and the 5G-SA architecture were introduced in Release 15 of the 3GPP standard. For a color version of all the figures in this chapter, see www.iste.co.uk/launay/5g.zip NG-RAN and 5G-NR: 5G Radio Access Network and Radio Interface, First Edition. Frédéric Launay. C ISTE Ltd 2021. Published by ISTE Ltd and John Wiley & Sons, Inc. NG-RAN and 5G-NR The 5G-NSA configuration implements the MR-DC (Multi Radio Dual Connectivity) architecture. SA mode Option 2 Control Plane User Plane NG-RAN Figure 1.1. Deployment in the SA mode Dual connectivity involves two RAN nodes, i.e. master node (MN) and secondary nodes (SN) which has the following features: - the MN is connected to the core network for the control plan (signaling) and for the user plane; - the SN is controlled by the MN. It is connected to the MN for the control plane (C-plane). The user plane (U-plane) is either connected to the MN or connected to the core network; - the master radio access node controls the secondary radio access node and establishes a bearer, if necessary, for the exchange of data between the two radio nodes. Dual connectivity defines the "Master Cell Group (MCG) bearer" and the "Secondary Cell Group (SCG) bearer". The MCG carries data that will be transmitted on the radio resources allocated by the MN. In the case of carrier aggregation, the MN supports data on the PCell (Primary Cell) and SCells (Secondary Cells). The SCG carries data that will be transmitted on the radio resources allocated by the SN. In the case of carrier aggregation, the SN supports data on the PCell and SCell. The split bearer consists of routing the traffic between the MN and the SN. According to the U-plane termination, the split bearer consists of splitting either the MCG bearer or the SCG bearer. NG-RAN Network - Functional Architecture For E-RABs configured as "MCG bearers", the U-plane termination point is located at the MN. For E-RABs configured as "SCG bearers", the U-plane termination point is located at the SN. For the core network configuration, each support 