Direct MQTT vs MQTT over WebSocket

问题:

What are merits of MQTT over WebSocket compared to direct MQTT?

I'm considering using MQTT in my project and so I want to know why some people choose MQTT over WebSocket instead of direct MQTT.

回答1:

You should only need to run MQTT over websockets if you intend to publish/subscribe to messages directly from within webapps (in page).

Basically I would run pure MQTT for everything and only add the websockets if you actually need it.

For all the none browser languages the MQTT client libraries only use native MQTT. For Javascript there is both a pure MQTT library and the Paho in page library that uses websockets.

Edit: The firewall tunnelling use case is a valid reason to use MQTT over websockets and since writing this answer more of the none web/JavaScript client libraries have added support

回答2:

MQTT over websockets is perfect if ever a certain webpage is the sending or the receiving MQTT client.

A good summary of the capabilities of MQTT over websockets can be found here.

回答3:

Two main reasons for using MQTT over Websockets (which effectively means going over HTTP/HTTPS):

• Web apps (those running in a browser - e.g. written in JavaScript)
• Any other applications that don't want to use the 1883/8883 port and want to go over HTTP/HTTPS instead - this could be so that there is less of a chance of being blocked by a firewall (e.g. in a corporate network), as most firewalls will let HTTP traffic through

If you don't need or worry about the above, use "direct" MQTT:

• it is more efficient
• there are more client libraries for various languages that work with "direct" MQTT

回答4:

MQTT is a protocol which supports following:

• Provides publish/subscribe mechanism
• Quality of Service policy
• Have minimal overhead in communication
• Specifically designed for narrowband communication channel and
  constrained devices.

Depending upon device there is an implementation available.

Browser : It use's websockets. Websocket provides browsers with a capability to establish a full duplex communication. There is Javascript library to implement MQTT functionality, see Eclipse Paho JavaScript Client

Android : Their is a MQTT client library written in Java for developing applications on Android. See Eclipse Paho Android Service

So it depends on device that is going to use this functionality. For standards and specifications please visit MQTT Version 3.1.1

Hoping this helps.

Cheers !

回答5:

MQTT over web sockets is also helpful if the application is running behind a firewall that allows only 443 and 80 traffic. And, you have no control over the policies of the firewall.

回答6:

With MQTT over websockets every browser can be a MQTT device.

Due to the publish/subscribe pattern of MQTT, you get a real time push to your browser when an event – literally anywhere in the world – occurs, as long as you subscribe to the correct topic.

In the case of MQTT over WebSockets, the websockets connection forms an outer pipe for the MQTT protocol. The server/broker places the MQTT packet into a websockets packet and send it to the client/server. The client/server unpacks the MQTT packet from the websockets packet and then processes it as a normal MQTT packet.

Moreover, it has a great influence on internet of things. Please read the following documentations for further details.

SAP Cloud Platform Internet of Things

AWS IoT

MQTT over Websockets with HiveMQ

回答7:

MQTT Broker:

The counterpart of the MQTT client is the MQTT broker. The broker is at the heart of any publish/subscribe protocol. Depending on the implementation, a broker can handle up to thousands of concurrently connected MQTT clients.

MQTT Client: When we talk about a client, we almost always mean an MQTT client. Both publishers and subscribers are MQTT clients. The publisher and subscriber labels refer to whether the client is currently publishing messages or subscribing to messages (publish and subscribe functionality can also be implemented in the same MQTT client).

WebSocket: We have learned in the MQTT Essentials that MQTT is ideal for constrained devices and unreliable networks. It’s also perfect for sending messages with a very low overhead. It would be quite nice to send and receive MQTT messages directly in the browser of a mobile phone or in general. This is possible by MQTT over WebSockets.

You can use a third-party protocol. PAHO, EMQTT, VerneMQ.