Using a simulation model for a benchmark VoIP access architecture, we investigate the performance issues associated with mixing real-time voice and congestion-sensitive data traffic. Arbitration of shared facility is accomplished via First Come First Serve (FCFS), Strictly Priority (SP), and Weighted Fair Queuing (WFQ) disciplines. The performance metrics used are facility utilization, transmission delay, queuing delay and packet loss. Engineering rules for sizing the network are provided. More specifically, our results indicate that proper engineering of the queue size under the SP discipline can prevent any packet loss of voice traffic; proper setting the weights of the WFQ scheduler can control the delay for voice traffic; and increasing the queuing delay of the WFQ scheduler can improve the packet loss rate of data traffic.