Digital switching unit for a multirate time-division multiplex digital switching network

Claim 1

A digital switching unit for use in a multirate time-division multiplex digital switching network, in which first-order digital data channels transmitting words consisting of a given number of bits and having first rates which are different from, but multiple of, one another are given a first multiplexing converting them into second-order digital data channels having a second predetermined rate, in which each said second-order channels each containing first-order channels of at least two different rates in accordance with multiplexing schemes which can differ for each second-order multiplex channel, and in which said second-order digital channels are given a second multiplexing converting them into third-order digital data channels having a third predetermined rate; said digital switching unit comprising: at least one buffer store in which the first-order channel words multiplexed into the third-order channels are grouped at a resultant address having fist and second part, whose first part is the address of the second-order channel containing the first-order channel word in the third-order channel and whose second part is the address of the first-order channel in the second order channel; means for inserting in each of the words of an an outgoing second-order channel bits forming a pseudorandom sequence having a known period so that the bits of a given rank of the words of a third-order outgoing channel form a number of interleaved pseudorandom sequences; means for separating said pseudorandom sequences contained in the words or said incoming second-order channels and for deriving therefrom the addresses of the words in said second-order channels; means for supplying from said addresses of the words in said second-order channels the first-order channel addresses associated with said word addresses in the second-order channels according to said multiplexing schemes, said supplying means comprising: a read-only memory containing for each first order channel word group a second-order channel which results from a multiplexing of P first-order channels according to said multiplexing schemes into a channel analogous to a first-order channel having a rate equal to the highest of said different rates of said first-order channels, a coded word representative of the combination of rates associated with said P first-order channels; and means for decoding each coded word to supply the P first-order channels addresses of each word group associated with a second-order channel to said buffer store.