A Perceptual Quality Model for Adaptive VoIP Applications∗

Quality models predict the perceptual quality of services as they calculate subjective ratings from measured parameters. In this paper we present a new quality model that evaluates VoIP telephone calls in order to control their transmission at run-time. In addition to packet loss rate, coding mode and delay it takes into account the impairments due to changes in the transmission con guration (e.g. switching the coding mode or re-scheduling the playout time). It is also computation e cient and open source. To demonstrate its potential, we apply our model to select the ideal coding and packet rate in bandwidthlimited environments. Furthermore we decide, based on model predictions, whether to delay the playout of speech frames after delay spikes. Delay spikes often occur after congestion and cause packets to arrive too late. We show a considerable improvement in perceptual speech quality if our model is applied.