I understand an MQTT client publishes data to a topic after connect message.
I am not sure how an MQTT client subscribing to a topic get updated when there is a publish to that topic.
Is it the subscriber that has to initiate a connection and then send a subscribe message each time to check the latest published update?
Or does the subscriber send a subscribe message once to the broker, and whenever there is a new publish, the broker automatically sends the published data to the subscriber?
Is there any option to automatically initiate a communication from broker to subscriber client to update the client with latest published data?