The invention relates to a method of measuring the quality of a service transmitted on a traffic channel and to a cellular radio network. In the method the transmitter transmits user data to the receiver, but does not transmit all data frames because the user data are missing. The transmitter transmits control data to the receiver using associated control channels, and calculates the number of frames transmitted to the receiver on the traffic channel during a certain period. The receiver calculates the number of all frames received and decoded correctly during a certain period. A quality value is calculated for a service to be transmitted on the traffic channel during a certain period by subtracting the number of frames transmitted during said period from the number of frames received during said period and by dividing the difference obtained by the number of frames transmitted during said period.