Data
A single unit of application data sent or received over a data track.
Parameters
payload
The application payload carried by this frame.
user
Optional sender-provided timestamp, opaque to the SDK and carried end-to-end unmodified. Publisher and subscriber agree on what it means, so a sensor's clock works as well as wall time. now and durationSinceTimestamp are the exception — they read it as milliseconds since the Unix epoch.