with a time stamp an observer is placed at selected ones of the plurality of nodes the observer being able to compute delays throughput and utilization the observer observes input output sequences for the selected nodes and compares those input output sequences with predetermined expected behaviors this results in identifying areas of the machine in which discrepancies between the input output sequences and the expected behaviors occur and for an area so identified the time stamp and arrival time of a selected input output sequence is monitored to compute an end to end delay of a corresponding input output pair the number of input output pairs passing through one of the selected nodes is monitored to determine whether the number is above or below a predetermined number per unit of time and a utilization factor is determined for a selected channel in the communicating finite state machine application_number US 36960703 A description in the following description the cfsm model is employed for avionics telecommunication networks to investigate performance management using passive testing first the concept of passive testing is introduced then the cfsm model and the observer model are introduced with appropriate assumptions and justification also introduced are the failure model and briefly the fault detection and location algorithms using passive testing finally the new passive testing approach for performance management based on the cfsm model is presented along with an illustration of the effectiveness of the new technique through simulation of a practical avionics telecommunication protocol example namely the aeronautical telecommunication network atn 24 in this section we introduce the passive testing based model used.