o Unit : Low Layer Level Figure 2.6. Virtualization of radio access The NG-RAN architecture offers two possible deployments: a non-centralized architecture and a centralized architecture. NG-RAN Network - Protocol Architecture Figure 2.7. NG-RAN architecture: distributed and centralized The non-centralized architecture allows evolution continuity of the radio access network through a swap. Each gNB entity can interconnect other gNB or ng-eNB entities via the Xn interface. The centralized architecture allows the implementation of the CoMP (Cooperation Multi-Point) coordination mechanism by synchronously controlling several gNB-DUs. The functional decomposition between gNB-DU and gNB-CU is also flexible. The eCPRI protocol offers several possible decompositions: - option 1 is similar to the 5G-NSA dual connectivity architecture. For this option, the RRC and SDAP protocols are hosted in the gNB-CU, while the PDCP, RLC, MAC and physical layer protocols are localized by the gNB-DU. This option allows centralization of the management of the radio interface via the RRC protocol, and the separation of the medium (split-bearer) is managed at the level of the distributed units; - option 2 has similarities with the Xn interface for the user plane. For the control plane, the RRC and PDCP protocols are hosted at the centralized gNB-CU and the RLC, MAC and physical layer protocols are located at the gNB-DU level. This option allows traffic aggregation between 4G and 5G base stations; - option 3 divides the RLC protocol into two parts: the RLC high layer manages the message acknowledgment function (ARQ) and the low function layer manages the segmentation of packets. The gNB-CU entity hosts the RRC and PDCP protocols and manages the higher functions of the RLC (RLC-high) protocols. The gNB-DU entity manages the lower functions of the lower RLC protocol (RLC-low), MAC and the physical layer. This option allows the aggregation of traffic between 4G radio access and 5G radio access and load balancing between the two nodes. RLC stat