call flow involving the F1 Setup and the Configuration Update procedures, shown in Figure 4.2.4. We then focus on the detailed description of the F1 Setup message and we gNB-DU gNB-CU gNB/eNB 0. Pre-operational state 1. F1 Setup Request 2. NG Setup/gNB Configuration Update 3. F1 Setup Response 4. gNB-CU Configuration Update 5. gNB-CU Configuration Update Ack 6. Xn/X2 Setup Figure 4.2.4 F1 startup and cell activation. (Source: Reproduced by permission of © 3GPP). 4 NG-RAN Architecture encourage the reader to study further details about F1 maintenance procedures in 3GPP TS 38.473. 0. At the beginning, basic information is assumed to be preconfigured by the OAM in a gNB-DU (e.g. a gNB-CU TNL address, list of cells, etc.) and in a gNB-CU (e.g. an AMF TNL address, list of PLMNs, etc.). 1. The gNB-DU initiates the setup procedure by sending the F1 Setup Request message to the gNB-CU, carrying the following information: gNB-DU ID, Name, RRC version, and a list of cells (with relevant information, e.g. frequency, bandwidth, etc.). 2. Optionally, a gNB-CU performs ether an NG Setup or gNB Configuration Update proce- dure with the AMF (in most cases, this should not be needed, as the NG interface would be operational already). 3. If the gNB-CU accepts the request, it replies with the F1 Setup Response message, carry- ing the following information: gNB-CU Name, RRC version, and a list of cells to activate. 4. During the F1 interface lifetime, both the gNB-CU and the gNB-DU may notify each other about the change in their configuration or operational state, using gNB-CU/gNB-DU Configuration Update procedures. 5. If the receiving node accepts the new configuration, it replies with gNB-CU/gNB-DU Configuration Update Acknowledge (or Configuration Update Failure otherwise). 6. Optionally, the gNB-CU performs the Xn Setup procedure (in most cases, this should not be needed, as the Xn interface would be operational already). The F1 Setup Request message, which is the first message sent by a gNB-DU on a newly established F1 interfac