Frame relay needs UPC function for the multiplexed logical connections to prevent malicious user traffic from incoming to network, to guarantee the QoS of conformed user traffic, and to protect the normal operation of network system. On the FR/ATM interworking in ATM networks, the UPC may be conducted either by cell-based ATM UPC or frame-based FR UPC. Frames come into and traverse ATm networks by segmentation to ATM cells. Of course, FR QoS should be guaranteed in spite of segmentation and reassembly in ATM networks. In this paper, we compared the QoS of cell-based ATM UPC and frame-based FR UPC in terms of analysis and simulation in case of ingress of excess traffic over negotiated traffic parameters at user-to-network interface. Also we studied frame-based UPC schemes including window-based FR UPC and frame-based VSA which is an ATM UPC algorithm recommended by ITU-T. We described introductions to frame relay including frame structure and FR/ATM interworking, FR traffic parameters and their relationship, comparison of FR QoS between frame-based FR UPC and cell-based ATM UPC, comparison of FR UPC schemes, necessities of egress traffic control, and conclusions.