Section: 8.5 F1 Startup and cells activation
Content: This function allows to setup the F1 interface between a gNB-DU and a gNB-CU and it allows to activate the gNB-DU cells. Figure 8.5-1: F1 startup and cell activation 0. The gNB-DU and its cells are configured by OAM in the F1 pre-operational state. The gNB-DU has TNL connectivity toward the gNB-CU. 1. The gNB-DU sends an F1 SETUP REQUEST message to the gNB-CU including a list of cells that are configured and ready to be activated. For each cell supporting NPN the gNB-DU includes NPN specific information. 2. In NG-RAN, the gNB-CU ensures the connectivity toward the core network. For this reason, the gNB-CU may initiate either the NG Setup or the gNB Configuration Update procedure towards 5GC. 3. The gNB-CU sends an F1 SETUP RESPONSE message to the gNB-DU that optionally includes a list of cells to be activated. The cells in the list of cells to be activated in F1 SETUP RESPONSE message become active, while the cells not in the list are inactive. The cells that are active are Out-of-Service until the gNB-DU indicates that they are In-Service . The gNB-DU will initiate the gNB-DU Configuration Update procedure towards the gNB-CU and includes the cell(s) that are In-Service and/or the cell(s) that are Out-Of-Service. The gNB-DU may also indicate cell(s) to be deleted, in which case the gNB-CU removes the corresponding cell(s) information. 4. The gNB-CU may send a GNB CU CONFIGURATION UPDATE message to the gNB-DU that optionally includes a list of cells to be activated, e.g., in case that these cells were not activated using the F1 SETUP RESPONSE message. 5. The gNB-DU replies with a GNB CU CONFIGURATION UPDATE ACKNOWLEDGE message that optionally includes a list of cells that failed to be activated. The gNB-CU regards all Active cells as Out-Of-Service until the gNB-DU indicates that they are In-Service. 6. The gNB-CU may initiate either the Xn Setup towards a neighbour NG-RAN node or the EN-DC X2 Setup procedure towards a neighbour eNB. NOTE 1: For NG-RAN in case that the F1 SETUP RESPONSE message is not used to activate any cell, step 2 may be performed after step 3. Over the F1 interface between a gNB-CU and a gNB-DU pair, the following two Cell States are possible: - Inactive: the cell is known by both the gNB-DU and the gNB-CU. The cell shall not serve UEs; - Active: the cell is known by both the gNB-DU and the gNB-CU. The cell should try to provide services to the UEs. The gNB-CU decides whether the Cell State should be “Inactive“ or “Active“. The gNB-CU can request the gNB-DU to change the Cell State using the F1 SETUP RESPONSE, theGNB DU CONFIGURATION UPDATE ACKNOWLEDGE, or the GNB CU CONFIGURATION UPDATE messages. The gNB-DU reports to the gNB-CU the Service Status. The Service Status is the state of the radio transmission over the air. The Service Status is reported by the gNB-DU for cells for which the Cell State is “Active “. The following Service Status are defined: - In-Service: the cell is operational and able to serve UEs. - Out-Of-Service: the cell is not operational, and it is not able to serve UEs. The gNB-DU is trying to make the cell operational. The gNB-DU reports the Service Status using the GNB DU CONFIGURATION UPDATE message. NOTE 2: If gNB-DU regards that one or more cells cannot become operational, the gNB-DU deletes them and reports them using the GNB DU CONFIGURATION UPDATE message.