→MQTT - Message Queue Telemetry Transport

according to Wikipedia (http://en.wikipedia.org/wiki/MQTT): MQTT (formerly Message Queue Telemetry Transport) is a publish-subscribe based "light weight" messaging protocol for use on top of the TCP/IP protocol. It is designed for connections with remote locations where a "small code footprint" is required and/or network bandwidth is limited. The Publish-Subscribe messaging pattern requires a message broker . The broker is responsible for distributing messages to interested clients based on the topic of a message. ...

Data transfer between PLCs via MQTT:

logi.CAD 3 provides MQTT blocks for transferring unencrypted data between →Raspberry Pis. See "Preparing/Realizing data transfer via MQTT".