In this paper, we discuss issues relating to the mapping of QoS parameters in an IP/ATM environment. We conduct preliminary experiments with constant IP packet rate, which after segmentation in AAL5, generates a jittered CBR cell stream. We use this stream to investigate the effect of parameter translation on the QoS received by the application. Results indicate that translation does have a significant impact on performance, in particular, on cell loss. There are also cost implications, as large buffers are required to achieve an acceptable level of performance.