5G UL CL上行分流器插入与DNAI重定位信令全链拆解

┌─────────────────────────────────────────────────────────────────┐
│                    UL CL vs BP 架构对比                          │
├───────────────────┬──────────────────┬──────────────────────────┤
│       特性         │      UL CL       │      Branching Point     │
├───────────────────┼──────────────────┼──────────────────────────┤
│ 适用PDU Session类型│ IPv4/IPv6/Ethernet│ 仅Multi-homed IPv6      │
├───────────────────┼──────────────────┼──────────────────────────┤
│ 分流方向           │ 上行分类         │ 上下行双向分支            │
├───────────────────┼──────────────────┼──────────────────────────┤
│ UE地址数量         │ 单一IP地址       │ 多个IPv6 Prefix          │
├───────────────────┼──────────────────┼──────────────────────────┤
│ PSA连接方式        │ N9隧道到多个PSA  │ N9隧道到多个PSA           │
├───────────────────┼──────────────────┼──────────────────────────┤
│ 典型场景           │ MEC本地分流      │ IPv6多宿主 + MEC          │
├───────────────────┼──────────────────┼──────────────────────────┤
│ 过滤规则           │ 基于PDR的UL分类  │ 基于IPv6 Prefix路由       │
└───────────────────┴──────────────────┴──────────────────────────┘

sequenceDiagram
    participant UE
    participant RAN as (R)AN
    participant AMF
    participant SMF
    participant PCF
    participant ULCL as UL CL UPF<br/>(I-UPF)
    participant PSA1 as PSA1 UPF<br/>(中心锚点)
    participant PSA2 as PSA2 UPF<br/>(边缘锚点)
    participant AF as AF/MEP

    Note over UE,AF: 阶段1: 触发UL CL插入（AF发起流量路由请求）

    AF->>PCF: Npcf_PolicyAuthorization<br/>AF请求更新Traffic Routing<br/>(Target DNAI=Edge-Site-A)
    PCF->>SMF: Npcf_SMPolicyControl_UpdateNotify<br/>PCC Rule含Traffic Steering Policy<br/>+ 目标DNAI信息

    Note over UE,AF: 阶段2: SMF决策与UPF选择

    SMF->>SMF: 根据DNAI选择UL CL UPF<br/>和PSA2(边缘UPF)<br/>验证UPF支持UL CL能力

    Note over UE,AF: 阶段3: N4会话建立（新UPF）

    SMF->>ULCL: N4 Session Establishment Request<br/>PDR(UL CL规则) + FAR(分流动作)<br/>+ QER(QoS执行规则)
    ULCL-->>SMF: N4 Session Establishment Response<br/>F-TEID(UL CL N3/N9地址)

    SMF->>PSA2: N4 Session Establishment Request<br/>PDR(边缘DN匹配) + FAR(转发到DN)<br/>+ Usage Reporting Rule
    PSA2-->>SMF: N4 Session Establishment Response<br/>F-TEID(PSA2 N9地址)

    Note over UE,AF: 阶段4: N4会话修改（已有UPF）

    SMF->>ULCL: N4 Session Modification Request<br/>更新FAR: DL到UE经N3隧道
    ULCL-->>SMF: N4 Session Modification Response

    SMF->>PSA1: N4 Session Modification Request<br/>更新FAR: UL到DN + DL到UL CL<br/>添加到PSA2的转发隧道
    PSA1-->>SMF: N4 Session Modification Response

    SMF->>RAN: N2 SM Information<br/>含新UL CL的N3 F-TEID<br/>(PDU Session Resource Setup)

    Note over UE,AF: 阶段5: RAN隧道切换

    RAN->>RAN: 切换UL隧道到UL CL UPF
    RAN-->>AMF: N2 SM Ack<br/>含新RAN侧N3 F-TEID

    AMF->>SMF: Namf_Communication_N1N2MessageTransfer ACK<br/>含RAN N3 F-TEID

    SMF->>ULCL: N4 Session Modification Request<br/>更新RAN侧N3 F-TEID
    ULCL-->>SMF: N4 Session Modification Response

    Note over UE,UE: 阶段6: UE通知（可选）

    SMF->>UE: PDU Session Modification Command<br/>(NAS消息, 经AMF转发)<br/>可能含QoS Rule更新
    UE-->>SMF: PDU Session Modification Command ACK

    Note over UE,AF: 阶段7: DNAI Change通知

    SMF->>PCF: Npcf_SMPolicyControl_Update<br/>通知DNAI Change事件
    PCF->>AF: Npcf_PolicyAuthorization_Notify<br/>通知DNAI从Central变更为Edge-Site-A

