The error indication function is used by the gNB-CU-UP or gNB-CU-CP to indicate to the gNB-CU-CP or gNB-CU-UP that an error has occurred. The reset function is used to initialize the peer entity after node setup and after a failure event occurred. This procedure can be used by both the gNB-CU-UP and the gNB-CU-CP. The E1 setup function allows to exchange application level data needed for the gNB-CU-UP and gNB-CU-CP to interoperate correctly on the E1 interface. The E1 setup is initiated by both the gNB-CU-UP and gNB-CU-CP. The gNB-CU-UP Configuration Update and gNB-CU-CP Configuration Update functions allow to update application level configuration data needed between the gNB-CU-CP and the gNB-CU-UP to interoperate correctly over the E1 interface. The E1 setup and gNB-CU-UP Configuration Update functions allow to inform NR CGI(s), S-NSSAI(s), PLMN-ID(s), QoS information and NID(s) supported by the gNB-CU-UP. The E1 setup and gNB-CU-UP Configuration Update functions allow the gNB-CU-UP to signal its capacity information to the gNB-CU-CP. The E1 gNB-CU-UP Status Indication function allows to inform the overloaded or non-overloaded status over the E1 interface.

The establishment of the E1 bearer context is initiated by the gNB-CU-CP and accepted or rejected by the gNB-CU-UP based on admission control criteria (e.g., resource not available). The modification of the E1 bearer context can be initiated by either gNB-CU-CP or gNB-CU-UP. The receiving node can accept or reject the modification. The E1 bearer context management function also supports the release of the bearer context previously established in the gNB-CU-UP. The release of the bearer context is triggered by the gNB-CU-CP either directly or following a request received from the gNB-CU-UP. This function is used to setup and modify the QoS-flow to DRB mapping configuration. The gNB-CU-CP decides flow-to-DRB mapping and provides the generated SDAP and PDCP configuration to the gNB-CU-UP. The gNB-CU-CP also decides the Reflective QoS flow to DRB mapping. The function is also used to send to the gNB-CU-UP the alternative QoS Parameters Sets when available for a QoS flow. For each PDU Session Resource to be setup or modified, the S-NSSAI, shall be provided in the E1 bearer context setup procedure and may be provided in the E1 bearer context modification procedure by gNB-CU-CP to the gNB-CU-UP. This function is used for the gNB-CU-CP to send the security information to the gNB-CU-UP. This function is used for the gNB-CU-CP to send the parameters for header compression for certain traffic types e.g. IP, Ethernet to the gNB-CU-UP. This function is used for the gNB-CU-UP to notify the event of DL data arrival detection to the gNB-CU-CP. With this function, the gNB-CU-UP requests gNB-CU-CP to trigger paging procedure over F1 or Xn to support RRC Inactive state. This function is used for the gNB-CU-UP to notify the gNB-CU-CP that an UL packet including a QFI value in the SDAP header not configured by the Flow Mapping Information IE is received for the first time at the default DRB. The gNB-CU-CP can take further action if needed. This function is used for the gNB-CU-UP to notify the event of user inactivity to the gNB-CU-CP. With this function, the gNB-CU-UP indicates that the inactivity timer associated with a bearer, a PDU session or a UE expires, or that user data is received for the bearer, the PDU session or the UE whose inactivity timer has expired. The gNB-CU-CP consolidates all the serving gNB-CU-UPs for the UE and takes further action. This function is used for the gNB-CU-UP to report data volume to the gNB-CU-CP. This function is used for the gNB-CU-CP to notify the suspension and resumption of bearer contexts to the gNB-CU-UP. This function also allows to support CA based packet duplication as described in TS 38.300, i.e. one data radio bearer should be configured with at least two GTP-U tunnels between gNB-CU-UP and a gNB-DU. This function is used to support the enhanced mobility operations as described in TS 38.300 in the gNB-CU-UP.

The Trace function provides means to control trace sessions for a UE over E1 interface.