An ATM network element receives a stream of data associated with a particular user. This data stream is further partitioned into frames and ATM cells. A predefined traffic set is associated with the user. The ATM network element evaluates the received data stream for conformance to the user's traffic set at every frame boundary. If a particular frame is conforming, the ATM network element provides a predefined quality of service (QoS) to the user. If a particular frame is non-conforming (and hence there is no commitment to the user of the corresponding QoS), the next (future) frame is evaluated only on the basis of the traffic characteristics of past conforming frames and the future frame. That is, past non-conforming user generated traffic is not used to determine any QoS commitments to future user generated traffic.