A WebSocket is very similar to a TCP socket, the key difference is that it allows a web browser to open a bi-directional communication pipe to a server. With this in place it is now possible to provide first class MQTT support for Web applications running in a web browser.

There are a couple of options

1. IBM's MQ 7.5 comes with websockets support
2. The Mosquitto broker has a Javascript client with an example running
3. The HiveMQ MQTT broker has native websockets support.
4. Mosca node.js-based broker has native websockets support.

The v3.1 protocol can flow as is but there are a couple of other WebSocket features that need to be specified to provide inter-operability. These are discussed on the Eclipse Paho wiki and both the IBM and Mosquitto implementations have collaborated on these. HiveMQ also implements these behaviours.

Typically a webserver will require an additional WebSockets module such as pywebsocket or lighthttpd's mod_websocket to do forwarding to an existing broker.