Yes, as mentioned in Steve-o’s comment MQTT via websockets is very possible. There are 2 options at the moment IBM’s MQ 7.5 comes with websockets support, you can find details here. The Mosquitto broker has a javascript client with an example running here. To answer your second question lighttpd has a websockets module that can … Read more
A summary of the message ordering capabilities in MQTT 3.1.1 can be found in the specification itself here. In summary: no guarantees are made about the relative ordering of messages published with different QoS values. (for example, QoS 0 can over take QoS 2 for example as it involves a single packet rather than the … Read more
LWT messages are not really concerned about detecting whether a client has gone offline or not (that task is handled by keepAlive messages). LWT messages are about what happens after the client has gone offline. The analogy is that of a real last will: If a person dies, she can formulate a testament, in which … Read more
There are few advantages in MQTT-SN (SN for Sensors Network) over MQTT, especially for embedded devices. Advantages MQTT-SN uses topic ID instead of topic name. First client sends a registration request with topic name and topic ID (2 octets) to a broker. After the registration is accepted, client uses topic ID to refer the topic … Read more
You need: an MQTT broker which runs on the server side. This could be something like the mosquitto broker which is Open Source. an MQTT client library which you include in your Android app, enabling your app to connect, subscribe, and publish messages. There are a number of Java options listed at http://mqtt.org/software to come … Read more
It depends on what you are trying to do and what hardware you are running. MQTT has very low keep-alive traffic. XMPP is a an IM protocol, and has a much, much higher overhead in handling presence messages between all the clients. If you have a small memory footprint constraint, then having to handle the … Read more
The main motive behind Kafka is scalability. MQTT is a protocol with public specification for lightweight client / message broker communications, allowing publish/subscribe exchanges. Multiple implementations of client libraries and brokers (Mosquitto, JoramMQ…) exist and are virtually compatible. MQTT just specifies the transport, and vaguely the application part (i.e. how data is handled and possibly … Read more
In separate terminal windows do the following: Start the broker: mosquitto Start the command line subscriber: mosquitto_sub -v -t ‘test/topic’ Publish test message with the command line publisher: mosquitto_pub -t ‘test/topic’ -m ‘helloWorld’ As well as seeing both the subscriber and publisher connection messages in the broker terminal the following should be printed in the … Read more
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 non-browser languages the MQTT client libraries only use native MQTT. For Javascript … Read more
Subscribing to # gives you a subscription to everything except for topics that start with a $ (these are normally control topics anyway). It is better to know what you are subscribing to first though, of course, and note that some broker configurations may disallow subscribing to # explicitly.