Method of and system for pre-fetching input cells in ATM switch

In a packet switch having an input buffer coupled to input ports, a multicast network coupled to the input buffer, a temporary buffer coupled to the multicast network, an output network coupled between the temporary buffer and output ports, and a feedback path coupled to the output network to transport data rejected by the output network due to contention, a method of transferring packets between the input ports and the output ports comprising the steps of:

• (a) in a current switching cycle, pre-fetching packets from the input buffer for processing by the multicast network,
• (b) loading the processed packets into the temporary buffer,
• (c) determining the number of feedback packets in the feedback path rejected by the output network in a switching cycle previous to the current switching cycle,
• (d) transferring the packets from the temporary buffer to the output network, the temporary buffer storing the packets until the number of the feedback packets rejected in the previous switching cycle is determined,
• (e) transferring the feedback packets rejected in the previous switching cycle to the output network,
• (f) transferring the packets from the temporary buffer and the feedback packets through the output network to the output ports in accordance with a contention resolving algorithm, and
• (g) supplying the packets rejected by the output network into the feedback path for presenting to the output network in a next switching cycle.

An ATM network for switching cells between input and output ports, comprising:

• an input buffer coupled to the input ports for storing an input cell queue,
• a multicast network coupled to the input buffer for pre-fetching multicast and unicast cells from the input cell queue to provide the multicast cells with destination data in a current switching cycle,
• an output network coupled between the multicast network and output ports for resolving contention between the cells and having first and second groups of inputs, the cells supplied to the first group of the inputs having a contention priority higher that the cells supplied to the second group of the inputs,
• a feedback path coupled to said output network for transferring cells rejected by said output network due to the contention in a previous switching cycle to present the rejected cells onto the first group of the inputs in the current switching cycle,
• a temporary buffer coupled to the multicast network for storing the cells with the destination data until the number of said rejected cells is determined, in order to enable said multicast network to provide the cells with the destination data independently from feedback operations in said feedback path, and
• a rotator coupled to said temporary buffer for transferring the cells read from the temporary buffer to the second group of the inputs.