What is EN-DC?
EN-DC (also called Option 3x) is the most widely deployed early 5G architecture. It allows a UE to simultaneously maintain connections to both a 4G LTE eNB (Master Node, control plane anchor) and a 5G NR gNB (Secondary Node, additional user plane throughput), enabling 5G speeds without requiring a new 5G Core network.
How Does EN-DC Work?
The LTE eNB controls all RRC signalling, anchored to the existing 4G EPC. The 5G gNB adds a Secondary Cell Group (SCG) for additional downlink and uplink throughput. User data is split at the PDCP layer: some flows go via LTE, others via NR. The combined throughput can reach several Gbps. The eNB and gNB coordinate via the X2/Xn interface.
Use Cases
The dominant 5G deployment model globally (2019–2023+). Enables operators to offer 5G services immediately by adding NR radio to existing 4G sites, without investing in a full 5GC.
3GPP / Standards Reference
3GPP TS 37.340 (Multi-RAT Dual Connectivity), TS 36.300, Release 15
Related Terms
NSA | SA | gNB | eNB | EPC | NR | Carrier aggregation
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