Speaker: Wenyu Jiang
Title: Quality and Performance Evaluation of VoIP End-points
We evaluate the QoS of a number of VoIP end-points, in terms of mouth-to-ear (M2E) delay, clock skew, silence suppression behavior and robustness to packet loss. Our evaluation results show that mouth-to-ear delay depends mainly on the receiving end-point. Hardware IP phones, when acting as receivers, usually achieve a low average M2E delay (45-90ms) under low jitter conditions. For software VoIP clients, this can range from 65ms to over 400ms, depending on the actual software. All tested end-points can compensate for clock skew, although some exhibit the symptom of occasional playout buffer underflow. Only a few of the tested end-points support silence suppression. We find that their silence detectors have a fairly long hangover time ($>$ 1sec), and they may falsely detect music as silence. All the hardware IP phones we tested support some form of packet loss concealment better than silence substitution. The concealment generally works well for two to three consecutive losses at 20ms packet intervals, but voice will quickly fade afterwards.