Most server-client communication on the web is based on a request and response structure. The client sends a request to the server and the server responds to this request. The WebSocket protocol provides a two-way channel of communication between a server and client, allowing servers to send messages to clients without first receiving a request. For more information on the WebSocket protocol and its implementation in InterSystems IRIS, see the links below.
This tutorial is an update of "Asynchronous Websockets -- a quick tutorial" for Caché 2016.2+ and InterSystems IRIS 2018.1+