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


Subprotocol Common Name


Subprotocol Definition


Solace Implementation Note

The Solace server supports WebSocket transport.

The Solace server supports WebSocket Secure transport.