A new method for VoIP quality of service control use combined adaptive sender rate and priority marking

Quality of service (QoS) control is an important issue in voice over IP (VoIP) applications because of the need to meet technical and commercial requirements. The main objective of this paper is to propose a new QoS control scheme that combines the strengths of adaptive rate and speech priority marking QoS control techniques to provide a superior QoS control performance, in terms of perceived speech quality. A second objective is to propose the use of an objective measure of perceived speech quality (i.e. objective MOS score) for adaptive control of sender behaviour as this provides a direct link to user-perceived speech quality, unlike individual network impairment parameters (e.g. packet loss and/or delay). Our results show that the new combined QoS control method achieved the best performance under different network congestion conditions compared to separate adaptive sender rate or packet priority marking method. Our results also show that the use of an objective MOS as the control parameter for the sender rate adaptation improves the overall perceived speech quality. The results reported here are based on a simulation platform that integrates DiffServ enabled NS-2 network simulator, a real speech codec (AMR codec) and the ITU-T standard speech quality evaluation tool (PESQ).