-RAN node receiving data from a second NG-RAN node to provide information associated with the transfer of the flow; - fast retransmission in the event of failure of one of the nodes. The messages of the XnAP protocol ensure coordination between the node hosting the PDCP sublayer and the corresponding node, to allow the transmission of data under good RF radio conditions by excluding the faulty node. 2.1.3. Protocol architecture on the F1 interface Several options define the functional split between the gNB-CU and gNB-DU modules. The two main criteria that determine the choice of the option are interface throughput and latency. NG-RAN and 5G-NR The 3GPP standardization proposes a division of the functionalities of the gNB entity on the NG-RAN access network and of the ng-eNB entity on the E-UTRAN access network into two units: a distributed unit (DU: Distributed Unit) and a centralized unit (CU: Centralized Unit). In Release R.15, RRC, SDAP and PDCP protocol layers are implemented in the gNB-CU (or en-gNB-CU) and RLC, MAC and physical layer protocol layers are implemented in the gNB unit-DU (or en-gNB-DU). A centralized unit is connected to one or more distributed units via the F1 interface. The gNB-CU and gNB-DU entities can be co-located on the same site or deployed at different sites. Co-location allows a swap of 4G base stations to 5G and ensures compatibility with the eNB entity. Deployment at relocation sites is intended for the virtualization of radio access (C-RAN: Cloud RAN) on COTS (Commercial Off The Shelf) server blades called LW-NFVI (Light-weight Network Function Virtualization Infrastructure) managed by an RIC (RAN Intelligent Controller). Management of virtual machines is carried out by an intelligent controller (NFVM: Network Function Virtualization Management), which is the responsibility of an orchestrator (MANO: NFV MANagement and Orchestration). RIC RAN Intelligent Controller - real time CU-CP CU-UP NFVI Platform : COTS gNB-DU : RLC/MAC/Physical layer : High Layer Level NFVI Platform COTS Radi