Description
NGEN-DC, which stands for E-UTRA NR Dual Connectivity with E-UTRAN connected to 5GC, is a specific dual connectivity (DC) architecture defined by 3GPP. In this configuration, a User Equipment (UE) maintains simultaneous connections with two different radio access nodes: a Master Node (MN) which is an LTE eNodeB (E-UTRA), and a Secondary Node (SN) which is a 5G NR gNB. The critical architectural aspect of NGEN-DC is that the Master eNodeB is connected to the 5G Core Network (5GC) via the NG interface, not the legacy Evolved Packet Core (EPC). This distinguishes it from EN-DC, where the eNodeB connects to the EPC. The LTE node provides the control plane anchor (via the NR RRC connection is conveyed via the LTE node), while both nodes can deliver user plane data to the UE, aggregating radio resources for higher throughput and reliability.
How NGEN-DC works involves sophisticated coordination between the Master eNodeB and the Secondary gNB. The UE initially connects to the LTE network, which is configured to support connectivity to the 5GC (this is known as an LTE anchor in 5GC). When conditions are favorable (e.g., strong NR signal available), the Master eNodeB can initiate the addition of a Secondary gNB for the UE. This process involves signaling between the eNodeB and gNB over the Xn interface (the inter-base station interface in 5G). The Master Node retains control of the UE's Radio Resource Control (RRC) connection and manages the connection to the 5GC's Access and Mobility Management Function (AMF). The Secondary Node provides additional radio resources (a secondary cell group, SCG) for data transmission. Data can be split at the PDCP layer (option 3 or 3a/3x architectures), where the Master Node's PDCP layer handles routing of packets to either its own RLC layer (for transmission over LTE) or to the Secondary Node's RLC layer (for transmission over NR).
Key components of NGEN-DC include the UE supporting both E-UTRA and NR radios, the LTE eNodeB acting as the Master Node (MN), the NR gNB acting as the Secondary Node (SN), and the 5G Core Network. The interfaces involved are the NG interface between the MN and the 5GC, the Xn interface between the MN and SN for coordination, and the Uu radio interface for both LTE and NR. The UE must support the necessary protocol stack, including dual PDCP entities for split bearer operation. The role of NGEN-DC in the network is to provide a crucial migration path for operators deploying 5G. It allows them to introduce 5G NR coverage in hotspots or new spectrum bands while relying on the ubiquitous LTE network for wide-area coverage and control plane reliability. This provides users with an early 5G data rate boost in supported areas while ensuring seamless mobility and service continuity on the LTE layer.
Purpose & Motivation
NGEN-DC was created to facilitate a flexible and efficient migration from 4G LTE networks to full 5G standalone (SA) networks. Before 5G SA, the initial 5G deployments used Non-Standalone (NSA) architecture, specifically EN-DC, where the NR gNB was an add-on to an LTE network connected to the EPC. While EN-DC provided a 5G speed boost, it did not allow access to new 5GC capabilities like network slicing or advanced QoS. NGEN-DC solves this by allowing the LTE network itself to connect to the new 5GC, enabling operators to deploy and trial the 5G core while still using their extensive LTE radio assets as the primary coverage layer.
The problem it addresses is the 'chicken and egg' scenario of 5G deployment: building a nationwide 5G NR coverage layer is time-consuming and expensive. NGEN-DC allows operators to launch 5G services (via the 5GC) much faster by leveraging their existing LTE radio access network (RAN) as the master and coverage layer. It provides a middle ground between pure NSA (EN-DC with EPC) and pure SA (NR connected to 5GC). This enables subscribers to benefit from new 5G core services and potentially higher data rates via NR secondary cells, even in areas where 5G NR coverage is sparse or non-existent.
Historically, it addresses the limitation of EN-DC, which tied 5G radio innovation to the legacy EPC. NGEN-DC decouples this by connecting the LTE RAN to the 5GC, making the LTE network '5GC-aware'. This was a strategic step in 3GPP Release 15, allowing for a more gradual transition where the core network could be modernized independently of achieving full NR coverage. It motivated operators to begin deploying 5GC infrastructure and testing new services without waiting for NR build-out to be complete, thereby accelerating the overall 5G ecosystem development.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (242 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the NGEN-DC function was introduced as a late drop, defining the dual connectivity architecture where a UE connects to the 5G Core Network via a Master Node in E-UTRAN and a Secondary Node in NR. This release captured necessary NR agreements into the E-UTRA specifications (TS 36.331) for operation connected to 5GC and introduced requirements to support its management. It also included foundational procedures and corrections for scenarios like SN change and re-establishment, while enabling performance measurements per QoS level using mapped 5QI or QCI for EN-DC.
