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mamiko · Member 2 Joined: 25 Dec 2017 Posts: 420

Use the SIMATIC controller as an MQTT client
https://support.industry.siemens.com/cs/document/109748872/use-the-simatic-controller-as-an-mqtt-client
MQTT (Message Queue Telemetry Transport) is a simple protocol on TCP/IP level. It is suitable for messaging between devices with minimum functionality and for transmission via unreliable networks. With the LMQTT library, the MQTT protocol is implemented in SIMATIC S7-1200/1500 Controllers.
Lean and fast: MQTT
MQTT is a simply structured binary Publish/Subscribe protocol on TCP/IP level. It is suitable for messaging between devices with minimum functionality and for transmission via unreliable networks with low bandwith and high latency. With these characteristics, MQTT plays a vital role for the IoT and in M2M communication.

Application-related implementation
The LMQTT library provides you with one function block for S7-1500 and S7-1200 CPUs. The “LMQTT_Client” function block integrates the MQTT client function and allows you to transmit MQTT messages to a broker (publisher role) and to confecÈ›ionate subscriptions (subscriber role). In this, the communication can be secured via a TLS connection. You can reach the broker with a static ip address or a qualified domain name.
The following picture shows the secure mqtt-messaging with a SIMATIC S7-1500.

Use the SIMATIC controller as an MQTT client Use the SIMATIC controller as an MQTT client

Use the SIMATIC controller as an MQTT client Use the SIMATIC controller as an MQTT client

The LMQTT library is part of the Libraries for Communication and can be downloaded separately in the entry https://support.industry.siemens.com/cs/document/109780503/libraries-for-communication-for-simatic-controllers

This entry shows the application of the library.The library blocks are already included in the application example.

Criteria of MQTT
The MQTT protocol stands out with the following characteristics:
Lightweight protocol with low transport overhead
Minimal need for network bandwith through push mechanism
Function for re-connecting after disconnection
Re-sending messages after disconnection
Mechanism for notifying interested parties after an unpredicted disconnection of a client
Simple use and implementation thanks to a small set of commands
Quality of Service (QoS level) with different reliability levels for the message delivery
Optional encryption of messages via SSL/TLS
Authentification of publishers and subscribers with username and password

Documentation and project example for an secure messaging (S7-1500, S7-1200)

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