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This paper investigates the effects of packet loss on speech quality in Voice over Internet Protocol (VoIP) applications by using ITU-T G.107, the E-model, whose parameters currently only cover limited VoIP scenarios. Several packet loss rates, packet sizes and error concealment techniques for codec G.729 are examined. Mean Opinion Score (MOS) is used as an index for speech quality and is measured by Perceptual Evaluation of Speech Quality (PESQ) algorithm. These effects on speech quality are assessed in the equipment impairment factor domain and then formulated into the E-model. The validation test shows good accuracy of the proposed formula, the prediction errors range between /spl mnplus/0.10 MOS for most cases with an absolute maximum of 0.14 MOS.