Most　of　the　VoIP　systems　were　based　on　the　speech　codec　with　a　fixed　rate,　which　made　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.