NSSF切片选择与AMF重选信令拆解

graph LR
    subgraph S-NSSAI
        SST["SST<br/>8-bit<br/>切片服务类型"]
        SD["SD<br/>24-bit<br/>切片区分符<br/>(可选)"]
    end
    SST -->|标准值| E["1=eMBB<br/>2=URLLC<br/>3=MIoT<br/>4=V2X"]
    SD -->|运营商自定义| F["同一SST下<br/>区分多实例"]

stateDiagram-v2
    [*] --> Configured: UE开机/PLMN变更
    Configured --> Requested: UE发起注册<br/>携带Requested NSSAI
    Requested --> Allowed: NSSF验证通过
    Requested --> Rejected: S-NSSAI不在签约数据中<br/>或TA不支持
    Allowed --> Requested: 移动性注册更新<br/>或新切片请求
    Rejected --> Requested: UE更换切片请求
    Allowed --> Configured: 注销/PLMN变更

sequenceDiagram
    participant UE
    participant RAN as (R)AN<br/>gNB
    participant IAMF as Initial AMF
    participant NSSF as NSSF
    participant UDM
    participant NRF
    participant TAMF as Target AMF

    Note over UE,TAMF: 阶段一：初始注册与切片查询

    UE->>RAN: 1. AN Message<br/>AN Parameters: Requested NSSAI, SUPI/5G-GUTI<br/>NAS: Registration Request<br/>(Registration type, Requested NSSAI, 5G-GUTI)

    RAN->>IAMF: 2. NGAP Initial UE Message<br/>Routing ID从5G-S-TMSI解析<br/>携带完整NAS容器

    Note over IAMF: Step 3: Initial AMF判断<br/>检查Requested NSSAI<br/>本AMF是否支持？

    IAMF->>UDM: 4. Nudm_SDM_Get (Supi)<br/>获取Subscription Data<br/>含Subscribed S-NSSAIs

    UDM-->>IAMF: 4a. Subscribed S-NSSAIs<br/>Default S-NSSAI指示

    Note over IAMF: Step 5: Initial AMF发现<br/>自身不支持UE请求的切片<br/>触发NSSF查询

    IAMF->>NSSF: 6. Nnssf_NSSelection_Get<br/>(home-plmn-id, target-plmn-id,<br/>s-nssai-list=Requested NSSAI,<br/>tai=当前TA, nf-type=AMF,<br/>slice-info-request-for-registration)

    Note over NSSF: Step 7: NSSF执行切片选择<br/>a) 匹配Subscribed S-NSSAI<br/>b) 确定Allowed NSSAI<br/>c) 选择NSI Instance<br/>d) 确定Target AMF Set

    NSSF-->>IAMF: 8. NssaiSelectionInfo<br/>{Allowed NSSAI,<br/>Configured NSSAI mapping,<br/>Target AMF Set ID,<br/>NSI Information List,<br/>Rejected NSSAI in PLMN/TA}

    Note over UE,TAMF: 阶段二：AMF重选与重路由

    alt Target AMF在不同AMF Set
        IAMF->>RAN: 9. NGAP Reroute NAS Request<br/>携带: 原始NAS Registration Request,<br/>Target AMF Set ID,<br/>Allowed NSSAI

        RAN->>TAMF: 10. NGAP Initial UE Message<br/>路由到Target AMF Set中的AMF
    else Target AMF在同一AMF Set
        IAMF->>NRF: 9a. Nnrf_NFDiscovery_Request<br/>(target-amf-set-id, s-nssai)
        NRF-->>IAMF: Candidate AMF List
        IAMF->>TAMF: 9b. Namf_Communication<br/>_N1MessageNotify<br/>转发NAS Registration Request
    end

    Note over UE,TAMF: 阶段三：Target AMF完成注册

    TAMF->>UE: 11. Authentication/Security<br/>标准认证流程
    UE-->>TAMF: 认证响应

    TAMF->>UDM: 12. Nudm_UECM_Registration<br/>注册UE上下文
    TAMF->>UDM: 13. Nudm_SDM_Get<br/>获取完整签约数据

