ICP DAS USA U-7500 Series, User Manual

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OPC UA I/O Series User Manual V4.0 – ICP DAS
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3.2.2 MQTT Client Setting of the UA I/O
UA I/O built-in MQTT Client function and itself is the MQTT Client side of the connect. When setting,
please set the connecting remote MQTT Broker device first, and then set the UA I/O module of the
MQTT client.
Reference for MQTT related basic knowledge:
MQTT
(MQ Telemetry Transport) is a lightweight publish/subscribe messaging protocol. An MQTT-based
application will include two or more clients , which are applications exchanging messages, and a broker ,
which is a server that accepts incoming messages and routes them to the appropriate destination client.
As with most
publish-subscribe systems, message sends involve publishing on a specified topic . The
broker then forwards the message to all subscribers of that topic. These primitives can be used to build
different interaction patterns. (as the picture below)
MQTT gives you flexibility by specifying a Quality of Service (QoS) with each message. QoS is a
parameter available on each publish call. It is one of three levels:

QoS 0: At most once

QoS 1: At least once

Q0S 2: Exactly once
Provides a Quality-of-Service data delivery: QoS can be selected based on the needs of the
application.
MQTT Retained messages: The last published message (with retained flag set to true) is stored at the
broker so that new subscribers can immediately obtain last known good value rather than wait for the
next update from publisher.
REFERENCES: (The above information is from the following websites.)
https://micropython-iot-hackathon.readthedocs.io/en/latest/mqtt.html
https://devopedia.org/mqtt