bearers). For EN-DC, the network can configure either E-UTRA PDCP or NR PDCP for MN terminated MCG bearers, while NR PDCP is always used for all other bearers. However, in MR-DC with 5GC, NR PDCP is always used for all bearer types. In (NG)EN-DC, E-UTRA RLC/MAC is used in the MN while NR RLC/MAC is used in the SN. In NE-DC, NR RLC/MAC is used in the MN while E-UTRA RLC/MAC is used in the SN. In NR-DC, NR RLC/MAC is used in both MN and SN. The user-plane radio protocol architecture at the network side for the different bearer types is shown in Figure 4.3.8 for EN-DC, and Figure 4.3.9 for MR-DC with 5GC (for NGEN-DC, NE-DC, and NR-DC). The user-plane handling at the UE side is independent of where the bearer is terminated on the network side. So from a UE perspective only three bearer types exist: MCG bearer, SCG bearer, and split bearer. The user-plane radio protocol architecture for the three bearer types from the UE point of view is shown in Figure 4.3.10 for EN-DC, and Figure 4.3.11 for MR-DC with 5GC (NGEN-DC, NE-DC, and NR-DC). Split Split Bearer Bearer Bearer Bearer Bearer Bearer E-UTRA/ NR PDCP NR PDCP NR PDCP NR PDCP NR PDCP NR PDCP E-UTRA E-UTRA EUTRA EUTRA NR RLC NR RLC E-UTRA MAC NR MAC Figure 4.3.8 Radio protocol architecture at the network side for MCG, SCG, and split bearers in EN-DC. (Source: Reproduced by permission of © 3GPP). 4.3 Multi-Radio Dual Connectivity Flows Flows Split Split Bearer Bearer Bearer Bearer Bearer Bearer NR PDCP NR PDCP NR PDCP NR PDCP NR PDCP NR PDCP MN RLC MN RLC SN RLC SN RLC MN MAC SN MAC Figure 4.3.9 Radio protocol architecture at the network side for MCG, SCG, and split bearers in MR-DC with 5GC (NGEN-DC, NE-DC, and NR-DC). (Source: Reproduced by permission of © 3GPP). Figure 4.3.10 Radio protocol architecture Split for MCG, SCG, and split bearers from a UE Bearer Bearer Bearer perspective in EN-DC. (Source: Reproduced by permission of © 3GPP). E- UTRA/ NR PDCP NR PDCP NR PDCP E- UTRA E- UTRA NR RLC NR RLC E- UTRA MAC NR MAC Figure 4.3.11 Radio protocol architecture for 