 Technology Dual Connectivity (MR-DC). The technical details of MR-DC can be seen in 3GPP's TS 37.340. MR-DC is a functionality for which multiple Receivers (Rx) or Transmitters (Tx) for mobile are configured to use radio resources from two radio access technologies. With MR-DC, the radio resources are scheduled for the mobile by two different schedulers, one from the eNB and the other from the gNB. In this architecture, the eNB is the master node that provides access to the control and user planes between the mobile and the core network, whereas the gNB is the secondary node and only provides access to the user plane. Both the gNB and eNB should be connected by a network interface, which is usually X2 in an NSA configuration. This interface carries the control plane between the gNB and eNB since in the NSA configuration 5G mobiles are not connected to the gNB for control signaling. So, these are the conditions required to make dual connectivity work properly in the NSA mode. To sum up, mobiles get connectivity and access the user plane from two different network nodes, getting LTE access from the eNB and NR access from the gNB. So far, we talked about the network perspective. Note that dual connectivity must be supported by mobiles as well. 5G network deployment architectures SA network architecture So, what about the SA network architecture? SA refers to having an independent network and consists of only one generation of radio access technology, SO mobile users can either use the 4G RAN and the EPC, or can use 5G NR and 5GC. In the case of 5G SA architecture, the connection to the 5G network does not rely on the 4G network as is the case with NSA architecture. 5G SA architecture provides both the control plane and the user plane for 5G mobiles. The following figure depicts 4G and 5G SA structures. As can be seen on the left, the mobile is connected to the EPC via the eNB with the control and user planes whereas, on the right, the mobile is connected to 5GC via the gNB with the control and user planes: Control 