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 Subprotocol 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 modify the registration of the WebSocket MQTT sub-protocol under the “WebSocket Subprotocol Name” registry with the following data:

Figure 6.6‑1 - IANA WebSocket Identifier

Subprotocol Identifier	mqtt
Subprotocol Common Name	mqtt
Subprotocol Definition	http://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html