Voice over Internet Protocol (VoIP) application is gaining popularity recently. Many people are finding it attractive and cost effective to merge and unify voice and data networks into one. Besides the cost issues, another advantage of VoIP is portability. The overall performance of VoIP is analysed in a simple 3-way long-distance conferencing calls for G.711 and G.723.1 voice Codecs. The performance with and without the presence of background traffic over our network to determine which type of voice codec is better suited for different networks is also examined. The performance of the network under different discard ratios were also analyzed and its concluded that the Internet QoS affects the quality of VoIP.