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Option 4 relies on the 5G core (5GC).

The gNB acts as an MN; it supports signaling exchange (MCG signaling bearer) with the 5G core network’s transport plane through the NG-C interface. The LTE user plane connections go via the 5G-NR through the NG-U interface.

The ng-eNB base station acts as a secondary node. It is controlled by the gNB base station through the Xn-C interface. The ng-eNB is a new generation of the 4G base station.

The gNB controls the ng-eNB through the Xn interface.

The data is transmitted to the ng-eNB entity via one of the following options (Figure 1.4):

1 – from the master node gNB, which performs the split bearer (option 4, MN terminated split bearer);

2 – from the 5GC network (option 4a, SCG bearer).

Figure 1.4. NE-DC architecture – option 4