Apparatus for detecting synchronisation data in an input serial-bit digital signal formed of a series of word blocks each including a predetermined serial group of m bits forming said synchronisation data, comprises a deserialiser for deserialising the input signal to parallel-bit p-bit words where p<m, a delay for delaying at least p-1 bits of each p-bit word by one p-bit word period, and logic for receiving successive groups of 2p-1 bits each formed of a said p-bit word and the adjacent p-1 bits of the preceding or succeeding word. The logic is arranged to detect an initial portion of said synchronisation data by comparing bit sequences in a said group of 2p-1 bits with the bit sequence at the beginning of said predetermined group of m bits. On detection of said initial portion of the synchronisation data, bits of one or more succeeding groups of 2p-1 bits are compared with succeeding bits of said predetermined m bits in dependence upon the position of said initial portion in the corresponding 2p-1 bits. On detection of all m bits of the synchronisation data, a control signal is generated for controlling alignment of the bits of the words of the input signal in parallel form in dependence upon the position of said initial portion of the synchronisation data in the corresponding 2p-1 bits.
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.
For the preparation of data such as digitized television channel signals or television channel bundles, useful data are periodically replaced by a frame marker (F) in at least one of N parallel partial data streams of different bit significance. For this replacement, a partial data stream of low bit significance is selected because there the degradation is lowest. Because of this measure, the bit rate does not have to be increased in order to include a frame marker and a simple structure is possible for the multiplexer and demultiplexer at the respective transmission interfaces.
A system and method are provided for built-in-self test of any bits that have slipped from their appropriate positions within a frame character clock cycle. If a bit has slipped, then the built-in-self test mechanism can also implement either a clock generation stretch operation or a barrel shift operation to readjust the frame boundary output from a receiver with a 1-to-N deserializer. A pseudo-random bit sequence can be generated having the same logic value in both the receiver and transmitter, where the output of the deserializer which receives the transmitted bits is compared bit-by-bit with the receiver-generated bits as part of the built-in-self test mechanism. If a bit is determined to have been slipped, then error correction occurs with aliasing and phase jitter in mind.
To present a digital broadcast demodulator, in a demodulator of digital terrestrial wave broadcast for transmitting coded digital video and audio information in a packet form, capable of detecting packet synchronism stably and precisely, controlling the AGC, and processing the clock regeneration, in spite of inferior environments for receiving broadcast, such as deterioration of C/N of signal due to weak electric field, or strong ghost or multipath characteristic of terrestrial waves.
A technique for controlling the flow of packets in a multi-port bridge according to availability of resources within the bridge. The bridge includes a memory for storing packets and a plurality of ports. Each port includes a receive buffer, a transmit buffer and a memory pointer buffer. A data packet is received by the receive buffer of a port. As the packet is still being received, a look-up table is utilized to determine which is the appropriate destination port for the packet. If the memory pointer buffer in the destination port is nearly full, the destination port generates a jam request. The source port receives the jam request and, in response, discards the incoming packet and sends a jam signal. Otherwise, the memory pointer is stored in the destination port until the packet can be retrieved from the memory for transmission by the destination port. Because packets are not stored in the ports, the receive buffer and the transmit buffer will not become full and, thus, need not be checked to determine whether to transmit a jam signal. Instead, only the memory pointer buffer in the destination port for a packet need to checked to determine whether to transmit a jam signal.
