Method for monitoring a system comprising a number of readers and a plurality of portable communication units

A method for monitoring a system comprising a number of reading devices and a plurality of portable communication units, wherein during operation of the system, for a given communication unit there are carried out a plurality of data transactions between at least one reading device and the given communication unit via a corresponding communication interface, wherein within the framework of a data transaction a first data set is transmitted from a reading device to the given communication unit and stored there and a second data set, which was stored in the given communication unit upon the most recently carried out data transaction, is transferred to the reading device, wherein in a computer unit:

• a chaining of data pairs comprising the first and second data set of the respective data transactions is formed in such a way that for two consecutive data pairs the first data set of the one data pair corresponds to the second data set of the other data pair;
• upon forming the chaining there is checked a criterion which is fulfilled when the chaining has several parallel chains of data pairs or when two data pairs are found which include different first data sets while the second data set is the same;
• a duplication of the given communication unit is recognized when the criterion is fulfilled.

A system comprising a number of reading devices and a plurality of portable communication units, wherein during operation of the system, for a given communication unit there are carried out a plurality of data transactions between at least one reading device and the given communication unit via a corresponding communication interface, wherein within the framework of a data transaction a first data set is transmitted from a reading device to the given communication unit and stored there and a second data set, which was stored in the given communication unit upon the most recently carried out data transaction, is transferred to the reading device, wherein the system includes in a computer unit by means of which:

• a chaining of data pairs comprising the first and second data set of the respective data transactions is formed in such a way that for two consecutive data pairs the first data set of the one data pair corresponds to the second data set of the other data pair;
• upon forming the chaining there is checked a criterion which is fulfilled when the chaining has several parallel chains of data pairs or when two data pairs are found which include different first data sets while the second data set is the same;
• a duplication of the given communication unit is recognized when the criterion is fulfilled.