VoNR EVS编解码协商信令拆解：SDP Offer/Answer五维参数博弈与CMR动态适配

┌──────────────────────────────────────────────────┐
│              EVS Codec Architecture              │
├──────────────────────────────────────────────────┤
│                                                  │
│  ┌─────────────────────────────────────────────┐ │
│  │         EVS Primary Mode (Mode 0)           │ │
│  │  ┌───────┐  ┌───────┐  ┌──────┐  ┌──────┐  │ │
│  │  │  NB   │  │  WB   │  │ SWB  │  │  FB  │  │ │
│  │  │4 kHz  │  │8 kHz  │  │16kHz │  │20kHz │  │ │
│  │  │5.9-24.4│ │5.9-24.4│ │5.9-24.4│ │16.4-24.4│ │
│  │  └───────┘  └───────┘  └──────┘  └──────┘  │ │
│  └─────────────────────────────────────────────┘ │
│                                                  │
│  ┌─────────────────────────────────────────────┐ │
│  │     EVS AMR-WB IO Mode (Mode 1)             │ │
│  │  ┌──────────────────────────────────────┐   │ │
│  │  │  WB (8 kHz): 6.6, 8.85, 12.65,      │   │ │
│  │  │  14.25, 15.85, 18.25, 19.85,         │   │ │
│  │  │  23.05, 23.85 kbps                   │   │ │
│  │  └──────────────────────────────────────┘   │ │
│  └─────────────────────────────────────────────┘ │
└──────────────────────────────────────────────────┘

┌───────────────────────────────────────────────────────────┐
│           SDP Offer/Answer 五维协商博弈空间                │
│                                                           │
│  Dim-1: evs-mode-switch ──→ 双模式开关                    │
│         0 = 仅EVS Primary                                 │
│         1 = Primary + AMR-WB IO                           │
│                                                           │
│  Dim-2: br (bitrate) ──→ 速率范围约束                     │
│         Offer: br=5.9-24.4 (允许范围)                      │
│         Answer: br=13.2 (锁定值)                          │
│                                                           │
│  Dim-3: bw (bandwidth) ──→ 带宽模式组合                   │
│         Offer: bw=nb-wb-swb (多选)                        │
│         Answer: bw=swb (单选)                             │
│                                                           │
│  Dim-4: cmr (codec mode request) ──→ 运行时适配范围       │
│         cmr=5.9-24.4 (允许CMR切换范围)                    │
│                                                           │
│  Dim-5: max-red + dtx ──→ 抗丢包策略                      │
│         max-red=220; dtx=on                               │
│                                                           │
│  约束: br范围 ∩ bw支持的速率 = 有效协商空间               │
└───────────────────────────────────────────────────────────┘

sequenceDiagram
    participant UE-A as 主叫UE-A<br/>(VoNR)
    participant gNB as gNB
    participant PCSCF_A as P-CSCF/SBC-A
    participant SCSCF as S-CSCF
    participant TAS as TAS/MMTel AS
    participant PCSCF_B as P-CSCF/SBC-B
    participant UE-B as 被叫UE-B<br/>(VoNR)

    Note over UE-A,UE-B: 阶段1: SDP Offer上行（EVS能力宣告）
    UE-A->>PCSCF_A: SIP INVITE<br/>SDP Offer: EVS Primary+AMR-WB IO<br/>a=rtpmap:96 EVS/16000/1<br/>a=fmtp:96 evs-mode-switch=1;<br/>br=5.9-24.4; bw=nb-wb-swb;<br/>cmr=5.9-24.4; max-red=220
    PCSCF_A->>PCSCF_A: ①P-CSCF策略检查<br/>授权b=AS带宽<br/>检查5QI=1 QoS Flow
    PCSCF_A->>SCSCF: INVITE(转发)<br/>SDP可能被SBC修改
    SCSCF->>TAS: INVITE(iFC触发)<br/>MMTel业务触发
    TAS->>SCSCF: INVITE(转发)
    SCSCF->>PCSCF_B: INVITE(路由)
    PCSCF_B->>PCSCF_B: ②被叫侧策略检查<br/>带宽授权
    PCSCF_B->>UE-B: INVITE(最终下发)<br/>SDP Offer可能被裁剪

