MQTT General

MQTT is a simple and easy protocol known from the IoT (Internet of Things) world.

The active part ist named "Client", the passive part "Broker".

A broker can support many clients. Each client needs a unique station name.

On standard the clients are writing data into the broker. The broker dispatches the data to other clients if they will need the data. So one station will dispatch the data to multiple partners.

Security can be used. If used an user name and password is required.

The quality of service allows stable communication in unstable networks also. Messages can be sent without acknowledges (QOS0), or an acknowledge ist used (QOS1). QOS2 uses a four way handshake. This is more stable but can be slowly in unstable networks.

The two different protocol versions are only different in the allowed station name length.

MQTT does not define data types. It can handle any data.

For special situations as offer MQTT data in OPC some optional settings exist:

- any data (default)

- all data are texts

- handle the Item Syntax neutral.