Method and communication system for exchanging data between several field devices

A communication system, comprising:

• field devices;
• and
• at least one data broker with a broker functionality;
• wherein, for the exchange of data between the field devices, the field devices are in a communication link based on a publish-subscribe principle via the data broker;
• wherein at least one of the field devices publishes at least one message with a message title to the data broker during operation of the communication system;
• wherein at least one field device subscribes to a message with at least one specific component of a message title at the data broker;
• wherein the message published to the data broker is received by the data broker and the data broker forwards the received message to the at least one of the field devices, which field device has subscribed to the message with corresponding component of the message title at the data broker;
• wherein the field devices and the data broker are set up in such a way that, during operation of the communication system, an exchange of data based on a request-response principle between a requesting field device and a responding field device is implemented by means of the publish-subscribe principle in that a unique field device identifier of the responding field device is made known at least to the requesting field device;
• wherein the responding field device subscribes to request messages whose message titles include a specification of the field device identifier of the responding field device;
• wherein the requesting field device subscribes to response messages whose message title includes a request identifier known to the requesting field device;
• wherein the requesting field device publishes a request message to the data broker;
• wherein a message title of the request message includes the request identifier and the specification of the field device identifier of the responding field device;
• wherein the responding field device receives the request message from the requesting field device on the basis of the subscription to the request messages, evaluates the request message and publishes a corresponding response message to the data broker, wherein a message title of the response message includes at least the request identifier;
• and
• wherein the requesting field device receives the response message from the responding field device on the basis of the subscription to the response message.