sequenceDiagram
participant UE
participant eNB
participant MME
participant AMF
participant SMF
participant gNB
participant UPF
eNB->>MME: ① Handover Required(target=5G)
MME->>AMF: ② Forward Relocation Request(N26)
AMF->>SMF: ③ Create SM Context
SMF->>UPF: ④ N4 Session Establishment
AMF->>gNB: ⑤ Handover Request
gNB-->>AMF: ⑥ Handover Request Ack
AMF-->>MME: ⑦ Forward Relocation Response
MME-->>eNB: ⑧ Handover Command
UE->>gNB: ⑨ 切换到5G
gNB->>AMF: ⑩ Handover Notify
图：4G 到 5G 切换流程概览
3GPP 补充：4G→5G 切换完成后，AMF 需向 UDM 注册，MME 侧的 UE 上下文被释放。EPS 承载映射回 QoS 流。