5G去注册(Deregistration)信令流四场景全链拆解

flowchart TD
    A[去注册触发] --> B{发起方?}
    B -->|UE| C[UE-Initiated Deregistration]
    B -->|AMF| D[AMF-Initiated Deregistration]
    B -->|UDM| E[UDM-Initiated Deregistration]
    B -->|Timer| F[Implicit Deregistration]

    C --> C1[关机/飞行模式]
    C --> C2[切换到EPS]
    C --> C3[USIM移除]

    D --> D1[O&M干预]
    D --> D2[AMF过载控制]
    D --> D3[负载重平衡 re-registration required]

    E --> E1[签约终止]
    E --> E2[Subscription Withdrawal]

    F --> F1[Mobile Reachable Timer超时]
    F --> F2[Implicit Deregistration Timer超时]

    C1 & C2 & C3 --> G[AMF释放PDU Session]
    D1 & D2 & D3 --> G
    E1 & E2 --> H[AMF收到Nudm_UECM_DeregistrationNotification]
    F1 & F2 --> I[AMF本地删除MM Context]

    G --> J[UDM注销 + N2释放]
    H --> D
    I --> J

stateDiagram-v2
    [*] --> 5GMM_DEREGISTERED : UE开机/未注册
    5GMM_DEREGISTERED --> 5GMM_REGISTERED : Registration成功
    5GMM_REGISTERED --> 5GMM_DEREGISTERED : Deregistration流程

    state 5GMM_REGISTERED {
        [*] --> CM_IDLE
        CM_IDLE --> CM_CONNECTED : Service Request / Paging
        CM_CONNECTED --> CM_IDLE : N2 Release / UE进入Idle
    }

    state 5GMM_DEREGISTERED {
        [*] --> PLMN_SEARCH
        PLMN_SEARCH --> INITIAL_REG : 选择新PLMN
    }

sequenceDiagram
    participant UE
    participant RAN as NG-RAN
    participant AMF
    participant SMF
    participant UDM
    participant UPF
    participant PCF

    Note over UE: 用户关机/飞行模式触发
    UE->>RAN: NAS Deregistration Request<br/>(5G-GUTI, Deregistration type=switch-off,<br/>Access type=3GPP)
    RAN->>AMF: N2 Uplink NAS Transport<br/>(NAS PDU, User Location Info)

    Note over AMF: 检查Deregistration type<br/>switch-off: 不需要回复Accept

    loop 每个PDU Session
        AMF->>SMF: Nsmf_PDUSession_Release_SMContext<br/>(SUPI, PDU Session ID, cause)
        SMF->>UPF: N4 Session Release Request
        UPF-->>SMF: N4 Session Release Response
        SMF->>PCF: Npcf_SMPolicyControl_Delete<br/>(释放策略关联)
        PCF-->>SMF: 200 OK
        SMF-->>AMF: Nsmf_PDUSession_Release_SMContext Response
    end

    AMF->>UDM: Nudm_SDM_Unsubscribe<br/>(取消订阅数据变更通知)
    UDM-->>AMF: 204 No Content

    AMF->>UDM: Nudm_UECM_Deregistration<br/>(SUPI, AMF ID)
    UDM-->>AMF: 200 OK<br/>(UDM删除AMF注册记录)

    Note over AMF: switch-off场景<br/>不发送Deregistration Accept

    AMF->>RAN: N2 UE Context Release Command<br/>(cause, NAS PDU可选)
    RAN-->>AMF: N2 UE Context Release Complete
    RAN->>UE: RRC Release（如果UE仍在线）

    Note over UE,AMF: 去注册完成，UE进入5GMM-DEREGISTERED

sequenceDiagram
    participant OAM as O&M/PCF
    participant AMF
    participant RAN as NG-RAN
    participant UE
    participant SMF
    participant UDM

    OAM->>AMF: 触发去注册<br/>(O&M命令/策略变更)
    Note over AMF: AMF决定去注册UE<br/>Deregistration type=<br/>re-registration required

    alt UE处于CM-CONNECTED
        AMF->>RAN: N2 Downlink NAS Transport<br/>(NAS: Deregistration Request)
        RAN->>UE: RRC DLInformationTransfer<br/>(携带NAS PDU)
    else UE处于CM-IDLE
        AMF->>RAN: N2 Paging（触发UE进入CONNECTED）
        RAN->>UE: Paging
        UE->>RAN: Service Request
        RAN->>AMF: N2 Uplink NAS Transport
        AMF->>RAN: N2 Downlink NAS Transport<br/>(NAS: Deregistration Request)
        RAN->>UE: RRC DLInformationTransfer
    end

    UE->>RAN: NAS Deregistration Accept
    RAN->>AMF: N2 Uplink NAS Transport<br/>(NAS PDU)

