An increasing number of applications are using the Internet for voice transmission, and hence there is a growing demand for the Internet phone. However, the internet was not originally designed for such isochronous traffic, and it is not clear that it is fully capable of providing the desired Quality of Service (QoS) for this applicaton. In this paper we describe a number of QoS parameters to measure the perceptual quality of audio, including measures of delay, rate, and loss. We investigate the factors influencing the QoS of Internet voice, such as packet period and packet size, threshold delay, buffer delay, time slots and Internet sites. We present results from our experiments on how these factors influence the QoS of Internet voice. Based on the results of our experiments, we propose a QoS driven dynamic scheduling algorithm for the real-time transmission of Internet voice packets.