In addition to publishing its data, the AVR®-IoT Development Boards are
capable of subscribing to a topic. When subscribing to a topic, it will receive data
from the Google Cloud whenever data is published to the cloud on the
subscription topic. Subscribing to topics is desired when the receiver is interested in
the information sent to the broker by other connected client devices publishing data
using the subscribed topic. After sending a SUBSCRIBE packet, all the messages published
on the specific topic of subscription are received by the board. As of now, the board
subscribes to the ‘/devices/{deviceID}/config’ topic. This is the only
topic provided by Google Cloud for subscribing using the MQTT
connection.