Abstract: A new generation of ATM switches with more sophisticated cell queueing and scheduling capabilities are becoming available. We discuss in this paper an effective approach to connection admission control (CAC) for the real-time variable-bit-rate (rtVBR) service category in an ATM switch with per-VC queueing and scheduling. The quality of service (QoS) requirements for rtVBR are given in terms of the cell loss ratio (CLR) and the cell delay variation (CDV). Given the rtVBR traffic descriptor and QoS parameters, we compute the capacity CrtV BR required to support all the ATM virtual circuits (VCs) in the rtVBR category while meeting their QoS requirement. As part of the process of computing CrtV BR, we also compute a per-VC effective bandwidth used to program the scheduler. We also characterize the admissible region in the 2-class case and show that it is made up of delay-dominant and loss-dominant regions.