This question was posed to me recently, with the added observation that it seemed no progress had been made in the last two years. From my perspective this isn’t quite true.
The specification is still maintained by IBM, no movement has been made to standardize it at OASIS like MQTT has been. That is not to say that the subject of MQTT-SN has not arisen in the MQTT OASIS Technical Committee (TC) discussions, it has. But amongst the numerous improvements that we wanted to make to MQTT 3.1.1, and an ambitious timescale — publishing the new version MQTT 5.0 this year (2017) — addressing non TCP networks in MQTT was put to one side.
There is a continual wavering in my mind as to the importance of MQTT-SN. On one hand, edge computing platforms are getting ever more powerful, on the other, low power consumption is very important for battery power. The powerful edge processors are likely to have TCP stacks for which MQTT is appropriate: but there are still use cases for which low power use is the crucial factor. UDP, Bluetooth Low Energy (BLE) are typical transports used in this case.
If there is enough interest in a standardized MQTT-SN, its features could be addressed by the MQTT OASIS TC. There are a number of options. Incorporating MQTT-SN or its features into the main MQTT specification is one. However MQTT currently requires a reliable underlying network transport (TCP). To change that assumption we would have to consider very carefully the implications, which could take a significant amount of time. It has been suggested that MQTT-SN could be dealt with as a committee note: I’m not sure what form that would take.
In the meantime, I’ve been trying to get more MQTT-SN capabilities added to the Eclipse® Paho project. After I contributed an initial MQTT-SN packet library a couple of years ago, and the RSMB broker with MQTT-SN support to the Eclipse Mosquitto project at its inception, things stalled for a while (but not for a lack of interest on my part). There are forks of RSMB with fixes to the MQTT-SN support, and various gateways and clients around. One of those, written by Tomoaki Yamaguchi, had gained some support and I forget exactly how it happened, but Tomoaki has now contributed an MQTT-SN transparent gateway to Paho.
Over the past months this gateway has matured nicely. I recently used it to replace the use of RSMB in this experiment of Benjamin Cabé’s and it worked well. If we add BLE support to the gateway, then the Node.js BLE to UDP MQTT-SN forwarder in that experiment would not be required either. The gateway is written with the intention of allowing other transports to be added, so this should be eminently feasible.
I do remember seeing an email or post or something recently describing some other MQTT-SN components written by the poster. But now I can’t find or remember where I saw it. If this wasn’t a dream, and you know of such a thing, or it was you, please do let me know.
Where do we go from here? Two avenues: practical implementations and the specification. After the MQTT 5.0 standard is published, we can see if there is any interest in the OASIS TC in pursuing the application of MQTT to non-TCP networks. In the meantime, I will continue working on and encouraging MQTT-SN contributions of the current specification to Paho and elsewhere.
If you are interested in MQTT-SN and would like to see it considered by the OASIS MQTT TC, or make any other comments to the TC, then you can use the mailing list. If you know of any other implementations or have any questions, or suggestions for Paho, then I will be happy to hear of them.