A video retrieval protocol with video data prefetch and packet retransmission considering play-out deadline

Most of current video retrieval systems use video transfer protocols such that servers simply transmit video packets at the same rate as clients play them. If any packets are corrupted during transmission, they will be lost and cannot be recovered by retransmission. In video retrieval systems however the video data are stored in servers and clients can prefetch them prior to playing. So, it might be possible for the video retrieval systems to make corrupted video packets retransmitted before the play-out deadline. However, the application of existing reliable protocols causes problems such that, if a packet does not arrives before the deadline due to retransmission, the packets following it will not be delivered to the upper layer even if they have already arrived. We propose a new video transfer protocol for video retrieval systems over an ATM network which provides video data prefetch, flow control for the video buffer, selective retransmission with a skipping function for video packets that are late for the play-out deadline, and a resynchronization function for the video buffer. We have implemented an experimental system using our protocol and evaluated the performance. The results of the performance evaluation shows that the proposed protocol decreases the number of unplayed video data to less than 1/70 compared with the conventional non-retransmission protocol when random bit errors with a BER of 10/sup -6/ are inserted in an ATM network.