- Add requirement to support EN-DC management TS 28.657CR0006
- Introduction of increased number of E-UTRAN data bearers TS 36.331CR3446
- Capture NR agreements into 36.331 for E-UTRA connected to 5GC TS 36.331CR3475
- Agreements for MR-DC TS 37.340CR0073
- Introduction of late drop NGEN-DC, NE-DC and NR-DC TS 38.331CR0916
- Miscellaneous EN-DC related corrections TS 36.331CR3386
+ 63 more changes
In Release 16, enhancements for NGEN-DC included the introduction of mobility improvements such as inter-RAT handover from NR to EN-DC and support for alternative cell reselection priority. The release also introduced new procedures like UE Radio Capability Mapping for EN-DC and added support for features like RACS (RAN-assisted Cell Selection) and specific measurements for Secondary Node Addition. Furthermore, it mandated full rate user plane integrity protection for MR-DC and provided corrections for overheating handling and IP address requesting within the EN-DC framework.
- Add measurements related to Secondary Node Addition for E-UTRA-NR Dual Connectivity TS 32.425CR0184
- Introduction of Even further Mobility enhancement in E-UTRAN TS 36.331CR4205
- 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
- Stage2 Introduction of ARPI&SPID for EN-DC TS 37.340CR0173
- Stage 2 CR for Inter-RAT HO between NR to EN-DC in Rel-16 TS 37.340CR0185
+ 62 more changes
In Release 17, enhancements for NGEN-DC included the introduction of Overheating Assistance Information for the FR2-2 frequency range and corrections to UE History Information procedures for MR-DC. The release also updated UE radio capability specifications for EN-DC band combinations, including support for higher uplink power limits in inter-band EN-DC and the addition of new EN-DC configurations like DC_1A-n78A. Furthermore, performance measurements for QoS were refined to be optionally calculated per QoS level, now mapped from either 5QI or QCI specifically for the EN-DC scenario.
- 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
+ 50 more changes
In Release 18, enhancements for NGEN-DC included the introduction of new performance measurements for connected mode power saving and for NR-NR Dual Connectivity, alongside the addition of new DRB measurements for Dual Connectivity scenarios. The release also introduced new UE capabilities, such as support for new intra-band EN-DC channel spacing and the addition of several new EN-DC band combination configurations to the supported tables. Furthermore, it provided signaling support for intra-band non-collocated NR-CA in EN-DC and included corrections to procedures like Handover Cancel in CHO with a Secondary Node.
- Adding new DRB measurements in case of Dual Connectivity TS 28.552CR0437
- New performance measurements for connected mode power saving mechanisms TS 28.552CR0523
- New performance measurements for NR-NR Dual Connectivity TS 28.552CR0524
- Protection against improper reselection to GERAN/UTRAN [RESELECTION_TO GSM_AND_UTRAN] TS 36.331CR4971
- Lower MSD capability for EN-DC TS 36.331CR4991
- Introduction of R18 positioning to MR-DC TS 37.340CR0371
+ 28 more changes
In Release 19, the enhancements for NGEN-DC primarily focused on expanding UE capability signaling and RF performance specifications for a wider set of EN-DC band combinations. This included the addition of new UE capability entries for Release 15, Release 16, and Release 19 EN-DC configurations within FR1, alongside updates to RF baseline implementation capabilities for both new and existing power class 2 (PC2) combinations. Furthermore, the release introduced protocol implementation conformance statement (PICS) provisions for several new EN-DC configurations to ensure standardized testing.
- Introduction of NB-IoT satellite information in E-UTRAN [EUTRAN-to-NBIoTNTN] TS 36.331CR5140
- 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
- Correction for the redirection from E-UTRAN TN to NB-IoT NTN [IoT_TN_NTN_redir] TS 36.331CR5173
- Indication of supported NB-IoT NTN band list in E-UTRAN [IoT_TN_NTN_redir] TS 36.331CR5183
- Addition of UE capability for R16 EN-DC combos within FR1 TS 38.508CR0832
+ 9 more changes
Explore further
Broader topics and technologies where NGEN-DC plays a role.
Defining Specifications
3GPP specifications that define or reference NGEN-DC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 28.552 vk10 | 5G Performance Management Measurements | Rel-20 |
| TS 28.657 vj00 | E-UTRAN NRM IRP Requirements | Rel-19 |
| TS 32.425 vj00 | E-UTRAN Performance Measurements | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 37.340 vj00 | Multi-Connectivity Operation Overview | Rel-19 |
| TS 37.473 vj00 | W1 Application Protocol (W1AP) Specification | Rel-19 |
| TS 37.571 vj00 | UE Conformance for Positioning | Rel-19 |
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | 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 |