Most of the VoIP systems were based on the speech codec with a fixed rate

which maked packet-loss serious

especially for continuous packet-loss.The degradation for the speech quality would be caused by the kind of packet-loss.A network communication system for preventing packet-loss was given.The performance of the system was analyzed by using advanced NS.The simulation results show that the proposed system outperforms traditional IP system over the packet-loss

average delay and subjective listening quality.