A method for monitoring a communication between a first communicating entity and a second communicating entity , wherein the method, performed by a network node , comprises: receiving metadata over a signaling plane from at least one of: the first communicating entity , the second communicating entity , and storing the metadata with an identifier identifying a communication session from which the metadata is stored from in a data storage, receiving measurement data indicative of a payload data between the first communicating entity and the second communicating entity , obtaining an identifier associated to the payload data from a payload data traffic, the identifier being indicative of the communication session, receiving metadata from data storage configured to store metadata received prior to the payload data traffic, the metadata being indicative of the payload data carried in a payload data traffic between the first communicating entity and the second communicating entity , wherein the metadata is received from the data storage by generating an inquiry to the data storage carrying the identifier associated to the payload data, the identifier defining the metadata inquired, comparing at least one parameter derivable from the measurement data to respective at least one parameter derivable from the metadata, and setting , in accordance with a comparison between the at least one parameter of the measurement data and the respective at least one parameter of the metadata, a detection result to express one of the following: (i) the payload data between the first communicating entity and the second communicating entity complies with the metadata, (ii) the payload data between the first communicating entity and the second communicating entity deviates from the metadata. receiving metadata over a signaling plane from at least one of: the first communicating entity , the second communicating entity , and storing the metadata with an identifier identifying a communication session from which the metadata is stored from in a data storage, receiving measurement data indicative of a payload data between the first communicating entity and the second communicating entity , obtaining an identifier associated to the payload data from a payload data traffic, the identifier being indicative of the communication session, receiving metadata from data storage configured to store metadata received prior to the payload data traffic, the metadata being indicative of the payload data carried in a payload data traffic between the first communicating entity and the second communicating entity , wherein the metadata is received from the data storage by generating an inquiry to the data storage carrying the identifier associated to the payload data, the identifier defining the metadata inquired, comparing at least one parameter derivable from the measurement data to respective at least one parameter derivable from the metadata, and setting , in accordance with a comparison between the at least one parameter of the measurement data and the respective at least one parameter of the metadata, a detection result to express one of the following: (i) the payload data between the first communicating entity and the second communicating entity complies with the metadata, (ii) the payload data between the first communicating entity and the second communicating entity deviates from the metadata. <EOS>