e list of supported cells, etc.). These procedures are: F1 Setup gNB-DU/gNB-CU Configuration Update gNB-DU Resource Coordination gNB-DU Status Indication Reset and Error Indication. Once a TNL association between a gNB-DU and gNB-CU becomes operational, the F1 Setup procedure must be initiated by the gNB-DU. As it is expected that new gNB-DUs can be added (e.g. to extend coverage and/or to add capacity) when the network is operational, it is the gNB-DU that initiates the interface setup by sending the F1 Setup Request message, rather than a gNB-CU. The F1 Setup message contains information about cells supported by the gNB-DU and its RRC version. In the normal F1 Setup scenario, when the gNB-CU accepts the request, 4 NG-RAN Architecture it responds with an F1 Setup Response message carrying the indication of which cells the gNB-CU requests the gNB-DU to activate, list of Public Land Mobile Networks (PLMNs) supported (which is important for RAN sharing between operator deployments), and gNB-CU's RRC version. The RRC version information is exchanged to ensure that both network nodes support the same version. This is important because, as mentioned above, the layer separation model in which RRC resides in the gNB-CU is not perfect. One such example is the case when a gNB-DU may trigger the RRC Reconfiguration procedure for a UE to be performed by the gNB-CU. If a gNB-CU cannot accept the setup request, for example due to RRC version mismatch or overload, it may also respond with a F1 Setup Failure message. If the issue is expected to be resolved automatically within a certain period of time, a gNB-CU may include the "time to wait" indication in the F1 Setup Failure message, during which a gNB-DU is not allowed to reattempt the setup. After the F1 Setup procedure is completed successfully, the gNB-DU is considered operational and can serve UEs. It is implicitly assumed in the setup procedure described here that certain information, such as a list of supported cells and PLMNs, is preconfigured in a gNB-DU and a gNB-CU 