An internet telephone communication system including a voice transmitting and receiving parts and a method of operating the system are disclosed. The voice transmitting part retransmits voice data packets at least once through an internet network according to a retransmission frequency information packet received from the voice receiving part. The voice receiving part transmits the retransmission frequency information packet to the voice transmitting part in order to request to retransmit the voice data packets R times, where R is determined based a data loss rate calculated. By retransmitting the voice data packets, the transmitting rate of the data and the corresponding VOIP conversation quality are greatly improved.