82 lines
3.1 KiB
Markdown
82 lines
3.1 KiB
Markdown
# T5.6 — Per-receiver layer selection at SFU
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**Status:** Pending Review
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**Agent:** Kimi Code CLI
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**Started:** 2026-05-12T18:45Z
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**Completed:** 2026-05-12T19:15Z
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**Commit:** 2bbb664
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**PRD:** ../PRD-video-simulcast.md
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## What I changed
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- `crates/wzp-relay/src/room.rs:185-220` — Added `ReceiverState` struct with:
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- `bwe_kbps`, `loss_pct` (AtomicU32/AtomicU8)
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- `selected_layer: AtomicU8`
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- `layer_changed_at: AtomicU64` (epoch ms)
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- `update(bwe, loss, now)` — applies thresholds with 3 s hysteresis
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- `crates/wzp-relay/src/room.rs:850-900` — Added `RoomManager::update_receiver_state()` and `selected_layer()`:
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- High layer: BWE > 3000 kbps && loss < 2%
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- Mid layer: BWE > 800 kbps
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- Low layer: default
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- `crates/wzp-relay/src/room.rs:1200-1300` — Updated `run_participant_plain` and `run_participant_trunked` forwarding loops to filter packets by `stream_id` against the receiver's `selected_layer`.
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- `crates/wzp-relay/src/room.rs:1960-2010` — Added 7 unit tests for `ReceiverState` and `RoomManager` isolation.
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## Why these choices
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Hysteresis prevents oscillation when BWE hovers near a threshold. Using `Atomic*` types lets `update_receiver_state` be called from any thread without locking the `RoomManager`. Layer selection is isolated per `(room, participant)` tuple so receivers in different rooms don't interfere.
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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 -- receiver_state
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Compiling wzp-relay v0.1.0
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Finished `test` profile [unoptimized + debuginfo] target(s) in 2.22s
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Running unittests src/lib.rs (target/debug/deps/wzp_relay-9174aebf89cae671)
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running 7 tests
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test room::tests::receiver_state_selects_high_on_good_link ... ok
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test room::tests::receiver_state_loss_blocks_high_layer ... ok
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test room::tests::receiver_state_defaults_to_layer_zero ... ok
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test room::tests::receiver_state_hysteresis_delays_switch ... ok
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test room::tests::receiver_state_selects_mid_on_medium_link ... ok
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test room::tests::room_manager_receiver_states_are_isolated_by_room ... ok
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test room::tests::room_manager_updates_receiver_state ... ok
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test result: ok. 7 passed; 0 failed; 0 ignored; 0 measured; 120 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 (new code only; pre-existing debt in federation/metrics/room allowed)
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```
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## Test summary
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- Tests added: 7
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- Tests modified: 0
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- Workspace test count before: 120 / 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. **Forwarding filter is O(N) per packet** — For large rooms this may become a bottleneck. Future optimization: pre-compute a `DashMap<receiver, layer>` cache refreshed every tick.
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2. **Hysteresis duration is hard-coded to 3 s** — May be too aggressive for mobile networks. Consider making it configurable per-room.
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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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