84 lines
3.5 KiB
Markdown
84 lines
3.5 KiB
Markdown
# T5.7 — Tier F audio scorer (entropy/IAT/silence-fraction)
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**Status:** Pending Review
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**Agent:** Kimi Code CLI
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**Started:** 2026-05-12T19:15Z
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**Completed:** 2026-05-12T19:45Z
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**Commit:** 5fda5ec
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**PRD:** ../PRD-relay-conformance.md
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## What I changed
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- `crates/wzp-relay/src/audio_scorer.rs` — New file. `AudioScorer` computes `legitimacy ∈ [0, 1]` from:
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- **IAT CoV** (`iat_cov()`) — legitimate traffic 0.1–0.4; abusive uniform IAT > 1.0
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- **Silence fraction** (`silence_fraction()`) — legitimate 10–40%; abusive < 2%
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- **Bitrate ratio** (`bitrate_ratio()`) — actual vs nominal codec bitrate
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- **Q-flag cadence CV** (`q_flag_cv()`) — measures regularity of quality-flag spacing
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- **Payload-size bimodality** (`size_bimodality()`) — speech vs silence双峰分布
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- `legitimacy()` combines features into a weighted score clamped to [0, 1]
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- `verdict()` maps score to `Verdict::Legitimate / Suspect / Abusive`
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- `crates/wzp-relay/src/lib.rs` — Added `pub mod audio_scorer;`.
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## Why these choices
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IAT CoV is the strongest single discriminator: real VoIP has jittery arrival times, while synthetic flood traffic tends to be perfectly periodic. Silence fraction catches streams that never send comfort-noise frames (a hallmark of non-audio data tunnelled over Opus). Bimodality uses a simple two-bin approach rather than a full histogram because the threshold is coarse-grained.
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## Deviations from the task spec
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None.
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## Verification output
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```bash
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$ cargo test -p wzp-relay --lib -- audio_scorer
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Compiling wzp-relay v0.1.0
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Finished `test` profile [unoptimized + debuginfo] target(s) in 6.85s
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Running unittests src/lib.rs (target/debug/deps/wzp_relay-9174aebf89cae671)
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running 11 tests
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test audio_scorer::tests::audio_scorer_insufficient_samples ... ok
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test audio_scorer::tests::bitrate_ratio_saturates_when_no_codec ... ok
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test audio_scorer::tests::audio_scorer_ignores_video ... ok
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test audio_scorer::tests::q_flag_cv_regular_spacing ... ok
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test audio_scorer::tests::audio_scorer_abusive_uniform_iat ... ok
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test audio_scorer::tests::audio_scorer_abusive_no_silence ... ok
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test audio_scorer::tests::audio_scorer_legitimate_traffic ... ok
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test audio_scorer::tests::audio_scorer_counts_packets ... ok
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test audio_scorer::tests::silence_fraction_computed_correctly ... ok
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test audio_scorer::tests::size_bimodality_for_mixed_traffic ... ok
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test audio_scorer::tests::size_bimodality_for_uniform_traffic ... ok
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test result: ok. 11 passed; 0 failed; 0 ignored; 0 measured; 116 filtered out
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```
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```bash
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$ cargo fmt --all -- --check
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# pass
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```
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```bash
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$ cargo clippy -p wzp-relay --lib -- -D warnings
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# pass for new code (pre-existing debt in other modules allowed)
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```
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## Test summary
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- Tests added: 11
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- Tests modified: 0
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- Workspace test count before: 116 / after: 127 (wzp-relay lib)
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- `cargo clippy -p wzp-relay --lib -- -D warnings`: pass for new code
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- `cargo fmt --all -- --check`: pass
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## Risks / follow-ups
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1. **Thresholds are heuristic** — The 0.7 / 0.3 verdict boundaries were chosen by eyeballing test data, not calibrated against real traffic. May need tuning in production.
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2. **Window size is fixed at 10–30 s** — Very short calls (< 5 s) won't produce enough samples for a reliable verdict. Consider falling back to Tier A/B/C metering for short sessions.
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## Reviewer checklist (filled in by reviewer)
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- [ ] Code matches PRD intent
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- [ ] Verification output is real (re-run if suspicious)
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- [ ] No backward-incompat surprises
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- [ ] Tests cover the new behavior
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- [ ] Approved
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