5G AF Traffic Influence与MEC UPF动态重选信令拆解

sequenceDiagram
    participant AF as AF(应用功能)
    participant NEF as NEF
    participant UDM as UDM
    participant PCF as PCF
    participant SMF as SMF
    participant UPF_old as UPF(旧锚点)
    participant UPF_new as UPF(新锚点/MEC)
    participant UE as UE

    Note over AF,UE: 阶段1: AF路由影响请求创建
    AF->>NEF: Nnef_TrafficInfluence_Create<br/>{AF-Router-Identity, TrafficDesc,<br/>RoutingReq, UPPathChangeNotif}
    NEF->>NEF: 鉴权AF请求<br/>检查AF是否授权
    NEF->>UDM: Nudm_SDM_Get<br/>查询UE路由签约数据
    UDM-->>NEF: {RoutingPermission, AllowedRoutes}

    alt AF直接请求模式
        NEF->>PCF: Npcf_PolicyAuthorization_Create<br/>{TrafficDesc, RoutingReq,<br/>AF-Router-Identity}
        PCF->>PCF: 生成/更新PCC规则<br/>映射路由需求到QoS参数
        PCF-->>NEF: 201 Created {PolicyDecision}
    else AF绕过PCF模式(NEF直接→SMF)
        Note over NEF,SMF: 仅当运营商策略允许
        NEF->>SMF: Nsmf_TrafficInfluence_Notify<br/>{RoutingReq, TrafficDesc}
    end

    NEF-->>AF: 201 Created<br/>{ResourceId, NotificationURI}

    Note over AF,UE: 阶段2: SMF执行UPF重选
    PCF->>SMF: Npcf_SMPolicyControl_Update<br/>{PCC-Rule-Update,<br/>RoutingRequirement}
    SMF->>SMF: 评估当前UPF拓扑<br/>决定是否需要UPF重选

    alt 需要UPF重选(新锚点)
        SMF->>UPF_new: N4 Session Establishment<br/>{FAR, PDR, QER, URR<br/>新锚点规则注入}
        UPF_new-->>SMF: N4 Session Establishment Response
        SMF->>UPF_old: N4 Session Modification<br/>{更新FAR/PDR,<br/>流量重定向至新锚点}
        UPF_old-->>SMF: N4 Session Modification Response

        Note over SMF,UE: 可选: 插入UL CL/BP分流
        SMF->>UPF_new: N4 Session Modification<br/>{UL CL规则注入}
    else 仅修改N4规则(同UPF)
        SMF->>UPF_old: N4 Session Modification<br/>{更新PDR/FAR,<br/>新增/修改路由规则}
        UPF_old-->>SMF: N4 Session Modification Response
    end

    Note over AF,UE: 阶段3: UP Path变更通知(可选)
    alt UPPathChangeNotif=true
        SMF->>PCF: Npcf_SMPolicyControl_Update<br/>{UPPathChange notification}
        PCF->>NEF: Nnef_TrafficInfluence_Notify<br/>{UPPathChange, NewUPF-Info}
        NEF->>AF: Nnef_TrafficInfluence_Notify<br/>{UPPathChange, NewUPF-Info,<br/>SourceIP-Addr}
    end

graph TB
    TD[TrafficDesc 流量描述符]
    TD --> IP5[IP五元组<br/>SrcAddr + DstAddr<br/>SrcPort + DstPort + Protocol]
    TD --> DNN[DNN匹配<br/>特定数据网络名称]
    TD --> SNSSAI[S-NSSAI匹配<br/>特定网络切片]
    TD --> MAC[MAC地址匹配<br/>以太网PDU会话]
    TD --> DNAD[DNAI匹配<br/>数据网络接入标识]

    IP5 --> MATCH{流量匹配<br/>逻辑}
    DNN --> MATCH
    SNSSAI --> MATCH
    MAC --> MATCH
    DNAD --> MATCH
    MATCH --> RULE[命中→应用路由规则<br/>未命中→默认路由]

flowchart TD
    START[SMF收到PCC路由规则] --> EVAL{评估当前<br/>UPF拓扑位置}
    EVAL -->|目标DNAI可达<br/>且当前UPF覆盖| SAME[同UPF执行<br/>仅更新N4规则]
    EVAL -->|目标DNAI不可达<br/>需新锚点| NEW[触发UPF重选]
    EVAL -->|多DNAI目标<br/>需分流| SPLIT[插入UL CL<br/>+新增BP锚点]

    SAME --> N4MOD[N4 Session Modification<br/>更新PDR/FAR/QER]
    N4MOD --> DONE[完成]

    NEW --> SELECT[SMF选择新UPF<br/>基于DNAI+拓扑+负载]
    SELECT --> N4EST[N4 Session Establishment<br/>向新UPF注入规则]
    N4EST --> N4MOD2[N4 Modification<br/>旧UPF更新转发规则]
    N4MOD2 --> ADDR{addrPreserInd?}
    ADDR -->|true: 保留IP| BP[插入Branching Point<br/>保持IP连续性]
    ADDR -->|false: 可换IP| DIRECT[直接切换锚点]
    BP --> DONE2[完成]
    DIRECT --> DONE2

    SPLIT --> ULCL[建立UL CL会话<br/>N4 Session Establishment]
    ULCL --> PSA1[PSA1(原锚点)<br/>保持Internet路由]
    ULCL --> PSA2[PSA2(新锚点/MEC)<br/>本地分流路由]
    PSA1 --> DONE3[完成]
    PSA2 --> DONE3

PCF → SMF:
  Npcf_SMPolicyControl_Update
  {
    "policyUpdate": {
      "pccRules": [{
        "pccRuleId": "pcc-rule-af-001",
        "refAppId": "app-mec-video",
        "flowInfos": [{"flowDesc": "permit out ip from 10.1.2.0/24 to 192.168.100.5/32"}],
        "routeToLocs": [{"dnai": "mec-site-bj-01", "routeProfId": "rp-1"}],
        "upPathChgNotif": {"notifyUri": "https://nef.example.com/notify/uppathchg", "notifCorreId": "nc-12345"}
      }]
    }
  }