Browser Support

Chrome 56+ · Firefox 44+ · Safari 11+ · Edge 79+

Overview

RTCDataChannel is an arbitrary data channel established on RTCPeerConnection. Unlike WebSocket, DataChannel uses P2P direct connection, no server relay, lower latency, and is bidirectional full-duplex.

Gamepad sync, file transfer, collaborative editing, real-time whiteboard — these scenarios fit DataChannel perfectly.

Quick Start

// === Caller ===
const pc = new RTCPeerConnection({ iceServers: [{ urls: 'stun:stun.l.google.com:19302' }] });

const channel = pc.createDataChannel('chat', { ordered: true });

channel.onopen = () => {
  channel.send('Hello, peer!');
};

channel.onmessage = (e) => {
  console.log('Received:', e.data);
};

// === Callee ===
pc.ondatachannel = (e) => {
  const recvChannel = e.channel;
  recvChannel.onopen = () => recvChannel.send('Reply: You too!');
  recvChannel.onmessage = (e) => console.log('Received:', e.data);
};

Reliability Modes

pc.createDataChannel('label', {
  ordered: true,    // Preserve order (like TCP)
  // ordered: false, // Prioritize low latency, no order guarantee (like UDP)
});

Mode	Use Case
ordered: true	File transfer, JSON messages, collaborative editing (order matters)
ordered: false	Gamepad, real-time position, voice commands (packet loss tolerable)

Comparison with WebSocket

Feature	RTCDataChannel	WebSocket
Transmission path	P2P direct	Via server relay
Latency	Extremely low	Higher
Reconnect on disconnect	Need to rebuild connection	Auto reconnect
Server cost	No relay server needed	Needed
Complexity	Complex signaling	Simple

Notes

• ICE negotiation must complete first: readyState becomes 'open' only after connection establishes
• Peer must be online: P2P means both ends must keep page open; no "offline message" concept
• Large data must be fragmented: Single send cannot exceed 16 MB
• NAT traversal failure = unusable: Like media streams, P2P data also depends on ICE