NSSF切片选择双阶段决策机制深度解析

┌──────────────────┬──────────────────────┐
│   SST (8 bits)   │   SD (24 bits, 可选)  │
└──────────────────┴──────────────────────┘

graph LR
    A[Subscribed S-NSSAI<br/>UDM签约数据] --> B[Requested NSSAI<br/>UE请求的切片]
    A --> C[Configured NSSAI<br/>网络配置给UE的切片]
    B --> D[Allowed NSSAI<br/>网络允许的切片]
    A --> E[Default S-NSSAI<br/>默认切片]
    F[Rejected S-NSSAI<br/>被拒绝的切片] --> G[Pending NSSAI<br/>等待NSSAA认证]

    style A fill:#4a90d9,color:#fff
    style D fill:#2ecc71,color:#fff
    style F fill:#e74c3c,color:#fff
    style G fill:#f39c12,color:#fff

sequenceDiagram
    participant UE
    participant RAN as (R)AN
    participant AMF
    participant NSSF
    participant UDM
    participant NRF

    Note over UE,NRF: 阶段一：Registration切片选择

    UE->>RAN: Registration Request<br/>+ Requested NSSAI<br/>+ Mapping of Requested NSSAI
    RAN->>AMF: N2 Message<br/>+ Registration Request

    rect rgb(240,248,255)
    Note over AMF: AMF本地检查<br/>是否能服务Requested NSSAI
    end

    AMF->>UDM: Nudm_SDM_Get<br/>(Subscribed S-NSSAIs)
    UDM-->>AMF: Subscribed S-NSSAIs<br/>+ Default S-NSSAI

    AMF->>NSSF: Nnssf_NSSelection_Get<br/>slice-info-request-for-registration

    rect rgb(255,250,240)
    Note over NSSF: NSSF四重决策:<br/>1.订阅交集运算<br/>2.S-NSSAI映射(HPLMN↔VPLMN)<br/>3.TA可用性过滤<br/>4.AMF能力匹配
    end

    NSSF-->>AMF: Allowed NSSAI<br/>+ Target AMF Set<br/>+ NSI Information<br/>+ NRF for NSI

    alt 需要AMF重选
        AMF->>AMF: 触发AMF Reselection<br/>(转发Registration Context)
        Note over AMF: 通过Namf_Communication<br/>转发到Target AMF
    end

    AMF-->>RAN: Registration Accept<br/>+ Allowed NSSAI<br/>+ Configured NSSAI(如需)
    RAN-->>UE: Registration Accept<br/>+ Allowed NSSAI

    Note over UE,NRF: 阶段二：PDU Session切片验证

    UE->>AMF: PDU Session Establishment Request<br/>+ S-NSSAI
    AMF->>AMF: 校验S-NSSAI ∈ Allowed NSSAI

    alt S-NSSAI需要NSSAA且未完成
        AMF->>AMF: 触发NSSAA流程<br/>(TS 33.501)
    end

    AMF->>NSSF: Nnssf_NSSelection_Get<br/>slice-info-request-for-pdu-session
    NSSF-->>AMF: NSI Information<br/>+ SMF Set for slice

    AMF->>NRF: Nnrf_NFDiscovery<br/>(SMF for S-NSSAI + DNN)
    NRF-->>AMF: SMF Instance(s)

{
  "subscribedNssai": [
    {"sst": 1, "sd": "000001"},
    {"sst": 2, "sd": "000002"},
    {"sst": 3}
  ],
  "requestedNssai": [
    {"sst": 1, "sd": "000001"},
    {"sst": 2}
  ],
  "mappingOfRequestedNssai": [
    {"sst": 1, "sd": "000001", "mappedSst": 1, "mappedSd": "010101"},
    {"sst": 2, "mappedSst": 2, "mappedSd": "020202"}
  ],
  "defaultConfiguredNssaiIndication": false,
  "ueUseSliceMbr": true
}

┌─────────────────────────────────────────────────┐
│              NsiInformation                      │
├─────────────────────────────────────────────────┤
│  nsiId: string          (切片实例标识)           │
│  nrfId: string          (该NSI对应的NRF URI)     │
│  nsApiRoot: string      (该NSI的API根路径)       │
│  supportedSnssaiList:   (该NSI支持的S-NSSAI)     │
│  ┌──────────────────────────────────┐            │
│  │  Snssai:                         │            │
│  │    sst: integer (0-255)          │            │
│  │    sd: string (可选, HEX)        │            │
│  └──────────────────────────────────┘            │
└─────────────────────────────────────────────────┘

输入:
  Requested NSSAI = [{SST:1, SD:000001}, {SST:2}, {SST:5, SD:000005}]
  Subscribed S-NSSAI = [{SST:1, SD:000001}, {SST:2, SD:000002}, {SST:3}]

运算规则:
  1. 精确匹配: SST+SD完全一致 → 匹配
  2. SST匹配: Requested中无SD, Subscribed中有SD → 以Subscribed为准
  3. Default S-NSSAI: 如果交集为空, 使用Default S-NSSAI

