Data element switch

Claim 1

An Asynchronous Transfer Mode Switch having a plurality of input stages (IS1 ... ISN) each for receiving a digital data transmission stream (DS1 ... 256) consisting of a series of cells, a cell comprising data and a header containing control data from which the destination of the cell can be determined, a plurality of central stages (41) connected to the input stages to receive the data from the input stages to be switched across the switch, and a plurality of output stages (OS1 ... OSN) each connected to the central stages, and wherein for every input stage there is a route to every central stage for the transmission of data, and from every central stage there is a route to every output stage, and wherein each input stage includes a circuit (52) for determining the destination of the cells of that data stream, and characterised in that the switch includes a circuit (63) for disassembling each cell into cell elements and for allocating to each cell element routing data to enable it to be routed across the central stages, means (54) for storing the cell elements in series, means (56) for requesting from a central stage permission to transmit a cell element in the series and after a predetermined delay a further request for the same destination point provided that the stored cell elements are derived from the same cell, means (56) for receiving a response from the central stage as to the availability of the requested destination between the sending of requests so that the sequence of sending a request for one cell element is interleaved with the response to the request for the preceding cell element, and means for transmitting each cell element to the central stage after a second predetermined delay from the receipt of a positive request.