5G URLLC冗余双径传输机制深度拆解：Redundant QoS Flow Pair与PDU Session Pair信令全链路解析

graph TB
    subgraph "方案一：Redundant QoS Flow Pair"
        UE1[UE] -->|QFI=1,QFI=2| gNB1[gNB]
        gNB1 -->|N3 Tunnel 1| UPF1A[PSA UPF]
        gNB1 -->|N3 Tunnel 2| UPF1B[I-UPF → PSA UPF]
        UPF1A --> DN1[DN]
        UPF1B --> DN1
    end

    subgraph "方案二：Redundant PDU Session Pair"
        UE2[UE] -->|PDU Session 1| gNB2A[gNB1]
        UE2 -->|PDU Session 2| gNB2B[gNB2]
        gNB2A -->|N3 Tunnel 1| UPF2A[PSA UPF 1]
        gNB2B -->|N3 Tunnel 2| UPF2B[PSA UPF 2]
        UPF2A --> DN2[DN]
        UPF2B --> DN2
    end

    subgraph "方案三：PDCP Duplication"
        UE3[UE] -->|PDCP复制| gNB3[gNB]
        gNB3 -->|RLC leg 1 CA/DC| RLC1[RLC Entity 1]
        gNB3 -->|RLC leg 2 CA/DC| RLC2[RLC Entity 2]
    end

sequenceDiagram
    participant UE
    participant gNB as gNB(RAN)
    participant AMF
    participant SMF
    participant UDM
    participant PCF
    participant UPF1 as PSA UPF
    participant UPF2 as I-UPF/PSA2

    Note over UE,UPF2: 步骤1-5: PDU Session建立（含冗余QoS Flow协商）

    UE->>gNB: 1. NAS PDU Session Establishment Request
    Note right of UE: 携带DNN/S-NSSAI<br/>DNN配置指示需冗余传输<br/>或URSP规则触发
    gNB->>AMF: 2. N2 NAS Transport (NAS PDU)
    AMF->>SMF: 3. Nsmf_PDUSession_CreateSMContext Request
    Note right of AMF: 携带SUPI/DNN/S-NSSAI<br/>SMF根据订阅数据判断<br/>是否启用冗余传输

    SMF->>UDM: 4. Nudm_SDM_Get (Session Management Subscription)
    UDM-->>SMF: 4a. Subscription Data (含Redundant Session Info)

    SMF->>PCF: 5. Npcf_SMPolicyControl_Create
    Note right of SMF: PCF可能提供冗余传输策略<br/>或通过本地策略决定
    PCF-->>SMF: 5a. SM Policy (含URLLC QoS参数)

    Note over SMF: SMF决策：启用Redundant QoS Flow Pair<br/>选择UPF1为主PSA<br/>选择UPF2为冗余路径PSA

    SMF->>UPF1: 6. N4 Session Establishment Request
    Note right of SMF: Create PDR (QFI=1, Priority=高)<br/>Create FAR (Forward to N6/DN)<br/>Create QER (QoS Enforcement)<br/>请求分配N3 DL F-TEID(Tunnel 1)

    UPF1-->>SMF: 6a. N4 Session Establishment Response
    Note left of UPF1: N3 DL F-TEID (IP1:TEID1)

    SMF->>UPF2: 7. N4 Session Establishment Request
    Note right of SMF: Create PDR (QFI=2, Priority=高)<br/>Create FAR (Forward to N6/DN)<br/>Create QER (QoS Enforcement)<br/>请求分配N3 DL F-TEID(Tunnel 2)

    UPF2-->>SMF: 7a. N4 Session Establishment Response
    Note left of UPF2: N3 DL F-TEID (IP2:TEID2)

    SMF->>AMF: 8. Namf_Communication_N1N2MessageTransfer
    Note right of SMF: N1: PDU Session Establishment Accept<br/>含QFI=1和QFI=2<br/>含Redundant QoS Flow Pair指示<br/><br/>N2: SM Information<br/>- QFI Pair (QFI1, QFI2)<br/>- N3 DL F-TEID (IP1:TEID1)<br/>- N3 DL F-TEID (IP2:TEID2)<br/>- Redundant QoS Flow Indication

