WebRTC implements NAT traversal through the ICE (Interactive Connectivity Establishment) framework, which integrates STUN and TURN protocols to solve peer-to-peer connection problems in NAT environments.
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STUN (Session Traversal Utilities for NAT):
- Role: Helps clients obtain their public IP address and port
- Working principle: The client sends a request to the STUN server, and the STUN server returns the client's public address information
- Applicable scenarios: Suitable for most NAT types, such as cone NAT
- Limitations: Cannot穿透 symmetric NAT
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TURN (Traversal Using Relays around NAT):
- Role: Acts as a relay server to forward media data when STUN cannot穿透 NAT
- Working principle: The client connects to the TURN server, and all media data is relayed through the TURN server
- Applicable scenarios: Suitable for complex network environments such as symmetric NAT
- Limitations: Increases latency and bandwidth consumption, requires additional server resources
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ICE (Interactive Connectivity Establishment):
- Role: Integrates STUN and TURN to find the best communication path for WebRTC connections
- Working principle:
- Collect all possible candidate addresses (local address, public address returned by STUN server, TURN server address)
- Sort these candidate addresses, prioritizing direct connection paths with low latency
- Try to establish connections with the other party's candidate addresses until a viable path is found
- Advantages: Improves connection success rate, automatically selects the best path
WebRTC's NAT traversal process:
- The client collects local ICE candidates
- Obtains public ICE candidates through the STUN server
- If a TURN server is configured, obtains relay ICE candidates
- Exchanges ICE candidates through the signaling server
- Both parties try to establish connections using these candidates
- Select the best connection path for communication