24/08/2022 - HackMD

# 24/08/2022 When you run OAI CU, it will first stop at ‘Entering ITTI signals handler’ waiting for connection to the OAI DU. This is related to F1 Setup Procedure betwen OAI DU and OAI CU (see this reference). It will wait for F1 Setup Request to be sent from OAI DU? What function triggers ‘[F1AP] DU Task Received F1AP_SETUP_REQ’? How does OAI DU generate F1 Setup Request message to be sent? How does OAI DU sent F1 Setup Request to OAI CU? How does OAI DU handle F1 Setup Request from OAI CU? :::success **References** - [How it works!](https://gitlab.flux.utah.edu/powder-mirror/openairinterface5g/-/blob/develop/doc/F1-design.md) - [5G(NR)-F1 Setup Procedure](https://www.5gfundamental.com/2021/04/5gnr-f1-setup-procedure.html) - [5G Wikipedia](https://wiki.patras5g.eu/radio-equipment/g-node-bs) - [Practical an example](https://codeantenna.com/a/UA432o36V7) ::: # What function triggers ‘[F1AP] DU Task Received F1AP_SETUP_REQ’? F1AP incoming messages SCTP tasks sends a ITTI message SCTP_DATA_IND to the CU task. A array of functions pointers and the F1AP standard identifier "procedureCode", the CU calls the appropriate function Hereafter the most significant messages processing CU_handle_F1_SETUP_REQUEST Transcodes information to the same message toward RRC (F1AP_SETUP_REQ) CU_handle_INITIAL_UL_RRC_MESSAGE_TRANSFER Transcodes information to the same message toward RRC (NR_RRC_MAC_CCCH_DATA_IND) CU_handle_UL_RRC_MESSAGE_TRANSFER Encode and send data to PDCP (calling pdcp_data_ind ()) for processing UL data. # How does OAI DU generate F1 Setup Request message to be sent? The task "gNB app" after rzading the configuration file, sends a first message F1AP_SETUP_REQ to DU task Using this message, the uniq DU task (Linux Thread) creates a DU instance context memory space, calls SCTP task to create a socket to the CU. # How does OAI DU sent F1 Setup Request to OAI CU? The task "gNB app" after rzading the configuration file, sends a first message F1AP_SETUP_REQ to DU task Using this message, the uniq DU task (Linux Thread) creates a DU instance context memory space, calls SCTP task to create a socket to the CU. When it receives from the SCTP task the socket creation success, the DU task encodes+sends the F1 setup message to the CU. # How does OAI DU handle F1 Setup Request from OAI CU? - ![](https://imgur.com/sIgJJzL.png) The gNB-DU initiates the procedure by sending a F1 SETUP REQUEST message including the appropriate data to the gNB-CU. The gNB-CU responds with a F1 SETUP RESPONSE message including the appropriate data. If the F1 SETUP REQUEST message contains the gNB-DU Name IE the gNB-CU may use this IE as a human readable name of the gNB-DU. # When you run OAI CU, it will first stop at ‘Entering ITTI signals handler’ waiting for connection to the OAI DU. This is related to F1 Setup Procedure betwen OAI DU and OAI CU (see this reference). It will wait for F1 Setup Request to be sent from OAI DU? The purpose of the F1 Setup procedure is to exchange application level data needed for the gNB-DU and the gNB-CU to correctly interoperate on the F1 interface. This procedure shall be the first F1AP procedure triggered after a TNL association has become operational. The procedure uses non-UE associated signalling, it is cell related procedure. This procedure erases any existing application level configuration data in the two nodes and replaces it by the one received. This procedure also re-initialises the F1AP UE-related contexts (if any) and erases all related signalling connections in the two nodes like a Reset procedure would do. The gNB-DU initiates the procedure by sending a F1 SETUP REQUEST message including the appropriate data to the gNB-CU. The gNB-CU responds with a F1 SETUP RESPONSE message including the appropriate data. If the F1 SETUP REQUEST message contains the gNB-DU Name IE the gNB-CU may use this IE as a human readable name of the gNB-DU. For NG-RAN, the gNB-DU shall include the gNB-DU System Information IE and the TAI Slice Support List IE. The gNB-CU may include the Cells to be Activated List IE in the F1 SETUP RESPONSE message. The Cells to be Activated List IE includes a list of cells that the gNB-CU requests the gNB-DU to activate. The gNB-DU shall activate the cells included in the Cells to be Activated List IE and reconfigure the physical cell identity for cells for which the NR PCI IE is included. For NG-RAN, the gNB-CU shall include the gNB-CU System Information IE in the F1 SETUP RESPONSE message. The exchanged data shall be stored in respective node and used as long as there is an operational TNL association. When this procedure is finished, the F1 interface is operational and other F1 messages may be exchanged. For NG-RAN, the gNB-DU may include the RAN Area Code IE in the F1 SETUP REQUEST message. The gNB-CU may use it according to TS. Procedure Code: every message has its procedure code, so that, that can be identified their class and message type by other nodes. Type of Message: The Type can be Initiating Message, Successful Outcome, Unsuccessful Outcome. it is selected by sending node. # Transaction ID The Transaction ID IE uniquely identifies a procedure among all ongoing parallel procedures of the same type initiated by the same protocol peer. Messages belonging to the same procedure shall use the same Transaction ID. The Transaction ID is determined by the initiating peer of a procedure.