    AMF->>gNB: 9. N2 PDU Session Resource Setup Request
    Note right of AMF: 携带N2 SM Information<br/>gNB解析双N3隧道端点<br/>识别冗余QoS Flow对

    gNB-->>AMF: 10. N2 PDU Session Resource Setup Response
    Note left of gNB: N3 UL F-TEID (IP3:TEID3) → Tunnel 1<br/>N3 UL F-TEID (IP4:TEID4) → Tunnel 2

    AMF->>SMF: 11. Nsmf_PDUSession_UpdateSMContext Request
    Note right of AMF: 携带gNB分配的<br/>双N3 UL F-TEID

    SMF->>UPF1: 12. N4 Session Modification Request
    Note right of SMF: 更新FAR: N3 UL F-TEID (IP3:TEID3)<br/>对应QFI=1的上行隧道

    UPF1-->>SMF: 12a. N4 Session Modification Response

    SMF->>UPF2: 13. N4 Session Modification Request
    Note right of SMF: 更新FAR: N3 UL F-TEID (IP4:TEID4)<br/>对应QFI=2的上行隧道

    UPF2-->>SMF: 13a. N4 Session Modification Response

    Note over UE,UPF2: 冗余传输路径建立完成

    Note over gNB: DL数据面：gNB通过PDCP复制<br/>将同一包发往Tunnel1和Tunnel2<br/>UPF1/UPF2各自转发到DN<br/>DN侧去重
    Note over UE: UL数据面：UE通过PDCP复制<br/>两个QoS Flow各自承载在<br/>不同DRB→不同N3隧道<br/>UPF侧去重

PFCP Session Establishment Request:
├─ Create PDR (Packet Detection Rule) #1
│  ├─ PDR ID: 1
│  ├─ Precedence: 100
│  ├─ PDI (Packet Detection Information):
│  │  ├─ Source Interface: ACCESS (N3)
│  │  ├─ F-TEID: TEID=TEID3, IP=IP3 (gNB UL Tunnel 1)
│  │  └─ QFI: 1
│  ├─ Outer Header Removal: GTP-U/UDP/IPv4
│  └─ FAR ID: 1 → Forward to CORE (N6)
│
├─ Create PDR #2 (DL方向)
│  ├─ PDR ID: 2
│  ├─ PDI:
│  │  ├─ Source Interface: CORE (N6)
│  │  └─ UE IP Address: x.x.x.x
│  ├─ FAR ID: 2 → Forward to ACCESS (N3)
│  │  └─ Outer Header Creation: TEID=TEID1, IP=IP1
│  └─ QER ID: 1 → QoS Enforcement (5QI=84)
│
├─ Create FAR (Forwarding Action Rule) #1
│  ├─ FAR ID: 1
│  ├─ Apply Action: FORW
│  └─ Forwarding Parameters:
│     └─ Destination Interface: CORE
│
├─ Create FAR #2
│  ├─ FAR ID: 2
│  ├─ Apply Action: FORW
│  └─ Forwarding Parameters:
│     ├─ Destination Interface: ACCESS
│     └─ Outer Header Creation: GTP-U/UDP/IPv4
│        └─ TEID=TEID1, IP=IP1 (DL F-TEID for gNB)
│
└─ Create QER (QoS Enforcement Rule) #1
   ├─ QER ID: 1
   ├─ QFI: 1
   ├─ GFBR UL/DL: 10 Mbps
   ├─ MFBR UL/DL: 20 Mbps
   └─ Packet Delay Budget: 5ms

sequenceDiagram
    participant UE
    participant gNB1 as gNB1(MN)
    participant gNB2 as gNB2(SN)
    participant AMF
    participant SMF1 as SMF-1
    participant SMF2 as SMF-2
    participant UPF1 as PSA UPF-1
    participant UPF2 as PSA UPF-2
    participant DN

    Note over UE,DN: 阶段一：建立PDU Session 1（主路径）

    UE->>gNB1: 1a. NAS PDU Session Establishment Request (PSI=1)
    Note right of UE: DNN=URLLC-DNN<br/>S-NSSAI=SST:2<br/>PCO含Redundant Session Info<br/>PDU Session Pair ID=Alpha

    gNB1->>AMF: 2a. N2 NAS Transport
    AMF->>SMF1: 3a. Nsmf_PDUSession_CreateSMContext (PSI=1)

