Design and Implementation of Abacus Switch: A Scalable Multicast ATM Switch

This paper describes a new architecture for a multicast ATM switch scalable from a few tens to a few thousands of input ports. The switch, called the Abacus switch, has a nonblocking switch fabric followed by small switch modules at the output ports. It has buffers at input and output ports. Cell replication, cell routing, output contention resolution, and cell addressing are all performed in a distributed way so that it can be scaled up to thousands of input and output ports. A novel algorithm has been proposed to resolve output port contention while achieving input buffers sharing, fairness among the input ports, and call splitting for multicasting. The channelgrouping mechanism is also adopted in the switch to reduce the hardware complexity and improve the switch’s throughput, while the cell sequence integrity is preserved. The switch can also handle multiple priority traffic by routing cells according to their priority levels. The performance study of the Abacus switch in throughput, average cell delay, and cell loss rate is presented. A key ASIC chip for building the Abacus switch, called the ARC (ATM routing and concentration) chip, contains a twodimensional array (32 32) of switch elements that are arranged in a crossbar structure. It provides the flexibility of configuring the chip into different group sizes to accommodate different ATM switch sizes. The ARC chip has been designed and fabricated using 0.8 m CMOS technology and tested to operate correctly at 240 MHz.