Description
E-UTRA NR Dual Connectivity (EN-DC) is a specific dual connectivity configuration defined by 3GPP where the User Equipment (UE) is concurrently connected to two different radio access technologies: LTE (E-UTRA) and 5G New Radio (NR). In this architecture, the LTE base station (eNodeB) acts as the Master Node (MN), forming the Master Cell Group (MCG). The 5G NR base station (gNB) acts as the Secondary Node (SN), forming the Secondary Cell Group (SCG). The UE maintains a single control plane connection to the LTE Master Node via the MCG. The core network connection is anchored in the Evolved Packet Core (EPC), not the 5G Core (5GC), which classifies EN-DC as a Non-Standalone (NSA) 5G deployment mode.
How it works involves coordinated operation between the eNodeB (MN) and the gNB (SN). The LTE eNodeB is the control plane anchor, handling all Radio Resource Control (RRC) signaling, mobility management, and connection to the EPC (specifically the MME and S-GW). The NR gNB is primarily responsible for providing additional user plane capacity. Data can be split at the PDCP layer (located at the MN) or at the core network (S-GW). The MN's PDCP layer can route data packets to its own RLC layer (for transmission over LTE) or to the SN's RLC layer (for transmission over NR) via the X2 interface (enhanced as X2-C and X2-U). This requires tight synchronization and coordination between the two nodes.
Key components include the UE supporting both LTE and NR radios, the LTE eNodeB (Master eNB or MeNB), the NR gNB (Secondary gNB or SgNB), and the EPC. The critical interfaces are the LTE-Uu interface between UE and eNodeB, the NR-Uu interface between UE and gNB, and the X2 interface between the eNodeB and gNB for control (X2-C) and user plane (X2-U) coordination. The role of EN-DC in the network was to serve as the primary early deployment path for 5G, allowing operators to leverage their dense LTE infrastructure to provide wide-area 5G coverage and high data rates without requiring immediate investment in a full 5G core network, accelerating time-to-market for 5G services.
Purpose & Motivation
EN-DC was created to solve the problem of how to introduce and deploy 5G New Radio technology rapidly and cost-effectively before the 5G Core network was fully standardized and deployed. The primary motivation was to enable operators to offer enhanced mobile broadband (eMBB) services with very high data rates using 5G NR spectrum, while relying on the mature, ubiquitous, and stable LTE network for control plane functions and coverage anchoring.
Historically, it addressed the limitations of a pure "greenfield" 5G Standalone (SA) deployment, which would have required simultaneous rollout of new radio and a new core network, a massive and slow capital investment. EN-DC, as a Non-Standalone architecture, allowed a phased approach. It leveraged the existing LTE infrastructure as a reliable control plane and coverage layer, overlaying 5G NR capacity only in targeted areas (e.g., dense urban hotspots, stadiums) where the high throughput was most needed.
It solved key technical and business challenges: It provided a clear migration path, reduced initial deployment risk and cost, and allowed for early device ecosystem development focused on data-centric use cases. By anchoring to the EPC, it also ensured backward compatibility and service continuity for voice (VoLTE) and other LTE services. EN-DC was the cornerstone of the first wave of commercial 5G deployments globally, bridging the gap between 4G and full 5G Standalone systems.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (338 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, EN-DC (E-UTRA-NR Dual Connectivity) was newly introduced, establishing the framework for an LTE master node and a secondary NR node (en-gNB) to operate with the EPC. The release added specific management requirements for this configuration and its different user plane connectivity options, while also introducing necessary support in core protocols like X2AP for cell resource coordination and NR multi-band operation.
- Add requirement to support EN-DC management TS 28.657CR0006
- Add requirements to support management of EN-DC and 5G interworking in EPC side TS 28.707CR0003
- Introduction of EN-DC into 36.212 TS 36.212CR0279
- Capture NR agreements into 36.331 for E-UTRA connected to 5GC TS 36.331CR3475
- Triggering UE capability info retrieval using DL NAS TRANSPORT TS 36.413CR1574
- X2AP corrections for agreed EN-DC BL CR TS 36.423CR1050
+ 109 more changes
In Release 16, enhancements for EN-DC included support for inter-RAT handover from NR to EN-DC, the introduction of MDT (Minimization of Drive Tests) support, and the addition of measurements related to Secondary Node Addition. Furthermore, the release introduced ARPI & SPID for EN-DC and provided support for RACS (RAN Assisted Connection Support) for EN-DC and MR-DC operations.
- Add measurements related to Secondary Node Addition for E-UTRA-NR Dual Connectivity TS 32.425CR0184
- Resource Level Authorization using Access Tokens TS 33.501CR0755
- Using EAP-TLS with TLS 1.3 TS 33.501CR0757
- 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
- MDT support for EN-DC TS 36.413CR1747
+ 86 more changes
In Release 17, specific enhancements for EN-DC included introducing support for User Plane IP for EPC-connected architectures using NR PDCP and further multi-RAT dual-connectivity enhancements. The release also provided corrections and clarifications on procedures such as E-UTRA - NR Cell Resource Coordination and data forwarding for SA to EN-DC handover. Furthermore, it updated UE capabilities for EN-DC band combinations, including support for FR2, and addressed higher power limit capability for inter-band uplink EN-DC.