    Note over UE-A,UE-B: 阶段2: SDP Answer下行（编解码锁定）
    UE-B->>PCSCF_B: 180 Ringing<br/>SDP Answer: 选择EVS SWB<br/>a=fmtp:96 evs-mode-switch=1;<br/>br=13.2; bw=swb;<br/>cmr=5.9-24.4; max-red=220
    PCSCF_B->>PCSCF_B: ③Answer策略验证<br/>确认QoS Flow建立
    PCSCF_B->>SCSCF: 180 Ringing(转发)
    SCSCF->>TAS: 180 Ringing(iFC路径)
    TAS->>SCSCF: 180 Ringing(转发)
    SCSCF->>PCSCF_A: 180 Ringing(路由)
    PCSCF_A->>PCSCF_A: ④主叫侧QoS确认<br/>触发N2 SMF/PCF交互
    PCSCF_A->>UE-A: 180 Ringing<br/>SDP Answer(最终确认)

    UE-A->>PCSCF_A: PRACK(可靠性确认)
    PCSCF_A->>UE-B: PRACK(端到端)

    Note over UE-A,UE-B: 阶段3: 200 OK与RTP流建立
    UE-B->>UE-A: 200 OK(INVITE确认)
    UE-A->>UE-B: ACK

    Note over UE-A,UE-B: 阶段4: RTP流建立+CMR动态适配
    UE-A->>UE-B: RTP EVS SWB 13.2kbps<br/>CMR=24.4(请求升速)
    UE-B->>UE-A: RTP EVS SWB 24.4kbps<br/>CMR=13.2(请求降速)
    UE-A->>UE-B: RTP EVS SWB 13.2kbps<br/>CMR=13.2(保持)

m=audio 49152 RTP/AVPF 96 97 98
a=rtpmap:96 EVS/16000/1
a=fmtp:96 evs-mode-switch=1; br=5.9-24.4; bw=nb-wb-swb;
    cmr=5.9-24.4; max-red=220; dtx=on; hf-only=0
a=rtpmap:97 AMR-WB/16000/1
a=fmtp:97 mode-set=0,1,2; mode-change-capability=2; max-red=220
a=rtpmap:98 telephone-event/16000
a=ptime:20
a=maxptime:240
b=AS:49
b=RS:0
b=RR:0
a=sendrecv

m=audio 49170 RTP/AVPF 96 98
a=rtpmap:96 EVS/16000/1
a=fmtp:96 evs-mode-switch=1; br=13.2; bw=swb;
    cmr=5.9-24.4; max-red=220; dtx=on
a=rtpmap:98 telephone-event/16000
a=ptime:20
b=AS:49
a=sendrecv

flowchart TB
    subgraph RTP_Payload["EVS RTP Payload结构"]
        CMR_Field["CMR字段 (4 bits)"]
        TOC_Field["TOC字段 (Table of Contents)"]
        Frame_Data["EVS帧数据"]
    end

    subgraph CMR_Mapping["CMR值→速率映射"]
        CMR_0["CMR=0: 5.9 kbps"]
        CMR_1["CMR=1: 7.2 kbps"]
        CMR_2["CMR=2: 8.0 kbps"]
        CMR_3["CMR=3: 9.6 kbps"]
        CMR_4["CMR=4: 13.2 kbps"]
        CMR_5["CMR=5: 16.4 kbps"]
        CMR_6["CMR=6: 24.4 kbps"]
        CMR_7["CMR=7: 32.0 kbps"]
        CMR_8["CMR=8: 48.0 kbps"]
        CMR_15["CMR=15: 无请求/保持"]
    end

    subgraph Adaptation_Logic["CMR自适应决策逻辑"]
        PLR["丢包率↑ → 请求降速<br/>(更多冗余空间)"]
        BW_Avail["带宽充裕 → 请求升速<br/>(更高质量)"]
        Delay["时延敏感 → 请求降速<br/>(减小帧大小)"]
        Jitter["抖动增大 → 请求降速<br/>(降低缓冲压力)"]
    end

    RTP_Payload --> CMR_Mapping
    CMR_Mapping --> Adaptation_Logic

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  CMR (4bits)  |R|  TOC (7bits)|   EVS Frame Data ...          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 0                   1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  CMR (3bits)  |  EVS Frame   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

sequenceDiagram
    participant UE as UE
    participant PCSCF as P-CSCF
    participant PCF as PCF
    participant SMF as SMF
    participant UPF as UPF
    participant gNB as gNB