    Note over UE,AF: 数据面路径: UE→RAN→UL CL→PSA2→边缘DN<br/>               UE→RAN→UL CL→PSA1→中心DN

graph TB
    subgraph "N4 Session: UL CL UPF规则结构"
        PDR1["PDR#1<br/>Source Interface: ACCESS<br/>Filter: 边缘App流量<br/>Priority: 100"]
        PDR2["PDR#2<br/>Source Interface: ACCESS<br/>Filter: Any<br/>Priority: 200"]
        FAR1["FAR#1<br/>Action: Forward<br/>Destination: PSA2 N9<br/>Tunnel: GTP-U"]
        FAR2["FAR#2<br/>Action: Forward<br/>Destination: PSA1 N9<br/>Tunnel: GTP-U"]
        QER1["QER#1<br/>QFI: 7<br/>Gate Status: Open<br/>MBR: 100Mbps"]

        PDR1 -->|"关联"| FAR1
        PDR1 -->|"关联"| QER1
        PDR2 -->|"关联"| FAR2
    end

    subgraph "N4 Session: PSA2 UPF规则结构"
        PDR3["PDR#1<br/>Source Interface: CORE<br/>Filter: 边缘DN响应<br/>Destination: UE IP"]
        FAR3["FAR#1<br/>Action: Forward<br/>Destination: UL CL N9<br/>Encap: GTP-U"]
        URR1["URR#1<br/>Method: Volume+Time<br/>Report Trigger: Periodic<br/>Threshold: 1GB"]

        PDR3 -->|"关联"| FAR3
        PDR3 -->|"关联"| URR1
    end

    style PDR1 fill:#e1f5fe
    style PDR2 fill:#fff3e0
    style FAR1 fill:#c8e6c9
    style FAR2 fill:#ffecb3

stateDiagram-v2
    [*] --> SinglePSA: PDU Session建立<br/>(SSC Mode 1/2/3)

    SinglePSA --> ULCL_Inserted: SMF触发<br/>UL CL插入<br/>(SSC Mode 1 or 3)

    state SinglePSA {
        [*] --> PSA1_Only
        note right of PSA1_Only: 数据路径:<br/>UE→PSA1→中心DN
    }

    state ULCL_Inserted {
        [*] --> ULCL_PSA1_PSA2
        note right of ULCL_PSA1_PSA2: 数据路径:<br/>UE→UL CL→PSA1→中心DN<br/>UE→UL CL→PSA2→边缘DNAI-A
    }

    ULCL_Inserted --> DNAI_Relocating: DNAI Change触发<br/>(UE移动到站点B)<br/>(SSC Mode 3)

    state DNAI_Relocating {
        [*] --> MakeBeforeBreak
        note right of MakeBeforeBreak: 双锚点并存:<br/>PSA2(DNAI-A) + PSA3(DNAI-B)<br/>数据转发隧道建立
    }

    DNAI_Relocating --> ULCL_Reconfigured: 旧锚点PSA2释放<br/>N4 Session Release

    state ULCL_Reconfigured {
        [*] --> ULCL_PSA1_PSA3
        note right of ULCL_PSA1_PSA3: 数据路径:<br/>UE→UL CL→PSA1→中心DN<br/>UE→UL CL→PSA3→边缘DNAI-B
    }

    ULCL_Inserted --> ULCL_Removed: SMF触发<br/>UL CL移除<br/>(UE离开边缘区)
    ULCL_Removed --> SinglePSA

    ULCL_Reconfigured --> ULCL_Removed

时间线:
  T0: SMF决定DNAI Change
  T1: PSA3 N4 Session建立完成
  T2: UL CL开始将新流量发送到PSA3
      PSA2仍然接收旧流量中的in-flight包
  T3: PSA2将缓存的DL包通过Forwarding Tunnel转发到PSA3
  T4: SMF确认无流量后释放PSA2的N4 Session

  [T0]────[T1]────[T2]────[T3]────[T4]>
    │       │       │       │       │
    │   建立PSA3  UL CL    数据    释放PSA2
    │       │      更新    转发      │
    ▼       ▼       ▼       ▼       ▼
  ┌─────────────────────────────────────┐
  │  PSA2 ════════╗                     │
  │              ║ Forwarding Tunnel    │
  │  PSA3 ════════╝                     │
  │  UL CL ──→ PSA3(新) + PSA2(旧)      │
  └─────────────────────────────────────┘

flowchart TD
    subgraph "AF/MEP"
        A1["AF请求<br/>Npcf_PolicyAuthorization"]
        A2["Traffic Descriptor<br/>+ Target DNAI"]
    end

    subgraph "PCF"
        B1["AF请求映射为<br/>PCC Rule"]
        B2["trafficSteeringPolId<br/>routeToLocs<br/>offline/online charging"]
        B3["SM Policy Decision<br/>下发到SMF"]
    end

    subgraph "SMF"
        C1["解析PCC Rule"]
        C2["UPF选择<br/>(DNAI→PSA映射)"]
        C3["生成N4 Rules<br/>PDR/FAR/QER/URR"]
    end

    subgraph "UPF(UL CL)"
        D1["执行分流<br/>基于PDR过滤"]
        D2["FAR转发到<br/>目标PSA"]
    end

