the target gNB and to establish an NG-C interface instance toward the target gNB. The message also carries the list of PDU sessions to be switched and the list of PDU sessions which failed to set up at the target gNB. 10. 5GC switches the downlink data path toward the target gNB. 11. The AMF confirms the Path Switch Request message with the Path Switch Request Acknowledge NG-AP message. The message carries the list of PDU sessions that have been switched and the list of PDU sessions to be released. 12. Upon reception of the NG-AP Path Switch Request Acknowledge message from the AMF, the target gNB sends the UE Context Release Xn-AP message to the source gNB, which can then release resources associated with the UE. 3.3.4.1.3 Mobility in Inactive State In the inactive state described in Section 3.4, a UE remains connected from the 5GC per- spective and can move within a RAN-based Notification Area (RNA) without notifying the network. The last serving gNB (who sent the UE into the inactive state) keeps the UE context and the UE-associated NG connection with the serving AMF and UPF. In order to send or receive data, a UE has to transition from inactive state to connected. This can be triggered by the network using paging or initiated by a UE. Two Xn procedures have been defined to support the inactive state: RAN paging Retrieve UE Context Request/Response/Failure. The usage of UE context retrieval functionality can be illustrated by the UE initiated inactive to connected mode transition, shown in Figure 3.3.8. 3 5G System Overview Last Serving gNB AMF 0. UEinRRC_INACTIVE CM-CONNECTED 1. RRC Resume Request 2. RETRIEVE UE CONTEXT REQUEST 3. RETRIEVE UE CONTEXT RESPONSE 4. RRC Resume UEinRRC_CONNECTED CM-CONNECTED 5. RRC ResumeComplete 6. Xn-UADDRESS INDICATION 7. PATH SWITCH REQUEST 8. PATH SWITCH REQUEST RESPONSE 9. UE CONTEXT RELEASE Figure 3.3.8 UE-triggered transition from inactive to connected state. (Source: Reproduced by permission of © 3GPP). 0. A UE is in RRC_INACTIVE, it has the information about previously e