Rel-12 |
| TR 28.837 vi00 | Technical Report on Trace/MDT Management | Rel-18 |
| TS 31.121 vi50 | UICC-terminal interface test specification | Rel-18 |
| TS 32.404 vj00 | Performance Management Definitions & Template | Rel-19 |
| TS 32.405 vj00 | UTRAN Performance Measurements Specification | Rel-19 |
| TS 32.406 vj00 | Performance Management for CN PS Domain | Rel-19 |
| TS 32.827 va10 | UE Management over Itf-N for MDT/SON | Rel-10 |
| TS 33.401 vj10 | EPS Security Architecture | Rel-19 |
| TS 33.821 v900 | LTE/SAE Security Threat Analysis and Countermeasures | Rel-9 |
| TR 33.841 vg10 | Security aspects; Study on 256-bit algorithms for 5G | Rel-16 |
| TS 33.859 vb10 | UTRAN Key Hierarchy Enhancement Study | Rel-11 |
| TS 34.124 vj00 | EMC Requirements for 3G UTRA Terminals | Rel-19 |
| TS 36.104 vj10 | Base Station (BS) radio transmission and reception | Rel-19 |
| TS 36.116 vj00 | E-UTRA Relay RF Requirements | Rel-19 |
| TS 36.117 vj00 | E-UTRA Relay RF Test Methods & Requirements | Rel-19 |
| TS 36.124 vj00 | EMC for E-UTRA User Equipment | Rel-19 |
| TS 36.133 vj20 | E-UTRA RRM Requirements | Rel-19 |
| TS 36.141 vj00 | E-UTRA BS Conformance Testing | Rel-19 |
| TS 36.143 vj00 | E-UTRA FDD Repeater RF Testing | Rel-19 |
| TS 36.171 vj10 | A-GNSS Minimum Performance Requirements for UE | Rel-19 |
| TS 36.201 vj00 | LTE Physical Layer General Description | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.302 vj00 | E-UTRA Physical Layer Services | Rel-19 |
| TS 36.304 vj00 | UE Idle Mode Procedures in E-UTRA | Rel-19 |
| TS 36.306 vj00 | E-UTRA UE Radio Access Capability Parameters | Rel-19 |
| TS 36.307 vj10 | Release-Independent Frequency Band Support | Rel-19 |
| TS 36.322 vj00 | E-UTRA Radio Link Control Protocol Specification | Rel-19 |
| TS 36.323 vj00 | PDCP Protocol Specification | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.355 vj00 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 36.360 vj00 | LTE-WLAN Aggregation Adaptation Protocol | Rel-19 |
| TS 36.361 vj00 | LWIP Encapsulation Protocol Specification | Rel-19 |
| TS 36.401 vj00 | E-UTRAN Overall Architecture Description | Rel-19 |
| TS 36.413 vj10 | S1 Application Protocol (S1AP) | Rel-19 |
| TS 36.876 vd00 | Study on Small Cell High Layer Aspects for LTE | Rel-13 |
| TS 36.878 vd00 | LTE Performance Enhancements for High Speed Scenarios | Rel-13 |
| TS 36.938 v900 | E-UTRAN to 3GPP2/Mobile WiMAX Mobility | Rel-9 |
| TR 36.976 vj00 | LTE-based 5G Terrestrial Broadcast Overview | Rel-19 |
| TS 37.141 vj10 | RF Test Methods for Multi-Standard Radio Base Stations | Rel-19 |
| TS 37.145 vj10 | AAS Base Station Conducted Conformance Testing | Rel-19 |
| TS 37.171 vj00 | UE Positioning Performance Requirements | Rel-19 |
| TS 37.320 vj00 | Minimization of Drive Tests (MDT) Overview | Rel-19 |
| TS 37.355 vj20 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 37.470 vj00 | W1 Interface Introduction for ng-eNB | Rel-19 |
| TS 37.473 vj00 | W1 Application Protocol (W1AP) Specification | Rel-19 |
| TS 37.571 vj00 | UE Conformance for Positioning | Rel-19 |
| TS 37.802 va10 | MSR BS RF Requirements for Non-Contiguous Spectrum | Rel-10 |
| TS 37.857 vd10 | Study on Indoor Positioning Enhancements | Rel-13 |
| TR 37.900 vj00 | Multi-Standard Radio (MSR) Base Station Requirements | Rel-19 |
| TR 37.901 vf10 | UE Application Layer Data Throughput Performance | Rel-15 |
| TS 38.124 vj00 | NR UE EMC Requirements | Rel-19 |
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | Rel-19 |
| TS 38.171 vj10 | 5G A-GNSS UE Positioning Requirements | Rel-19 |
| TS 38.174 vj10 | NR Integrated Access and Backhaul Radio Spec | Rel-19 |
| TS 38.176 vj20 | IAB Conformance Testing Specification | Rel-19 |
| TS 38.201 vj00 | NR Physical Layer General Description | Rel-19 |
| TS 38.304 vj00 | UE RRC_IDLE and RRC_INACTIVE Procedures | Rel-19 |
| TS 38.323 vj00 | Packet Data Convergence Protocol (PDCP) | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.401 vj10 | NG-RAN Architecture Specification | Rel-19 |
| TS 38.470 vj10 | F1 Interface Introduction | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |
| TS 38.508 vj11 | 5G NR UE Radio Transmission & Reception | Rel-19 |
| TS 38.522 vj11 | UE Conformance Test Applicability Statement | Rel-19 |
| TR 38.869 vi00 | Study on low-power wake up signal and receiver for NR | Rel-18 |
| TR 38.878 vi40 | Technical Report on Advanced Receiver for MU-MIMO | Rel-18 |
| TS 43.051 vj00 | GERAN Stage 2 Service Description | Rel-19 |
| TR 43.901 vj00 | Generic Access to A/Gb Interface Feasibility Study | Rel-19 |
| TS 44.060 vj00 | GERAN RLC/MAC Protocol Specification | Rel-19 |
| TS 44.160 vg00 | GERAN Iu Mode RLC/MAC Protocol Specification | Rel-16 |
| TS 44.318 vj00 | Generic Access Network (GAN) Interface Procedures | Rel-19 |
| TR 45.902 vj00 | Flexible Layer One (FLO) for GERAN | Rel-19 |
| TR 45.913 vj00 | Optimized Transmit Pulse Shape for EGPRS2-B | Rel-19 |
| TR 45.914 vj00 | MUROS Feasibility Study for Voice Capacity | Rel-19 |
