[RQ8.6] The MonitoringNumber in the ResponseSPDU shall be a copy of the MonitoringNumber received in the corresponding RequestSPDU. See Clause 8.1.3.1.

The SafetyConsumer uses the ResponseSPDU.MonitoringNumber to detect mis-timed SPDUs, e.g. such SPDUs which are continuously repeated by an erroneous network storing element. A different MonitoringNumber is used in every RequestSPDU of a given SafetyConsumer, and a ResponseSPDU will only be accepted, if its MonitoringNumber is identical to its matching RequestSPDU.