Pulse or digital communications – Synchronizers
Patent
1998-02-03
2000-08-29
Chin, Stephen
Pulse or digital communications
Synchronizers
375365, 375366, 375368, 370503, 370509, 370512, 370513, 370514, 714758, 714775, 714789, 714798, H04L 700
Patent
active
061119245
ABSTRACT:
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.
REFERENCES:
patent: 5502748 (1996-03-01), Wilkinson
patent: 5570370 (1996-10-01), Lin
patent: 5600646 (1997-02-01), Polomski
patent: 5903619 (1999-05-01), Claisemartin
patent: 5956377 (1999-09-01), Lang
International Telecomunication Union, "Video Codec for Audiovisual Services at p.times.64 kbit/s," ITU-T Recommendation H.261 (Mar. 1993).
Chin Stephen
Ha Dac V.
VideoServer, Inc.
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