2 Architecture and Operations of Abacus

This paper describes a new architecture for a scalable multicast ATM switch from a few tens to thousands of input ports. The switch, called Abacus switch, has a nonblocking memoryless switch fabric followed by small switch modules at the output ports; the switch has input and output buuers. Cell replication, cell routing, output contention resolution, and cell addressing are all performed distributedly in the Abacus switch so that it can be scaled up to thousands input and output ports. A novel algorithm has been proposed to resolve output port contention while achieving input buuers sharing, fairness among the input ports, and multicast call splitting. The channel grouping concept is also adopted in the switch to reduce the hardware complexity and improve the switch's throughput. The Abacus switch has a regular structure and thus has the advantages of: (1) easy expansion, (2) relaxed synchronization for data and clock signals, and (3) building the switch fabric using existing CMOS technology.