# 25/08/2022 Trace the OAI source code and use figures and flowchart to describe the following questions: How does OAI DU handle gNB CU Configuration Update? How does OAI DU generate gNB CU Configuration Update Ack? :::success **References** - [5G Wikipedia](https://wiki.patras5g.eu/radio-equipment/g-node-bs) - [How it works](https://www.etsi.org/deliver/etsi_TS/138400_138499/138473/15.03.00_60/ts_138473v150300p.pdf) ::: - ![](https://imgur.com/r9VKBEH.png) # How does OAI DU handle gNB CU Configuration Update? The purpose of the gNB-CU Configuration Update procedure is to update application level configuration data needed for the gNB-DU and gNB-CU to interoperate correctly on the F1 interface. This procedure does not affect existing UE-related contexts, if any. The procedure uses non-UE associated signalling. - ![](https://imgur.com/u5przoz.png) # How does OAI DU generate gNB CU Configuration Update Ack? The gNB-CU initiates the procedure by sending a GNB-CU CONFIGURATION UPDATE message including the appropriate updated configuration data to the gNB-DU. The gNB-DU responds with a GNB-CU CONFIGURATION UPDATE ACKNOWLEDGE message to acknowledge that it successfully updated the configuration data. If an information element is not included in the GNB-CU CONFIGURATION UPDATE message, the gNB-DU shall interpret that the corresponding configuration data is not changed and shall continue to operate the F1-C interface with the existing related configuration data. The updated configuration data shall be stored in the respective node and used as long as there is an operational TNL association or until any further update is performed. If Cells to be Activated List Item IE is contained in the GNB-CU CONFIGURATION UPDATE message, the gNB-DU shall activate the cell indicated by NR CGI IE and reconfigure the physical cell identity for which the NR PCI IE is included. If Cells to be Deactivated List Item IE is contained in the GNB-CU CONFIGURATION UPDATE message, the gNB-DU shall deactivate the cell indicated by NR CGI IE. If Cells to be Activated List Item IE is contained in the GNB-CU CONFIGURATION UPDATE message and the indicated cells are already activated, the gNB-DU shall update the cell information received in Cells to be Activated List Item IE. If Cells to be Activated List Item IE is included in the GNB-CU CONFIGURATION UPDATE message, and the information for the cell indicated by the NR CGI IE includes the IAB Info IAB-donor-CU IE, the gNB-DU shall, if supported, apply the IAB STC Info IE therein to the indicated cell. If the gNB-CU System Information IE is contained in the gNB-CU CONFIGURATION UPDATE message, the gNB-DU shall include the Dedicated SI Delivery Needed UE List IE in the GNB-CU CONFIGURATION UPDATE ACKNOWLEDGE message for UEs that are unable to receive system information from broadcast. If Dedicated SI Delivery Needed UE List IE is contained in the GNB-CU CONFIGURATION UPDATE ACKNOWLEDGE message, the gNB-CU should take it into account when informing the UE of the updated system information via the dedicated RRC message. If the gNB-CU TNL Association To Add List IE is contained in the gNB-CU CONFIGURATION UPDATE message, the gNB-DU shall, if supported, use it to establish the TNL association(s) with the gNB-CU. The gNB-DU shall report to the gNB-CU, in the gNB-CU CONFIGURATION UPDATE ACKNOWLEDGE message, the successful establishment of the TNL association(s) with the gNB-CU as follows: A list of TNL address(es) with which the gNB-DU successfully established the TNL association shall be included in the gNB-CU TNL Association Setup List IE; A list of TNL address(es) with which the gNB-DU failed to establish the TNL association shall be included in the gNB-CU TNL Association Failed To Setup List IE. If the GNB-CU CONFIGURATION UPDATE message includes gNB-CU TNL Association To Remove List IE, and the Endpoint IP address IE and the Port Number IE for both TNL endpoints of the TNL association(s) are included in the gNB-CU TNL Association To Remove List IE, the gNB-DU shall, if supported, initiate removal of the TNL association(s) indicated by both received TNL endpoints towards the gNB-CU. If the Endpoint IP address IE, or the Endpoint IP address IE and the Port Number IE for one or both of the TNL endpoints is included in the gNB-CU TNL Association To Remove List IE, the gNB-DU shall, if supported, initiate removal of the TNL association(s) indicated by the received endpoint IP address(es). If the gNB-CU TNL Association To Update List IE is contained in the gNB-CU CONFIGURATION UPDATE message the gNB-DU shall, if supported, overwrite the previously stored information for the related TNL Association(s). If in the gNB-CU CONFIGURATION UPDATE message the TNL Association usage IE is included in the gNB-CU TNL Association To Add List IE or the gNB-CU TNL Association To Update List IE, the gNB-DU node shall, if supported, use it as described. For NG-RAN, the gNB-CU shall include the gNB-CU System Information IE in the GNB-CU CONFIGURATION UPDATE message. The SIB type to Be Updated List IE shall contain the full list of SIBs to be broadcast. If Protected E-UTRA Resources List IE is contained in the GNB-CU CONFIGURATION UPDATE message, the gNB-DU shall protect the corresponding resource of the cells indicated by E-UTRA Cells List IE for spectrum sharing between E-UTRA and NR. If the GNB-CU CONFIGURATION UPDATE message contains the Protected E-UTRA Resource Indication IE, the receiving gNB-DU should forward it to lower layers and use it for cell-level resource coordination. The gNB-DU shall consider the received Protected E-UTRA Resource Indication IE when expressing its desired resource allocation during gNB-DU Resource Coordination procedure. The gNB-DU shall consider the received Protected E-UTRA Resource Indication IE content valid until reception of a new update of the IE for the same gNB-DU. If Available PLMN List IE, and optionally also Extended Available PLMN List IE, is contained in GNB-CU CONFIGURATION UPDATE message, the gNB-DU shall overwrite the whole available PLMN list and update the corresponding system information. If Available SNPN ID List IE is contained in GNB-CU CONFIGURATION UPDATE message, the gNB-DU shall overwrite the whole available SNPN ID list and update the corresponding system information. If Cells Failed to be Activated Item IE is contained in the GNB-CU CONFIGURATION UPDATE ACKNOWLEDGE message, the gNB-CU shall consider that the indicated cells are out-of-service as defined. If the Neighbour Cell Information List IE is present in the GNB-CU CONFIGURATION UPDATE message, the receiving gNB-DU shall use the received information for Cross Link Interference management and/or NR-DC power coordination. The gNB-DU shall consider the received Neighbour Cell Information List IE content valid until reception of an update of the IE for the same cell(s). If the Intended TDD DL-UL Configuration NR IE is absent from the Neighbour Cell Information List IE, whereas the corresponding NR CGI IE is present, the receiving gNB-DU shall remove the previously stored Neighbour Cell Information IE corresponding to the NR CGI. If the GNB-CU CONFIGURATION UPDATE message includes Transport Layer Address Info IE, the gNB-DU shall, if supported, take into account for IPSec tunnel establishment. If the GNB-CU CONFIGURATION UPDATE ACKNOWLEDGE message includes Transport Layer Address Info IE, the gNB-CU shall, if supported, take into account for IPSec tunnel establishment. If the GNB-CU CONFIGURATION UPDATE message contains the Uplink BH Non-UP Traffic Mapping IE, the gNB-DU shall, if supported, consider the information therein for mapping of non-UP uplink traffic. If the IAB Barred IE is included in the GNB-CU CONFIGURATION UPDATE message, the gNB-DU shall, if supported, consider it as an indication of whether the cell allows IAB-node access or not.