    A1 --> B1
    A2 --> B1
    B1 --> B2
    B2 --> B3
    B3 --> C1
    C1 --> C2
    C2 --> C3
    C3 --> D1
    D1 --> D2

PDR #1 (边缘流量匹配):
├── PDR ID: 1
├── Precedence: 100 (高优先级)
├── PDI (Packet Detection Information):
│   ├── Source Interface: ACCESS (来自UE/RAN)
│   ├── F-TEID: [RAN分配的N3 TEID]
│   ├── UE IP Address: [UE IP]
│   └── SDF Filter: [边缘应用IP/Port/Protocol]
├── Outer Header Removal: Yes (去除GTP-U头)
├── FAR ID: 1 → 转发到PSA2
└── QER ID: 1 → QoS限速

PDR #2 (默认流量匹配):
├── PDR ID: 2
├── Precedence: 200 (低优先级)
├── PDI:
│   ├── Source Interface: ACCESS
│   ├── F-TEID: [RAN分配的N3 TEID]
│   └── UE IP Address: [UE IP]
├── Outer Header Removal: Yes
└── FAR ID: 2 → 转发到PSA1

FAR #1 (边缘分流):
├── FAR ID: 1
├── Apply Action: FORK (复制) 或 FORWARd
├── Forwarding Parameters:
│   ├── Destination Interface: CORE (N9方向)
│   ├── Network Instance: [边缘DN实例名]
│   ├── Outer Header Creation:
│   │   ├── Outer Header: GTP-U/UDP/IPv4
│   │   ├── TEID: [PSA2分配的N9 TEID]
│   │   └── IP Address: [PSA2 N9接口IP]
│   └── Transport Level Marking: [DSCP值]
└── Duplication Parameters: (可选, 用于LI)

FAR #2 (默认转发):
├── FAR ID: 2
├── Apply Action: FORWARD
├── Forwarding Parameters:
│   ├── Destination Interface: CORE
│   ├── Outer Header Creation:
│   │   ├── TEID: [PSA1分配的N9 TEID]
│   │   └── IP Address: [PSA1 N9接口IP]
│   └── Transport Level Marking: [DSCP值]

graph TD
    UE["UE<br/>(IP: 10.1.1.2)"]
    RAN["(R)AN<br/>gNB"]

    subgraph "UL CL UPF (I-UPF)"
        ULCL["UL CL Function<br/>PDR#1: 匹配边缘App → FAR#1<br/>PDR#2: 匹配默认流量 → FAR#2"]
    end

    subgraph "中心数据中心"
        PSA1["PSA1 UPF<br/>(中心锚点)<br/>DNAI: Central"]
        CDN["中心DN<br/>(Internet/Org DNS)"]
    end

    subgraph "边缘站点A"
        PSA2["PSA2 UPF<br/>(边缘锚点)<br/>DNAI: Edge-Site-A"]
        MEC["MEC Server<br/>(EHE)<br/>低时延应用"]
    end

    UE -->|"N3 GTP-U"| RAN
    RAN -->|"N3 GTP-U"| ULCL

    ULCL -->|"PDR#1匹配<br/>N9隧道"| PSA2
    ULCL -->|"PDR#2匹配<br/>N9隧道"| PSA1

    PSA1 -->|"N6"| CDN
    PSA2 -->|"N6"| MEC

    PSA1 -.->|"DL: N9→UL CL→N3→UE"| ULCL
    PSA2 -.->|"DL: N9→UL CL→N3→UE"| ULCL

    style ULCL fill:#bbdefb,stroke:#1565c0
    style PSA1 fill:#c8e6c9,stroke:#2e7d32
    style PSA2 fill:#fff9c4,stroke:#f57f17
    style MEC fill:#ffccbc,stroke:#d84315

触发条件: SMF检测到DNAI Change
    ↓
SMF通知UE: 发送EAS Rediscovery指示
    (通过PDU Session Modification Command中的
     "EAS rediscovery indication" IE)
    ↓
UE收到指示后: 
    → 重新发起DNS查询 → 获取新EAS地址
    → 或等待AF推送新EAS信息
    ↓
UE连接到新EAS: 建立新TCP/TLS会话