createDataChannel

createDataChannel is a method of the WebRTC RTCPeerConnection API that creates a data channel for bidirectional data transfer between peers. It returns an RTCDataChannel immediately and begins the in-band signaling process to establish the channel over the DTLS-SCTP transport. The remote peer typically receives the channel via the ondatachannel event when the channel is created.

Usage and parameters: The method takes a mandatory label string that identifies the data channel, and an optional dataChannelDict (DataChannelInit) object that configures the channel. The DataChannelInit dictionary can specify ordered (default true), maxPacketLifeTime (for unreliable delivery, in milliseconds), maxRetransmits (alternative to maxPacketLifeTime for unreliable delivery), protocol (application protocol string), negotiated (whether to negotiate out of band), and id (channel identifier used when negotiated is true). It is not valid to set both maxPacketLifeTime and maxRetransmits at the same time.

Behavior and data transfer: The returned RTCDataChannel exposes a readyState (connecting, open, closing, closed) and supports the send method to transmit data. Data can be text strings or binary data such as ArrayBuffer, TypedArray, or Blob. The channel fires events such as open, message, close, and error to signal state changes and incoming data.

Negotiation model: By default, data channels are negotiated in-band as part of the WebRTC signaling flow, with the remote peer creating a corresponding channel or receiving it via ondatachannel. If negotiated is set to true, both peers must explicitly create the channel with a matching id, using out-of-band signaling to agree on the channel.

Applications and considerations: Data channels are suitable for low-latency messaging, file transfer, and real-time collaboration. All data is transmitted over the secured DTLS transport, with SCTP providing reliability options as configured. Browser support is broad in modern environments, with some differences in options across implementations.