e information is saved at the upper RLC sublayer and managed with the UE context. Retransmission is also managed at the level of the gNB-CU; it is thus possible to increase the number of terminals connected to the gNB_DU; NG-RAN and 5G-NR - option 4: the RLC protocol and higher layers are located in the gNB-CU, while the MAC protocol, as well as the physical layer, are hosted in the gNB-DU; - option 5 splits the MAC functions and groups the low layer MAC function with the physical layer on the gNB-DU. Thus, the H-ARQ protocol is localized by the gNB-DU, while the scheduler is centralized at the level of the gNB-CU, thus making it possible to improve real-time management of interference between cells (ICIC: Inter-Cell Interference Coordination); - option 6: the MAC protocol and the upper layers are hosted in the gNB-CU, while the physical layer is located in the gNB-DU. As the MAC protocol is centralized, coordination between transmission points is facilitated (COMP JT Joint Transmission); - option 7 splits the physical layer into two parts: physical functionalities of the lower layer are implemented at the level of the gNB-DU; the other radio functionalities of the upper layer, the MAC, RLC, PDCP and RRC protocols are hosted at the gNB-CU level. Interface F1 Centralized Unit Distributed Unit High- High- Option Option Option Option Option Option Option Option Figure 2.8. gNB-CU and gNB-DU functional decomposition options The main goal of gNB decomposition is to reduce the throughput on the eCPRI link. High layer protocols host in the gNB-CU and low layer protocols host in the gNB-DU. The radio signal is reconstructed at the level of the active antenna (F2 interface). The functionalities of the physical layer are split into several primary physical functions to transform the transport block transmitted by the MAC layer into an RF signal transmitted at the level of the antennas. Option 7 is divided into three variants: - variant 7.1: the lower part hosted in the gNB-DU includes the inverse fast Fourier transform (IF