    Note over SMF1: SMF-1识别冗余请求<br/>选择UPF-1作为PSA

    SMF1->>UPF1: 4a. N4 Session Establishment
    UPF1-->>SMF1: 5a. N4 Response (N3 DL F-TEID-1)

    SMF1->>AMF: 6a. N1N2MessageTransfer
    Note right of SMF1: N1: PDU Session Est Accept<br/>N2: N3 DL F-TEID-1<br/>Redundant Session Pair Indicator

    AMF->>gNB1: 7a. N2 PDU Session Resource Setup
    gNB1-->>AMF: 8a. N2 Response (N3 UL F-TEID-1)

    AMF->>SMF1: 9a. UpdateSMContext (N3 UL F-TEID-1)
    SMF1->>UPF1: 10a. N4 Session Modification

    Note over UE,DN: 阶段二：建立PDU Session 2（冗余路径）

    UE->>gNB2: 1b. NAS PDU Session Establishment Request (PSI=2)
    Note right of UE: DNN=URLLC-DNN（相同）<br/>S-NSSAI=SST:2（相同）<br/>PCO含Redundant Session Info<br/>PDU Session Pair ID=Alpha（关联标识）

    gNB2->>AMF: 2b. N2 NAS Transport
    AMF->>SMF2: 3b. Nsmf_PDUSession_CreateSMContext (PSI=2)

    Note over SMF2: AMF选择不同的SMF-2<br/>SMF-2选择UPF-2作为PSA<br/>（确保与UPF-1不同）

    SMF2->>UPF2: 4b. N4 Session Establishment
    UPF2-->>SMF2: 5b. N4 Response (N3 DL F-TEID-2)

    SMF2->>AMF: 6b. N1N2MessageTransfer
    Note right of SMF2: N1: PDU Session Est Accept<br/>N2: N3 DL F-TEID-2<br/>Redundant Session Pair Indicator

    AMF->>gNB2: 7b. N2 PDU Session Resource Setup
    gNB2-->>AMF: 8b. N2 Response (N3 UL F-TEID-2)

    AMF->>SMF2: 9b. UpdateSMContext (N3 UL F-TEID-2)
    SMF2->>UPF2: 10b. N4 Session Modification

    Note over UE,DN: 双路径冗余传输激活

    rect rgb(200, 230, 200)
        Note over UE: UE PDCP层：复制每个数据包
        Note over UE: 原始包 → PDU Session 1 → gNB1 → UPF1 → DN
        Note over UE: 副本包 → PDU Session 2 → gNB2 → UPF2 → DN
        Note over DN: DN应用层：去重（基于序号）
    end

graph TD
    A[UE发起冗余PDU Session] --> B{关联方式}
    B -->|方式1| C[PCO携带Redundant PDU Session Info]
    C --> C1[PDU Session Pair ID]
    C --> C2[Redundant PDU Session Indicator]
    B -->|方式2| D[URSP规则触发]
    D --> D1[Traffic Descriptor匹配]
    D --> D2[RSD中指示redundant session]
    B -->|方式3| E[SMF本地策略]
    E --> E1[基于DNN判断]
    E --> E2[基于S-NSSAI判断]

    C1 --> F[SMF关联两个PDU Session]
    C2 --> F
    D2 --> F
    E1 --> F
    E2 --> F

    F --> G[SMF确保：<br/>1. 不同UPF选择<br/>2. 不同N3传输路径<br/>3. 通知RAN冗余对关系]

flowchart TD
    subgraph DN侧
        AF[Application Server] -->|发送数据包P1| DUP1[复制点]
    end

    DUP1 -->|P1原始| UPF1[PSA UPF-1]
    DUP1 -->|P1副本| UPF2[PSA UPF-2]

    UPF1 -->|N3 Tunnel 1<br/>GTP-U SN=100| gNB1[gNB-1]
    UPF2 -->|N3 Tunnel 2<br/>GTP-U SN=100| gNB2[gNB-2]

    gNB1 -->|DRB-1| UE1[UE RLC-1]
    gNB2 -->|DRB-2| UE2[UE RLC-2]

