October 2019
Intermediate to advanced
350 pages
9h 5m
English
Content preview from Hands-On Internet of Things with MQTT
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QoS 0 – fire and forget
Messages sent with QoS 0 are officially labeled as message delivery: they, at most once, are sent without caring if they ever reach the subscriber(s). It is the equivalent of sending a letter by post—it probably will be delivered, but something could go wrong. You never know for sure if it fell off a box and went missing.
While at most once does not sound very reliable (I would not send my packages with a postal service that claims they deliver their packets at most once), in most cases, MQTT packets sent with QoS 0 are delivered correctly anyway.
If you are wondering about the at most part, it just means that messages won't be delivered twice, or even more times, which can happen under certain circumstances when using ...
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