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
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
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
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
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.