5G ATSSS五径分流与MA-PDU会话博弈

graph TB
    subgraph UE侧
        A1[MPTCP Client<br/>TCP流量多路径]
        A2[ATSSS-LL功能<br/>非TCP流量分流]
        A3[PMF客户端<br/>性能测量]
        A1 --> A4[MA-PDU会话<br/>用户面承载]
        A2 --> A4
        A3 -.->|RTT/丢包探测| A1
        A3 -.->|RTT/丢包探测| A2
    end

    subgraph 网络侧
        B1[SMF<br/>ATSSS策略下发]
        B2[UPF/PSA<br/>MPTCP Proxy + ATSSS-LL]
        B3[PCF<br/>ATSSS策略决策]
        B4[AMF<br/>NAS透传]
        B3 -->|PCC Rules| B1
        B1 -->|N4 ATSSS Rules| B2
        B1 -->|NAS ATSSS Rules| B4
        B4 -->|DL NAS Transport| UE侧
    end

    subgraph 双接入
        C1[3GPP接入<br/>gNB/ng-eNB]
        C2[非3GPP接入<br/>N3IWF/TNGF]
    end

    A4 -->|N3| C1
    A4 -->|NWtt/Yaan3| C2
    C1 -->|N3| B2
    C2 -->|N3| B2
    B2 -->|N6| DN[Data Network]

sequenceDiagram
    participant UE
    participant AMF_3G as AMF(3GPP接入)
    participant AMF_N3 as AMF(非3GPP接入)
    participant SMF
    participant PCF
    participant UDM
    participant UPF as UPF/PSA
    participant N3IWF

    Note over UE,N3IWF: 前提：UE已通过3GPP和非3GPP接入完成注册

    rect rgb(230,240,255)
    Note over UE,AMF_3G: Step 1-2: UE发起MA-PDU会话建立请求
    UE->>AMF_3G: UL NAS Transport<br/>PDU Session Establishment Request<br/>MA-PDU Request=1<br/>ATSSS Capability Indication
    AMF_3G->>SMF: Nsmf_PDUSession_CreateSMContext Request<br/>{MA-PDU Indicator, ATSSS Capability,<br/>S-NSSAI, DNN, 3GPP Access Type}
    end

    rect rgb(255,240,230)
    Note over SMF,UDM: Step 3-4: 订阅数据获取与策略决策
    SMF->>UDM: Nudm_SDM_Get<br/>{SUPI, DNN, S-NSSAI}
    UDM-->>SMF: Subscription Data<br/>{ATSSS Allowed, Steering Mode,<br/>MA-PDU Permitted}
    SMF->>PCF: Npcf_SMPolicyControl_Create<br/>{SUPI, DNN, MA-PDU Indicator,<br/>ATSSS Capability}
    PCF-->>SMF: PCC Rules + ATSSS Policy<br/>{Steering Mode, Traffic Filters,<br/>Thresholds, Measurement Req}
    end

    rect rgb(230,255,230)
    Note over SMF,UPF: Step 5-6: UPF选择与N4会话建立
    SMF->>UPF: N4 Session Establishment Request<br/>{ATSSS Rules for UPF,<br/>PDR/FAR/QER per access,<br/>MPTCP Proxy Config,<br/>PMF Configuration}
    UPF-->>SMF: N4 Session Establishment Response<br/>{F-TEID (3GPP), F-TEID (Non-3GPP),<br/>MPTCP Proxy Address}
    end

    rect rgb(255,230,255)
    Note over SMF,UE: Step 7-9: 向UE返回ATSSS规则
    SMF-->>AMF_3G: Nsmf_PDUSession_CreateSMContext Response<br/>{N2 SM Info, PDU Session Accept,<br/>ATSSS Rules for UE}
    AMF_3G->>UE: DL NAS Transport + N2 RAN msg<br/>PDU Session Establishment Accept<br/>{MA-PDU Accepted, Steering Mode,<br/>ATSSS Rules, MPTCP Proxy Info,<br/>3GPP Tunnel Info}
    end

    rect rgb(240,240,230)
    Note over UE,N3IWF: Step 10-12: 非3GPP接入路径建立
    UE->>AMF_N3: UL NAS Transport (Non-3GPP)<br/>PDU Session Establishment Request<br/>Existing MA-PDU Session<br/>{PSI, MA-PDU Session ID}
    AMF_N3->>SMF: Nsmf_PDUSession_UpdateSMContext<br/>{Add Non-3GPP Access,<br/>MA-PDU Session ID}
    SMF->>UPF: N4 Session Modification<br/>{Add Non-3GPP PDR/FAR,<br/>F-TEID for Non-3GPP}
    UPF-->>SMF: N4 Response

