British Telecommunications Public Limited Company

Alan D Clark

Michael N Turner

Abdullah Hashim

A data switching node includes a plurality of data lines including high speed data (link) lines and low speed data (port) lines and a switch connected to the data lines. The switch is a distributed multiplexer comprising a number of switching modules connected in common to a data bus. The switching modules are arranged to communicate data with the common data bus. A control module is also connected to the bus and arranged to control the addressing of the switching modules so that data received by a switching module connected to one data line is transmitted directly via the common data bus to a switching module connected to a selected other one of the data lines in response to a control signals from the control module identifying the said switching module, the data being transmitted in association with a logical channel number associated with the switching module connected to the selected other one of the data lines. IN a method of operating a multiplexer particularly suitable for use with the data switching node a plurality of channels are received and transmitted as byte-interleaved frames. Each incoming channel is assigned a logical channel number and written to a byte or bit position of the outgoing data frame selected in accordance with the logical channel number. The outgoing frame is assembled and output substantially coincidentally with the incoming date frame.

Data switching nodes

A hybrid data communication system comprises synchronous line cards(3) and asynchronous line cards(2) connected to a common data bus(1) includes a contention bus(7) arranged to communicate contention signals between the line cards(2,3). The synchronous line cards are arranged to transmit a high priority contention signal to suspend any outgoing transmission by an asynchronous card(3) and to gain access to the bus(1) of synchronous data. The contention bus includes an acknowledgement line(ACK) which is driven low by a receiving line card to indicate that it is receiving data. The receiving line card performs error checking and only receives the acknowledgement when the received data is determined to be error free. In a preferred example, the asynchronous line cards(2) are arranged to monitor the contention line(7) to detect the initiation of a contention cycle by a synchronous line card(3). Subsequently on the completion of the contention cycle the asynchronous cards(2) interrupt ant outgoing transmission of a data frame to allow the transmission of data by the synchronous card(3).

Hybrid data communications systems

Data compression with dynamically compiled dictionary

A method of processing data for transmission from a transmitter (T) to a receiver (R) both of which are switchable between a compression mode in which the data stream is encoded or decoded with a data compression algorithm and a transparent mode in which the data stream is transmitted or received unencoded, comprising reading an input data stream at the transmitter (T), encoding at least part of the input data stream with the data compression algorithm to form a compressed data stream, monitoring the efficiency of compression of the compressed data stream and controlling the switching of the mode of the transmitter (T) and receiver (R) so that the input data stream is transmitted efficiently. In the transparent mode both the receiver and the transmitter check independently the efficiency of compression and switch to the compression mode if the transparent mode is determined to be inefficient. In the compression mode the transmitter (T) determines the efficiency of compression and transmits a control code to the receiver (R), switching both the receiver and transmitter to the transparent mode if the compression mode is determined to be inefficient.

Data communication having transmitter-controlled mode switching from

Method and apparatus for encoding, decoding and transmitting data in

An adaptive system for binary data compression incorporating a coding scheme which is simple to implement, which limits codeword length and which can be implemented by software. Data compression is achieved by assigning four bit codes to the eight most frequently occurring characters in the data and eight or nine bit codes to the remaining characters wherein the code assignment is made according to a continuously updated evaluation of character frequency distribution. Run length encoding may be used in conjunction with this technique, to achieve further data compression. For transmission, error control protocols are applied to the compressed data where such protocols may include the use of forward error correcting (FEC) coding and an automatic repeat request (ARQ) system. The data may be transmitted using a burst error control system based on interleaving so that a single error correcting FEC coding can corrects bursts of errors characteristic of a telephone system.

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Ipswich, United Kingdom

Alan D Clark