Switching fabrics with internal backpressure using the ATLAS I single-chip ATM switch

ATLAS I is a single-chip ATM switch with optional credit-based (backpressure) flow control. This 4-million-transistor 0.35-micron CMOS chip, which is currently under development, offers 20 Gbit/s aggregate I/O throughput, sub-microsecond cut-through latency, 256-cell shared buffer containing multiple logical output queues, priorities, multicasting, and load monitoring. This paper discusses the use of backpressure inside networks based on ATLAS I chips: in switching fabrics of large ATM switches, or in wormhole-style workstation cluster LANs. We explain and we show by simulation that the ATLAS I backpressure provides a switching fabric with high performance, comparable to an output queued switch, at low cost, comparable to an input buffered switch.