TRA or NR access. In MR-DC, one network node acts as the master node (MN) and the other as the secondary node (SN). The MN and SN entities are connected via a network interface and the MN is connected to the CN. The NR MR-DC scheme is designed based on the assumption of non-ideal backhaul between different nodes but can also be used in the case of ideal backhaul. The LTE network supports MR-DC via EN-DC, in which a UE is connected to one eNB that acts as the MN and one en-gNB 11 that acts as a SN. The eNB is connected to the EPC via the S1 interface and to the en-gNB via the X2 interface. The en-gNB may also be connected to the EPC via the S1-U interface and other en-gNBs via the X2-U interface [4]. The NG-RAN supports NG-RAN EN-DC (NGEN-DC), in which a UE is connected to one ng-eNB that acts as the MN and one gNB that acts as an SN. The ng-eNB is connected to the 5GC and the gNB is connected to the ng-eNB via the Xn interface. The NG-RAN fur- ther supports NR-E-UTRA DC (NE-DC), in which a UE is connected to one gNB that acts as the MN and one ng-eNB that acts as an SN. The gNB is connected to 5GC and the ng- eNB is connected to the gNB via the Xn interface. Another important scenario is NR-NR dual connectivity (NR-DC), in which a UE is connected to one gNB that acts as the MN and another gNB that acts as the SN. The master gNB is connected to the 5GC via the NG interface and to the secondary gNB via the Xn interface. The secondary gNB may also be connected to the 5GC via the NG-U interface. In addition, NR-DC can also be used when a UE is connected to two gNB-DUs, one serving the MCG and the other serving the SCG, connected to the same gNB-CU, acting both as the MN and the SN. When the UE is config- ured with SCG, it is configured with two MAC entities: one MAC entity for the MCG and one MAC entity for the SCG [4]. In MR-DC, the UE has a single RRC state, based on the MN RRC and a single control- plane connection toward the CN. Each radio node has its own RRC entity (LTE version, if the node is an eNB or NR vers