结果:
  初始Allowed = [{SST:1, SD:000001}, {SST:2, SD:000002}]
  Rejected = [{SST:5, SD:000005}]  (不在签约中)

graph TB
    subgraph HPLMN["HPLMN S-NSSAI"]
        H1["SST:128, SD:AABBCC<br/>运营商A的URLLC"]
        H2["SST:1<br/>标准eMBB"]
    end

    subgraph NSSF_Mapping["NSSF映射引擎"]
        M["S-NSSAI Mapping Table"]
    end

    subgraph VPLMN["VPLMN S-NSSAI"]
        V1["SST:2, SD:112233<br/>VPLMN的URLLC"]
        V2["SST:1<br/>标准eMBB(直通)"]
    end

    H1 -->|"映射规则#1"| M
    H2 -->|"标准值直通"| M
    M --> V1
    M --> V2

    style NSSF_Mapping fill:#fff3cd
    style HPLMN fill:#d4edda
    style VPLMN fill:#cce5ff

步骤:
  1. 从初始Allowed = [{SST:1, SD:000001}, {SST:2, SD:000002}]出发
  2. 查询TA NSSAI Availability:
     TAC=0x0001 → 支持 [{SST:1, SD:000001}, {SST:3}]
  3. 过滤结果:
     Allowed NSSAI = [{SST:1, SD:000001}]  (SST:2在当前TA不可用)
  4. 被TA拒绝的: [{SST:2, SD:000002}] → 放入rejectedNssaiInTa

stateDiagram-v2
    [*] --> Check_Current_AMF: AMF查询NSSF

    state Check_Current_AMF {
        [*] --> AMF_Supports_All: S-NSSAI ⊆ AMF能力
        [*] --> AMF_Partial: 部分S-NSSAI不支持
        [*] --> AMF_None: 完全不支持
    }

    AMF_Supports_All --> Return_Allowed: 直接返回Allowed NSSAI
    AMF_Partial --> Check_Slice_Aware_AMF: 需要评估AMF重选
    AMF_None --> Must_Reselect: 必须AMF重选

    state Check_Slice_Aware_AMF {
        [*] --> Find_AMF_Set: 查询支持目标切片的AMF Set
        Find_AMF_Set --> Single_Set: 唯一AMF Set
        Find_AMF_Set --> Multiple_Sets: 多个候选AMF Set
        Single_Set --> Return_Target_Set
        Multiple_Sets --> Prioritize: 按负载/优先级排序
    }

    Return_Target_Set --> AMF_Reselection: 返回targetAmfSet + NRF
    Prioritize --> AMF_Reselection

    AMF_Reselection --> [*]
    Return_Allowed --> [*]

Initial AMF → Target AMF:
  Namf_Communication_RegistrationContextTransfer
  {
    "ueContext": {
      "supi": "imsi-460001234567890",
      "allowedNssai": [...],
      "registrationRequest": { ... },
      "nssfInfo": { "targetAmfSet": "AMF-Set-2" }
    }
  }

Initial AMF → RAN: Reroute NAS Request
  (包含Target AMF的GUAMI或AMF Set ID)
RAN → Target AMF: N2 NAS Forward
  (原始Registration Request)

sequenceDiagram
    participant UE
    participant V_RAN as VPLMN (R)AN
    participant V_AMF as VPLMN AMF
    participant V_NSSF as VPLMN NSSF
    participant H_NSSF as HPLMN NSSF
    participant UDM as HPLMN UDM

    UE->>V_RAN: Registration Request<br/>+ Requested NSSAI(VPLMN值)
    V_RAN->>V_AMF: N2 + Registration Request

    V_AMF->>UDM: Nudm_SDM_Get<br/>(获取Subscribed S-NSSAI)
    UDM-->>V_AMF: Subscribed S-NSSAI<br/>(HPLMN格式)

    V_AMF->>V_NSSF: Nnssf_NSSelection_Get<br/>+ home-plmn-id<br/>+ roaming-indication=HOME_ROUTED

    V_NSSF->>H_NSSF: Nnssf_NSSelection_Get<br/>(跨PLMN查询HPLMN切片策略)
    H_NSSF-->>V_NSSF: HPLMN切片映射规则<br/>+ HPLMN Allowed NSSAI

    rect rgb(255,245,238)
    Note over V_NSSF: VPLMN NSSF执行:<br/>1.HPLMN S-NSSAI → VPLMN S-NSSAI映射<br/>2.过滤VPLMN TA可用的切片<br/>3.确定VPLMN的AMF Set
    end

    V_NSSF-->>V_AMF: Allowed NSSAI(VPLMN格式)<br/>+ Mapping of Allowed NSSAI<br/>+ Target AMF Set

    V_AMF-->>UE: Registration Accept<br/>+ Allowed NSSAI

stateDiagram-v2
    [*] --> Non_Pending: S-NSSAI无需NSSAA
    [*] --> Pending: S-NSSAI需NSSAA

    state Pending {
        [*] --> EAP_Started: AMF触发EAP
        EAP_Started --> EAP_Success: 认证成功
        EAP_Started --> EAP_Failure: 认证失败
        EAP_Success --> Authorized: 加入Allowed NSSAI
        EAP_Failure --> Rejected: 从Allowed NSSAI移除
    }

    Authorized --> [*]
    Non_Pending --> [*]
    Rejected --> [*]