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What is 5G EN-DC | What is 5G NR Dual Connectivity

This page describes 5G EN-DC or 5G NR Dual connectivity. In 5G NR EN-DC term stands for E-UTRA-NR Dual Connectivity.

The 5G EN-DC has been introduced in 3GPP release 15. The term EN-DC (Evolved-Universal Terrestrial Radio Access-New Radio) refers to E-UTRA NR Dual connectivity. This feature allows mobile device to exchange data between itself and NR base station along with simultaneous connection with LTE base station. This is possible when there is tight interworking between LTE and 5G NR base station has been established.

EN-DC overall architecture

In this dual connectivity mode, UE may be simultaneously connected to LTE and NR or to LTE for control plane and NR for user plane. In this dual connectivity feature, UE leverages benefits of both LTE and 5G connectivity simultaneously.

Control Plane:
• To set up and modify the EN-DC operation, a mobile device must comprehend both the LTE and NR RRC control signaling.
• To transport these RRC messages between the network and a mobile device, a set of signaling radio bearers (SRBs) are used:
• Master Cell Group (MCG) SRB (SRB1, SRB2):
• Split SRB (SRB1+SRB1S, SRB2+SRB2S)
• Secondary Cell Group (SCG) SRB (SRB3)

User Plane:
• When it comes to the user plane, where the user data is transported between the network and a mobile device, data radio bearers (DRBs) are used. EN-DC support MCG DRBs, MCG split DRBs and SCG DRBs
• An additional data radio bearer SCG split DRB has been introduced in EN-DC.

Features of 5G EN-DC | 5G NR Dual Connectivity

The figure-1 depicts 5G EN-DC. Following are the features of 5G EN-DC.
• RRC termination: Both the master node and secondary node.
• Control Plane termination towards the core network: Only at the master node
• Supported DRBs: Direct, Split
• Supported SRBs: MCG SRB (Optionally including NR RRC), Split SRB (Optionally including NR RRC), SCG SRB (including only NR RRC).
• Packet duplication/path switching for split DRBs/SRBs: Path switching support as well as packet duplication feature (at least in downlink) for both split DRBs and split SRBs.
• Mobility: Master node controls mobility in LTE, while either the master node or the secondary node can control mobility in NR (Depending on network configuration).


This 5G tutorial also covers following sub topics on the 5G technology:
5G basic tutorial
5G Frequency Bands
5G millimeter wave tutorial
5G mm wave frame
5G millimeter wave channel sounding
Difference between 4G and 5G
5G testing and test equipments
5G network architecture

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