Decoding 3GPP RRC Specifications: LTE vs 5G
The Radio Resource Control (RRC) protocol has undergone significant evolution from LTE to 5G NR (New Radio), introducing enhanced state management, improved mobility procedures, and support for new use cases.
This presentation explores the key differences between LTE and 5G RRC specifications, highlighting the technical advancements that enable enhanced Mobile Broadband (eMBB), Ultra-Reliable Low Latency Communications (URLLC), and massive Machine Type Communications (mMTC).
3GPP RRC Specifications Overview
LTE Specifications 5G NR Specifications TS 36.331: Core RRC protocol TS 38.331: Core RRC protocol TS 36.300: System architecture TS 38.300: System architecture TS 36.304: UE idle procedures TS 38.304: UE idle/inactive procedures TS 36.133: RRM requirements TS 38.133: 5G RRM measurements Both LTE and 5G have comprehensive specification suites covering all aspects of radio resource management. The 5G specifications build upon LTE foundations while introducing new capabilities and enhanced performance parameters. The parallel numbering system (36.xxx for LTE, 38.xxx for 5G) reflects the evolutionary relationship between the technologies, with each specification addressing similar functional areas across generations.
RRC State Management Evolution
The most significant advancement in 5G state management is the introduction of RRC_INACTIVE state, which maintains UE context at both device and network sides while reducing signaling overhead and power consumption.
This intermediate state enables faster connection resumption compared to LTE, where devices had to transition from IDLE to CONNECTED with full signaling exchange. The result is significantly reduced latency for applications requiring intermittent connectivity.
Connection Management Improvements
- LTE Approach Simple attach/detach procedures with limited mobility optimization and single RAT connectivity
- Multi-RAT Dual Connectivity Simultaneous connection to LTE and 5G networks
- Conditional Handover Pre-configured handover execution based on radio conditions
- Dual Active Protocol Stack Zero-interruption handover maintaining connectivity
Bearer and QoS Management
LTE Approach
- Bearer-based architecture
- Quality of Service Class Identifier (QCI)
- Limited granularity
- Static QoS mapping
5G NR Enhancements
- QoS Flow-based architecture
- 5G QoS Identifier (5QI)
- Protocol Data Unit (PDU) Sessions
- Reflective QoS for dynamic mapping
5G's flow-based QoS architecture represents a fundamental shift from LTE's bearer-based approach, enabling more granular service differentiation. This allows networks to precisely allocate resources based on application requirements rather than broad service categories.
The introduction of reflective QoS enables dynamic adaptation to traffic patterns, improving efficiency for applications with varying performance needs.