 bearer is a function to allow the split of data going to a node (MN or SN) from the core side into two paths, the 1st path through the air interface (MN or SN) towards the UE and the 2nd path towards the X2/Xn interface with the other node (respectively SN or MN) which will transfer this data through the air interface towards the UE. Traffic splitting is performed by the PDCP entity and is transmitted to the RLC entities of the master cell and the secondary cell. The MR-DC (Multi-RAT Dual Connectivity) is triggered by the MN (master node) which transmits the order to add a secondary SN node via the X2C/X2n control interface. Several configurations are possible: - dual EN-DC connectivity (E-UTRA - NR-DC): the master node is the eNB entity, and the secondary node is the gNB entity (5G-NSA option 3); - dual NE-DC connectivity (NR-DC - E-UTRA): the master node is the gNB entity, and the secondary node is the eNB entity; - NGEN-DC dual connectivity (E-UTRA - NR-DC): the master node is the ng-eNB entity, and the secondary node is the gNB entity. Each radio node has its own RRC entity (E-UTRA RRC for the eNB base station and NR RRC for the gNB base station). The SRB signaling radio bearer carries RRC messages over the radio interface. 5G-NR Radio Interface - Data Link Layer The initial configuration of the secondary SN node (RRC message) is transmitted via the X2-AP or Xn-AP protocol from the secondary SN node to the master node (MN) through the X2-C/Xn-C interface. For 5G-NSA, option 3, the SRB1 signaling bearer supports the establishment of the initial PDCP E-UTRA connection. The subsequent signaling messages: - SRB1 and SRB2 are transmitted by the PDCP E-UTRA entity or the PDCP NR entity from the master node to the mobile. The SN RRC messages from the gNB entity are transmitted to the master eNB node, and encapsulated in an MN RRC message; - SRB3 is transmitted by the PDCP NR entity from the secondary node to the mobile, allowing the RRC messages from the gNB entity to be transported directly to the mobile. The SRB 