Abstract: A complementary network quality testing method for conducting a test on the quality of service with regard to data transmission taking place in a telecommunication network includes setting up a committed bucket of a committed burst size to receive tokens introduced thereinto at a committed information rate; receiving normal protocol data units and/or test protocol data units, followed by storing the normal protocol data units in a data queue and/or storing the test protocol data units in a test queue; determining whether the normal protocol data units are present in the data queue; and retrieving selectively the test protocol data units from the test queue or determining, selectively and again, whether the normal protocol data units are present in the data queue, depending on whether the tokens are present in the committed bucket.