This Recommendation defines quality of service metrics for characterizing performance in the case of FR/ATM service interworking. The specified metrics can be used to quantify the performance of either the FR/ATM interworking function/unit or the quality of the end-to-end data connection. This Recommendation is complementary to ITU-T Rec. X.140 as it is a specific case of the general techniques described therein for assessing performance. The specified metrics allow users and network operators to assess the performance from a user perspective. The metrics provide a simple manner by which either users or network operators could characterize the end-to-end performance. The defined metrics are not intended to be a replacement for the frame layer or ATM layer primary performance parameters but can be used to provide a user-oriented perspective of end-to-end performance.