    UE->>PCSCF: SIP INVITE(SDP Offer)<br/>b=AS:49, EVS SWB
    PCSCF->>PCF: N7/Rx: AAR<br/>Media-Type=Audio<br/>Bandwidth=49kbps<br/>Codec=EVS SWB 24.4kbps
    PCF->>PCF: 策略决策:<br/>5QI=1(GBR)<br/>ARP=优先级<br/>MBR=49kbps<br/>GBR=32kbps
    PCF->>SMF: N7: PCC Rule<br/>5QI=1, Flow=RTP
    SMF->>SMF: QoS Flow创建:<br/>QFI=1, GBR=32kbps
    SMF->>UPF: N4: PDR/FAR<br/>QoS Flow规则
    SMF->>gNB: N2: PDU Session<br/>Resource Setup<br/>5QI=1, GBR
    gNB->>gNB: DRB配置:<br/>RLC-UM, PDCP<br/>逻辑信道优先级
    gNB-->>SMF: N2: Resource Setup Response
    SMF-->>PCF: N7: 确认
    PCF-->>PCSCF: N7/Rx: AAA<br/>QoS授权确认
    PCSCF->>UE: 180 Ringing(SDP Answer)

# INVITE中的SDP Offer
m=audio 49152 RTP/AVPF 96 97 98
a=rtpmap:96 EVS/16000/1          ← EVS Payload Type
a=fmtp:96 evs-mode-switch=1; br=5.9-24.4; bw=nb-wb-swb; max-red=220

# 180 Ringing中的SDP Answer
m=audio 49170 RTP/AVPF 96 98
a=rtpmap:96 EVS/16000/1          ← 确认选择EVS
a=fmtp:96 evs-mode-switch=1; br=13.2; bw=swb; max-red=220
                                  ← 锁定SWB 13.2kbps

# INVITE中的SDP Offer（包含EVS）
m=audio 49152 RTP/AVPF 96 97 98
a=rtpmap:96 EVS/16000/1
a=fmtp:96 evs-mode-switch=1; br=5.9-24.4; bw=nb-wb-swb
a=rtpmap:97 AMR-WB/16000/1       ← 回退候选

# 200 OK中的SDP Answer（选择AMR-WB）
m=audio 49170 RTP/AVPF 97 98
a=rtpmap:97 AMR-WB/16000/1        ← 被叫选了AMR-WB!
a=fmtp:97 mode-set=0,1,2; max-red=220
# EVS PT=96被移除 → 协商失败

# 过滤SIP INVITE中的SDP
sip.Request-Line contains "INVITE" && sdp.payload_type == "96"

# 过滤EVS RTP流
rtp.payload_type == 96

# 检查CMR变化（需要解析EVS payload）
rtp.payload_type == 96 && frame.len > 100

# 过滤SDP fmtp参数
sdp.fmtp contains "evs-mode-switch"

stateDiagram-v2
    [*] --> Idle: UE空闲态
    Idle --> SDP_Offer_Sent: SIP INVITE<br/>(构造SDP Offer)
    SDP_Offer_Sent --> Wait_Answer: P-CSCF转发

    Wait_Answer --> EVS_Negotiated: 180/200 OK<br/>SDP Answer选择EVS
    Wait_Answer --> AMRWB_Fallback: SDP Answer<br/>选择AMR-WB
    Wait_Answer --> Codec_Mismatch: 488 Not Acceptable<br/>无公共编解码
    Wait_Answer --> SDP_Offer_Sent: 重发INVITE<br/>(超时重试)

    EVS_Negotiated --> RTP_Active: ACK确认<br/>RTP流建立
    AMRWB_Fallback --> RTP_Active: ACK确认<br/>AMR-WB RTP流

    RTP_Active --> CMR_Adaptation: RTP流中<br/>CMR动态调整
    CMR_Adaptation --> CMR_Adaptation: 速率升降<br/>(在SDP范围内)
    CMR_Adaptation --> Mode_Switch: EVS Primary↔<br/>AMR-WB IO切换
    Mode_Switch --> CMR_Adaptation: 继续适配

    RTP_Active --> Reinvite: SIP re-INVITE/<br/>UPDATE<br/>(重大参数变更)
    Reinvite --> EVS_Negotiated: 新SDP协商
    Reinvite --> AMRWB_Fallback: 降级协商

    RTP_Active --> Session_End: BYE
    Codec_Mismatch --> Idle: 会话终止
    Session_End --> Idle: 回到空闲