Path allocation in a three-stage ATM switch is the process whereby bandwidth is reserved through the second stage of the switch for each cell. Cell-level path allocation, performed once in every time slot, ensures that cells are routed through the second stage of the switch without delay or contention. A new algorithm for cell-level path allocation was previously proposed by the author. The motive for supporting intermediate channel grouping in the algorithm is described. The results of the path allocation process must be forwarded to the appropriate cells by a routing tag assignment network. A fast method of routing tag assignment is described, which employs a non-blocking copy network. This reduces the clock rate required of the circuitry, for a given switch size