Description
E-UTRA/5GC is a key deployment configuration introduced in 3GPP Release 15, where the existing Evolved Universal Terrestrial Radio Access (E-UTRA) network—the radio technology for 4G LTE—is connected to the new 5G Core (5GC) network. This architecture decouples the radio access technology from the core network, allowing legacy LTE radios to deliver services over the advanced, cloud-native 5GC. In this mode, the LTE eNodeB (eNB) connects to the 5GC via the NG interface (specifically, the NG-eNB connects to the Access and Mobility Management Function (AMF) and User Plane Function (UPF)). The control plane signaling between the eNB and the AMF uses the NGAP protocol, while the user plane data flows through the N3 interface to the UPF. This setup enables LTE user equipment (UE) to register and establish Packet Data Unit (PDU) sessions with the 5GC, gaining access to services like network slicing, policy control via the Policy Control Function (PCF), and authentication via the Authentication Server Function (AUSF). The UE operates in a mode often referred to as "LTE-only" but with a 5G core, meaning it uses the E-UTRA radio protocols but the NAS signaling is with the 5GC's AMF. This configuration is a cornerstone of non-standalone (NSA) 5G deployment, often used as an intermediate step where LTE provides wide-area coverage anchoring the 5G NR layer for capacity. It allows operators to leverage their extensive LTE investments while introducing the benefits of the 5G core, such as network slicing for different service types, edge computing integration, and a service-based architecture (SBA) with modular network functions.
Purpose & Motivation
E-UTRA/5GC was created to facilitate a smooth and cost-effective migration from 4G to 5G networks. The primary problem it solves is the need to introduce the advanced capabilities of the 5G Core—like network slicing, edge computing, and a service-based architecture—without requiring an immediate and complete overhaul of the existing radio access network (RAN). Before this, LTE was exclusively paired with the Evolved Packet Core (EPC), which lacked the flexibility and cloud-native design needed for 5G's diverse service requirements (eMBB, URLLC, mMTC). The motivation was to allow operators to deploy the new 5GC independently of rolling out new 5G NR radio coverage, enabling early launch of 5G services over LTE coverage areas. This approach reduces initial capital expenditure, accelerates time-to-market for 5G services, and provides a seamless user experience during the transition. It also allows for the introduction of 5G-specific features like enhanced QoS and policy control to LTE users, bridging the gap between generations. Historically, this decoupling represents a significant shift from the tight integration seen in previous generations, offering greater deployment flexibility.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (75 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the E-UTRA/5GC function introduced the RRC_INACTIVE state for UEs connected to the 5G Core, enabling connection suspension with context storage. It also defined specific mobility procedures between E-UTRA/5GC and other RATs, including E-UTRA/EPC and NR, and established the framework for EN-DC operation where NR PDCP could be configured for SRBs. Furthermore, the release specified new UE capability handling for mobility and introduced procedures for RRC connection resume and suspension specifically for the 5GC.
- Capture NR agreements into 36.331 for E-UTRA connected to 5GC TS 36.331CR3475
- Miscellaneous EN-DC related corrections TS 36.331CR3386
- Miscellaneous EN-DC related corrections TS 36.331CR3481
- Miscellaneous corrections on E-UTRA connected to 5GCN TS 36.331CR3586
- Open issues on E-UTRA connected to 5GC for UAC TS 36.331CR3587
- Open issues on E-UTRA connected to 5GC for INACTIVE TS 36.331CR3588
+ 34 more changes
In Release 16, enhancements for E-UTRA/5GC focused on improving the EN-DC (E-UTRA-NR Dual Connectivity) operation, including support for inter-RAT handover from NR to EN-DC and the introduction of an alternative cell reselection priority for EN-DC. The release also introduced procedures for on-demand system information broadcast (SIB) acquisition while in the CONNECTED state. Furthermore, it provided specific support for handling overheating conditions and included corrections for fast MCG link recovery within the EN-DC framework.
- Support of inter-RAT handover from NR to EN-DC in TS 36.331 TS 36.331CR4232
- Introduce of alternative cell reselection priority for EN-DC TS 36.331CR4229
- Support of inter-RAT handover from NR to EN-DC in TS 38.331 TS 38.331CR1505
- Inter-node messaging for supporting intra-band EN-DC scenarios TS 38.331CR2377
- 36.331 CR for overheating in (NG)EN-DC and NR-DC TS 36.331CR4324
- Correction to RRC connection release procedure without security for EN-DC cell reselection TS 36.331CR4418
+ 16 more changes
In Release 17, enhancements for E-UTRA/5GC included the introduction of user plane integrity protection for DRBs when connected to 5GC, aligning with the security framework of NR. The release also specified mobility procedures between E-UTRA/5GC and other RATs, including CDMA2000 and E-UTRA/EPC. Furthermore, it defined the suspension and resumption of the RRC connection to and from RRC_INACTIVE state, including a protected resume request procedure.
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 36.331CR4763
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 38.331CR2904
- Overheating assistance info for FR2-2 in (NG)EN-DC - RIL E801 TS 36.331CR4820
- Correction to support higher power limit capability for inter-band UL EN-DC TS 38.331CR4494
- Introduction of intra-band EN-DC contiguous capability for UL TS 38.331CR4158
In Release 18, enhancements for E-UTRA/5GC primarily focused on refining EN-DC (E-UTRA-NR Dual Connectivity) capabilities. This included introducing new capabilities for intra-band EN-DC channel spacing and providing signaling support for intra-band non-collocated NR-CA within EN-DC. The release also delivered corrections for specific procedures, such as SI reception in RRC_CONNECTED and the `flightPathInfoAvailable` parameter when a UE is connected to the 5G Core.
- Lower MSD capability for EN-DC TS 36.331CR4991
- Signaling support for intra-band non-collocated NR-CA, EN-DC TS 38.331CR4396
- Introduction of new capability for intra-band EN-DC channel spacing [Intra-Band_EN-DC_Channelspacing] TS 38.331CR5013
- Correction to flightPathInfoAvailable when connected to 5GC TS 36.331CR4959
- Correction on SI Reception in RRC CONNECTED TS 36.331CR5066
- [H075-H077] Miscellaneous corrections on intra-band non-collocated NR-CA, EN-DC TS 38.331CR4622
+ 1 more changes
In Release 19, a key enhancement for E-UTRA/5GC introduced signaling support for intra-band non-collocated EN-DC deployments, specifically defining new receiver type(s) for the UE. This advancement improves the performance and flexibility of Multi-Radio Dual Connectivity (MR-DC) operations where the LTE and NR components are not co-located. The update builds upon the existing framework for EN-DC where the NR PSCell is managed as part of the Secondary Cell Group (SCG).
- Introduction of signaling support for intra-band non-collocated EN-DC/NR-CA deployment Phase 2: new receiver type(s) TS 38.331CR5479
Explore further
Broader topics and technologies where E-UTRA/5GC plays a role.
Defining Specifications
3GPP specifications that define or reference E-UTRA/5GC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |