Section: 10.12.1 EN-DC
Content: The Activity Notification function is used to report user plane activity within SN resources. It can either report inactivity or resumption of activity after inactivity was reported. In EN-DC the Activity Reporting is provided from the SN only. The MN may take further actions. EN-DC Activity Notification Figure 10.12.1-1: Support of Activity Notification in EN-DC Support of Activity Notification in EN-DC is used to keep the MN informed about user traffic activity in resources owned by the SN. The MN may take appropriate action upon receiving such notification. 1. The SN informs the MN about user data inactivity of resources owned by the SN. 2. The MN decides to keep SN resources. 3. After a while the SN reports resumption of user plane activity. EN-DC with suspended RRC connection – SCG configuration released in SN The Activity Notification function may be used to enable EN-DC with suspended RRC connected operation. The MN node may decide, after inactivity is reported from the SN and also MN resources show no activity, to send the UE to suspended RRC connection. Resumption to RRC_CONNECTED may take place after activity is reported from the SN for SN terminated bearers. Figure 10.12.1-2: Support of Activity Notification in EN-DC with suspended RRC connection – SCG configuration released in SN Figure 10.12.1-2 shows how Activity Notification function interacts with E-UTRAN functions for suspended RRC connection and SgNB Modification procedures in order to keep the higher layer EN-DC E-UTRAN resources established for UEs in suspended RRC connection, including S1 and X2 interface C-plane, U-plane and bearer contexts established while lower layer MCG and SCG resources are released. E-UTRAN memorises the cell group configuration for MCG in order to apply delta signalling at resume, as specified in TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [4]. After the UE has transited successfully back to RRC_CONNECTED, lower layer SCG resources are established afterwards by means of RRC Connection Reconfiguration. 1. The SN notifies the MN about user data inactivity for SN terminated bearers. 2. The MN decides to send the UE to suspended RRC connection. 3/4. The MN triggers the MN initiated SgNB Modification procedure, requesting the SN to release lower layers. 5. The UE is sent to suspended RRC connection. 6-8. After a period of suspended RRC connection, upon activity notification from the SN, the UE returns to RRC_CONNECTED. 8bis. MN decides whether to reactivate the SN terminated bearers. If (e.g. due to UE mobility), MN decides not to reactivate the SN terminated bearers, it initiates the MN initiated SN release procedure and the procedure ends. 9/10. The MN triggers the MN initiated SgNB Modification procedure to re-establish lower layers. The SN provides configuration data within an SN RRC configuration message. 11-14. The RRC Connection Reconfiguration procedure commences. EN-DC with suspended RRC connection - SCG configuration suspended in SN The Activity Notification function may be used to enable EN-DC with suspended RRC connection operation. The MN node may decide, after inactivity is reported from the SN and also MN resources show no activity, to send the UE to suspended RRC connection, while keeping the SCG configuration. Resumption to RRC_CONNECTED may take place after activity is reported from the SN for SN terminated bearers. Figure 10.12.1-3: Support of Activity Notification in EN-DC with suspended RRC connection - SCG configuration suspended in SN Figure 10.12.1-3 shows how Activity Notification function interacts with functions for suspended RRC connection and SgNB Modification procedures in order to keep the full EN-DC resources established for UEs in suspended RRC connection. When the UE transits successfully back to RRC_CONNECTED, lower layer MCG and SCG configurations are restored or reconfigured by means of RRC Connection Resume. 1. The SN notifies the MN about user data inactivity for SN terminated bearers. 2. The MN decides to send the UE to suspended RRC connection. 3/4. The MN triggers the MN initiated SN Modification procedure, requesting the SN to suspend lower layers. 5. The UE is sent to suspended RRC connection. 6-7. After a period of suspended RRC connection, the MN receives activity notification from the SN. 8. The MN decides whether to reactivate the SN terminated bearers. If (e.g. due to UE mobility), the MN decides not to reactivate the SN terminated bearers, it initiates the MN initiated SN release procedure, rather than the MN initiated SN modification procedure in steps 9/10. If the MN decides to return the UE to RRC_CONNECTED, the network triggered state transition from suspended RRC connection to RRC_CONNECTED commences. 9/10. The MN triggers the MN initiated SN Modification procedure to resume the SCG lower layers. If the SCG configuration needs to be updated, the SN provides the configuration data within an SN RRC configuration message. 11/12. The UE is instructed to resume both the MCG and the SCG. If the SCG configuration is to be updated, the new configuration is provided in the RRCConnectionResume message. 13. The MN informs the SN that the UE has completed the reconfiguration procedure successfully, via the SgNB Reconfiguration Complete message, including the SN RRC response message, if received from the UE. 14. The UE performs synchronisation towards the PSCell of the SN.