Section: 10.7.1 EN-DC
Content: Inter-Master Node handover with/without MN initiated Secondary Node change is used to transfer context data from a source MN to a target MN while the context at the SN is kept or moved to another SN. During an Inter-Master Node handover, the target MN decides whether to keep or change the SN (or release the SN, as described in clause 10.8). NOTE 1: Void. Figure 10.7.1-1: Inter-MN handover with/without MN initiated SN change Figure 10.7.1-1 shows an example signaling flow for inter-Master Node handover with or without MN initiated Secondary Node change: NOTE 2: For an inter-Master Node handover without Secondary Node change, the source SN and the target SN shown in Figure 10.7.1-1 are the same node. 1. The source MN starts the handover procedure by initiating the X2 Handover Preparation procedure including both MCG and SCG configuration. The source MN includes the (source) SN UE X2AP ID, SN ID and the UE context in the (source) SN in the Handover Request message. NOTE 3: The source MN may trigger the MN-initiated SN Modification procedure (to the source SN) to retrieve the current SCG configuration before step 1. 2. If the target MN decides to keep the UE context in SN, the target MN sends SgNB Addition Request to the SN including the SN UE X2AP ID as a reference to the UE context in the SN that was established by the source MN. If the target MN decides to change the SN allowing delta configuration, the target MN sends the SgNB Addition Request to the target SN including the UE context in the source SN that was established by the source MN. Otherwise, the target MN may send the SgNB Addition Request to the target SN including neither the SN UE X2AP ID nor the UE context in the source SN that was established by the source MN. 3. The (target) SN replies with SgNB Addition Request Acknowledge. The (target) SN may include the indication of the full or delta RRC configuration. NOTE 3a: In case the target SN includes the indication of the full RRC configuration, the MN performs release of the SN terminated radio bearer configuration and release and add of the NR SCG configuration part towards the UE. NOTE 3b: Void. 4. The target MN includes within the Handover Request Acknowledge message a transparent container to be sent to the UE as an RRC message to perform the handover, and may also provide forwarding addresses to the source MN. The target MN indicates to the source MN that the UE context in the SN is kept if the target MN and the SN decided to keep the UE context in the SN in step 2 and step 3. 5. The source MN sends SgNB Release Request to the (source) SN including a Cause indicating MCG mobility. The (source) SN acknowledges the release request. The source MN indicates to the (source) SN that the UE context in SN is kept, if it receives the indication from the target MN. If the indication as the UE context kept in SN is included, the SN keeps the UE context. 6. The source MN triggers the UE to apply the new configuration. 7/8. The UE synchronizes to the target MN and replies with RRCConnectionReconfigurationComplete message. 9. If configured with bearers requiring SCG radio resources, the UE synchronizes to the (target) SN. NOTE 3b1: The order the UE performs Random Access towards the MN (step 7) and performs the Random Access procedure towards the SN (step 9) is not defined. 10. If the RRC connection reconfiguration procedure was successful, the target MN informs the (target) SN via SgNB Reconfiguration Complete message. 11a. The SN sends the Secondary RAT Data Usage Report message to the source MN and includes the data volumes delivered to and received from the UE over the NR radio for the related E-RABs. NOTE 4: The order the source SN sends the Secondary RAT Data Usage Report message and performs data forwarding with MN/target SN is not defined. The SgNB may send the report when the transmission of the related bearer is stopped. 11b. The source MN sends the Secondary RAT Report message to MME to provide information on the used NR resource. 12. For bearers using RLC AM, the source MN sends the SN Status Transfer message, including, if needed, SN Status received from the source SN to the target MN. The target forwards the SN Status to the target SN, if needed. 13. If applicable, data forwarding takes place from the source side. If the SN is kept, data forwarding may be omitted for SN-terminated bearers kept in the SN. 14-17. The target MN initiates the S1 Path Switch procedure. NOTE 5: If new UL TEIDs of the S-GW are included, the target MN performs the MN initiated SN Modification procedure to provide them to the SN. 18. The target MN initiates the UE Context Release procedure towards the source MN. 19. Upon reception of the UE Context Release message, the (source) SN releases C-plane related resources associated to the UE context towards the source MN. Any ongoing data forwarding may continue. The SN shall not release the UE context associated with the target MN if the UE context kept indication was included in the SgNB Release Request message in step 5.