    SMF-->>AMF_N3: Nsmf_PDUSession_UpdateSMContext Response
    AMF_N3->>N3IWF: NWu Session Setup
    N3IWF-->>UE: IKEv2/IPsec Tunnel Established
    AMF_N3-->>UE: DL NAS Transport<br/>PDU Session Establishment Accept<br/>{Non-3GPP Tunnel Info}
    end

    Note over UE,UPF: MA-PDU会话建立完成<br/>3GPP和Non-3GPP双路径均就绪

ATSSS Capability
├── ATSSS-LL Indicator (1 bit) — UE支持ATSSS-LL功能
├── MPTCP Indicator (1 bit) — UE支持MPTCP功能
├── MPTCP with MP-QUIC Indicator (1 bit) — UE支持MP-QUIC (Rel-17+)
└── Spare bits (5 bits) — 保留

flowchart LR
    subgraph PMF测量框架
        A[UE PMF客户端] -->|RTT Probe<br/>间隔=T_ms| B[3GPP PMF端点]
        A -->|RTT Probe<br/>间隔=T_ms| C[Non-3GPP PMF端点]
        B -->|RTT Response| A
        C -->|RTT Response| A
        A -->|RTT_3GPP, RTT_Non3GPP| D[Steering决策<br/>选RTT最小的接入]
    end
    subgraph UPF侧
        E[UPF PMF功能] -->|RTT Probe| F[UE 3GPP PMF]
        E -->|RTT Probe| G[UE Non-3GPP PMF]
        E -->|下行RTT比较| H[下行Steering决策]
    end

graph TB
    subgraph "UE协议栈"
        APP[Application<br/>TCP/UDP/QUIC]
        APP -->|TCP流| MPTCP_C[MPTCP Client<br/>Subflow Manager]
        APP -->|QUIC流| MPQUIC_C[MP-QUIC Endpoint]
        APP -->|所有流量| ATSSS_LL[ATSSS-LL<br/>L2/L3分割]
        MPTCP_C --> SF1[Subflow 1<br/>3GPP N3]
        MPTCP_C --> SF2[Subflow 2<br/>Non-3GPP N3]
        MPQUIC_C --> QP1[QUIC Path 1<br/>3GPP N3]
        MPQUIC_C --> QP2[QUIC Path 2<br/>Non-3GPP N3]
        ATSSS_LL --> LL1[Path 1<br/>3GPP N3]
        ATSSS_LL --> LL2[Path 2<br/>Non-3GPP N3]
    end

    subgraph "UPF协议栈"
        SF1 --> MP[MPTCP Proxy<br/>MPTCP→TCP转换]
        SF2 --> MP
        QP1 --> QP[MP-QUIC Proxy<br/>MP-QUIC→QUIC转换]
        QP2 --> QP
        LL1 --> ULL[ATSSS-LL<br/>上行→单路转发]
        LL2 --> ULL
        MP --> DN_TCP[DN Server<br/>Regular TCP]
        QP --> DN_QUIC[DN Server<br/>Regular QUIC]
        ULL --> DN_ALL[DN Server]
    end

graph LR
    subgraph "PCF PCC Rules"
        P1[PCC Rule 1<br/>SDF: App=Video<br/>Steering: Load-Balancing<br/>Percentage: 70/30]
        P2[PCC Rule 2<br/>SDF: App=VoIP<br/>Steering: Smallest-Delay<br/>Threshold: RTT<50ms]
        P3[PCC Rule 3<br/>SDF: App=FTP<br/>Steering: MPTCP]
    end

