5G SSC三模式锚点迁移与UPF重选信令拆解

flowchart TD
    A[应用发起连接请求] --> B{UE是否有SSCMSP策略?}
    B -->|是| C[根据URSP中的SSCMSP确定SSC模式]
    B -->|否| D{UE是否有本地配置?}
    D -->|是| E[根据本地配置选择SSC模式]
    D -->|否| F[不指定SSC模式发起PDU会话请求]
    C --> G[UE在PDU Session Establishment Request中携带SSC模式]
    E --> G
    F --> G
    G --> H{SMF校验订阅数据}
    H --> I{UE请求的SSC模式在允许列表中?}
    I -->|是| J[SMF接受请求的SSC模式]
    I -->|否| K[SMF拒绝并返回允许的SSC模式列表]
    K --> L[UE使用允许的SSC模式重新请求]
    J --> M[SSC模式确定,建立PDU会话]

flowchart LR
    subgraph AF请求
        A1[AF提供DNAI]
        A2[AF订阅UP路径事件]
    end
    subgraph PCF策略
        B1[PCC规则中包含DNAI]
        B2[业务路由策略]
    end
    subgraph SMF选择
        C1[根据DNAI匹配UPF]
        C2[考虑UPF服务区域]
        C3[评估UPF负载]
    end
    subgraph UPF部署
        D1[UPF1: DNAI-1]
        D2[UPF2: DNAI-2]
        D3[UPF3: DNAI-3]
    end
    A1 --> B1
    B1 --> C1
    C2 --> C1
    C3 --> C1
    C1 --> D1
    C1 --> D2
    C1 --> D3

sequenceDiagram
    participant UE
    participant RAN
    participant AMF
    participant SMF1 as SMF(旧)
    participant SMF2 as SMF(新)
    participant UPF1 as UPF1(旧PSA)
    participant UPF2 as UPF2(新PSA)
    participant UDM
    participant PCF

    Note over SMF1: Step 1: SMF判决PSA需要变更
    SMF1->>SMF1: 检测到UPF1不再最优<br/>(UE移出服务区/AF请求/负载均衡)

    alt UPF1无法连接target DNAI
        SMF1->>AMF: Nsmf_PDUSession_SMContextStatusNotify<br/>(target DNAI信息, SMF重选指示)
        AMF->>AMF: 存储target DNAI用于后续SMF选择
    end

    Note over SMF1,UE: Step 2: 释放旧PDU会话
    SMF1->>AMF: Namf_Communication_N1N2MessageTransfer<br/>(N1: PDU Session Release Command,<br/>Cause=#39 "reactivation required")
    AMF->>RAN: N2 PDU Session Release Command
    RAN->>UE: NAS PDU Session Release Command<br/>(Cause: re-establishment to same DN required)
    UE->>RAN: NAS PDU Session Release Ack
    RAN->>AMF: N2 PDU Session Release Response
    AMF->>SMF1: Nsmf_PDUSession_UpdateSMContext
    SMF1->>UPF1: N4 Session Release Request
    UPF1->>SMF1: N4 Session Release Response

    Note over UE,UPF2: Step 3: UE立即重建PDU会话
    UE->>UE: 生成新PDU Session ID
    UE->>RAN: NAS PDU Session Establishment Request<br/>(新PDU Session ID, SSC mode 2,<br/>相同DNN/S-NSSAI)
    RAN->>AMF: N2 + NAS消息转发

    alt AMF存有target DNAI
        AMF->>AMF: 使用target DNAI选择新SMF
        AMF->>SMF2: Nsmf_PDUSession_CreateSMContext<br/>(含target DNAI)
        AMF->>AMF: 删除存储的target DNAI
    else 无target DNAI
        AMF->>SMF1: Nsmf_PDUSession_CreateSMContext<br/>(可能选择相同SMF)
    end

