MQTT

MQTT (Message Queuing Telemetry Transport) is a messaging protocol which works on top of the TCP/IP protocol and is meant for communication in networks with limited bandwidth.

An MQTT communication network consists of at least one server (a broker) and several clients. The protocol is publish-subscribe-based, which means that a client can either publish data or subscribe to it.

Publish/Subscribe

A client can publish any arbitrary topic. MQTT clients subscribed to the topic will receive the messages. However, data cannot be exchanged directly between publisher and subscriber. A broker is necessary to handle the connection between them. The broker receives the messages, filters and distributes them to the appropriate subscribers. Thus, all publishers and subscribers need to know hostname/IP address and port number of the broker to send/receive data.

WinCC OA driver

The WinCC OA MQTT driver represents an MQTT client which can either publish or subscribe to data and allows to establish and handle connections to MQTT brokers. The MQTT driver is able to connect to an arbitrary number of brokers and also supports redundant connections.

Chapter		Description
MQTT driver, basics		Introduction and links to other chapters.
Requirements and installation		Requirements and installation of the MQTT driver.
Configuration of the MQTT driver		Description of the configuration of a MQTT driver.
Configuration - Tabs
	Connection tab	Description of the Connection tab which allows the configuration of IP address, port number etc.
	Advanced tab	Description of the "Advanced" tab which is used to define timeouts, etc.
	Last will	Description of the "Last will" tab to define last will settings if the driver loses connection.
	State tab	Description of the "State details" tab which provides information on the connection state.
	Statistics tab	Description of the "Statistics" tab which displays statistical data on received and sent data.
Defining the peripheral address for the MQTT driver		Information for defining a peripheral address for the MQTT driver.
Possible config entries [mqtt]		List of all config entries available for the MQTT driver.
Redundancy		Information on the redundancy behavior.
Internal data points of the MQTT driver		Description of the internal data points of the MQTT driver.
Details on the MQTT driver		Description of debug flags and error codes.