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 36.331CR4763
- Introduction of further multi-RAT dual-connectivity enhancements TS 36.331CR4774
- Introducing support of UP IP for EPC connected architectures using NR PDC TS 37.340CR0294
- Introduction of further multi-RAT dual-connectivity enhancements TS 37.340CR0309
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 38.331CR2904
- Introduction of further multi-RAT dual-connectivity enhancements TS 38.331CR2954
+ 68 more changes
In Release 18, the EN-DC function saw enhancements including the introduction of a new capability for intra-band EN-DC channel spacing, the addition of several new EN-DC combination configurations to the supported tables, and signaling support for intra-band non-collocated operation. The release also provided clarifications on procedures like the EN-DC Configuration Update and introduced new UE RF baseline implementation capabilities for specific frequency ranges.
- Adding new DRB measurements in case of Dual Connectivity TS 28.552CR0437
- New performance measurements for NR-NR Dual Connectivity TS 28.552CR0524
- Authentication for UE behind 5G-RG and FN-RG using NSWO TS 33.501CR1593
- NSWO support in SNPN without CH and with CH using AUSF/UDM TS 33.501CR1756
- Lower MSD capability for EN-DC TS 36.331CR4991
- Signaling support for intra-band non-collocated NR-CA, EN-DC TS 38.331CR4396
+ 36 more changes
In Release 19, enhancements for EN-DC included the introduction of signaling support for intra-band non-collocated deployments and the addition of new UE radio capabilities for various EN-DC combinations within FR1, including those for Release 15, 16, and 19 configurations. The release also updated RF baseline implementation capabilities for new power class 2 EN-DC combos and added Protocol Implementation Conformance Statement (PICS) for several configurations. Furthermore, corrections and updates were made to the management system requirements to support the NR node (en-gNB) in EN-DC operation.
- Introduction of signaling support for intra-band non-collocated EN-DC/NR-CA deployment Phase 2: new receiver type(s) TS 38.331CR5479
- Rel-19 CR TS 28.552 update the use of EN-DC TS 28.552CR0633
- Corrections in clause 6.10.2 of TS 33.501 regarding dual connectivity TS 33.501CR2196
- Addition of UE capability for R16 EN-DC combos within FR1 TS 38.508CR0832
- Addition of UE capability for R15 EN-DC combos within FR1 TS 38.508CR0833
- Addition of RF baseline implementation capabilities for new PC2 EN-DC combos within FR1 TS 38.508CR0847
+ 9 more changes
Explore further
Broader topics and technologies where EN-DC plays a role.
Defining Specifications
3GPP specifications that define or reference EN-DC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 28.540 vk10 | 5G Network Resource Model (NRM) Management | Rel-20 |
| TS 28.552 vk10 | 5G Performance Management Measurements | Rel-20 |
| TS 28.554 vk00 | 5G Network & Slice KPI Specification | Rel-20 |
| TS 28.558 vj50 | UE Level Measurements for 5G System | Rel-19 |
| TS 28.657 vj00 | E-UTRAN NRM IRP Requirements | Rel-19 |
| TS 28.707 vj00 | EPC NRM IRP Requirements | Rel-19 |
| TS 29.281 vj20 | GTPv1-U Protocol Specification | Rel-19 |
| TS 32.425 vj00 | E-UTRAN Performance Measurements | Rel-19 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TS 36.212 vj10 | LTE Multiplexing and Channel Coding | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.413 vj10 | S1 Application Protocol (S1AP) | Rel-19 |
| TS 36.423 vj10 | X2 Application Protocol (X2AP) Specification | Rel-19 |
| TS 36.424 vj00 | X2 Interface User Plane Transport Protocols | Rel-19 |
| TS 37.340 vj00 | Multi-Connectivity Operation Overview | Rel-19 |
| TS 37.473 vj00 | W1 Application Protocol (W1AP) Specification | Rel-19 |
| TS 37.483 vj10 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 37.571 vj00 | UE Conformance for Positioning | Rel-19 |
| TS 37.717 | 3GPP TR 37.717 | Rel-15 |
| TS 37.718 | 3GPP TR 37.718 | Rel-15 |
| TS 37.719 vj00 | 3GPP TR 37.719: Dual Connectivity Band Combinations | Rel-19 |
| TS 37.825 vg00 | High Power UE (PC2) for EN-DC TDD-TDD | Rel-16 |
| TS 38.101 vj31 | NR User Equipment Radio Transmissions | 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 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TS 38.307 vj20 | NR UE Release Independent Requirements | 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 38.423 vj10 | Xn Application Protocol (XnAP) specification | Rel-19 |
| TS 38.425 vj10 | NR User Plane Protocol Specification | Rel-19 |
| TS 38.463 vj00 | E1 Application Protocol (E1AP) | 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 38.521 vj20 | NR Physical Layer UE Conformance Testing | Rel-19 |
| TS 38.522 vj11 | UE Conformance Test Applicability Statement | Rel-19 |
| TS 38.523 vj20 | 5G NR UE Conformance Testing: Idle/Inactive | Rel-19 |
| TS 38.755 vj10 | NR FR1 DL Fragmented Carriers Study | Rel-19 |
| TS 38.793 vj00 | Simultaneous Rx/Tx Band Combinations TR | Rel-19 |
| TR 38.839 vh00 | Simultaneous Rx/Tx band combinations | Rel-17 |
| TR 38.846 vi10 | Technical Report | Rel-18 |
| TR 38.881 vi00 | Technical Report on Lower MSD for Inter-band CA/EN-DC/DC | Rel-18 |
| TR 38.894 vi00 | Technical Report | Rel-18 |