Performance Evaluation of an IP Voice Terminal

This paper examines the issues related to the transmission of voice over packet networks using the Internet Protocol (IP). We focus on studying the delays that are generated in the terminal, which is a Unix workstation equipped with IP voice application software. Delay components in the terminal are presented. We measure the processing delays in the terminal using different audio codecs and measure the end-to-end delays using different scheduling parameters for the IP voice application. A significant part of the delay is shown to be caused by buffering at the receiving terminal. This is a feature of the application software and can be removed by modifying the source code. We also make a comparison of adaptive algorithms that are used to calculate the playout times of the voice packets. Algorithms are simulated using different network loads and thus different delay distributions of the voice packets in an Ethernet. We present a new playout algorithm, which is a combination of two existing algorithms. This algorithm is shown to outperform the other two real-time algorithms that are compared in our studies. 2 Harri Marjamäki, M.Sc.