Abstract: Apparatus for assessing the performance of telecommunications systems by comparison of a reference signal with the same signal as degraded by the system under test tends to give unreliable results when used to test connectionless packet-switching equipment. This is because variable delay in delivery of the individual packets can result in the test signal and reference signal becoming unsynchronised. This may lead to the apparatus recording a poorer performance than a human tester would have recorded. To overcome this problem, the invention separates the test signal into a series of individual sections, which are synchgronised and analysed separately, and a quality value, aggregated over all the sections, is derived.