Voice over Internet Protocol (VoIP) allows data network and voice networks to converge. The bandwidth is saved in VoIP system by not sending the IP packets during silence periods in the conversation and this saved bandwidth can be used for other applications. VoIP system uses Internet Protocol (IP) which is a network layer protocol according to the seven-layer Open System Interconnected (OSI) model. Simulative investigations related to the network impairment on the voice signal quality of VoIP system using MATLAB Simulink model. The effect of the network impairments on the perceived speech quality of G. 711, G. 729A based VoIP system has been analyzed. The VoIP signal has been processed through signal processing algorithm such as Power Spectral Density (PSD), Fast Fourier Transform (FFT) and spectrogram, to evaluate the performance of the system. The comparison of the G. 711 and G. 729A based VoIP system has been evaluated through spectral analysis. It was observed from the spectral analysis that the quality of the VoIP signal goes on decreasing as the effect of Network impairments increases.