    Note over AMF: 如果re-registration required<br/>UE将立即发起Registration

    loop 每个PDU Session
        AMF->>SMF: Nsmf_PDUSession_Release_SMContext
        SMF-->>AMF: Release Response
    end

    AMF->>UDM: Nudm_SDM_Unsubscribe
    UDM-->>AMF: 204 No Content

    AMF->>UDM: Nudm_UECM_Deregistration
    UDM-->>AMF: 200 OK

    AMF->>RAN: N2 UE Context Release Command
    RAN-->>AMF: N2 UE Context Release Complete

    Note over UE: 如果re-registration required<br/>UE自动发起新Registration

sequenceDiagram
    participant Operator as 运营商系统
    participant UDM
    participant AMF
    participant SMF
    participant UE
    participant RAN as NG-RAN

    Operator->>UDM: 删除用户签约<br/>(Subscription Withdrawal)
    Note over UDM: UDM决定通知所有<br/>注册的AMF

    UDM->>AMF: Nudm_UECM_DeregistrationNotification<br/>(SUPI, Access Type, Deregistration Reason)

    Note over AMF: AMF收到通知后<br/>转为AMF-initiated Deregistration

    AMF->>RAN: N2 Downlink NAS Transport<br/>(NAS: Deregistration Request<br/>type=re-registration not required)
    RAN->>UE: 携带NAS PDU

    UE->>RAN: NAS Deregistration Accept
    RAN->>AMF: N2 Uplink NAS Transport

    loop 每个PDU Session
        AMF->>SMF: Nsmf_PDUSession_Release_SMContext
        SMF->>UDM: Nudm_SDM_Unsubscribe
        UDM-->>SMF: 204 No Content
        SMF-->>AMF: Release Response
    end

    AMF->>UDM: Nudm_UECM_Deregistration<br/>(SUPI, AMF ID)
    Note over UDM: UDM确认已删除<br/>AMF注册记录

    AMF->>UDM: Nudm_SDM_Unsubscribe
    UDM-->>AMF: 204 No Content

    AMF->>RAN: N2 UE Context Release Command
    RAN-->>AMF: N2 UE Context Release Complete

flowchart TD
    A[UE进入CM-IDLE] --> B[AMF启动<br/>Mobile Reachable Timer<br/>默认54分钟]
    B --> C{UE是否发起<br/>Periodic Registration?}
    C -->|是| B
    C -->|否 Timer超时| D[AMF启动<br/>Implicit Deregistration Timer<br/>默认4分钟]
    D --> E{UE是否恢复联系?}
    E -->|是| B
    E -->|否 Timer超时| F[AMF执行<br/>Implicit Deregistration]
    F --> G[删除MM Context]
    G --> H[通知SMF释放<br/>所有PDU Session]
    H --> I[通知UDM<br/>注销AMF注册]
    I --> J[AMF可选执行<br/>Purge UE Procedure]

sequenceDiagram
    participant AMF
    participant UDM
    participant SMF

    Note over AMF: Implicit Deregistration Timer超时<br/>UE仍不可达

    AMF->>AMF: 删除UE的MM Context<br/>标记UE为Deregistered

    loop 每个PDU Session
        AMF->>SMF: Nsmf_PDUSession_Release_SMContext<br/>(SUPI, PDU Session ID, cause=implicit)
        SMF-->>AMF: Release Response
    end

    AMF->>UDM: Nudm_UECM_Deregistration<br/>(SUPI, purgeFlag=TRUE)
    Note over UDM: UDM标记UE为Purged<br/>保留用户签约数据
    UDM-->>AMF: 200 OK

    AMF->>UDM: Nudm_SDM_Unsubscribe
    UDM-->>AMF: 204 No Content

    Note over AMF,UDM: Purge完成<br/>如果UE后续重新注册<br/>UDM通过Initial Registration流程<br/>恢复AMF注册

sequenceDiagram
    participant AMF
    participant SMF
    participant UPF
    participant PCF
    participant UDM as UDM/BSF

    AMF->>SMF: Nsmf_PDUSession_Release_SMContext<br/>POST /nsmf-pdusession/v1/sm-contexts/{smContextId}/release<br/>{json: PDU Session ID, cause, accessType}

    SMF->>UPF: N4 Session Release Request<br/>(Release所有N4规则)
    UPF-->>SMF: N4 Session Release Response

    SMF->>PCF: Npcf_SMPolicyControl_Delete<br/>DELETE /npcf-smpolicycontrol/v1/policies/{polId}
    PCF-->>SMF: 204 No Content

    opt SMF订阅了UDM数据
        SMF->>UDM: Nudm_SDM_Unsubscribe<br/>DELETE /nudm-sdm/v1/{supi}/sdm-subscriptions/{subId}
        UDM-->>SMF: 204 No Content
    end

    SMF-->>AMF: Nsmf_PDUSession_Release_SMContext Response<br/>200 OK