    TAMF-->>UE: 14. Registration Accept<br/>Allowed NSSAI<br/>Configured NSSAI (如需更新)<br/>5G-GUTI

flowchart TD
    A[收到Registration Request] --> B{AMF本地支持<br/>Requested NSSAI中<br/>的所有S-NSSAI?}
    B -->|是| C[直接处理注册<br/>无需NSSF]
    B -->|否| D{Requested NSSAI<br/>是否为空?}
    D -->|空| E{UE是否有<br/>Default S-NSSAI?}
    E -->|是| F[使用Default S-NSSAI<br/>作为Allowed NSSAI]
    E -->|否| G[查询NSSF获取<br/>Configured NSSAI]
    D -->|非空| H[查询NSSF执行<br/>切片选择]
    H --> I{NSSF返回<br/>Target AMF Set?}
    I -->|是,与本AMF同Set| J[无需重路由<br/>本地处理]
    I -->|是,与本AMF不同Set| K[触发NGAP<br/>RerouteNASRequest]
    I -->|否| L[按NSSF返回的<br/>Allowed NSSAI处理]
    G --> M[NSSF返回<br/>Configured NSSAI]
    M --> N[UE Configuration Update<br/>下发Configured NSSAI]

flowchart LR
    subgraph NSSF内部决策
        A[Requested NSSAI] --> B[S-NSSAI匹配<br/>vs Subscribed S-NSSAIs]
        B --> C[TA可用性验证]
        C --> D[NSI Instance选择]
        D --> E[AMF Set确定]
        E --> F[生成NssaiSelectionInfo]
    end

graph TD
    subgraph Nnssf_NSSelection_Get Response
        A[NssaiSelectionInfo] --> B[Allowed NSSAI]
        A --> C[Configured NSSAI]
        A --> D[Target AMF Set]
        A --> E[NSI Information List]
        A --> F[Rejected NSSAI]

        B --> B1["S-NSSAI #1: SST=1, SD=0x010203"]
        B --> B2["S-NSSAI #2: SST=2, SD=null"]

        E --> E1["NSI Info #1"]
        E1 --> E1a["nsiId: NSI-001"]
        E1 --> E1b["nrfId: https://nrf1..."]

        E --> E2["NSI Info #2"]
        E2 --> E2a["nsiId: NSI-002"]
        E2 --> E2b["nrfId: https://nrf2..."]

        F --> F1["Rejected in PLMN: SST=3"]
        F --> F2["Rejected in TA: SST=4"]
    end

Mapping Of NSSAI ::= SEQUENCE {
    servingPlmnSnssai  Snssai,   -- 当前服务PLMN的S-NSSAI
    homePlmnSnssai     Snssai    -- 对应的HPLMN S-NSSAI
}

sequenceDiagram
    participant UE
    participant AMF as AMF/Initial AMF
    participant NSSF
    participant UDM

    Note over UE: 本地存储:<br/>Configured NSSAI (PLMN-specific)

    UE->>AMF: Registration Request<br/>携带: Requested NSSAI<br/>(从Configured NSSAI中选取)

    AMF->>UDM: Nudm_SDM_Get<br/>获取Subscribed S-NSSAIs

    UDM-->>AMF: Subscribed S-NSSAIs<br/>含Default S-NSSAI指示

    AMF->>NSSF: Nnssf_NSSelection_Get<br/>Requested NSSAI + TA + Subscribed

    Note over NSSF: 交集运算:<br/>Requested ∩ Subscribed ∩ TA-Supported

    NSSF-->>AMF: Allowed NSSAI<br/>+ Rejected NSSAI<br/>+ Target AMF Set

    AMF-->>UE: Registration Accept<br/>Allowed NSSAI<br/>Configured NSSAI (更新)

    Note over UE: 更新本地存储:<br/>Allowed NSSAI (当前RA有效)<br/>Configured NSSAI (PLMN有效)