When to use MQTT and when to use REST for event submission

Question

The IBM IoT Foundation allows devices to submit events to the IBM cloud for consumption and recording. There appear to be two primary mechanisms to achieve the transmission of events ... MQTT and REST (HTTP POST requests). Assuming that a project will have sensors with direct TCP connectivity to IBM cloud over the Internet, what might we consider as the potential distinctions between the two technologies? What factors would cause us to choose MQTT or REST as the technology to use? Are there any substantial performance differences at the final mile at the IBM end that would say that one technology is preferred over another?

Answer 1

MQTT is designed to be a fast and lightweight messaging protocol, and is as a result, faster and more efficient at this than HTTP when used to do the equivalent. More efficient not only means less traffic data and more speed, but sometimes it can mean less electrical power as well. MQTT is particularly good where bandwidth is a concern.

MQTT does, however, need a client implementation (like Paho) which is possibly a rarer thing than an HTTP client implementation, which would be more ubiquitous and therefore more likely/easily available on any given device.

There are also TCP/IP port considerations, where some network hardware may require HTTP ports 80 or 443 (although IoTF supports MQTT and MQTTWS on port 443).

There may also be an ideological or philosophical reason for choosing HTTP instead of MQTT (or COAP for that matter), but usually, I would say the reasons for choosing HTTP instead of MQTT would be network related or client support related.

There is no official paper on the performance differences yet, but safe to say MQTT will be more efficient and faster given just about any messaging scenario (long lived connections or adhoc etc.)