split is supported for SRB1 and SRB2 media. The RRC messages are encrypted and fully protected by the NR-PDCP entity of the master node (MN). The support separation takes place: - option 3: at the level of the master node eNB; - option 3x: at the level of the secondary node gNB. Each node is responsible for allocating resources for its cell. 8.2.1.5. PDU duplication PDU duplication is supported for the user plane and for the control plane. Duplication is configured at the RRC layer. Duplication involves transmitting the PDCP frame multiple times through different RLC sublayers. The primary and secondary RLC layers are activated for each DRB radio bearer. In case of dual connection, the following configurations are defined in the Release 16 specification: - EN-DC: the duplication can be applied to the aggregation of carriers at the level of the master node and at the level of the secondary node but only under the control of the E-UTRAN PDCP entity and provided that there is no DC duplication. 214 NG-RAN and 5G-NR - NGEN-DC or NE-DC: the duplication can only be configured at the level of the gNB entity, either at the level of the secondary support SCG (Secondary Cell Group) bearer for the NGEN-DC option or at the level of the MCG (Master Cell Group) bearer master support. - NR-DC: duplication takes place on both radio nodes. On reception, the duplicated packets are deleted (discard). 8.2.2. Operations 8.2.2.1. Operations relating to the SRB bearer Figure 8.6 describes the operations relating to the SRB bearer. At transmission, the RRC messages are subject to a reorder procedure which helps the detection of duplicate messages on the receiver side. The Message Authentication Code for Integrity (MAC-I) allows integrity control of the PDCP frame. The calculation of the MAC-I is done with the following information: - the PDCP frame that contains the PDCP header and RRC message; - the COUNT parameter that aggregates the Hyper Frame Number (HFN) and the PDCP frame sequence number; - the DIR parameter which indicates wheth