6 Using WebSocket as a network transport

If MQTT is transported over a WebSocket [RFC6455] connection, the following conditions apply:

• MQTT Control Packets MUST be sent in WebSocket binary data frames. If any other type of data frame is received the recipient MUST close the Network Connection[MQTT-6.0.0-1].
• A single WebSocket data frame can contain multiple or partial MQTT Control Packets. The receiver MUST NOT assume that MQTT Control Packets are aligned on WebSocket frame boundaries[MQTT-6.0.0-2].
• The client MUST include “mqtt” in the list of WebSocket Sub Protocols it offers[MQTT-6.0.0-3].
• The WebSocket Sub Protocol name selected and returned by the server MUST be “mqtt”[MQTT-6.0.0-4].
• The WebSocket URI used to connect the client and server has no impact on the MQTT protocol.

6.1 IANA Considerations

This specification requests IANA to register the WebSocket MQTT sub-protocol under the “WebSocket Subprotocol Name” registry with the following data:

Figure 6.1 - IANA WebSocket Identifier

Subprotocol Identifier	mqtt
Subprotocol Common Name	mqtt
Subprotocol Definition	http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html