In this section, we will have a look at four common protocols and technologies used for communication between IoT devices. ZigBee and Thread are both technologies that use radio to transmit information. ZigBee has long been the preferred way to transmit information between devices locally (without using the internet, but using radio signals), but is about to be replaced by Thread.

CoAP and MQTT, on the other hand, communicate over the internet. They are both intended to be used with constrained devices and have different areas where each protocol shines. We won't go into too much detail about CoAP and will concentrate on MQTT, starting with Chapter 3, Getting Started with MQTT, instead.