Abstract: A data switch for handling packets of information; the switch includes input traffic managers, ingress routers, a memoryless cyclic switch fabric, egress routers and output traffic managers all acting under the control of a switch controller. Each ingress router includes a set of virtual output buffers one for each output traffic manager and each message priority. Each data packet or cell as it arrives is examined to identify the output traffic manager address and its message priority. The switch controller uses a first arbitration and selection process to schedule the passage of the next cell across the switch fabric which the ingress router uses a second arbitration and selection process to select the appropriate virtual output queue for use in the switch fabric transfer.

Abstract: A priority selector includes buffers receiving control information relating to data to be transmitted through a data switching apparatus (each buffer is arranged to store control information having a respective one of a predetermined number of priority levels and arranged to deliver an overflow signal when contents reach a first predetermined level), storage storing digital priority symbols representative of different priority levels denoted by control information received by the buffers, a random number generator generating a succession of numbers each of which selects a corresponding priority symbol from the storage, a gate responsive to the receipt of the overflow signal from any one of the buffers to change the priority symbol generated by the storage to that designating the buffer giving rise to the overflow signal to change the priority symbol generated by the storage, and a selector responsive to the gate output to select a buffer output.