5G • RAN
EN-DC
E-UTRA - NR Dual Connectivity
The dual connectivity technology enabling a device to simultaneously connect to a 4G Master eNodeB and a 5G Secondary gNodeB in NSA mode.
Technical Explanation
EN-DC is the technical mechanism behind 3GPP NSA Option 3/3a/3x architectures. The UE is simultaneously connected to a 4G LTE eNB acting as the Master Node (MN) and a 5G NR gNB acting as the Secondary Node (SN). In Option 3x (the dominant global deployment), the 5G gNB connects directly to the 4G EPC SGW for user plane data (S1-U) and splits traffic with the LTE eNB over the X2 interface, while LTE handles all RRC control signaling.
Key Functions
- Simultaneous data aggregation across 4G LTE and 5G NR carriers
- Control plane anchoring in LTE RRC with secondary NR configuration
- Traffic splitting at the PDCP layer in the Secondary Node (SN-terminated split bearer)
- Seamless fallback to 4G when exiting 5G radio coverage
Specifications
3GPP TS 37.340
Interfaces
X2-C (eNB - gNB)X2-U (eNB - gNB)S1-U (gNB - SGW)S1-MME (eNB - MME)
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