WebRTC (P2P): как это работает на практике

Question

Accepted Answer

Signaling — ваш канал для SDP/ICE. ICE + STUN/TURN находят path. Всё encrypted (SRTP/DTLS). ~10–20% нужен TURN.

## Разбор

**Signaling yours to build.** WebRTC standardizes media, not discovery. SDP blobs — offer/answer + ICE candidates — over WebSocket, SSE, copy-paste.

**ICE finds path.** Candidates: local IP (host), public via **STUN** (server-reflexive), relay via **TURN**. Connectivity checks → best pair wins.

**STUN vs TURN — money question.** STUN cheap: «how outside sees you» → direct. **Symmetric NATs** defeat STUN — different port per destination. Then **TURN** relay — all media through it. Real bandwidth cost; **~10–20% need TURN**. No TURN = mysterious failures.

**Everything encrypted.** Media SRTP, `DataChannel` DTLS over SCTP. No opt-out. `DataChannel` configurable `unreliable`/`unordered` (UDP-like games) or reliable/ordered (TCP-like files).

## Итог

Ship signaling + STUN + TURN budget; symmetric NAT без TURN = silent user failures.