This invention relates to measurement of error characteristics of a communication channel. The invention is of particular use for measuring perceived transmission performance of the communication channel. The invention provides a method and apparatus for measuring the transmission error characteristics of a channel employing frame based transmission in which a frame classification indicator is generated for an expected frame, according to data received via said channel, and in which the following steps are repeatedly performed: generating frame classification data relating to the expected frame; updating a statistical representation of the transmission error characteristics according to said frame classification. The invention also provides a method and apparatus for measuring perceived transmission performance of a communications channel in which the perceived transmission performance is generated according to measured transmission error characteristics.