Abstract: For determining the quality of virtual connections between input lines and output lines of an ATM switching equipment, the plurality of accepted and output message cells is separately acquired in a call-associated manner in the ATM switching equipment on the basis of cell headers of the message cells accepted via the input lines and, respectively, output to the output lines. In response to the cleardown of a respective virtual connection, the loss rate of the message cells is then calculated as a measure for the quality of the respective virtual connection from the previously, separately-acquired plurality of accepted and output message cells.