e NG-RAN Node Configuration Update procedure. Additionally, this procedure can be used to add, remove, and modify additional SCTP endpoints, which is used when new computa- tional resources are added or removed in virtualized NG-RAN. The Xn interface also supports switching off and on cells for energy-saving reasons. When a gNB decides to switch off a cell (e.g. because there are no UEs to serve), it indicates SO using the Deactivation Indication IE in the NG-RAN Node Configuration Update messages. A neighbor node may request to turn that cell on using a different message - Cell Activation Request. As for NG, Xn interface management messages use non-UE-associated signaling. 3.3.4.1.2 Connected Mode Mobility We first describe the Xn-C support for connected mode mobility, which is performed using the following messages: Handover preparation Handover Request Handover Request Acknowledge Handover Preparation Failure Handover execution SN Status Transfer Handover completion UE Context Release. 3 5G System Overview Source gNB Target gNB UPF(s) User Data User Data 0. Mobility control information provided by AMF Measurement Control and Reports 2. Handover Decision 3. HANDOVER REQUEST 4. Admission Control 5. HANDOVER REQUEST ACKNOWLEDGE 6. RAN Hand over Initiation 7. SN STATUS TRANSFER Detach from old cell Synchronize to new cell Deliver buffered data and new data from UPF(s) User Data Buffer User Data from Source gNB 8. RAN Handover Completion User Data User Data 9. PATH SWITCH REQUEST 10. Path Switchin UPF(s) End Marker User Data 11. PATH SWITCH REQUEST ACKNOWLEDGE 12. UECONTEXT RELEASE Figure 3.3.7 Xn handover. (Source: Reproduced by permission of © 3GPP). The usage of these procedures can be illustrated by the call flow example shown in Figure 3.3.7. Note that the procedure also uses some NG messages. 0. The UE is in RRC_CONNECTED, sending and receiving uplink and downlink data; the source gNB has the UE context, which contains information that may affect UE mobility decisions, such as mobility restrictions, radio cap