The RTCIceCandidate interface's read-only tcpType property is included on TCP candidates to provide additional details about the candidate type.

The tcpType field's value is set from the candidateInfo options object passed to the RTCIceCandidate() constructor. You can't specify the value of tcpType directly in the options object, but its value is automatically extracted from the object's candidate a-line, if it's formatted properly.

If the protocol is "tcp", tcpType has one of the following values:

"active"

The transport will try to open an outbound connection but won't receive incoming connection requests.

"passive"

The transport will receive incoming connection requests but won't try to open an outbound connection.

"so"

The transport will try to open a connection simultaneously with its peer.

tcpType is null for UDP candidates.

In this example, the candidate's protocol and tcpType are used to adjust the user interface for simultaneous-open TCP candidates.

if (candidate.protocol === "tcp" && candidate.tcpType === "so") {
  adjustForSimultaneousOpen(candidate);
}

• WebRTC API
• Introduction to WebRTC protocols
• WebRTC connectivity
• RTCIceCandidate.protocol
• RTCIceCandidate.type