    UE1 --> PDCP[PDCP层去重]
    UE2 --> PDCP

    PDCP -->|基于PDCP SN去重<br/>先到先收，后到丢弃| APP[上层应用]

    style DUP1 fill:#f9f,stroke:#333
    style PDCP fill:#bbf,stroke:#333

stateDiagram-v2
    [*] --> WaitingFirst: 初始状态
    WaitingFirst --> PacketReceived: 收到PDCP SN=N
    PacketReceived --> ForwardToApp: 首次收到SN=N
    ForwardToApp --> WaitingDuplicate: 记录SN=N为已转发
    WaitingDuplicate --> DuplicateReceived: 收到重复SN=N
    DuplicateReceived --> Discard: 丢弃重复包
    Discard --> WaitingDuplicate
    WaitingDuplicate --> Timeout: SN=N去重窗口超时
    Timeout --> WaitingFirst: 清除SN=N记录

    note right of ForwardToApp
        关键参数：
        - t-Duplication: 去重窗口定时器
        - PDCP SN范围: 12/18 bit
        - 窗口大小: 由SMF/RRC配置
    end note

PFCP Session Establishment Request (复制UPF):
├─ Create PDR #1 (检测DL业务)
│  ├─ PDI: Source Interface = CORE, UE IP = x.x.x.x
│  └─ FAR ID: 1
│
├─ Create FAR #1 (复制并双路转发)
│  ├─ FAR ID: 1
│  ├─ Apply Action: DUPL (Duplication)
│  └─ Duplication Parameters:
│     ├─ Destination 1: ACCESS, Outer Header = GTP-U(TEID1, IP1)
│     │  → 映射到QFI=1, N3 Tunnel 1
│     └─ Destination 2: ACCESS, Outer Header = GTP-U(TEID2, IP2)
│        → 映射到QFI=2, N3 Tunnel 2
│
├─ Create PDR #2 (检测UL Tunnel 1)
│  ├─ PDI: Source Interface = ACCESS, F-TEID = TEID3, QFI = 1
│  └─ FAR ID: 2 → Forward to CORE
│
├─ Create PDR #3 (检测UL Tunnel 2)
│  ├─ PDI: Source Interface = ACCESS, F-TEID = TEID4, QFI = 2
│  └─ FAR ID: 3 → Forward to CORE
│
└─ Create URR (Usage Reporting Rule) #1
   ├─ URR ID: 1
   ├─ Measurement Method: VOLUME
   ├─ Report Triggers: PERIODIC
   └─ Redundant Transmission Reporting: ENABLED
      (确保冗余流量不计入双倍配额)

sequenceDiagram
    participant gNB
    participant UPF as PSA UPF
    participant SMF

    Note over gNB,SMF: UL Delay Monitoring

    gNB->>UPF: N3 Data Packet (GTP-U)
    Note right of gNB: GTP-U Header携带:<br/>DL Delay Result (gNB→UE)<br/>UL Delay Result (UE→gNB)<br/>Send Timestamp T1

    UPF->>SMF: N4 Session Report
    Note left of UPF: 计算UL N3 Delay = T_arrival - T1<br/>汇总端到端时延<br/>UL Path Delay = UE→gNB + N3 + UPF处理

    Note over gNB,SMF: DL Delay Monitoring

    UPF->>gNB: N3 Data Packet (GTP-U)
    Note left of UPF: GTP-U Header携带:<br/>DL Send Timestamp T2

    gNB->>SMF: N2 QoS Monitoring Report
    Note right of gNB: 计算 N3 DL Delay = T_arrival - T2<br/>端到端 DL Delay = UPF→gNB + gNB→UE

    SMF->>SMF: 比较Path1和Path2时延
    Note over SMF: 若Path1时延持续优于Path2<br/>可触发SMF调整UPF选择<br/>或通知PCF调整策略

# 过滤PDU Session Establishment中的冗余指示
nas-5gs.sm.message_type == 0xc1 && pco.option.type == 0x##(Redundant Session Info)

# 过滤N2 SM Information中的双N3隧道
ngap.pDUSessionResourceSetupItemTransferRel && ngap.uL_NG_UP_TNLInformation

# 过滤PFCP N4 Session中的冗余参数
pfcp.f_seid && pfcp.create_far && pfcp.apply_action == DUPL

# 过滤GTP-U中的QoS Monitoring时间戳
gtp.v1.ext_header_type == 0x85 && gtp.timestamp