    SMF2->>UDM: Nudm_SDM_Get(订阅数据)
    SMF2->>PCF: Npcf_SMPolicyControl_Create
    SMF2->>SMF2: 根据target DNAI选择UPF2作为新PSA
    SMF2->>UPF2: N4 Session Establishment Request
    UPF2->>SMF2: N4 Session Establishment Response
    SMF2->>AMF: Nsmf_PDUSession_CreateSMContext Response<br/>(N2 SM Info: CN Tunnel Info)
    AMF->>RAN: N2 PDU Session Establishment Request
    RAN->>UE: RRC Reconfiguration(N3 Tunnel Info)
    UE->>RAN: RRC Reconfiguration Complete
    RAN->>AMF: N2 PDU Session Establishment Response<br/>(AN Tunnel Info)
    AMF->>SMF2: Nsmf_PDUSession_UpdateSMContext<br/>(AN Tunnel Info)
    SMF2->>UPF2: N4 Session Modification Request<br/>(AN Tunnel Info)
    UPF2->>SMF2: N4 Session Modification Response

    Note over UE,UPF2: 新PDU会话建立完成<br/>UE获得新IP地址

sequenceDiagram
    participant UE
    participant RAN
    participant AMF
    participant SMF1 as SMF1(旧)
    participant SMF2 as SMF2(新)
    participant UPF1 as UPF1(旧PSA)
    participant UPF2 as UPF2(新PSA)
    participant AF
    participant PCF

    Note over SMF1: Step 1: SMF判决PSA/SMF需要变更

    alt UPF1无法连接target DNAI
        SMF1->>AMF: Nsmf_PDUSession_SMContextStatusNotify<br/>(target DNAI, SMF Context ID)
        AMF->>AMF: 存储target DNAI和SM Context ID
    end

    alt AF运行时协调使能
        SMF1->>AF: Early Notification(源DNAI)
        AF->>SMF1: Notification Response
        alt AF返回否定响应
            SMF1->>SMF1: 终止锚点迁移
        end
    end

    Note over SMF1,UE: Step 2: 触发UE建立新会话
    SMF1->>AMF: Namf_Communication_N1N2MessageTransfer<br/>(PDU Session ID, SMF Reallocation指示,<br/>N1: PDU Session Modification Command<br/>Cause=reactivation required,<br/>PCO: PDU Session Address Lifetime)
    AMF->>UE: NAS PDU Session Modification Command
    UE->>UE: 将Address Lifetime传递给上层
    UE->>AMF: NAS PDU Session Modification Command ACK
    AMF->>SMF1: Nsmf_PDUSession_UpdateSMContext(N1 ACK)

    Note over UE: Step 4: UE发起建立新PDU会话
    UE->>UE: 生成新PDU Session ID
    UE->>RAN: NAS PDU Session Establishment Request<br/>(新PDU Session ID + Old PDU Session ID)
    RAN->>AMF: N2 + NAS转发

    alt SMF重选
        AMF->>SMF2: Nsmf_PDUSession_CreateSMContext<br/>(含target DNAI, SM Context ID)
    else 不重选
        AMF->>SMF1: Nsmf_PDUSession_CreateSMContext<br/>(含Old PDU Session ID)
    end

    SMF2->>SMF1: Nsmf_PDUSession_ContextRequest<br/>(请求AF Coordination Info)
    SMF1->>SMF2: Nsmf_PDUSession_ContextResponse<br/>(AF Coordination Info, notification correlation id)

    SMF2->>SMF2: 选择UPF2作为新PSA
    SMF2->>UPF2: N4 Session Establishment
    UPF2->>SMF2: N4 Session Establishment Response

    alt AF订阅Late Notification
        SMF2->>AF: Late Notification(源DNAI, UE IP)
    end

    SMF2->>AMF: CreateSMContext Response(N2 SM Info)
    AMF->>RAN: N2 PDU Session Setup
    RAN->>UE: RRC Reconfiguration
    UE->>RAN: RRC Complete
    RAN->>AMF: N2 Response(AN Tunnel Info)
    AMF->>SMF2: UpdateSMContext(AN Tunnel Info)
    SMF2->>UPF2: N4 Session Modification

