| 摘要 |
A de-framer (72) in a communications gateway (22) translates videoconferencing information from a circuit-switched format to a packet-switched format. A demultiplexor (78) extracts a bitstream containing video information that includes error-correction-code fields disposed at predetermined locations with respect to synchronization bits spaced by a synchronization interval and forming a predetermined synchronization sequence. A frame checker (88) for checking the error-correction code finds codeword boundaries by comparing the predetermined synchronization sequence with sequences of synchronization-interval-spaced video-bitstream bits until it finds a match. To do so, the frame checker (88) takes a group of video-bitstream words offset from each other by the synchronization interval. It compares each word in the group with a respective synchronization word consisting of a word-width replication of a respective synchronization bit. Enough words resulting from the comparisons are ORed together that the result will be all ones unless each video-bitstream word contains a respective synchronization bit in a corresponding bit position. If the result does contain a zero, then it can be inferred that the video bitstream contains synchronization bits in corresponding bit positions.
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