    subgraph "SMF规则转换"
        P1 --> S1[ATSSS Rule for UE<br/>UL: 按概率70%走3GPP<br/>30%走Non-3GPP]
        P1 --> S1U[ATSSS Rule for UPF<br/>DL: 同理]
        P2 --> S2[ATSSS Rule for UE<br/>UL: PMF测量→选RTT小的]
        P2 --> S2U[ATSSS Rule for UPF<br/>DL: 同理]
        P3 --> S3[MPTCP Config for UE<br/>Proxy Address + Port]
        P3 --> S3U[N4 MPTCP Proxy Config<br/>Enable MPTCP termination]
    end

    subgraph "N4接口规则集"
        S1U --> N4_1[Create PDR<br/>Source: 3GPP/Non-3GPP<br/>FAR: Apply ATSSS Rule]
        S2U --> N4_2[Create PDR<br/>+ PMF Measurement Req]
        S3U --> N4_3[Create PDR<br/>+ MPTCP Proxy Enable]
    end

sequenceDiagram
    participant UE
    participant UPF_3G as UPF(3GPP侧)
    participant UPF_N3 as UPF(Non-3GPP侧)

    loop 每个测量周期 T_ms
        UE->>UPF_3G: PMF Probe Request<br/>Seq=N, T1=timestamp
        UPF_3G-->>UE: PMF Probe Response<br/>Seq=N, T2=recv, T3=send

        UE->>UPF_N3: PMF Probe Request<br/>Seq=M, T1=timestamp
        UPF_N3-->>UE: PMF Probe Response<br/>Seq=M, T2=recv, T3=send
    end

    Note over UE: 计算 RTT_3GPP = (T4-T1) - (T3-T2)<br/>计算 RTT_Non3GPP = (T4'-T1') - (T3'-T2')

    alt Smallest Delay模式
        Note over UE: 选择 RTT 值更小的接入发送新流量
    else Priority-based模式
        Note over UE: 如果高优先级接入RTT > 阈值<br/>则溢出到低优先级接入
    end

stateDiagram-v2
    [*] --> Idle: UE未建立PDU Session

    Idle --> SingleAccess: PDU Session<br/>Establishment Request<br/>(普通PDU Session)

    Idle --> MA_Pending: MA-PDU Request<br/>ATSSS Capability<br/>(双注册场景)

    MA_Pending --> MA_Active: SMF接受<br/>双接入隧道建立成功

    MA_Pending --> SingleAccess: SMF拒绝MA-PDU<br/>或非3GPP不可用

    SingleAccess --> MA_Active: PDU Session<br/>Modification<br/>添加非3GPP接入

    MA_Active --> MA_Active: Steering Mode变更<br/>ATSSS规则更新<br/>PMF阈值调整

    MA_Active --> MA_Degraded: 一条接入<br/>链路中断

    MA_Degraded --> MA_Active: 中断接入<br/>恢复

    MA_Degraded --> SingleAccess: 中断接入<br/>长期不可达<br/>SMF移除该路径

    MA_Active --> MA_Handover: N2切换<br/>3GPP侧gNB变更

    MA_Handover --> MA_Active: 切换完成<br/>N4更新

    MA_Active --> Idle: PDU Session Release<br/>双接入路径均释放

    MA_Degraded --> Idle: PDU Session Release

    SingleAccess --> Idle: PDU Session Release

# 识别MA-PDU请求
nas-5gs.nas_msg_emm.ma_pdu_session_request == 1

# 识别ATSSS Capability
nas-5gs.nas_msg_emm.atsss_capability

# 识别ATSSS Rules（在PDU Session Establishment Accept中）
nas-5gs.nas_msg_sm.atsss_steering_mode

# ATSSS Control Information IE
pfcp.ie_type == 107  # ATSSS Control Information

# MPTCP Proxy Configuration
pfcp.ie_type == 107 && pfcp.mptcp_proxy_information

# PMF使用GTP-U通道内的特殊包类型
# 目标端口：SMF配置的PMF端口（默认端口待厂商实现）
# 包内容：包含PMF Type + Seq Num + Timestamp