    Note over UE: Step 5: 新旧会话并存期
    UE->>UE: 新流量使用新IP地址/前缀<br/>可主动迁移旧流量到新会话

    Note over SMF1: Step 6: 旧会话释放
    alt UE主动释放(在timer到期前)
        UE->>SMF1: PDU Session Release Request(旧会话)
    else Timer超时后SMF释放
        SMF1->>UE: PDU Session Release Command(旧会话)
    end
    SMF1->>UPF1: N4 Session Release

flowchart TD
    subgraph 阶段1_锚点准备["阶段1: 新PSA准备"]
        A1[SMF决定分配新PSA] --> A2[SMF选择UPF2作为新PSA]
        A2 --> A3[N4建立: UPF2配置为PSA]
        A3 --> A4[分配新IPv6前缀 IP@2]
        A4 --> A5[通知PCF新前缀<br/>PCF更新BSF绑定]
    end

    subgraph 阶段2_BP插入["阶段2: Branching Point插入"]
        B1[SMF选择BP UPF] --> B2[N4配置BP<br/>UL转发规则: 按源IPv6前缀分流]
        B2 --> B3[提供AN Tunnel Info和CN Tunnel Info]
        B3 --> B4[N4修改PSA1/PSA2<br/>建立N9隧道: BP↔PSA1, BP↔PSA2]
    end

    subgraph 阶段3_路径切换["阶段3: N3路径切换"]
        C1[SMF发送N2 SM Info给AMF<br/>含BP的CN Tunnel Info] --> C2[AMF→RAN: N2 Request]
        C2 --> C3[RAN→AMF: N2 Response<br/>含新AN Tunnel Info]
        C3 --> C4[SMF更新BP: AN Tunnel Info]
    end

    subgraph 阶段4_UE通知["阶段4: IPv6前缀通知"]
        D1[SMF通过新PSA发Router Advertisement<br/>携带新前缀IP@2] --> D2[SMF通过旧PSA发Router Advertisement<br/>旧前缀IP@1: preferred_lifetime=0<br/>valid_lifetime=T]
        D2 --> D3[UE开始用IP@2发起所有新流量<br/>可主动迁移旧流量]
    end

    subgraph 阶段5_旧锚点释放["阶段5: 旧锚点释放"]
        E1[valid_lifetime定时器超时] --> E2[SMF释放旧IPv6前缀IP@1]
        E2 --> E3[N4修改BP: 释放N9隧道<br/>BP↔旧PSA]
        E3 --> E4[N4释放旧PSA UPF1]
        E4 --> E5[可选: 释放BP<br/>UPF2直接作为唯一PSA]
    end

    阶段1_锚点准备 --> 阶段2_BP插入
    阶段2_BP插入 --> 阶段3_路径切换
    阶段3_路径切换 --> 阶段4_UE通知
    阶段4_UE通知 --> 阶段5_旧锚点释放

sequenceDiagram
    participant SMF
    participant AF
    participant NEF

    Note over SMF: 锚点迁移开始

    rect rgb(230, 245, 255)
        Note over SMF,AF: Early Notification（新PSA选定后，配置前）
        SMF->>AF: Nsmf_EventExposure_Notify<br/>(Event: "Early Notification",<br/>Source DNAI, Target DNAI)
        alt AF acknowledgment required
            AF->>SMF: Notification Response
            alt 否定响应
                SMF->>SMF: 终止锚点迁移流程
            end
        end
    end

    Note over SMF: 配置新PSA、更新N4规则

    rect rgb(255, 240, 230)
        Note over SMF,AF: Late Notification（UP路径激活后）
        SMF->>AF: Nsmf_EventExposure_Notify<br/>(Event: "Late Notification",<br/>Source DNAI, Target DNAI,<br/>UE IP address @ Source DNAI)
        alt AF acknowledgment required
            AF->>SMF: Notification Response
        end
    end