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Voice over Internet Protocol (VoIP) services are susceptible to Internet Protocol (IP) network burstiness causing packets drop and momentary gap in the call. The main objective of this paper is to study the effect of various voice codec schemes on the VoIP Quality of Service (QoS). Popular voice codecs such as G.711, G.729A Conjugate-Structure Algebraic-Code-Excited Linear-Prediction (CS-ACELP), G.723.1 and G.726 Adaptive Differential Pulse Code Modulation (ADPCM) are studied and VoIP simulation models are built. The voice codec performance is determined with the best performance codec identified. From the simulations, the end-to-end delay (Ta) results for each of the users were obtained. The results were averaged out to gain the average end-to end delay (Ta) for every simulation. From the simulation results it can be seen that for most of the locations, G.711 without using silence suppression has the highest average end-to-end delay (Ta). On the other hand, G.723.1 with silence suppression has the lowest average Ta.